Matrix effects in ultra-high performance supercritical fluid chromatography-mass spectrometry analysis of vitamin E in plasma: The effect of sample preparation and data processing

The approaches to matrix effects determination and reduction in ultra-high performance supercritical fluid chromatography with mass spectrometry detection have been evaluated in this study using different sample preparation methods and investigation of different calibration models. Five sample preparation methods, including protein precipitation, liquid-liquid extraction, supported liquid extraction, and solid phase extraction based on both "bind and elute" and "interferent removal" modes, were optimized with an emphasis on the matrix effects and recovery of 8 forms of vitamin E, including α-, β-, γ-, and δ-tocopherols and tocotrienols, from plasma. The matrix effect evaluation included the use and comparison of external and internal calibration using three models, i.e., least square with no transformation and no weighting (1/x0), with 1/x2 weighting, and with logarithmic transformation. The calibration model with logarithmic transformation provided the lowest %-errors and the best fits. Moreover, the type of the calibration model significantly affected not only the fit of the data but also the matrix effects when evaluating them based on the comparison of calibration curve slopes. Indeed, based on the used calibration model, the matrix effects calculated from calibration slopes ranged from +92% to - 72% for α-tocopherol and from -77% to +19% in the case of δ-tocotrienol. Thus, it was crucial to calculate the matrix effect by Matuszewski's post-extraction approach at six concentration levels. Indeed, a strong concentration dependence was observed for all optimized sample preparation methods, even if the stable isotopically labelled internal standards (SIL-IS) were used for compensation. The significant differences between individual concentration levels and compounds were observed, even when the tested calibration range covered only one order of magnitude. In methods with wider calibration ranges, the inappropriate use of calibration slope comparison instead of the post-extraction addition approach could result in false negative results of matrix effects. In the selected example of vitamin E, solid-phase extraction was the least affected by matrix effects when used in interferent removal mode, but supported liquid extraction resulted in the highest recoveries. We showed that the calibration model, the use of a SIL-IS, and the analyte concentration level played a crucial role in the matrix effects. Moreover, the matrix effects can significantly differ for compounds with similar physicochemical properties and close retention times. Thus, in all bioanalytical applications, where different analytes are typically determined in one analytical run, it is necessary to carefully select the data processing in addition to the method for the sample preparation, SIL-IS, and chromatography.

Quantitative determination of R/S-methadone in human serum using ultra-high performance supercritical fluid chromatography-tandem mass spectrometry: A method for routine use

Methadone has two enantiomers, which exhibit differences in pharmacological effects, with R-methadone being the active and S-methadone the inactive enantiomer. A robust, simple and rapid method for chiral separation of the two enantiomers in serum samples using ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MSMS) has been developed and validated. Enantiomeric separation was achieved using a Chiralpak IH-3 column with a mobile phase consisting of CO2 and 30mM ammonium acetate in methanol/water (98/2, v/v). Runtime was 4 minutes. Sample preparation was semi-automated using a Hamilton ML Star robot with protein precipitation, and phospholipid removal was carried out using a Waters OSTRO™ 96-well plate. The calibration range was 50.0-1,500 nM for each enantiomer. The between-assay relative standard deviations were in the range of 1.2-3.6%. Matrix effects ranged from 99% to 115% corrected with internal standard. The method has been implemented in our laboratory and has proven to be a robust and reliable method for determining the ratio of R/S-methadone in authentic patient samples.

Enantiomer-specific analysis of amphetamine in urine, oral fluid and blood

Illegal amphetamine is usually composed of a racemic mixture of the two enantiomers (S)- and (R)-amphetamine. However, when amphetamine is used in medical treatment, the more potent (S)-amphetamine enantiomer is used. Enantiomer-specific analysis of (S)- and (R)-amphetamine is therefore used to separate legal medical use from illegal recreational use. The aim of the present study was to describe our experience with enantiomer-specific analysis of amphetamine in urine and oral fluid, as well as blood, and examine whether the distribution of the two enantiomers seems to be the same in different matrices. We investigated 1,722 urine samples and 1,977 oral fluid samples from prison inmates, and 652 blood samples from suspected drugged drivers, where prescription of amphetamine was reported. Analyses were performed using ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS-MS). The enantiomer separation was achieved by using a chiral column, and results from the method validation are reported. Samples containing <60% (S)-amphetamine were interpreted as representing illegal use of amphetamine. The distribution of the two enantiomers was compared between different matrices. In urine and oral fluid, the mean amount of (S)-amphetamine was 45.2 and 43.7%, respectively, while in blood, the mean amount of (S)-amphetamine was 45.8%. There was no statistically significant difference in the amount of (S)-amphetamine between urine and oral fluid samples and between urine and blood samples, but the difference was significant in blood compared to oral fluid samples (P < 0.001). Comparison of urine and oral fluid between similar populations indicated that enantiomers of amphetamine can be interpreted in the same way, although marginally higher amounts of (R)-amphetamine may occur in oral fluid. Oral fluid, having several advantages, especially during collection, could be a preferred matrix in testing for illegal amphetamine intake in users of medical amphetamine.

