Trine Grønhaug Halvorsen

• Skjærvø, Øystein; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2019). All-in-one paper-based sampling chip for targeted protein analysis. Analytica Chimica Acta.  ISSN 0003-2670. . doi: https://doi.org/10.1016/j.aca.2019.08.043.
• Skjærvø, Øystein; Solbakk, Eirik; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2019). Paper-based immunocapture for targeted protein analysis. Talanta: The International Journal of Pure and Applied Analytical Chemistry.  ISSN 0039-9140.  195, s 764- 770 . doi: 10.1016/j.talanta.2018.12.013
• Skjærvø, Øystein; Trimpin, Sarah & Halvorsen, Trine Grønhaug (2019). Matrix assisted ionization mass spectrometry in targeted protein analysis – an initial evaluation. Rapid Communications in Mass Spectrometry.  ISSN 0951-4198. . doi: https://doi.org/10.1002/rcm.8437
• Andersen, Ida Kristine Lysgaard; Rosting, Cecilie; Gjelstad, Astrid & Halvorsen, Trine Grønhaug (2018). Volumetric absorptive MicroSampling vs. other blood sampling materials in LC-MS-based protein analysis - preliminary investigations. Journal of Pharmaceutical and Biomedical Analysis.  ISSN 0731-7085.  156, s 239- 246 . doi: 10.1016/j.jpba.2018.04.036 Fulltekst i vitenarkiv.
• Levernæs, Maren Christin Stillesby; Brandtzaeg, Ole Kristian; Amundsen, Sunniva Furre; Reubsaet, Leon; Lundanes, Elsa; Halvorsen, Trine Grønhaug & Wilson, Steven Ray Haakon (2018). Selective Fishing for Peptides with Antibody Immobilized Acrylate Monoliths, Coupled Online with NanoLC-MS. Analytical Chemistry.  ISSN 0003-2700.  90, s 13860 . doi: 10.1021/acs.analchem.8b00935
• Rosting, Cecilie; Tran, Elin Vyvy; Gjelstad, Astrid & Halvorsen, Trine Grønhaug (2018). Determination of the Low-Abundant Protein Biomarker hCG from Dried Matrix Spots using Immunocapture and Nano Liquid Chromatography Mass Spectrometry. Journal of Chromatography B: Biomedical Sciences and Applications.  ISSN 1387-2273.  1077-1078, s 44- 51 . doi: 10.1016/j.jchromb.2018.01.016 Fulltekst i vitenarkiv.
• Skjærvø, Øystein; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2018). Smart blood spots for whole blood protein analysis. The Analyst.  ISSN 0003-2654.  143(13), s 3184- 3190 . doi: 10.1039/c8an00317c
• Halvorsen, Trine Grønhaug & Reubsaet, Leon (2017). Antibody based affinity capture LC-MS/MS in quantitative determination of proteins in biological matrices. TrAC. Trends in analytical chemistry.  ISSN 0165-9936.  95, s 132- 139 . doi: 10.1016/j.trac.2017.08.009 Fulltekst i vitenarkiv.
• Levernæs, Maren Christin Stillesby; Nordlund, Marianne Sparby; Reubsaet, Leon & Halvorsen, Trine Grønhaug (2017). To elute or not to elute in immunocapture bottom-up LC?MS. Journal of chromatography. B.  ISSN 1570-0232.  1055-1056, s 51- 60 . doi: 10.1016/j.jchromb.2017.03.044 Fulltekst i vitenarkiv.
• Rossetti, Cecilia; Ore, Odd Gøran; Sellergren, Börje; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2017). Exploring the peptide retention mechanism in molecularly imprinted polymers. Analytical and Bioanalytical Chemistry.  ISSN 1618-2642.  409(24), s 5631- 5643 . doi: 10.1007/s00216-017-0520-6 Fulltekst i vitenarkiv.
• Rossetti, Cecilia; Switnicka-Plak, Magdalena; Halvorsen, Trine Grønhaug; Cormack, Peter A G; Sellergren, Börje & Reubsaet, Leon (2017). Automated protein biomarker analysis: On-line extraction of clinical samples by Molecularly Imprinted Polymers. Scientific Reports.  ISSN 2045-2322.  7 . doi: 10.1038/srep44298 Fulltekst i vitenarkiv.
• Rosting, Cecilie; Gjelstad, Astrid & Halvorsen, Trine Grønhaug (2017). Expanding the knowledge on dried blood spots and LC-MS-based protein analysis: two different sampling materials and six protein targets. Analytical and Bioanalytical Chemistry.  ISSN 1618-2642.  409(13), s 3383- 3392 . doi: 10.1007/s00216-017-0280-3
• Skjærvø, Øystein; Rosting, Cecilie; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2017). Instant on-paper protein digestion during blood spot sampling. The Analyst.  ISSN 0003-2654.  142(20), s 3837- 3847 . doi: 10.1039/c7an01075c Fulltekst i vitenarkiv.
• Ask, Kristine Skoglund; Turgay, Bardakci; Parmer, Marthe Petrine; Halvorsen, Trine Grønhaug; Øiestad, Elisabeth Leere; Pedersen-Bjergaard, Stig & Gjelstad, Astrid (2016). Parallel artificial liquid membrane extraction as an efficient tool for removal of phospholipids from human plasma. Journal of Pharmaceutical and Biomedical Analysis.  ISSN 0731-7085.  129, s 229- 236 . doi: 10.1016/j.jpba.2016.07.011
• Egeland, Siri Valen; Reubsaet, Leon & Halvorsen, Trine Grønhaug (2016). The pros and cons of increased trypsin-to-protein ratio in targeted protein analysis. Journal of Pharmaceutical and Biomedical Analysis.  ISSN 0731-7085.  123, s 155- 161 . doi: 10.1016/j.jpba.2016.02.011
• Egeland, Siri Valen; Reubsaet, Leon; Paus, Elisabeth & Halvorsen, Trine Grønhaug (2016). Dual-immuno-MS technique for improved differentiation power in heterodimeric protein biomarker analysis: determination and differentiation of human chorionic gonadotropin variants in serum. Analytical and Bioanalytical Chemistry.  ISSN 1618-2642.  408(26), s 7378- 7391 . doi: 10.1007/s00216-016-9818-z
• Hildonen, Siri; Skarpen, Ellen; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2016). Isolation and mass spectrometry analysis of urinary extraexosomal proteins. Scientific Reports.  ISSN 2045-2322.  6 . doi: 10.1038/srep36331 Fulltekst i vitenarkiv.
• Reubsaet, Leon & Halvorsen, Trine Grønhaug (2016). Determination of very low-abundance diagnostic proteins in serum using immuno-capture LC-MS-MS. LC GC Europe.  ISSN 1471-6577.  29(7) Fulltekst i vitenarkiv.
• Rossetti, Cecilia; Levernæs, Maren Christin Stillesby; Reubsaet, Leon & Halvorsen, Trine Grønhaug (2016). Evaluation of affinity-based serum clean-up in mass spectrometric analysis: Plastic vs monoclonal antibodies. Journal of Chromatography A.  ISSN 0021-9673.  1471, s 19- 26 . doi: 10.1016/j.chroma.2016.09.069
• Rosting, Cecilie; Sæ, Christine Østvik; Gjelstad, Astrid & Halvorsen, Trine Grønhaug (2016). Evaluation of water-soluble DBS for small proteins: A conceptual study using insulin as a model analyte. Bioanalysis.  ISSN 1757-6180.  8(10), s 1051- 1065 . doi: 10.4155/bio-2016-0002
• Kaupang, Åsmund; Hildonen, Siri; Halvorsen, Trine Grønhaug; Mortén, Magnus; Vik, Anders & Hansen, Trond Vidar (2015). Involvement of covalent interactions in the mode of action of PPARβ/δ antagonists. RSC Advances.  ISSN 2046-2069.  5(93), s 76483- 76490 . doi: 10.1039/c5ra15707b
• Kaupang, Åsmund; Paulsen, Steinar Martin; Steindal, Calin Constantin; Ravna, Aina Westrheim; Sylte, Ingebrigt; Halvorsen, Trine Grønhaug; Thoresen, G. Hege & Hansen, Trond Vidar (2015). Synthesis, biological evaluation and molecular modeling studies of the PPARβ/δ antagonist CC618. European Journal of Medicinal Chemistry.  ISSN 0223-5234.  94, s 229- 236 . doi: 10.1016/j.ejmech.2015.03.006 Fulltekst i vitenarkiv.
