Simultaneous determination of propranolol and 4-hydroxy propranolol in human plasma by solid phase extraction and liquid chromatography/electrospray tandem mass spectrometry

A very sensitive, reliable, reproducible and highly selective assay for the simultaneous determination of free and total (conjugated and unconjugated) propranolol and its equipotent hydroxyl metabolite, 4-hydroxy propranolol, in human plasma was developed and validated. The analytes were simultaneously extracted from 0.300 mL of human plasma using solid phase extraction and detected in positive ion mode by tandem mass spectrometry with a turbo ionspray interface. Deuterium-labeled propranolol and 4-hydroxy propranolol, propranolol-d7 and 4-hydroxy propranolol-d7, were used as internal standards. The method has a lower limit of quantitation (LOQ) of 0.20 ng/mL for both analytes with the limits of detection (LOD) 50 and 100 pg/mL for propranolol and 4-hydroxy propranolol, respectively, based on a signal-to-noise ratio of 5. The assay was linear over a range 0.20–135.00 ng/mL for free propranolol and 0.20–25.00 ng/mL for free 4-hydroxy propranolol and linear over range 1.00–500.00 ng/mL for total propranolol and 1.00–360.00 ng/mL for total 4-hydroxy propranolol, with coefficient of determination greater than 0.99 for both analytes. The extraction recoveries were >96 and >64% on an average for propranolol and 4-hydroxy propranolol, respectively. The analytes were found stable in human plasma through five freeze (−15 °C)–thaw (room temperature) cycles and under storage on bench-top for at least 6.5 h, and also in mobile phase at 10 °C for at least 48 h. The method has shown tremendous reproducibility, with intra- and inter-day precision <11.3% (RSD), and intra- and inter-day accuracy <11% of nominal values, for both analytes, and has proved to be highly reliable for the analysis of clinical samples.     

Quantification of artemisinin in human plasma using liquid chromatography coupled to tandem mass spectrometry

A liquid chromatographic tandem mass spectroscopy method for the quantification of artemisinin in human heparinised plasma has been developed and validated. The method uses Oasis HLB™ μ-elution solid phase extraction 96-well plates to facilitate a high throughput of 192 samples a day. Artesunate (internal standard) in a plasma–water solution was added to plasma (50 μL) before solid phase extraction. Artemisinin and its internal standard artesunate were analysed by liquid chromatography and MS/MS detection on a Hypersil Gold C18 (100 mm × 2.1 mm, 5 μm) column using a mobile phase containing acetonitrile–ammonium acetate 10 mM pH 3.5 (50:50, v/v) at a flow rate of 0.5 mL/min. The method has been validated according to published FDA guidelines and showed excellent performance. The within-day, between-day and total precisions expressed as R.S.D., were lower than 8% at all tested quality control levels including the upper and lower limit of quantification. The limit of detection was 0.257 ng/mL for artemisinin and the calibration range was 1.03–762 ng/mL using 50 μL plasma. The method was free from matrix effects as demonstrated both graphically and quantitatively.     

Simultaneous analysis of frequently used licit and illicit psychoactive drugs in breast milk by liquid chromatography tandem mass spectrometry

A liquid chromatography tandem mass spectrometry (LC-MS-MS) method for the quantification of frequently used licit (caffeine, nicotine and cotinine) and illicit drugs (opiates, cocaine, cannabinoids and amphetamines) in breast milk was developed and fully validated. Chromatography was performed on a reverse-phase column using a gradient of 2mM ammonium acetate, pH 6.6, and methyl alcohol as mobile phase at a flow rate of 0.35 mL/min. Separated analytes were quantified by electrospray ionization tandem mass spectrometry in positive ion mode using multiple reaction monitoring. Milk samples were kept at -20 °C until analysis and the compounds under investigation were extracted from the matrix by Bond Elut Certify cartridges. The concentration range covered was LOQ to 1000 ng/mL for all the investigated drugs. Intra- and inter-assay imprecision was less than 20%, analytical recovery ranged between 51.6% and 86.5%, matrix effect between 71.1% and 116.6% and process efficiency between 46.8% and 84.0%. Analytes were stable after three freeze-thaw cycles, after 6 months at -20 °C and after the pasteurization process (differences to the initial concentration always lower than 10%). matrix effect ranged from 77.6% to 116.6%, recovery from 51.6% to 86.5%, and process efficiency from 46.8% to 79.0%. This LC-MS-MS assay was applied to screen samples from the largest Spanish milk bank and samples coming from drug addicted mothers. The developed method provided adequate sensitivity and performance characteristics to prove the presence of only caffeine in a small percentage of samples from milk donating nursing mothers and the presence or absence of most commonly used illicit drugs in breast milk from addicted lactating mothers.     

