High-Throughput Quantitative LC-MS/MS Analysis of Barbiturates in Human Urine

We hereby present a fast, high-throughput, and clinical LC-MS/MS assay for the simultaneous analysis of barbiturates in human urine. It is deployed as a quantitative assay for phenobarbital, butalbital, pentobarbital/amobarbital, and secobarbital, as well as for confirmations following positive immunoassay drug screens in patient urine. Briefly, urine specimens are processed via dilute and shoot, i.e., by mixing the sample with 20 times volume of internal standard reagent and injecting 50 μL of that mixture into the analytical instrument. Chromatographic separation is performed using a reversed-phase C18 column in a mobile-phase system doped with <1 mM ammonium fluoride. Mass spectrometric detection occurs via negative-mode electrospray ionization multiple reaction monitoring in the TSQ Quantiva triple-quadrupole instrument. All the analytes in the mixture are detected and quantified simultaneously with respect to internal calibration in the range 20-2500 ng/mL. However, the assay cannot distinguish pentobarbital from amobarbital, which are isobaric analytes. Nonetheless, the assay is sensitive, robust, and amenable to harmonization with other assays that employ barbiturate cutoffs in the range of 20-150 ng/mL.

Analysis of Barbiturates in Urine by LC-MS/MS

In the method described here, an aliquot of a urine sample is analyzed to detect barbiturates through dilution and ultra-high-performance chromatography-tandem mass spectrometry (UPLC-MS/MS) using deuterated internal standards. This assay detects the presence of nine barbiturate drugs-amobarbital, barbital, butalbital, butabarbital, mephobarbital, secobarbital, pentobarbital, phenobarbital, and thiopental. This protocol describes two LC separation methods-first LC method (2.2 min/sample) is intended to be used as a first step of the analysis that does not separate amobarbital and pentobarbital, and a second, longer (2.7 min/sample) LC method is intended to be used only for samples which have a peak in the amobarbital/pentobarbital retention time on the shorter LC method. Since the frequency at which amobarbital and pentobarbital are observed in clinical populations is low, the shorter LC method helps gain efficiency in a high-volume laboratory environment. Additional features of this protocol that help in efficiency gain are automated extraction using Hamilton™ liquid handling system and algorithmic data review using Ascent™ software.

New approach for barbiturates, phenytoin, methyprylon and glutethimide determination and fragmentation (UHPLC-MS/MS)

Barbiturates which are old pharmaceutical drugs are still widely used in medical treatment of epilepsy and for general anesthesia. To date, more than 2500 different barbituric acid analogs have been synthesized, and 50 of them were introduced into medical use over the last century. Due to their highly addictive properties, pharmaceuticals containing barbiturates are under strict control in many countries. However, by considering the worldwide problem with new psychoactive substances (NPS) the introduction of new designer barbiturate analogs into the dark market might serve a serious public health problem in the near future. For this reason there is an increasing need for application methods for barbiturates monitoring in biological samples. The UHPLC-QqQ-MS/MS method for determination of 15 barbiturates, phenytoin, methyprylon and glutethimide was developed and fully validated. The biological sample volume was reduced to only 50 µL. A simple LLE (pH 3 with ethyl acetate) was successfully applied. The lower LOQ was 10 ng/mL. The method enables differentiation of structural isomers: hexobarbital and cyclobarbital; as well as amobarbital and pentobarbital. Chromatographic separation was achieved with the use of the alkaline mobile phase (pH 9) and Acquity UPLC BEH C18 column. Furthermore, the novel fragmentation mechanism of barbiturates was proposed, which may have a great impact in identification of novel barbiturates analogs introduced to illegal marketplaces. The presented technique has a great potential to be applied in forensic, clinical and veterinary toxicological laboratories, as was evidenced by the positive results of international proficiency tests.