• Pedersen-Bjergaard, Stig; Gjelstad, Astrid & Halvorsen, Trine Grønhaug (2015). Sample preparation, In Steen Honoré Hansen & Stig Pedersen-Bjergaard (ed.),  Bioanalysis of pharmaceuticals : sample preparation, separation techniques and mass spectrometry.  Wiley-Blackwell.  ISBN 978-111871682-3.  s 73 - 121
• Rosting, Cecilie; Gjelstad, Astrid & Halvorsen, Trine Grønhaug (2015). Water-Soluble Dried Blood Spot in Protein Analysis: A Proof-of-Concept Study. Analytical Chemistry.  ISSN 0003-2700.  87(15), s 7918- 7924 . doi: 10.1021/acs.analchem.5b01735
• Vestrheim, Anne Cathrine; Moen, Anders; Egge-Jacobsen, Wolfgang; Reubsaet, Leon; Halvorsen, Trine Grønhaug; Bratlie, Diane Bryant; Paulsen, Berit Smestad & Michaelsen, Terje Einar (2014). A pilot study showing differences in glycosylation patterns of IgG subclasses induced by pneumococcal, meningococcal, and two types of influenza vaccines. Immunity,Inflammation and Disease.  ISSN 2050-4527.  2(2), s 76- 91
• Hildonen, Siri; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2014). Why less is more when generating tryptic peptides in bottom-up proteomics. Proteomics.  ISSN 1615-9853.  14(17-18), s 2031- 2041 . doi: 10.1002/pmic.201300479
• Lund, Hanne; Paus, Elisabeth; Berger, Peter; Stenman, Ulf-Håkan; Torcellini, Tamara; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2014). Epitope analysis and detection of human chorionic gonadotropin (hCG) variants by monoclonal antibodies and mass spectrometry. Tumour Biology.  ISSN 1010-4283.  35(2), s 1013- 1022 . doi: 10.1007/s13277-013-1135-y
• Rossetti, Cecilia; Abdel Qader, Abed; Halvorsen, Trine Grønhaug; Sellergren, Börje & Reubsaet, Leon (2014). Antibody-free biomarker determination: Exploring molecularly imprinted polymers for pro-gastrin releasing peptide. Analytical Chemistry.  ISSN 0003-2700.  86(24), s 12291- 12298 . doi: 10.1021/ac503559c
• Torsetnes, Silje Bøen; Levernæs, Maren Christin Stillesby; Nordlund, Marianne Sparby; Paus, Elisabeth; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2014). Multiplexing determination of small cell lung cancer biomarkers and their isovariants in serum by immunocapture LC-MS/MS. Analytical Chemistry.  ISSN 0003-2700.  86(14), s 6983- 6992 . doi: 10.1021/ac500986t
• Torsetnes, Silje Bøen; Nordlund, Marianne Sparby; Paus, Elisabeth; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2014). Determining ProGRP and isoforms in lung and thyroid cancer patient samples: Comparing an MS method with a routine clinical immunoassay. Analytical and Bioanalytical Chemistry.  ISSN 1618-2642.  406(11), s 2733- 2738 . doi: 10.1007/s00216-014-7634-x
• Lund, Hanne; Snilsberg, Ann Helene; Halvorsen, Trine Grønhaug; Hemmersbach, Peter J & Reubsaet, Leon (2013). Comparison of newly developed immuno-MS method with existing DELFIA (R) immunoassay for human chorionic gonadotropin determination in doping analysis. Bioanalysis.  ISSN 1757-6180.  5(5), s 623- 630 . doi: 10.4155/bio.13.8
• Torsetnes, Silje Bøen; Nordlund, Marianne Sparby; Paus, Elisabeth; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2013). Immunocapture and LC-MS/MS for selective quantification and differentiation of the isozymes of the biomarker neuron-specific enolase in serum. Journal of Chromatography B: Biomedical Sciences and Applications.  ISSN 1387-2273.  929, s 125- 132 . doi: 10.1016/j.jchromb.2013.04.010
• Torsetnes, Silje; Nordlund, Marianne Sparby; Paus, Elisabeth; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2013). Digging Deeper into the Field of the Small Cell Lung Cancer Tumor Marker ProGRP: A Method for Differentiation of Its Isoforms. Journal of Proteome Research.  ISSN 1535-3893.  12, s 412- 420 . doi: 10.1021/pr300751j
• Lund, Hanne; Løvsletten, Karoline; Paus, Elisabeth; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2012). Immuno-MS Based Targeted Proteomics: Highly Specific, Sensitive, and Reproducible Human Chorionic Gonadotropin Determination for Clinical Diagnostics and Doping Analysis. Analytical Chemistry.  ISSN 0003-2700.  84(18), s 7926- 7932 . doi: 10.1021/ac301418f
• Lund, Hanne; Snilsberg, Ann Helene; Paus, Elisabeth; Halvorsen, Trine Grønhaug; Hemmersbach, Peter J & Reubsaet, Leon (2012). Sports drug testing using immuno-MS: clinical study comprising administration of human chorionic gonadotropin to males. Analytical and Bioanalytical Chemistry.  ISSN 1618-2642.  405(5), s 1569- 1576 . doi: 10.1007/s00216-012-6566-6
• Wangensteen, Helle; Phan, Thi Thanh; Rise, Frode; Halvorsen, Trine Grønhaug & Malterud, Karl Egil (2012). New labdane diterpenes from Solidago canadensis. Natural Product Research.  ISSN 1478-6419.  26(14), s 1348- 1354 . doi: 10.1080/14786419.2011.565005
• Balchen, Marte; Halvorsen, Trine Grønhaug; Reubsaet, Jan Leo & Pedersen-Bjergaard, Stig (2009). Rapid isolation of angiotensin peptides from plasma by electromembrane extraction. Journal of Chromatography A.  ISSN 0021-9673.  1216(41), s 6900- 6905 . doi: 10.1016/j.chroma.2009.08.037
• Lund, Hanne; Torsetnes, Silje; Paus, Elisabeth; Nustad, Kjell; Reubsaet, Jan Leo & Halvorsen, Trine Grønhaug (2009). Exploring the Complementary Selectivity of Immunocapture and MS Detection for the Differentiation between hCG Isoforms in Clinically Relevant Samples. Journal of Proteome Research.  ISSN 1535-3893.  8(11), s 5241- 5252 . doi: 10.1021/pr900580n
• Winther, Bjørn; Paus, Elisabeth; Nordlund, Marianne Sparby; Reubsaet, Jan Leo & Halvorsen, Trine Grønhaug (2009). Immuno-capture as ultimate sample cleanup in LC-MS/MS determination of the early stage biomarker ProGRP. Journal of Separation Science.  ISSN 1615-9314.  32(17), s 2937- 2943 . doi: 10.1002/jssc.200900233
• Pedersen-Bjergaard, Stig; Rasmussen, Knut Einar; Brekke, Anders; Si Ho, Tung & Halvorsen, Trine Grønhaug (2005). Liquid-phase microextraction of basic drugs - Selection of extraction mode based on computer calculated solubility data. Journal of Separation Science.  ISSN 1615-9314.  28, s 1195- 1203
• Andersen, Solveig Norheim; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig; Rasmussen, Knut Einar; Tanum, Lars & Refsum, Helge (2003). Stereospecific determination of citalopram and desmethylcitalopram by capillary electrophoresis and liquid-phase microextraction. Journal of Pharmaceutical and Biomedical Analysis.  ISSN 0731-7085.  33, s 263- 273
• Bjørhovde, Anett; Halvorsen, Trine Grønhaug; Rasmussen, Knut Einar & Pedersen-Bjergaard, Stig (2003). Liquid-phase microextraction of drugs from human breast milk. Analytica Chimica Acta.  ISSN 0003-2670.  491, s 155- 161
• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig; Reubsaet, Jan Leo & Rasmussen, Knut Einar (2003). Liquid-phase microextraction combined with liquid chromatography-mass spectrometry. Extraction from small volumes of biological samples. Journal of Separation Science.  ISSN 1615-9314.  26(17), s 1520- 1526 Vis sammendrag