Analytical strategy for the confirmatory analysis of the non-steroidal anti-inflammatory drugs firocoxib, propyphenazone, ramifenazone and piroxicam in bovine plasma by liquid chromatography tandem mass spectrometry

A sensitive and selective method for the simultaneous determination of non-steroidal anti-inflammatory drugs in bovine plasma was developed. Confirmatory analysis was carried out by liquid chromatography coupled with an electrospray ionisation tandem mass spectrometer (LC-ESI-MS/MS). Target compounds were acidified in plasma and extracted with acetonitrile. Sodium chloride was added to assist separation of the plasma and acetonitrile mixture. The acetonitrile extract is then subjected to liquid-liquid purification by the addition of hexane. Accuracy of the methods in plasma was between 93 and 102%. The precision of the method for the basic NSAIDs in plasma expressed as % RSD, for the within-laboratory reproducibility was less than 10%. Decision limit (CCα values) and detection capability (CCβ) values were established. The methods were validated according to Commission Decision 2002/657/EC.     

Simple and accurate quantitative analysis of ten antiepileptic drugs in human plasma by liquid chromatography/tandem mass spectrometry

A simple, accurate, and sensitive liquid chromatography (LC)-tandem mass spectrometry (MS/MS) method has been developed for the simultaneous quantification of 10 antiepileptic drugs (AEDs; gabapentin (GBP), levetiracetam (LEV), valproic acid (VPA), lamotrigine (LTG), carbamazepine-10,11-epoxide (CBZ-epoxide), zonisamide (ZNS), oxcarbazepine (OXC), topiramate (TPM), carbamazepine (CBZ), phenytoin (PHT)) in human plasma as a tool for drug monitoring. d₁₀-Phenytoin (d₁₀-PHT) and d_6-valproic acid (d₆-VPA) were used as internal standards for the positive- and negative-ionization modes, respectively. Plasma samples were precipitated by the addition of acetonitrile, and supernatants were analyzed on a C18 reverse-phase column using an isocratic elution. Detection was carried out in selected reaction monitoring (SRM) mode. The calibration curves were linear over a 50-fold concentration range, with correlation coefficients (r²) greater than 0.997 for all AEDs. The intra- and inter-day precision was less than 12%, and the accuracy was between 85.9 and 114.5%. This method was successfully used in the identification and quantitation of AEDs in patients undergoing mono- or polytherapy for epilepsy.     

Simultaneous determination of dextromethorphan, dextrorphan, and guaifenesin in human plasma using semi-automated liquid/liquid extraction and gradient liquid chromatography tandem mass spectrometry

A method for the simultaneous determination of dextromethorphan (DEX), dextrorphan (DET), and guaifenesin (GG) in human plasma was developed, validated, and applied to determine plasma concentrations of these compounds in samples from six clinical pharmacokinetic (PK) studies. Semi-automated liquid handling systems were used to perform the majority of the sample manipulation including liquid/liquid extraction (LLE) of the analytes from human plasma. Stable-isotope-labeled analogues were utilized as internal standards (ISTDs) for each analyte to facilitate accurate and precise quantification. Extracts were analyzed using gradient liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Use of semi-automated LLE with LC-MS/MS proved to be a very rugged and reliable approach for analysis of more than 6200 clinical study samples. The lower limit of quantification was validated at 0.010, 0.010, and 1.0 ng/mL of plasma for DEX, DET, and GG, respectively. Accuracy and precision of quality control (QC) samples for all three analytes met FDA Guidance criteria of +/-15% for average QC accuracy with coefficients of variation less than 15%. Data from the thorough evaluation of the method during development, validation, and application are presented to characterize selectivity, linearity, over-range sample analysis, accuracy, precision, autosampler carry-over, ruggedness, extraction efficiency, ionization suppression, and stability. Pharmacokinetic data are also provided to illustrate improvements in systemic drug and metabolite concentration-time profiles that were achieved by formulation optimization.     

