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  • 1.
    Lindegårdh, Niklas
    et al.
    Dalarna University, School of Technology and Business Studies, Chemical Engineering.
    Ashton, M
    Bergqvist, Yngve
    Dalarna University, School of Technology and Business Studies, Chemical Engineering.
    Automated Solid-Phase Extraction Method for the Determination of Piperaquine in Plasma by Peak Compression Liquid Chromatography2003In: Journal of Chromatographic Science, ISSN 0021-9665, E-ISSN 1945-239X, Vol. 41, no 1, p. 44-49Article in journal (Refereed)
  • 2. Lindegårdh, Niklas
    et al.
    Blessborn, Daniel
    Dalarna University, School of Technology and Business Studies, Chemical Engineering.
    Bergqvist, Yngve
    Dalarna University, School of Technology and Business Studies, Chemical Engineering.
    Simultaneous quantification of the highly lipophilic atovaquone and the hydrophilic strong basic proguanil and its metabolites, using a new mixed-mode SPE approach and Steep-Gradient LC2005In: Journal of Chromatographic Science, ISSN 0021-9665, E-ISSN 1945-239X, Vol. 43, no 5, p. 259-266Article in journal (Refereed)
    Abstract [en]

    A bioanalytical method is described for the simultaneous quantitative analysis of the highly lipophilic atovaquone and the strong basic proguanil with metabolites in plasma. The drugs are extracted from protein precipitated plasma samples on a novel mixed-mode solid-phase extraction (SPE) column containing carboxypropyl and octyl silica as functional groups. The analytes are further separated and quantitated using a steep-gradient liquid chromatograhic method on a Zorbax SB-CN column with UV detection at 245 nm. Two different internal standards (IS) are used in the method to compensate for both types of analytes. A structurally similar IS to atovaquone is added with acetonitrile to precipitate proteins from plasma. A structurally similar IS to proguanil and its metabolites is added with phosphate buffer before samples are loaded onto the SPE columns. A single elution step is sufficient to elute all analytes. The method is validated according to published guidelines and shows excellent performance. The within-day precisions, expressed as relative standard deviation, are lower than 5% for all analytes at three tested concentrations within the calibration range. The between-day precisions are lower than 13% for all analytes at the same tested concentrations. The limit of quantitation is 25nM for the basic substances and 50nM for atovaquone. Several considerations regarding development and optimization of a method for determination of analytes with such a difference in physiochemical properties are discussed.

  • 3.
    Malm, Mikaela
    et al.
    Dalarna University, School of Technology and Business Studies, Chemical Engineering.
    Lindkvist, Jenny
    Bergqvist, Yngve
    Dalarna University, School of Technology and Business Studies, Chemical Engineering.
    Importance of pre-analytical factors contributing to measurement uncertainty, when determining sulfadoxine and sulfamethoxazole from capillary blood dried on sampling paper.2008In: Journal of Chromatographic Science, ISSN 0021-9665, E-ISSN 1945-239X, Vol. 46, no 9, p. 837-843Article in journal (Refereed)
    Abstract [en]

    A bioanalytical method is developed and validated for determination of sulfadoxine (SD) and sulfamethoxazole (SM) in 100 µL capillary blood dried on sampling paper (Whatman 31ET Chr). SD and SM are extracted with 2000 µL perchloric acid and the liquid phase is loaded onto ENV+ solid-phase extraction columns. SD, SM, and the internal standard are separated on a Purospher STAR RP-18 liquid chromatography column (150 × 4.6 mm) with a mobile phase consisting of acetonitrile–sodium acetate buffer pH 5.2, I = 0.1 (33:67, v/v). Analytes are detected with UV at 256 nm. Lower limit of quantitation is 5 µmol/L, where precisions are 4.2% and 3.9% for SD and SM, respectively. Three brands of sampling papers have been compared with respect to absorption properties, extraction recoveries, and variations. Punching out dried blood spots (DBS) instead of cutting spots into strips prior to extraction has been evaluated by examining precision and accuracy of SD and SM determinations. Importance of uniformity of types of sampling paper, sampling volume and biological matrix, benefit of punching out discs from DBS, and impact on absorption properties of different brands of sampling papers are discussed. Avoiding pre-analytical errors whenever possible results in concentrations determined being more accurate and precise.

  • 4.
    Malm, Mikaela
    et al.
    Dalarna University, School of Technology and Business Studies, Chemical Engineering.
    Römsing, Susanne
    Dalarna University, School of Technology and Business Studies, Chemical Engineering.
    Obua, Celestino
    Bergqvist, Yngve
    Dalarna University, School of Technology and Business Studies, Chemical Engineering.
    Determination of lamivudine, zidovudine and nevirapine, in capillary blood sampled on filter paper, by liquid chromatography2009In: Journal of Chromatographic Science, ISSN 0021-9665, E-ISSN 1945-239X, Vol. 47, no 10, p. 855-862Article in journal (Refereed)
    Abstract [en]

    A bioanalytical method for determination of lamivudine (3TC), zidovudine (AZT), and nevirapine (NVP) in 100 μL capillary blood applied onto sampling paper has been developed and validated. The antiretroviral drugs (ARV) were analyzed by reversed phase gradient liquid chromatography with UV detection. Separation was performed on a Zorbax SB C8 (250 × 4.6 mm) column with a twostep gradient: (i) methanol.0.05 mol/L acetic acid-sodium acetate buffer (pH 3.95, 15:85 v/v) and (ii) methanol.0.05 mol/L acetic acid-sodium acetate buffer (pH 3.95, 50:50 v/v) with a flow rate of 1.0 mL/min. UV detection was performed at 260 nm. Total assay precisions were 6.3, 4.7, and 4.9% for 3TC at 0.34, 0.69, and 3.9 μg/mL, and 5.1, 5.5, and 3.2% for AZT at 0.40, 0.80, and 4.5 μg/mL. For NVP, total assay precisions were 5.2, 8.3, and 3.5% at 2.6, 4.5, and 8.8 μg/mL. Lower limit of quantifications (LLOQ) were 0.11 and 0.13 μg/mL for 3TC and AZT where the precisions were 2.0% for both the analytes. For NVP, LLOQ was 1.3 μg/mL where precision was 2.6%. Concentrations were determined for 10 h for two subjects receiving standard twice daily antiretroviral therapy containing 3TC, AZT, and NVP. Maximum 3TC concentrations were 2.5 and 2.8 μg/mL for subject 1 and 2, respectively. For AZT, maximum concentrations were 1.8 and 1.1 μg/mL while being 15 and 9.6 μg/mL for NVP. Pre-dose trough concentration of NVP was 11 μg/mL for subject 1 and 9.6 μg/mL for subject 2.

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