Rapid determination of losartan and losartan acid in human plasma by multiplexed LC–MS/MS

A rapid LC–MS/MS method has been developed and validated for the determination of losartan (LOS) and its metabolite losartan acid (LA) (EXP‐3174) in human plasma using multiplexing technique (two HPLC units connected to one MS/MS). LOS and LA were extracted from human plasma by SPE technique using Oasis HLB® cartridge without evaporation and reconstitution steps. Hydroflumethiazide (HFTZ) was used as an internal standard (IS). The analytes were separated on Zorbax SB C‐18 column. The mass transition [M–H] ions used for detection were m/z 421.0 → 127.0 for LOS, m/z 435.0 → 157.0 for LA, and m/z 330.0 → 239.0 for HFTZ. The proposed method was validated over the concentration range of 2.5–2000 ng/mL for LOS and 5.0–3000 ng/mL for LA with correlation coefficient ?0.9993. The overall recoveries for LOS, LA, and IS were 96.53, 99.86, and 94.16%, respectively. Total MS run time was 2.0 min/sample. The validated method has been successfully used to analyze human plasma samples for applications in 100 mg fasted and fed pharmacokinetic studies.     

Quantification of Quetiapine in Human Plasma by LC–MS–MS

A rapid liquid chromatographic method with electrospray ionization tandem mass spectrometric detection has been developed and validated for quantification of quetiapine in heparinized human plasma. Plasma samples, without a drying and reconstitution step, were extracted by solid-phase extraction and eluted with acetonitrile. The analyte and zolpidem tartrate (internal standard, IS) were chromatographed on a C₁₈ column; the mobile phase was 85:15 (v/v) acetonitrile–5 mM ammonium formate, pH adjusted to 4.5 with formic acid, at a flow rate of 0.5 mL min⁻¹. The retention times of quetiapine and the IS were 1.25 and 1.05 min, respectively, and the run time was 1.8 min per sample. Selected reaction monitoring of MH⁺ at m/z 384.12 and 308.11 resulted in stable fragment ions with m/z 253.02 and 235.09 for quetiapine and the IS, respectively. Response was a linear function of concentration in the range 1.0–240.0 ng mL⁻¹, with r ≥ 0.9994. Recovery of quetiapine and the IS ranged from 74.82 to 85.57%. The assay has excellent characteristics and has been successfully used for analysis of quetiapine in healthy human subjects in a bioequivalence study.

     

Diversity in Gold‐Catalyzed Formal Cycloadditions of Ynamides with Azidoalkenes or 2H‐Azirines: [3+2] versus [4+3] Cycloadditions

Gold‐catalyzed cycloadditions of ynamides with azidoalkenes or 2H‐azirines give [3+2] or [4+3] formal cycloadducts of three classes. Cycloadditions of ynamides with 2H‐azirine species afford pyrrole products with two regioselectivities when the C_β‐substituted 2H‐azirine is replaced from an alkyl (or hydrogen) with an ester group. For ynamides substituted with an electron‐rich phenyl group, their reactions with azidoalkenes proceed through novel [4+3] cycloadditions to deliver 1H‐benzo[d]azepine products instead.     

Quantification of Quetiapine in Human Plasma by LC–MS–MS

A rapid liquid chromatographic method with electrospray ionization tandem mass spectrometric detection has been developed and validated for quantification of quetiapine in heparinized human plasma. Plasma samples, without a drying and reconstitution step, were extracted by solid-phase extraction and eluted with acetonitrile. The analyte and zolpidem tartrate (internal standard, IS) were chromatographed on a C₁₈ column; the mobile phase was 85:15 (v/v) acetonitrile–5 mM ammonium formate, pH adjusted to 4.5 with formic acid, at a flow rate of 0.5 mL min^?1. The retention times of quetiapine and the IS were 1.25 and 1.05 min, respectively, and the run time was 1.8 min per sample. Selected reaction monitoring of MH⁺ at m/z 384.12 and 308.11 resulted in stable fragment ions with m/z 253.02 and 235.09 for quetiapine and the IS, respectively. Response was a linear function of concentration in the range 1.0–240.0 ng mL^?1, with r ≥ 0.9994. Recovery of quetiapine and the IS ranged from 74.82 to 85.57%. The assay has excellent characteristics and has been successfully used for analysis of quetiapine in healthy human subjects in a bioequivalence study.     

Rapid and specific approach for direct measurement of glimepiride in human plasma by LC-ESI-MS-MS employing automated 96 well format: application to a bioequivalence study

A rapid liquid chromatographic method with electrospray ionization tandem mass spectrometric (LC-MS-MS) detection is developed and validated for quantification of glimepiride in heparinized human plasma. Plasma samples, without a drying and reconstitution step, are extracted by solid-phase extraction (SPE) and eluted with 0.9 mL of acetonitrile-methanol (1:1, v/v) containing 0.05% formic acid. The analyte and glimepiride d8 (internal standard, IS) are chromatographed on a C(18) column; the mobile phase is acetonitrile-2 mm ammonium formate (88:12, v/v), with the pH adjusted to 3.5 with formic acid, at a flow rate of 0.5 mL/min. The retention times of glimepiride and the IS are 0.93 min, and the runtime is 1.6 min per sample. Selected reaction monitoring of MH(+) at m/z 491.20 and 499.26 result in stable fragment ions with m/z 351.80 and 359.96 for glimepiride and the IS, respectively. The response was a linear function of the concentration in the range of 2.0-650.0 ng/mL, with r ≥ 0.9994. The recovery of glimepiride and the IS ranged from 81.91 to 83.36%. The assay has excellent characteristics and has been successfully used for the analysis of glimepiride in healthy human subjects in a bioequivalence study. It was well suited to clinical studies of the drug involving large numbers of samples.     

A rapid and specific approach for direct measurement of donepezil concentration in human plasma by LC-MS/MS employing solid-phase extraction

A selective, rapid and simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method is described for assay of donepezil in human plasma using escitalopram as an internal standard. Chromatographic separation was achieved on a Betabasic-C(8), 5 microm, 100 x 4.6 mm column using methanol:water:formic acid (90:9.97:0.03, v/v/v) as mobile phase. Detection of donepezil and internal standard was achieved by ESI MS/MS in positive ion mode using 380.20/91.10 and 325.13/262.00 transitions, respectively. The linearity over the concentration range of 0.15-50 ng/mL for donepezil was obtained and the lower limit of quantification was 0.15 ng/mL. For each level of quality control samples, inter-day and intra-day precisions (RSD) were < or =8.92 and 10.35% and accuracy (%RE) were < or =7.33% and 9.33%, respectively. The recovery was more than 88.50% for both donepezil and internal standard by solid-phase extraction, eliminating evaporation and reconstitution steps.