Quantitative analysis of thiamylal and its metabolite secobarbital using liquid chromatography-tandem mass spectrometry in adipose tissue, serum, and liver

Thiamylal is an ultrashort-acting barbiturate used for intravenous administration or general anesthesia induction. However, some cases of poisoning and suicide with thiamylal administration have been reported. Additionally, there are few reports on its analysis in the organs and adipose tissue, which requires purification by column chromatography and evaporation. A rapid and sensitive method was developed for quantifying thiamylal and its metabolite, secobarbital, in the adipose tissue, serum, and liver using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Samples were prepared using modified QuEChERS extraction. For adipose tissue samples, an acetonitrile-hexane partitioning step was added to the extraction. This method was applied to investigate a suspected self-poisoning autopsy case. The quantitation accuracy for thiamylal added to porcine pericardial fat (0.18 µg/g), human serum (0.015 µg/mL), and porcine liver (0.18 µg/g) was 103%, 113%, and 95.3%, respectively. The quantitation limits calculated for porcine pericardial fat, human serum, and porcine liver at a signal-to-noise ratio of 10 were 0.06 µg/g, 0.005 µg/mL, and 0.06 µg/g, respectively. In addition, the thiamylal and secobarbital levels in the forensic autopsy case were 140 and 1.5 µg/g, respectively, in myocardial fat; 3.5-4.9 and 0.12-0.20 µg/mL, respectively, in serum; and 6.2-42 and 0.58-1.1 µg/g, respectively, in liver tissue. Thiamylal is especially distributed in the adipose tissue. The thiamylal-to-fat ratio may help estimate the time from administration to death. The developed modified QuEChERS extraction method with acetonitrile-hexane partitioning is suitable for analyzing hydrophobic compounds, such as thiamylal, in the adipose tissue.

Quantitative Determination of Methohexital in Human Whole Blood by Liquid Chromatography Tandem Mass Spectrometry

A rapid, simple and sensitive liquid chromatography tandem mass spectrometry method for the determination of methohexital in human whole blood was developed and validated. Ethyl acetate/n-hexane (9:1) was used as extraction solvent while aprobarbital was used as internal standard. Methohexital was recovered by liquid-liquid extraction from 100 μL of human whole blood. The mobile phase was water-acetonitrile, and an ACQUITY BEH C18 (2.1 × 100 mm, 1.7 μm) column was adopted. Negative electrospray ionization source and multiply reaction monitoring mode were applied. The transitions of m/z were 261.2/42.2 and 261.2/119.0 for methohexital. The limit of detection was 0.5 ng/mL, which was lower than the previous methods. Wide linear range (2-2,000 ng/mL) with a good correlation coefficient (r > 0.99) was also obtained. The intra- and inter- day precisions represented by relative standard deviation were <11.5%, and the recoveries were >79.67%. This analytical method involved small sample volume and had been proven to be rapid, easy, sensitive and specific. Therefore, it could be used for the clinical analysis of methohexital.

Use of high resolution/accurate mass full scan/data-dependent acquisition for targeted/non-targeted screening in equine doping control

High-resolution mass spectrometry (HRMS) is a very powerful technology for equine doping control analysis. The more recently developed hybrid type of Orbitrap-based HRMS instrument allows for both targeted and non-targeted screening analyses in a single liquid chromatography-high resolution tandem mass spectrometry (LC-HRMS/MS) run. In the present study, an LC-HRMS/MS method was developed and validated to detect prohibited substances in equine sports. The substances were recovered from equine plasma by liquid-liquid extraction (LLE) using methyl tert-butyl ether and were separated on a C18 reversed-phase column using mobile phases of 5 mM ammonium formate and acetonitrile. A 7.5 min LC gradient was employed to elute substances and results indicated that the LC method generated sharp and symmetric chromatographic peaks. An in-house equine doping compound database and a spectral library were built to increase method specificity for substances of interest. Five criteria, i.e. accurate mass, retention time, isotope pattern, selected HRMS/MS fragment ions (compound database) and HRMS/MS spectra (spectral library), were employed for targeted screening. We utilized these criteria to validate targeted detection of 451 substances within our in-house equine doping compound database. By using all five criteria in screening, the false screening positive rate is significantly reduced. A screening strategy and a Microsoft Excel macro were developed to facilitate interpretation and reporting of results. As the simultaneous acquisition of the full scan HRMS data provides the opportunity for retrospective non-targeted analysis, our findings highlight the use of this novel methodology as a simple, rapid, and reliably reproducible strategy to meet the challenge of identifying an increasing number of doping substances that could potentially impact the integrity of the horse racing community.