Profiling cocaine residues and pyrolytic products in wastewater by mixed‐mode liquid chromatography–tandem mass spectrometry

This work provides a new analytical method for the determination of cocaine, its metabolites benzoylecgonine and cocaethylene, the pyrolytic products anhydroecgonine and anhydroecgonine methyl ester, and the pharmaceutical levamisole in wastewater. Samples were solid‐phase extracted and extracts analyzed by liquid chromatography–tandem mass spectrometry using, for the first time in the illicit drug field, a stationary phase that combines reversed‐phase and weak cation‐exchange functionalities. The overall method performance was satisfactory, with limits of detection below 1 ng/L, relative standard deviations below 21%, and percentages of recovery between 93% and 121%. Analysis of 24‐hour composite raw wastewater samples collected in Santiago de Compostela (Spain) and Brasilia (Brazil) highlighted benzoylecgonine as the compound showing the highest population‐normalized mass loads (300–1000 mg/day/1000 inhabitants). In Brasilia, cocaine and levamisole loads underwent an upsurge on Sunday, indicating a high consumption, and likely a direct disposal, of cocaine powder on this day. Conversely, the pyrolytic product resulting from the smoke of crack, anhydroecgonine methyl ester, and its metabolite anhydroecgonine were relatively stable over the four days, agreeing with a non‐recreational‐associated use of crack.     

Analysis of a residual diamine in a pharmaceutical polymer using solid phase extraction with analysis by gas chromatography mass spectrometry

A method was developed for the analysis of 4,4′-methylenebiscyclohexylamine (DMDA) and 4,4′-methylenedicyclohexylisocyanate (DMDI) in a pharmaceutical polymer. The DMDA was extracted from the polymer with either buffer (0.1 M potassium phosphate pH 3.1) and the extract was passed through a SCX solid phase extraction cartridge. It was eluted from the cartridge with methanolic ammonia and then converted to its heptafluorobutyramide (HFB) derivative prior to analysis by gas chromatography–negative chemical ionisation mass spectrometry (GC–MS) in the negative ion chemical ionisation (NICI) mode. It was not possible to directly measure DMDI and it was thus analysed by selecting extraction conditions such that it would decompose to DMDA. The quantification of the residues in the polymer was based on the method of standard additions since this gave a better indication of the recovery from the complex matrix.     

Identification of thymol phase I metabolites in human urine by headspace sorptive extraction combined with thermal desorption and gas chromatography mass spectrometry

Development of a novel highly sensitive headspace sorptive extraction (HSSE) method in combination with thermal desorption gas chromatography coupled to a mass spectrometer (TD-GC/MS) allowed the identification of thymol and several phase I metabolites in human urine. Combined with an enzymatic hydrolysis of glucuronated or sulphated phase II metabolites of thymol and of the respective phase I metabolites prior to analysis, even trace quantities of hitherto not detected thymol phase I metabolites could be identified in urine samples of test persons after oral administration of 50 mg thymol. It was proven, that human metabolism leads to a hydroxylation of the aromatic ring as well as of the iso-propyl side chain. Hydroxylation of the iso-propyl group results in the formation of the rather unstable p-cymene-3,8-diol and the corresponding dehydration product p-cymene-3-ol-8-ene which could be clearly detected in human urine samples. Furthermore, the aromatic hydroxylation products p-cymene-2,5-diol, its oxidation product p-cymene-2,5-dione and p-cymene-2,3-diol were also unambiguously identified by comparison with synthesized reference compounds.     