  Liquid-phase microextraction (LPME) is a sample preparation technique based on disposable polypropylene hollow fibres, which results in efficient sample clean-up and high preconcentration. The present paper describes the combination of LPME with LC-MS utilising electrospray ionisation for high sensitivity. Nine antidepressant drugs were extracted from 50 or 500 µl of plasma or whole blood samples, through a thin layer of dodecyl acetate immobilised in the pores of the hollow fibre and into 15 µl of 200 mM formic acid as acceptor solution inside the hollow fibre. Analyte recoveries in the range 12-68 % and 9-52 % were obtained from 50 µl of plasma and whole blood respectively. The acceptor solution (15 µl) was diluted with 60 µl of 5 mM ammonium formate pH=2.7 prior to injection into the LC-MS system. The system was qualitatively investigated for matrix effects utilising a post-column infusion system. Whole blood from 5 different persons were cleaned-up by LPME and injected onto the analytical column while a solution of the 9 model compounds was continuously infused post-column. No signs of ion suppression were seen for any of the model compounds. Limits of quantification (S/N=10) were in the low ng/ml area for 6 of the 9 model compounds utilising a sample volume of only 50 µl of whole blood. The repeatability of the extractions was investigated utilising paroxetine as internal standard. Acceptable RSDs (%) were obtained (< 20%)for 5 of the antidepressants. By increasing the sample volume from 50 to 500 µl of whole blood RSDs below 20 % (3-16 %) were seen.

• Ho, Si Tung; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2003). Liquid-phase microextraction of hydrophilic drugs by carrier-mediated transport. Journal of Chromatography A.  ISSN 0021-9673.  998, s 61- 72
• Andersen, Solveig Norheim; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2002). Liquid-phase microextraction combined with capillary electrophoresis, a promising tool for the determination of chiral drugs in biological matrices. Journal of Chromatography A.  ISSN 0021-9673.  963, s 303- 312 Vis sammendrag

  A disposable device for liquid-phase microextraction (LPME) based on porous polypropylene hollow fibres has recently been introduced. In the present paper, LPME was combined with capillary electrophoresis (CE)and the combination was for the first time evaluated for chiral determination of drugs in biological matrices. The chiral antidepressant drug mianserin was selected as model compound. The mianserin enantiomers were extracted from 0.5 ml of plasma added internal standard and made alkaline with 0.25 ml of 2 M NaOH. The unionised analytes were extracted into di-n-hexyl ether impregnated in the pores of the hollow fibre, and into an acidic solution inside the hollow fibre. This resulted in a three-phase system where the extracts were aqueous, and hence directly compatible with the CE system. Efficient sample clean-up was seen and the extraction recovery was 80% for both enantiomers. Discrimination between the enantiomers in the extraction system was not observed. The limit of quantitation (S/N=10; 12.5 ng/ml for both enantiomers) and the limit of detection (S/N=3; 4 ng/ml for both enantiomers) were below the therapeutic range for mianserin. The method was validated and successfully applied to determine R- and S-mianserin in plasma samples from seven patients treated with mianserin, indicating that LPME¿CE is a promising combination for analysis of racemic drugs present in low concentrations in biological matrices.

• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2001). Liquid-Phase Microextraction and capillary electrophoresis of citalopram, an antidepressant drug. Journal of Chromatography A.  ISSN 0021-9673.  909, s 87- 93 Vis sammendrag

  A newly developed disposable device for liquid-phase microextraction (LPME) was evaluated for the capillary electrophoresis (CE) of the antidepressant drug citalopram (CIT) and its main metabolite N-desmethylcitalopram (DCIT) in human plasma. CIT and DCIT were extracted from 1 ml plasma samples through hexyl ether immobilised in the pores of a porous polypropylene hollow fibre and into 25 µl of 20 mM phosphate buffer (pH 2.75) present inside the hollow fibre (acceptor phase). Prior to extraction, the samples were made strongly alkaline in order to promote LPME of the basic drugs. Owing to the high ratio between the volumes of sample and acceptor phase, and owing to high partition coefficients, CIT and DCIT were enriched by a factor of 25 to 30. In addition, sample clean-up occurred during LPME since salts, proteins, and the majority of endogenic substances were unable to penetrate the hexyl ether layer. Since the extracts were aqueous, they were injected directly into the CE instrument. Limits of quantification (S/N=10) for CIT and DCIT in plasma were 16.5 ng/ml and 18 ng/ml respectively, while the limits of detection (S/N=3) were 5 ng/ml and 5.5 ng/ml respectively. This enabled CIT (and DCIT) to be analysed within the therapeutic range by LPME-CE and detection limits were comparable with previously reported HPLC methods.

• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2001). Reduction of extraction times in liquid-phase microextraction. Journal of chromatography. B.  ISSN 1570-0232.  760(2), s 219- 226 Vis sammendrag

  Recently, we introduced a simple and inexpensive disposable device for liquid-phase microextraction (LPME) based on porous polypropylene hollow fibres. In the present paper, extraction times were significantly reduced by an increase of the surface of the hollow fibres. The model compounds methamphetamine and citalopram, were extracted from 2.5 ml of urine, plasma, and whole blood after dilution with water and alkalisation with 125 µl of 2M NaOH though a porous polypropylene hollow fibre impregnated with hexyl ether and into an aqueous acceptor phase consisting of 0.1 M HCl. Two commercially available hollow fibres, which differed in surface area, wall thickness and internal diameter, were compared. An increase in the contact area of the hollow fibre with the sample solution by a factor of approximately two resulted in reduction in equilibrium times by approximately the same factor. Thus, the model compounds were extracted to equilibrium within 15 minutes from both urine and plasma, and within 30 minutes from whole blood. For the first time LPME was utilised to extract drugs from whole blood, and the extracts were comparable with plasma both with regard to sample clean-up and extraction recoveries. Extraction recoveries for methamphetamine and citalopram varied from 60 to 100 % utilising the two fibres and the different matrices.

• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig; Reubsaet, Jan Leo & Rasmussen, Knut Einar (2001). Liquid-phase microextraction combined with flow-injection tandem mass spetrometry. Rapid screening of amphetamines from biological matrices. Journal of Separation Science.  ISSN 1615-9314.  24, s 615- 622 Vis sammendrag

  Liquid-phase microextraction based on polypropylene hollow fibres was combined with flow-injection tandem mass spectrometry for rapid screening of drugs in biological matrices. Amphetamine and analogues were utilised as model compounds. These drugs were extracted from 0.5 ml samples of whole blood or urine. The samples were made alkaline with 0.5 ml of 1 M NaOH. The uncharged analytes were then extracted through a hollow fibre impregnated with dihexyl ether into 25 µl of 0.01 M HCl inside the hollow fibre. Parallel extraction of 20-30 samples was performed for 15 minutes. After extraction 20 µl of the extract was injected directly into the flow-injection tandem mass spectrometry system. Atmospheric pressure ionisation opereated in the positive mode was used as ion spray. All analytes were detected simultaneously after 0.1 min, utilising a combination of selected ion monitoring mass spectrometry and selected reaction monitoring tandem mass spectrometry. Limits of detection (S/N=5) varied between the compounds and were estimated to 2-100 ng/ml in urine and 0.4-14 ng/ml in whole blood. Comparison of injection of pure acceptor solution with urine and whole blood extracts demonstrated the efficient sample clean-up by LPME. Ion suppression due to matrix effects was not seen, rendering LPME-FIA-APCI-MS-MS a promising alternative for rapid screening of drugs in biological matrices.