Matrix effect in bioanalytical assay development using supercritical fluid chromatography-mass spectrometry

Matrix effect (ME) is commonly caused by coelution of compounds with target analytes, resulting in either suppression or enhancement of analyte ionization. Thus, to achieve the desired accuracy, precision, and sensitivity, ME needs to be evaluated and controlled during bioanalytical method development. As the application of supercritical fluid chromatography-mass spectrometry (SFC-MS) for analysis of biological samples has increased, ME using SFC-MS has also been investigated with a focus on the difference in ME in SFC-MS compared to other chromatographic techniques used for achiral separation in biological samples. Here, we provide a summary of the status of ME evaluation and mitigation in SFC-MS methods. This review presents an overview of the phenomenon of ME and methods for evaluating ME in bioanalysis. Next, the factors that can impact ME in SFC-MS-based bioanalytical methods are discussed in detail with an emphasis on SFC. A literature review of the evaluation of ME in targeted bioanalytical methods using SFC-MS is included at the end. Robust instrumentation, effective sample preparation, and superb separation selectivity are the foundations of reliable analytical methods as well as the ability to mitigate detrimental ME in SFC-MS methods.

Driving under the Influence of Amphetamine: Analytical Evaluation of Illegal or Prescription Drug Intake Using Chiral UHPLC-MS-MS

Differentiation between consumption of illegal and prescription drugs remains an important aspect in forensic toxicology. While illicit amphetamine is most often racemic, the medicinal drugs marketed in Denmark for the treatment of attention-deficit hyperactivity disorder contain the pure (S)-enantiomer or a prodrug thereof. In this study, we present a simple and efficient analytical workflow to provide information about the origin of amphetamine consumed in forensic cases concerning driving under the influence of drugs (DUID). Following quantification of amphetamine and methamphetamine using our conventional multi-target ultra-high performance liquid chromatography-tandem mass spectrometry method, determination of (R)- and (S)-amphetamine was performed by reinjecting the sample extract on a Phenomenex LUX® AMP chiral column using the same analytical instrument and mobile phases. Chiral separation was performed isocratic within a run time of 6 min. The analytical workflow was applied to blood samples from 5,248 suspected DUID cases within a 2-year period. Amphetamine was detected in 18.7% of the samples, of which both enantiomers were detected in 89.5% of the cases, indicating the consumption of illegal racemic amphetamine. In 6.1% of the positive cases, both amphetamine and methamphetamine were detected, indicating either co-consumption of both amphetamines or consumption of methamphetamine. In the remaining 4.4%, only (S)-amphetamine was detected indicating the consumption of prescription drugs containing (S)-amphetamine or a prodrug thereof. Implementation of a simple and rapid chiral method in the conventional analytical workflow for routine forensic casework proved to be an efficient way to elucidate whether a positive amphetamine result originates from illegal or prescription drug consumption, without increasing turnaround time nor costs to any significant extent, as no additional sample preparation was required.

Supercritical Fluid Chromatography for Chiral Analysis, Part 2: Applications

In the second part of this review article, the recent progress in supercritical fluid chromatography (SFC) for enantiomeric separations is evaluated. With the substantial developments carried out over the past years in instrumentation, columns, and detector hyphenation, the interest in chiral SFC has been steadily growing in various fields. In combination with novel developments in chiral stationary phase chemistries, the enantioselective analysis range has been significantly extended. Several applications reported on the enantioselective separation of drugs and pharmaceutical compounds using chiral SFC are discussed, including pharmaceutical applications, clinical research, forensic toxicology, and environmental sciences.

Enantioselective Quantification of Amphetamine and Metabolites in Serum Samples: Forensic Evaluation and Estimation of Consumption Time

In forensic toxicology, amphetamine intoxications represent one of the most common case groups and present difficult questions for toxicologists. Estimating the time of consumption and the current influence of the stimulant is particularly difficult when only total amphetamine concentrations are considered. Stereoselective analysis and the consideration of metabolites can provide valuable information to facilitate interpretation. An enantioselective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for detection of amphetamine, norephedrine and 4-hydroxyamphetamine was developed. Validation showed satisfactory selectivity, sensitivity, linearity (0.5-250 ng/mL), precision and accuracy for all enantiomers. The method was applied to a collective of 425 forensic serum samples and 30 serum samples from psychiatric inpatients stating their last time of amphetamine consumption. Norephedrine and 4-hydroxyamphetamine were detected more frequently at higher amphetamine concentrations and at lower amphetamine (R)/(S) concentration ratios, possibly indicating recent consumption. Mean (R)/(S) ratio of amphetamine was 1.14, whereas higher ratios (mean 1.36) were found for amphetamine concentrations below 100 ng/mL. The (R)/(S) ratios of psychiatric inpatients significantly correlated with the reported time intervals to last consumption. The use of amphetamine (R)/(S) ratios and the simultaneous detection of metabolites are promising factors that can facilitate estimation of consumption time and current impairment.