A method for multiple mycotoxin analysis in wines by solid phase extraction and multifunctional cartridge purification, and ultra-high-performance liquid chromatography coupled to tandem mass spectrometry

An analytical method using two solid phase extractions and ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) was developed for the identification and quantification of 14 mycotoxins (patulin, deoxynivalenol, aflatoxins B(1), B(2), G(1), G(2), M(1), T-2 toxin, HT-2 toxin, zearalenone, fumonisins B(1), B(2), B(3), and ochratoxin A) in domestic and imported wines. Mycotoxins were purified with an Oasis HLB cartridge, followed by a MultiSep(TM) #229 Ochra. As a result, sufficient removal of the pigments and highly polar matrices from the red wines was achieved. UHPLC conditions were optimized, and 14 mycotoxins were separated in a total of 13 min. Determinations performed using this method produced high correlation coefficients for the 14 mycotoxins (R > 0.990) and recovery rates ranging from 76 to 105% with good repeatability (relative standard deviation RSD < 12%). Twenty-seven samples of domestic and imported wines were analyzed using this method. Although ochratoxin A (OTA) and fumonisins (FMs) were detected in several samples, the FM levels were less than limits of quantification (LOQs) (1 μg/L), and even the largest of the OTA levels was below the EU regulatory level (2 μg/L). These results suggest that the health risk posed to consumers from the wines available in Japan is relatively low.     

Simultaneous detection and quantification of 3-nitrotyrosine and 3-bromotyrosine in human urine by stable isotope dilution liquid chromatography tandem mass spectrometry

Nitration and bromination of proteins, giving rise to the respective 3-nitrotyrosine (3NT) and 3-bromotyrosine (3BT), are implicated in asthma, allergic inflammatory disorders, and cancer. We have developed an isotope dilution liquid chromatography electrospray ionization tandem mass spectrometry (LC/MS/MS) assay for simultaneous analysis of protein-bound 3NT and 3BT in human urine. The detection limits (S/N = 3) were 10 pg (44 fmol) for 3NT and 5.0 pg (19 fmol) for 3BT injected on-column. The average levels of protein-bound 3NT and 3BT in 23 healthy individuals were 9.7 ± 11.0 (mean ± S.D.) in 10⁵ tyrosine and 4.4 ± 3.9 (mean ± S.D.) in 10³ tyrosine, respectively, using this highly sensitive LC/MS/MS under the selective reaction monitoring mode. Furthermore, the levels of urinary 3NT and 3BT show a statistically significant correlation (R² = 0.55, p = 0.0065, n = 23). The high specificity and accuracy of this LC/MS/MS method render it a valuable tool in measurement of 3NT and 3BrT in the human urinary protein as promising noninvasive biomarkers for protein tyrosine nitration and bromination in vivo.     

A rapid and simple ultraperformance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) method for the detection of glucuronic acid-conjugated steroid metabolites

In the present study, we effectively detected 10 steroids and glucuronic acid-conjugated steroid metabolites in 12 min by ultraperformance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS). Steroids testosterone (T), 5α-dihydrotestosterone (DHT), androsterone (ADT), etiocholanolone (ETIO), estradiol (E₂) and their glucuronide conjugates were well-separated on an Eclipse Plus C₁₈ column (2.1 mm×50 mm, RRHD 1.8 µm). The mobile phase consisted of a mixture of methanol and ultrapure water (containing 1 mM ammonium formate) at a ratio of 60:40 (v/v), and the flow rate was set at 0.25 mL/min. The LC eluate was detected by electrospray ionization (ESI) source in both positive and negative ion modes. Neutral loss (NL of 176, 194, 211 and 229 Da in positive mode) and precursor ion (PI of m/z 141, 159 and 177 in positive mode and 75, 85 and 133 in negative mode) methods were applied for the detection of steroid glucuronides. The multiple reaction monitoring (MRM) transitions were m/z 289.3→97.1, 291.3→105, 291.3→199.2, 273.2→145.4 and 255.2→159.1 for T, DHT, ADT, ETIO and E₂ in positive mode, respectively; as well as m/z 463.3→85 for T glucuronide (T-G), m/z 465.3→75 for DHT glucuronide (DHT-G), ADT glucuronide (ADT-G), ETIO glucuronide (ETIO-G) and m/z 447.3→271 for E₂ glucuronide (E₂-G) in negative mode. In addition, the analytical method was also applied for the detection of steroid glucuronides in pooled human liver microsomes (HLM), which might serve as a basis for further investigation of steroid metabolism in vivo and in vitro.     