• Pedersen-Bjergaard, Stig & Halvorsen, Trine Grønhaug (2000). Microemulsion Electrokinetic Chromatography in Suppressed Electroosmotic Flow Environment for the Analysis of Pharmaceuticals. Chromatographia.  ISSN 0009-5893.  52, s 593- 598
• Rasmussen, Knut Einar; Pedersen-Bjergaard, Stig; Krogh, Mette; Grefslie, Hege & Halvorsen, Trine Grønhaug (2000). Development of a Simple In-Vial Liquid-Phase Microextraction Device (LPME) for Drug Analysis Compatible with both Capillary Gas Chromatography, Capillary Electrophoresis, and High Performance Liquid Chromatography. Journal of Chromatography A.  ISSN 0021-9673.  873, s 3- 11

Se alle arbeider i Cristin

• Skjærvø, Øystein; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2019). Smart blood-spot sampling for MS based bottom-up protein analysis.
• Brandtzaeg, Ole Kristian; Levernæs, Maren Christin Stillesby; Halvorsen, Trine Grønhaug; Reubsaet, Leon; Røen, Bent Tore; Vehus, Tore; da Silva, Meire Ribeiro; Røberg-Larsen, Hanne; Lundanes, Elsa & Wilson, Steven Ray Haakon (2018). Online sample processing systems for targeted nano liquid chromatography mass spectrometry bioanalysis.
• Skjærvø, Øystein; Pilarova, Veronika; Khalikova, Maria; Reubsaet, Leon; Halvorsen, Trine Grønhaug; Gjelstad, Astrid; Øiestad, Elisabeth Leere; Lundanes, Elsa; Wilson, Steven Ray Haakon & Pedersen-Bjergaard, Stig (2018). Those Who Can, Teach: Pharma Stars. The Analytical Scientist.  ISSN 2051-4077.  1118, s 40- 45
• Skjærvø, Øystein; Pilarova, Veronika; Khalikova, Maria; Reubsaet, Leon; Halvorsen, Trine Grønhaug; Gjelstad, Astrid; Øiestad, Elisabeth Leere; Lundanes, Elsa; Wilson, Steven Ray Haakon & Pedersen-Bjergaard, Stig (2018). Those Who Can, Teach: Pharma Stars. The Analytical Scientist.  ISSN 2051-4077.  1118, s 40- 45
• Vehus, Tore; Wilson, Steven Ray Haakon; Lundanes, Elsa; Krauss, Stefan; Halvorsen, Trine Grønhaug & Morth, Jens Preben (2018). Nano Liquid Chromatography-Tandem Mass Spectrometry Platforms for Determination of Low Abundant Wnt/Beta-Catenin Proteins in Cancer Research. Series of dissertations submitted to the Faculty of Mathematics and Natural Sciences, University of Oslo.. 1962.
• Rossetti, Cecilia; Ore, Odd Gøran; Sellergren, Börje; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2017). Correction to: Exploring the peptide retention mechanism in molecularly imprinted polymers (Analytical and Bioanalytical Chemistry, (2017), 409, 24, (5631-5643), 10.1007/s00216-017-0520-6). Analytical and Bioanalytical Chemistry.  ISSN 1618-2642.  410(5), s 1607- 1608 . doi: 10.1007/s00216-017-0797-5
• Halvorsen, Trine Grønhaug (2016). Hva er viktig når jeg lager mobilfase til LC-MS?.
• Halvorsen, Trine Grønhaug; Rossetti, Cecilia; Levernæs, Maren Christin Stillesby & Reubsaet, Leon (2016). The Impact of Sample Clean-up Technique in Bottom-up based LC-MS Analysis of Low Abundance Serum Biomarkers.
• Ask, Kristine Skoglund; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Gjelstad, Astrid (2015). Phospholipid removal from human plasma samples by Parallel Artificial Liquid Membrane Extraction.
• Halvorsen, Trine Grønhaug; Egeland, Siri Valen & Reubsaet, Leon (2015). Dual immunocapture combined with targeted LC-MS/MS for increased differentiation power in protein biomarker determination.
• Kaupang, Åsmund; Hildonen, Siri; Halvorsen, Trine Grønhaug; Mortén, Magnus; Vik, Anders & Hansen, Trond Vidar (2015). Investigations on the covalent antagonistic modulation of PPARβ/δ.
• Reubsaet, Leon & Halvorsen, Trine Grønhaug (2015). Analysis of Peptide and Protein Drugs in Biological Fluids, In Steen Honoré Hansen & Stig Pedersen-Bjergaard (ed.),  Bioanalysis of pharmaceuticals : sample preparation, separation techniques and mass spectrometry.  Wiley-Blackwell.  ISBN 978-111871682-3.  10.  s 261 - 282
• Halvorsen, Trine Grønhaug (2014). Mobilfaser i HPLC - Ti uvaner du bør unngå.
• Halvorsen, Trine Grønhaug; Lund, Hanne & Reubsaet, Leon (2014). Immunoaffinity + LC-MS/MS: An alternative approach for antibody selectivity evaluation?.
• Halvorsen, Trine Grønhaug; Lund, Hanne & Reubsaet, Leon (2013). Targeted biomarker analysis by combined immunoaffinity and LC-MS/MS.Potential and possibilities.
• Lund, Hanne; Reubsaet, Léon; Halvorsen, Trine Grønhaug; Paus, Elisabeth & Lundanes, Elsa (2013). Targeted Proteomics Applied in Clinical Diagnostics and Doping Analysis - Immuno-MS based Determination of Human Chorionic Gonadotropin..
• Torsetnes, Silje Bøen; Halvorsen, Trine Grønhaug; Reubsaet, Leon; Paus, Elisabeth; Nordlund, Marianne Sparby & Levernæs, Maren C. S. (2013). ”Breaking barriers in cancer marker determination, Simultaneous differentiation of ProGRP isoforms and NSE isoenzymes by bottom-up immuno-LC-MS/MS”, M. C. S. Levernæs, S. B. Torsetnes, M. S. Nordlund, T. G. Halvorsen, E. Paus, L. Reubsaet. NCMS (Nordic NSMS), Hafjell, 2013.
• Halvorsen, Trine Grønhaug (2012). Mobilfaser i omvendt fase HPLC.
• Halvorsen, Trine Grønhaug; Lund, Hanne; Torsetnes, Silje & Reubsaet, Leon (2012). Immunoaffinity based sample preparation combined with LC-MS/MS in targeted proteomics – a match of high sensitivity and differentiation power.
• Løvbak, Sandra G.; Torsetnes, Silje Bøen; Reubsaet, Leon; Halvorsen, Trine Grønhaug; Paus, Elisabeth & Nordlund, Marianne Sparby (2012). “Hvordan én LC-MS-analyse avdekker biomarkørens diversitet – NSE-differensiering i SCLC”, S. G. Løvbak, S. B. Torsetnes, M. S. Nordlund, T. G. Halvorsen, E. Paus, L. Reubsaet. 20. Norske Symposium i Kromatografi, Sandefjord, 2012.
• Torsetnes, Silje; Nordlund, Marianne Sparby; Paus, Elisabeth; Halvorsen, Trine Grønhaug & Reubsaet, Leon (2012). Digging deeper into samll cell lung cancer. Can targeted LC-MS reveal tomorrows diagnostic level?.
• Halvorsen, Trine Grønhaug (2011). Immunoekstraksjon og LC-MS/MS - et hjelpemiddel for mer presis diagnose av sykdommer.
• Halvorsen, Trine Grønhaug; Lund, Hanne; Paus, Elisabeth; Nustad, Kjell & Reubsaet, Leon (2011). Immunocapture combined with tandem-MS detection for differentiation between hCG isoforms in clinical relevant samples.
• Halvorsen, Trine Grønhaug (2010). Valg og tillaging av mobilfaser i HPLC.
• Lund, Hanne; Paus, Elisabeth; Nustad, Kjell; Halvorsen, Trine Grønhaug & Reubsaet, Léon (2010). Immuno-MS as s reference method for the evaluation of the selectivity of antibodies used for hCG detection in clinical diagnostics.
• Halvorsen, Trine Grønhaug; Winther, Bjørn & Reubsaet, Jan Leo (2009). Efficient immuno-capture based sample clean-up and LC-MS/MS analysis of the early stage small cell lung cancer biomarker ProGRP.
• Reubsaet, Jan Leo; Lund, Hanne; Winther, Bjørn & Halvorsen, Trine Grønhaug (2009). Immunocapture as ultimate sample clean-up in LC-MS/MS of biomarkers.
• Halvorsen, Trine Grønhaug (2003). Liquid-phase microextraction of drugs in biological matrices.
• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2003). Liquid-Phase Microextraction - Efficient and Simple Sample Preparation of Biological Matrices.
• Andersen, Solveig Norheim; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2002). Kiral terapikontroll vha. væskefasemikroekstraksjon og kapillærelektroforese. Enantiomer bestemmelse av mianserin i plasma hos psykiatriske pasienter. Vis sammendrag

  Kirale legemidler blir i de fleste tilfeller gitt som racemater selv om de to enantiomere formene har forskjellig farmakologisk virkning, terapeutisk effekt og metabolisme. Optimalisering av hurtige kirale analyser med høy effektivitet og oppløsning er derfor viktig slik at kiral terapikontroll kan utføres og de ulike enantiomerenes farmakologiske egenskaper samt enantiomer renhet av kirale legemidler i farmasøytiske formuleringer kan studeres. Til nå har kromatografiske metoder vært mest utbredt i stereospesifikk legemiddel monitorering, men ved bruk av disse teknikkene er man avhengig av relativt dyre kirale stasjonærfaser. I løpet av de siste årene har kapillær elektroforese (CE) vist seg å være en teknikk som gir billige kirale analyser med høy effektivitet og oppløsning. Metoden gir i tillegg høy selektivitet og analysetidene er korte. CE er derfor et godt alternativ i kiral analyse. Ulempen er at man ikke har kunnet benytte CE til terapeutisk legemiddel monitorering da teknikken har for høye deteksjons- og kvantifiseringsgrenser. Væskefasemikroekstraksjon (LPME) er en relativt ny prøveopparbeidelsesteknikk som er spesielt godt egnet i kombinasjon med CE. Analytter blir ekstrahert fra en biologisk prøve gjennom en porøs hulfiber impregnert med organsikk løsningsmiddel og inn i en akseptorfase på innsiden av fiberen. Denne akseptorfasen er vandig i kombinasjon med CE, og ekstraktet kan dermed injiseres direkte i CE-apparatet. Det resulterende tre-fase systemet ved LPME gir spesielt god opprensing av prøvene. På grunn av en stor volumforskjell mellom prøveløsningen (0.5-4 ml) og akseptorfasen (25 µl) er det mulighet for høy oppkonsentrering av legemidlene. Denne høye oppkonsentreringen og den effektive prøveopprensingen sammen med fordelene av CE i kiral analyse gjør LPME/CE til en god kombinasjon ved kiral terapikontroll. I dette prosjektet ble det utviklet en metode hvor mianserinenantiomerene ble oppkonsentrert fra 0.5 ml plasma gjennom en hulfiber impregnert med heksyleter og inn i en akseptorfase bestående av 0.01 M HCl. Den enantiomere separasjonen ble utført ved bruk av hydroxypropyl-&#946;-cyclodekstrin som kiral selektor. Metoden ble validert og brukt til å bestemme R- og S-mianserin i plasmaprøver fra 7 pasienter behandlet med racemisk mianserin. Resultatene viste ulik hastighet av metabolismen til enantiomerene. Alle pasientene hadde høyest konsentrasjon av den mest aktive enantimeren, S-mianserin. I tillegg kunne man se at konsentrasjonen av S-mianserins hovedmetabolitt var tilsvarende lavere i forhold til konsentrasjonen av R-mianserins hovedmetabolitt.

• Andersen, Solveig Norheim; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig; Rasmussen, Knut Einar; Tanum, Lars & Refsum, Helge (2002). CHIRAL ANALYSIS OF MIANSERIN IN PLASMA BY LIQUID-PHASE MICROEXTRACTION AND CAPILLARY ELECTROPHORESIS. Vis sammendrag

  Chiral drugs are usually administered as racemates although the two enantiomers often exhibit different behaviour in terms of pharmacological action and therapeutic efficiency. The optimisation of fast enantioselective analytical methods offering high efficiency and resolution is, therefore, important for the study of pharmacokinetic and pharmacodynamic properties of racemic drugs, and to control the enantiomeric purity of pharmaceutical preparations. In the present work a relatively new sample preparation technique called liquid-phase microextraction was combined with capillary electrophoresis, and the combination was evaluated for chiral determination of drugs in biological matrices. The antidepressant drug mianserin was chosen as a model compound. Mianserin is a chiral drug administered as a racemic mixture. The two enantiomers of mianserin exhibit different degree of antidepressant activity, the S-enantiomer being significantly more active than the R-enantiomer. The mianserin enantiomers were extracted from 0.5 ml of plasma samples made alkaline with NaOH, through a thin phase of hexyl ether inside the pores of a polypropylene hollow fibre, and finally into a 25 µl acidic solution inside the hollow fibre. Following sample clean-up and preconcentration by liquid-phase microextraction, the acceptor solutions were analyzed by capillary electrophoresis. The enantiomeric separation was performed using a cyclodextrin as the chiral selector. The method was validated and successfully applied to determine R- and S-mianserin in plasma samples from seven patients treated with mianserin. The results indicate that liquid-phase microextraction combined with capillary electrophoresis is a promising tool for analysis of racemic drugs present in low concentrations in biological matrices.

• Andersen, Solveig Norheim; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig; Rasmussen, Knut Einar; Tanum, Lars & Refsum, Helge (2002). STEREOSPECIFIC DRUG MONITORING OF ANTIDEPRESSANT DRUGS. Vis sammendrag

  Many drugs used to treat psychiatric disorders contain one or more chiral centres. Most chiral drugs are available as the racemate, in which equal proportions of the two enantiomers are administered concurrently, although the two enantiomers may exhibit different pharmacodynamic and pharmacokinetic properties. Mianserin and citalopram are examples of chiral antidepressant drugs currently marketed as racemic mixtures, despite the fact that pharmacological activity reside primarily in one enantiomer. The S-enantiomer of both mianserin and citalopram are more active than the corresponding R-enantiomers. In the present project, stereospecific drug monitoring of mianserin and citalopram was accomplished by liquid-phase microextraction (LPME) combined with capillary electrophoresis (CE). Determinations of enantiomer concentrations of mianserin and citalopram were done in plasma from patients treated with racemic mianserin or citalopram. The results showed stereoselectivity in the metabolism of both mianserin and citalopram. A variation in the enantiomer ratio of both drugs was observed. No significant correlation between the administered dose and resulting plasma concentration could be demonstrated. The results suggest that separate determination of each enantiomer reflects antidepressant activity better than determination of the total mianserin or citalopram concentration.