Stereoselective determination of venlafaxine and its three demethylated metabolites in human plasma and whole blood by liquid chromatography with electrospray tandem mass spectrometric detection and solid phase extraction

A stereoselective method is described for simultaneous determination of the S- and R-enantiomers of venlafaxine and its three demethylated metabolites in human plasma and whole blood samples. This validated method involved LC/MS/MS with positive electrospray ionization and solid phase extraction. Chromatographic separation was performed on a 250 mm × 2.1 mm Chirobiotic V column with a total run time of 35 min. In plasma, calibration curves were in the range of 1–1000 nM for the S- and R-enantiomers of venlafaxine and O-desmethylvenlafaxine, and 0.5–500 nM for N-desmethylvenlafaxine and N,O-didesmethylvenlafaxine. In whole blood the corresponding concentrations were 10–4000 and 5–2000 nM, respectively. The intra-day precision was <6.3% and the inter-day precision was <9.9% for plasma and <15% and <19% for whole blood. LLOQ ranged between 0.25 and 0.5 nM. No ion suppression/enhancement or other matrix effects were observed. The method was successfully applied for determination of venlafaxine and its metabolites in plasma from patients and whole blood samples from forensic autopsy cases.     

Identification of metabolites of meisoindigo in rat, pig and human liver microsomes by UFLC-MS/MS

3-(1,2-Dihydro-2-oxo-3H-indol-3-ylidene)-1,3-dihydro-1-methyl-2H-indol-2-one, abbreviated as meisoindigo, has been a routine therapeutic agent in the clinical treatment of chronic myelogenous leukemia in China since the 1980s. To gain an understanding of the interspecies differences in the metabolism of meisoindigo, the relevant metabolism studies were carried out for the first time in rat, pig and human liver microsomes of different genders by ultra fast liquid chromatography/tandem mass spectrometry (UFLC-MS/MS). The qualitative metabolite identification was accomplished by multiple reaction monitoring (MRM) in combination with Enhanced Product Ion (EPI). The semi-quantitative metabolic stability and metabolite formation were simultaneously measured by MRM. The in vitro metabolic pathways of meisoindigo in three species were proposed as 3,3′ double bond reduction, followed by N-demethylation, and reduction followed by phenyl mono-oxidation. Two novel metabolic pathways involving direct phenyl mono-oxidation without reduction in the three species, and direct N-demethylation without reduction in only pig and human, were also proposed. It may be noted that the two metabolites formed after reduction followed by phenyl mono-oxidation at positions 4, 5, 6 or 7, as well as one metabolite formed from direct phenyl mono-oxidation at either of the two phenyl rings without reduction were found to be uniquely present in human. The in vitro t_1/2 and in vitro CL_int values of meisoindigo were calculated. Statistical analysis showed there were no significant differences in the metabolic stability profiles of meisoindigo among three species, and gender effect on the metabolic stability of meisoindigo was negligible. Formation profiles of the most significant reductive metabolites were obtained in the three species.     