• Halvorsen, Trine Grønhaug; Andersen, Solveig Norheim; Rasmussen, Knut Einar & Pedersen-Bjergaard, Stig (2002). Chiral analysis of drugs at the low ng/ml level in human plasma by liquid-phase microextraction and capillary electrophoresis. Vis sammendrag

  In the present work, the potential of liquid-phase microextraction (LPME) combined with capillary zone electrophoresis(CZE) for the chiral monitoring of drugs in human plasma was evaluated. Mianserin and citalopram were selected as model drugs which are administered as racemates, and the concentration leves studied where within the range from 10 to 1000 ng/ml (which included the therapeutic levels). By LPME, the drugs were extracted from 0.5 ml of plasma through an organic liquid (typically di-hexyl ether) immobilised in the pores of a small porous polypropylene hollow fibre and into a small acceptor solution of 25 µl 10 mM HCl inside the lumen of the hollow fibre. Subsequently, the acceptor phase was directly subjected to analysis by CZE utilising different charged cyclodextrins as chiral selectors. With LPME, the drugs were preconcentrated by a factor 15 to 20 which enabled their detection down to the 5-10 ng/ml level by CZE with UV-detection. In addition, the three-phase nature of LPME ensured very high clean-up from plasma eliminating most potential interferences. In conclusion, the high analyte enrichment of LPME was successfully combined with the excellent chiral resolving power of CZE and enabled rapid determinations of drugs in human plasma an the low ng/ml level.

• Halvorsen, Trine Grønhaug; Ho, Si Tung; Rasmussen, Knut Einar & Pedersen-Bjergaard, Stig (2002). Liquid-phase microextraction: Efficient sample clean-up and superior enrichment of drugs in biological matrices. Vis sammendrag

  We have recently presented a novel extraction method, known as liquid-phase microextraction (LPME) for extraction of trace level of pharmaceuticals from biological matrices (1-2). The protocol utilises organic liquid membranes supported on porous hollow fibres and operates in the static mode. The technique can handle sample volumes ranging from 0.5-5.0 ml with pharmaceutical concentrations of 1.0 ng or less. It makes use of extraction liquid volumes of 0.025 ml, which facilitates analyte enrichments of several orders of magnitude. It is compatible with gas chromatography (GC), high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Extraction times range from 15 to 30 minutes and extracts can be injected directly into CE, LC and LC-MS systems without further manipulation. Whole blood, serum, plasma or urine samples can be analysed without any pre-treatment. In the current, communication, parameters that can be varied to impart selectivity on the extraction process are discussed. Making use of a host of acidic and basic pharmaceuticals and their metabolites the selective extraction of specific analytes is demonstrated. (1) K.E.Rasmussen, S.Pedersen-Bjergaard, M.Krogh, H.G.Ugland and T.Grønhaug, J. Chromatogr. A, 873 (2000) 3. (2) S. Pedersen-Bjergaard, K.E. Rasmussen, Anal. Chem 72 (1999) 2650.

• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2002). Simple and selective sample preparation of biological matrices by liquid-phase microextraction. Vis sammendrag

  A novel extraction method, known as liquid-phase microextraction (LPME) for extraction of trace level of pharmaceuticals from biological matrices has recently been introduced (1-2). Organic liquid membranes are supported on porous hollow fibres and the system is operated in the static mode. The technique is well suited for sample volumes of 0.5-4.0 ml containing pharmaceutical concentrations in the low ng/ml-region. It makes use of extraction liquid volumes of 0.015-0.025 ml, which facilitates analyte enrichments of several orders of magnitude. It is compatible with gas chromatography (GC), high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Extraction time range from 15 to 30 minutes and extracts can be injected directly into CE, LC and LC-MS systems without further manipulation. Whole blood, serum, plasma or urine samples can be analysed without any pre-treatment. In the current communication, the combination of LPME and LC-MS is discussed with respect to selectivity and efficiency. The combination has been evaluated by determination and quantification of 9 antidepressant drugs in plasma. LPME of the plasma samples was performed for 30 minutes, and a volatile extraction liquid (formic acid) was used. The following analysis of the extracts by LC-MS demonstrated the high selectivity and efficient sample clean-up of the extraction system, two important parameters in reducing the possibilities of ion suppression in ESI-MS. (1) K.E. Rasmussen, S. Pedersen-Bjergaard, M. Krogh, H.G. Ugland and T. Grønhaug, J. Chromatogr. A, 873 (2000) 3. (2) S. Pedersen-Bjergaard, K.E. Rasmussen, Anal. Chem 72 (1999) 2650.

• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2002). Væskefasemikroekstraksjon - Enkel og effektiv prøveopparbeidelse av legemidler i biologiske prøver. Vis sammendrag

  Kort tid tilbake ble en ny prøveopparbeidelsesteknikk introdusert (1). Denne teknikken, kalt væskefasemikroekstraksjon (LPME), er basert på porøse polypropylen hulfibre og kan benyttes i kombinasjon med gasskromatografi (GC), væskekromatografi (HPLC) og kapillærelektroforese (CE). Analyttene ekstraheres fra små prøver med biologisk materiale gjennom en porøs hulfiber impregnert med organisk løsningsmiddel og videre inn i hulrommet inni hulfiberen hvor det er plassert en akseptorfase. Både sure, basiske og nøytrale stoffer kan opparbeides ved hjelp av LPME. Stor volumforskjell mellom prøveløsningen (1-4 ml) og akseptorløsningen (25 µl) gir mulighet for høy oppkonsentrering av analyttene så fremt fordelingskoeffesienten mellom fasene er høy. Løsningsmiddelforbruket er lavt da kun et lite volum (~15 µl) impregneres i hulfiberen. Carry-over effekter unngås da de enkelte ekstraksjonsenhetene kun benyttes en gang. Et stort antall prøver kan ekstraheres parallelt. Teknikken er benyttet til å oppkonsentrere og opprense legemidler fra både urin, plasma og fullblod. Prøveopparbeidelse ved bruk av LPME har vist seg å gi svært rene ekstrakter. Det er ikke nødvendig med forbehandling av fullblod før ekstraksjon. I denne presentasjonen vil fokus bli rettet mot de siste utviklingene av teknikken. (1) K.E.Rasmussen, S.Pedersen-Bjergaard, M.Krogh, H.G.Ugland and T.Grønhaug, J. Chromatogr. A, 873 (2000) 3.

• Ho, Si Tung; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2002). Ion-pair Liquid Phase Microextraction of Hydrophilic Drugs.
• Ho, Si Tung; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2002). Ion-pair Liquid Phase Microextraction of Hydrophilic Drugs.
• Andersen, Solveig Norheim; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2001). Kiral analyse av mianserin i plasma hos psykiatriske pasienter Bestemmelse ved hjelp av væskefasemikroekstraksjon og kapillærelektroforese. Vis sammendrag