高分离度快速液相色谱-三重串联四极杆质谱快速检查半夏和虎掌南星中水麦冬酸

目的 建立半夏及其伪品虎掌南星中水麦冬酸的专属性检测方法。方法 样品经水超声提取,利用高分离度快速液相色谱-三重四极杆质谱（rapid resolution liquid chromatography coupled with triple quadrupole electrospray tandem mass spectrometry,RRLC-QQQ/MS）检测水麦冬酸。采用Agilent SB-C₁₈（2.1 mm×50 mm,1.8 μm）色谱柱,以乙腈-0.1%甲酸（5∶95）为流动相。柱温30℃,体积流量0.2 mL/min,进样量1 μL。离子化模式为ESI^-,选择m/z187→143和m/z187→99作为检测离子对,进行多反应监测。结果 检出限为4.6 μg/L。11批半夏中有3批检出水麦冬酸,7批虎掌南星均检出水麦冬酸,半夏中水麦冬酸含量低于虎掌南星。结论 所建方法专属、准确、快速、简便,可为半夏的质量控制提供参考。     

A highly sensitive and selective method for the determination of Leukotriene B4 in human plasma by negative ion chemical ionization/gas chromatography/tandem mass spectrometry

We have developed a highly sensitive and highly selective method for the determination of Leukotriene B₄ (LTB₄) in human plasma using negative ion chemical ionization/gas chromatography/tandem mass spectrometry (NICI/GS/MS/MS) analysis. The developed method was summarized as follows. Deuterated LTB₄ (d₄-LTB₄) was added to human plasma samples as an internal standard, and samples were extracted by a Sep-pak C18 column. Extracted LTB₄ was derivatized into the pentafluorobenzyl ester of bis-trimethylsilyl ether (PFB-TMS-LTB₄) and quantified on the basis of selected reaction monitoring (SRM) at m/z 299 of [M-PFB-2TMSOH]⁻ by NICI/GC/MS/MS analysis, which was the product ion of [M-PFB]⁻. The detection limit for the quantification of LTB₄ in human plasma was 10 pg ml⁻¹, sufficiently sensitive to determine the concentrations of endogenous LTB₄ in human plasma. The plasma level of LTB₄ measured in healthy male volunteers was 33.85 ± 33.91 pg ml⁻¹ (mean ± S.D. in six volunteers). The technique of MS/MS used in this method offers much greater sensitivity and selectivity than single-stage mass spectrometry. The developed method showed good reproducibility with a simple and rapid extraction procedure, and would be useful for examining the relationship between various disease states and the levels of LTB₄ in biological fluids.     

Development and validation of a liquid chromatography‐tandem mass spectrometry method for simultaneous detection of 10 illicit drugs in oral fluid collected with FLOQSwabs™ and application to real samples

According to French law, the roadside testing for drugs of abuse (DOA) should be performed in oral fluid (OF) using an immunological screening kit. If the screening is positive, confirmation has to be done in OF collected by a special swab, called the FLOQSwab? (FS). Unlike other sampling kits, this device was not designed to collect OF since it does not contain an elution buffer. An analytical method was developed for the simultaneous detection of 10 DOA under control in France: tetrahydrocannabinol (THC) at 1 ng/mL, and cocaine, benzoylecgonine (BZE), morphine, 6‐monoacetylmorphine (6‐MAM), amphetamine, methamphetamine, 3,4‐methylenedioxy‐N‐ethylamphetamine (MDEA), 3,4‐methylenedioxyamphetamine (MDA), and 3,4‐methylenedioxy‐N‐methylamphetamine (MDMA) at 10 ng/mL. Samples were eluted using the Quantisal^® buffer and extracted by liquid–liquid extraction for THC and by solid‐phase extraction for the remaining analytes. Analyses were performed by ultra‐high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC–MS/MS). The validated method made it possible to detect the concentrations required by law and was successfully applied to samples from drivers who screened positive. The main limitations of this kit are the large variability of the collected OF volume and the poor stability of DOA in OF, requiring the use of a conservation buffer.     