  Kirale legemidler blir i de fleste tilfeller gitt som racemater selv om de to enantiomere formene er forskjellig med henblikk på farmakologisk virkning, terapeutisk effekt og metabolisme. Optimalisering av hurtige kirale analyser som har høy effektivitet og oppløsning er derfor viktig slik at farmakodynamiske og farmakokinetiske egenskaper av racemiske legemidler samt renhet av enantiomerene i farmasøytiske formuleringer kan studeres. Til nå har kromatografiske metoder vært mest utbredt i stereospesifikk legemiddel monitorering, men ved bruk av disse teknikkene er man avhengig av relativt dyre kirale stasjonærfaser. I løpet av de siste årene har kapillær elektroforese (CE) vist seg å være en teknikk som gir billige kirale analyser med høy effektivitet og oppløsning. I tillegg gir metoden høy selektivitet og analysetidene er korte. CE er derfor et godt alternativ i kiral analyse. Ulempen er at man ikke har kunnet benytte CE til terapeutisk legemiddel monitorering da teknikken har for høye deteksjons- og kvantifiseringsgrenser. Væskefasemikroekstraksjon (LPME) er en relativt ny prøveopparbeidelsesteknikk som er spesielt godt egnet i kombinasjon med CE. Analytter blir ekstrahert fra en biologisk prøve gjennom en porøs hulfiber og inn i en akseptorfase på innsiden av fiberen. Denne akseptorfasen er vandig i kombinasjon med CE, noe som resulterer i et tre-fase system som gir spesielt god opprensing av prøvene. På grunn av en stor volumforskjell mellom prøveløsningen (0.5-4 ml) og akseptorfasen (25 µl) er det mulighet for høy oppkonsentrering av legemidlene. Denne høye oppkonsentreringen og den effektive prøveopprensingen sammen med fordelene av CE i kiral analyse gjør LPME/CE til en god kombinasjon i enantiomere seperasjoner. I dette prosjektet har vi utviklet en metode hvor mianserinenantiomerene ble oppkonsentrert fra 0.5 ml plasma gjennom en hulfiber impregnert med heksyleter og inn i en akseptorfase bestående av 0.01 M HCl. Den enantiomere separasjonen ble utført ved å bruke hydroxypropyl-&#946;-cyclodekstrin som kiral selektor. Metoden ble validert og brukt til å bestemme R- og S-mianserin i plasmaprøver fra 7 pasienter behandlet med racemisk mianserin. Resultatene viste ulik hastighet av metabolismen til enantiomerene. Alle pasientene hadde høyest konsentrasjon av den mest aktive enantimeren, S-mianserin. I tillegg kunne man se at konsentrasjonen av S-mianserins hovedmetabolitt var tilsvarende lavere i forhold til konsentrasjonen av R-mianserins hovedmetabolitt. Resultatene av analysene vil bli diskutert.

• Andersen, Solveig Norheim; Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2001). Liquid-phase microextraction combined with capillary electrophoresis for the determination of mianserin enantiomers in plasma. Vis sammendrag

  The combination of liquid-phase microextraction (LPME), a recently developed sample preparation technique [1], with capillary electrophoresis (CE), resulted in a powerful method for the determination of mianserin enantiomers in plasma. CE provides chiral analysis with high efficiency, resolution and selectivity at a low cost. However, relatively high detection limits have restricted the use of chiral CE in therapeutic drug monitoring where only small amounts of sample are available. LPME is a sample preparation technique especially suitable for combination with CE. In LPME analytes are extracted from biological matrices through a porous polypropylene hollow fibre impregnated with an organic solvent and into an acceptor phase, which is aqueous in combination with CE. This three-phase system results in efficient sample clean-up. A large volume difference between the sample solution (0.5-4 ml) and the acceptor solution (25 µl) results in high preconcentration. High preconcentration and efficient sample clean-up together with the advantages of CE in chiral analysis makes LPME/CE an ideal combination for enantiomeric separations. In this project, mianserin enantiomers were extracted from 0.5 ml of plasma samples, through a hollow fibre impregnated with hexyl ether and into an acceptor phase consisting of 0.01 M HCl. The enantiomeric separation was performed using hydroxypropyl-&#946;-cyclodextrin as the chiral selector. The method was validated and used for determination of R- and S-mianserin in plasma samples from 7 patients treated with mianserin. [1] K.E.Rasmussen, S.Pedersen-Bjergaard, M.Krogh, H.G.Ugland and T.Grønhaug, J. Chromatogr. A, 873 (2000) 3.

• Halvorsen, Trine Grønhaug (2001). Væskefasemikroekstraksjon - hva er det?.
• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2001). Liquid-phase microextraction as a sample preparation technique in bioanalysis. Vis sammendrag

  Liquid-phase microextraction (LPME) utilising polypropylene hollow fibres in a simple and inexpensive device have recently been introduced (1). The technique is compatible with gas chromatography (GC), high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Analytes are extracted from biological matrices through a porous hollow fibre impregnated with an organic solvent and into an acceptor phase. LPME is applicable to acidic, basic and neutral substances. The combination of a large volume difference between the sample (1-4 ml) and the acceptor solution (25 µl) and high partition coefficients enables high preconcentration. In addition, extraction to equilibrium ensures high extraction recoveries. The technique has a low solvent consumption and carry-over effects are eliminated due to disposable extraction devices. In addition, a large number of different samples may be extracted in parallel providing a high number of samples per unit time capacity. High selectivity has been achieved when extractions have been performed from different biological matrices (urine, plasma and whole blood), and extractions from whole blood requires no extra pretreatment compared with extractions from other biological matrices. LPME hence combines high extraction efficiency with simple and inexpensive extraction device and is therefore a promising technique. (1) K.E.Rasmussen, S.Pedersen-Bjergaard, M.Krogh, H.G.Ugland and T.Grønhaug, J. Chromatogr. A, 873 (2000) 3.

• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig; Krogh, Mette & Rasmussen, Knut Einar (2000). Væskefasemikroekstraksjon kombinert med kapillærelektroforese ¿ Et nytt konsept for bestemmelse av legemidler i biologiske prøver. Vis sammendrag

  Kapillærelektroforese (CE) er en forholdsvis ny teknikk innen legemiddelanalyse. Metoden er rask, separerer legemidler effektivt og har et lavt løsningsmiddelforbruk. En ulempe med teknikken er at den gir forholdsvis høye deteksjons- og kvantifiseringsgrenser. Metoden har derfor til nå hatt begrenset anvendelse ved bestemmelse av legemidler i biologiske væsker. Vi har utviklet et enkelt og billig oppsett for væskefase mikroekstraksjon (LPME)(1). LPME utføres på prøver i små komersielle prøveglass; analyttene ekstraheres fra prøven (typisk 1-5 ml vann, urin, plasma etc.) gjennom en porøs hullfiber impregnert med løsningsmiddel, til en vandig mikro-væskefase (5-25 µl). Ekstraktet kan så injiseres direkte på CE. Prosessen gir både oppkonsentrering av analytt og opprensing av prøven. I tillegg kan et stort antall prøver ekstraheres samtidig, noe som gir høy effektivitet. Teknikken kan benyttes både på sure og basiske legemidler. Oppkonsentrering og opprensing av prøvene er basert på analyttenes fordeling mellom donor- og akseptorfasen. Det immobiliserte løsningsmidlet vil fungere som barriere og bærer mellom de to fasene. Prøveløsningen pH-justeres slik at analyttene er nøytrale og har redusert løselighet. Analyttene ekstraheres over i løsningsmidlet og videre inn i akseptorfasen. pH i akseptorfasen velges slik at analyttene har ladning og dermed er svært løselig. Større molekyler (som proteiner) vil være uløselige i det immobiliserte løsningsmidlet og forbli i donorfasen. Ved optimale betingelser vil nær 100 % av analyttene kunne gjenfinnes i akseptorfasen. På grunn av den store forskjellen i donor- og akseptorvolum vil graden av oppkonsentrering være høy (vanligvis 40-100 ganger). LPME forener kraftig oppkonsentrering og høy effektivitet med enkelt og billig ekstraksjonsoppsett, noe som gjør det til en lovende teknikk. (1) Pedersen-Bjergaard, S.; Rasmussen, K. E. Anal. Chem. 1999, 71, 2650-6.

• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2000). Liquid-Phase Microextraction and Capillary Electrophoresis. Vis sammendrag

  Capillary electrophoresis (CE) of analytes in biological samples requires both analyte preconcentration and sample clean-up. We have developed a simple and inexpensive device for liquid-phase micro extraction (LPME). LPME is carried out from samples present in small commercial sample vials; the analytes of interest are extracted from aqueous samples (typically 1- 5 ml urine, plasma etc.) through a porous hollow fibre into a micro liquid-phase acceptor solution (5- 25µl). Using an aqueous acceptor solution, the extract can be injected directly into an aqueous CE-system. The process offers both enrichment and sample clean up. In addition, a large number of different samples may be extracted in parallel providing a high number of samples per unit time capacity. The technique is applicable on both acidic and basic drugs (analytes). Enrichment and sample clean up is based on the partition of analytes between the samples and the acceptor solution. A solvent immiscible with water is immobilised at the hollow fibre and functions as a barrier and carrier between the two aqueous phases. Larger molecules (like proteins) and salts will be insoluble in the immobilised solvent and remain in the sample solution. Optimal conditions render the possibility to recover nearly 100 % of the analytes in the acceptor phase. Due to the large size difference between sample and acceptor solution, the degree of enrichment will be high (usually 40- 100 times). LPME combines high extraction efficiency with simple and inexpensive extraction devices and is therefore a promising technique.

• Halvorsen, Trine Grønhaug; Pedersen-Bjergaard, Stig & Rasmussen, Knut Einar (2000). Væskefasemikroekstraksjon kombinert med kapillærelektroforese - et nytt kosept for bestemmelse av legemidler i biologisk materiale. Vis sammendrag

  Kapillærelektroforese (CE) er en forholdsvis ny separasjonsteknikk innen legemiddelanalyse. Metoden er rask, separerer legemidler effektivt og har et lavt løsningsmiddelforbruk. En ulempe med teknikken er at den gir forholdsvis høye deteksjons- og kvantifiseringsgrenser. Metoden har derfor til nå hatt begrenset anvendelse ved bestemmelse av legemidler i biologiske væsker. Vi har utviklet et enkelt og billig oppsett for væskefasemikroekstraksjon (LPME). LPME utføres på prøver i små komersielle prøveglass; analyttene ekstraheres fra prøven (typisk 1-5 ml vann, urin, plasma etc.) gjennom en porøs hullfiber impregnert med løsningsmiddel, til en vandig mikro-væskefase (5-25 µl). Ekstraktet kan så injiseres direkte på CE. Prosessen gir både oppkonsentrering av analytt og opprensing av prøven. I tillegg kan et stort antall prøver ekstraheres samtidig, noe som gir høy effektivitet. Teknikken kan benyttes både på sure og basiske legemidler. Oppkonsentrering og opprensing av prøvene er basert på analyttenes fordeling mellom prøveløsningen og den vandige mikro-væskefasen. Løsningsmidlet i hullfiberen fungerer som en barriere mellom de to fasene. Prøveløsningen pH-justeres slik at analyttene er nøytrale og har redusert løselighet. Analyttene ekstraheres over i løsningsmidlet og videre inn i mikro-væskefasen. pH i akseptorfasen velges slik at analyttene har ladning og dermed er svært løselig. Større molekyler (som proteiner) ekstraheres ikke over i mikro-væskefasen. Ved optimale betingelser vil nær 100 % av analyttene kunne gjenfinnes i akseptorfasen. På grunn av den store forskjellen i prøve- og mikrovæskefasevolum vil graden av oppkonsentrering være høy (vanligvis 40-100 ganger). LPME forener kraftig oppkonsentrering og høy effektivitet med enkelt og billig ekstraksjonsoppsett, noe som gjør det til en lovende teknikk.

• Halvorsen, Trine Grønhaug; Christensen, Hege Staaland; Nordbø, Kirsten; Johnsen, Einar Broch & Krogh, Mette (1999). Automated Determination of Citalopram and N-desmethylcitalopram with On-line Dialysis and High-Performance Liquid Chromatography. Vis sammendrag

  An automated method for determination of citalopram and N-desmethylcitalopram is described. The procedure combines on-line dialysis and trace enrichment prior to high-performance liquid chromatography (HPLC). An existing method for determination of citalopram and its four metabolites was modified and optimalised. Proteins and particles were removed by dialysis before trace enrichment on a C8 column. Separation was performed on a C18 analytical column, and the analytes were subsequently detected with a fluorescence detector at an excitation wavelength of 249 nm and an emission wavelength of 302 nm. The correlation coeffisient were 0.994 or above. Automated determination of the total concentration of citalopram and N-desmethylcitalopram in plasma by the automated dialysis-HPLC was shown to be an accurate and reproducible method. The sample throughput was 70 samples in 24 h. In a minor clinical study, blood samples from eight patients treated with citalopram were analysed using the method. The aim of this study was to examine the correlation between adverse effects/interactions of citalopram and plasma drug concentration. A correlation between citalopram dose and plasma concentration was found. No correlation between adverse effects and plasma drug concentration was observed.

• Pedersen-Bjergaard, Stig; Rasmussen, Knut Einar; Krogh, Mette; Grefslie, Hege & Halvorsen, Trine Grønhaug (1999). New Directions in Microextraction Techniques for Drugs in Biofluids.
• Halvorsen, Trine Grønhaug (1998). Utvikling av en Helautomatisk Metode for Bestemmelse av Citalopram og N-desmetylcitalopram i Plasma Undersøkelse av Bivirkninger og Sammenheng med Serumkonsentrasjon hos Citaloprambehandlede Pasienter. Vis sammendrag

  En helautomatisk metode til bestemmelse av totalkonsentrasjonen av citalopram og N-desmetylcitalopram i plasma ble utviklet. Metoden kombinerer "on-line" dialyse, oppkonsentrering og HPLC (high-performance liquid chromatography). En eksisterende metode til bestemmelse av citalopram og alle dens fire metabolitter ble modifisert og optimalisert. Proteiner og partikler ble fjernet ved dialyse, og dialysatet ble oppkonsentrert på en C-8 oppkonsentreringskolonne. Etter kolonne-svitsjing ble de retarderte stoffene eluert med HPLC-mobilfase inn på analysekolonnen, som var pakket med C-18 materiale. Citalopram og metabolitten ble detektert ved fluorescens deteksjon med eksitasjonsbølgelengde på 249 nm og emmisjonsbølgelengde på 302 nm. Metoden hadde en korrelasjonskoeffesient på 0.994 eller bedre. Metoden viste relativt god presisjon og nøyaktighet. Intra- og inter-assay variasjonen viste et relativt standardavvik bedre enn henholdsvis 5.09% og 15.43%, og en nøyaktighet, vist som avvik fra "sann" verdi, bedre enn henholdsvis 11.20% og 19.00%. Citalopram og N-desmetylcitalopram kunne detekteres ned til 2 ng/ml og kvantifiseres ned til 10 ng/ml. Terapeutiske serumkonsentrasjoner for citalopram ligger vanligvis mellom 20 og 110 ng/ml. Metabolitten har ikke klinisk relevant effekt og medbestemmes bare for å lette bestemmelsen av citalopram. Med automatisk "on-line" dialyse og kolonne-svitisjing HPLC kan 70 prøver opparbeides og analyseres helautomatisk på 24 timer. Metoden ble benyttet i en klinisk studie med åtte pasienter behandlet med citalopram. Formålet med den kliniske studien var å undersøke om man kunne se korrelasjon mellom bivirkninger og serumkonsentrasjon hos pasienter behandlet med citalopram. Bivirknings- og interaskjons-tendensen til citalopram ble også undersøkt. Pasientene ble intervjuet angående bivirkninger i oppstarts- og vedlikeholdsfasen med citalopram. Det ble tatt blodprøver av pasientene i begge behandlingsfasene hvis behandling med citalopram ble startet opp mens studien pågikk. Hvis citaloprambehandlingen hadde pågått i lengre tid, ble det kun tatt en blodprøve i vedlikeholds-fasen. Etter bearbeidelse av data fra intervju og serumkonsentrasjonmålinger, kunne man se en korrelasjon mellom citalopramdose og serumkonsentrasjon. Det ble ikke funnet korrelasjon mellom bivirkninger og serumkonsentrasjon. Da få pasienter deltok i studien, var det vanskelig å si noe om bivirknings- og interaksjonstendensen til citalopram.

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