Rapid and simultaneous measurement of midazolam, 1'-hydroxymidazolam and digoxin by liquid chromatography/tandem mass spectrometry: application to an in vivo study to simultaneously measure P-glycoprotein and cytochrome P450 3A activity

In order to simultaneously determine in vivo P-glycoprotein (P-gp) and Cytochrome P450 3A (CYP3A) activity, a new, rapid and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method has been developed and fully validated to simultaneously determine midazolam (MDZ, as CYP3A substrate), 1'-hydroxymidazolam (1'-OHMDZ) and digoxin (DG, as P-gp substrate) in rat plasma using digitoxin as the internal standard (IS). After a single step liquid-liquid extraction with tert-butyl methyl ether/dichloromethane (75:25, v/v), analytes were subjected to LC-MS/MS analysis using positive electro-spray ionization (ESI(+)) under selected reaction monitoring mode (SRM). Chromatographic separation was performed on an XTerra MS C18 column (50mm×2.1mm, i.d. 3.5μm). The MS/MS detection was conducted by monitoring the fragmentation of 326.05 → 244.00 (m/z) for MDZ, 342.02 →168.01 (m/z) for 1'-OHMDZ, 798.33 → 651.36(m/z) for DG and 782.67 → 635.24 (m/z) for IS. The method had a chromatographic running time of 3min and linear calibration curves over the concentrations of 2-400ng/mL for MDZ and 1'-OHMDZ and 0.5-100ng/mL for DG. The recoveries of the method were 86.8-96.3% for MDZ, 84.6-86.4% for 1'-OH MDZ, and 81.7-85.1% for DG. The lower limit of quantification (LLOQ) of the method was 2ng/mL for MDZ and 1'-OHMDZ and 0.5ng/mL for DG. The intra- and inter-batch precision were less than 15% for all quality control samples at concentrations of 5, 50 and 320ng/mL for MDZ and 1'-OHMDZ and 1, 10 and 80ng/mL for DG. The validated LC-MS/MS method has been successfully used to analyze the concentrations of MDZ, 1'-OH MDZ and DG in rat plasma for simultaneous measurement of in vivo P-gp and CYP 3A activity.     

A sensitive and rapid liquid chromatography-tandem mass spectrometry method for the quantification of the novel neurokinin-1 receptor antagonist aprepitant in rhesus macaque plasma,and cerebral spinal fluid,and human plasma with application in translational NeuroAIDs research

A sensitive and rapid liquid chromatography-tandem mass spectrometry method has been developed for to assess therapeutic exposures of aprepitant in HIV-infected patients and rhesus macaques. The method utilized a simple sample-preparation procedure of protein precipitation with methanol. Chromatographic separation was performed on a reversed phase C₈ column (Hypersil Gold, 50 mm × 2.1 mm, 3 μm) using a mobile phase composed of acetonitrile and water in 0.5% formic acid through gradient elution. Electro-spray ionization in positive mode was incorporated in the tandem mass spectrometric detection. The lower limit of quantitation of aprepitant in plasma of rhesus macaques and human and cerebral spinal fluid of rhesus macaques were 1, 1, and 0.1 ng/mL, respectively. The method has been successfully employed to measure aprepitant in preclinical and clinical samples collected from three SIV-infected rhesus macaques and ten patients with HIV infection. In conclusion, this liquid chromatography-tandem mass spectrometry method is suitable for preclinical–clinical translational research exploring exposure–response relationships with aprepitant as well as therapeutic drug monitoring of aprepitant.     

Reaction of human albumin with aspirin in vitro: Mass spectrometric identification of acetylated lysines 199, 402, 519, and 545

The aspirin esterase activity of human plasma is due to butyrylcholinesterase and albumin. Our goal was to identify the amino acid residues involved in the aspirin esterase activity of albumin. Fatty acid-free human albumin and human plasma were treated with aspirin for 5 min-24 h. Acetylated residues were identified by LC/MS/MS and MALDI-TOF/TOF mass spectrometry of tryptic peptides. Treatment with 0.3 mM aspirin resulted in acetylation of Lys-199, Lys-402, Lys-519, and Lys-545. Treatment with 20 mM aspirin resulted in acetylation of 26 lysines. There was no acetylation of Tyr-411, under any conditions. Acetylated lysine was stable for at least 21 days at pH 7.4, 37 °C. Albumin acetylated by aspirin had reduced esterase activity with β-naphthyl acetate as shown on gels stained for esterase activity. It was concluded that the aspirin esterase activity of albumin is a pseudo-esterase activity in which aspirin stably acetylates lysines and releases salicylate.