Rapid quantification of digitoxin and its metabolites using differential ion mobility spectrometry-tandem mass spectrometry.

This study focuses on the quantitative analysis of the cardiac glycoside drug digitoxin and its three main metabolites digitoxigenin-bisdigitoxose, digitoxigenin-monodigitoxose, and digitoxigenin using electrospray ionization-differential ion mobility spectrometry-tandem mass spectrometry (ESI-DMS-MS/MS). Despite large molecular weight differences, gas-phase separation of the four compounds in the DMS drift cell was not possible, even by utilizing additional volatile chemical modifiers. Baseline separation was achieved after adduct formation with alkali metal ions, however, and efficiency was shown to improve with increasing size of the alkali ion, reaching optimum conditions for the largest cesium ion. Subsequently, an assay was developed for quantification of digitoxin and its metabolites from human serum samples and its analytical performance assessed in a series of proof-of-concept experiments. The method was applied to spiked human serum pools with concentration levels between 2 and 80 ng/mL. After a short reversed-phase chromatographic step for desalting the sample, rapid DMS separation of the analytes was carried out, resulting in a total run time of less than 1.5 min. The instrumental method showed good repeatability; the calculated coefficients of variation ranged from 2% to 13%.

Recent advances in sample preparation techniques to overcome difficulties encountered during quantitative analysis of small molecules from biofluids using LC-MS/MS.

Liquid chromatography-mass spectrometry analysis of small molecules from biofluids requires sensitive and robust assays. Because of the very complex nature of many biological samples, efficient sample preparation protocols to remove unwanted components and to selectively extract the compounds of interest are an essential part of almost every bioanalytical workflow. This review describes the most common problems encountered during sample preparation, ways to optimize established sample preparation techniques and important recent developments to reduce or eliminate major interferents from biofluids.

Quantification of vancomycin in human serum by LC-MS/MS.

BACKGROUND: The aim of our work was to develop and validate a reliable LC-MS/MS-based measurement procedure for the quantification of vancomycin in serum, to be applied in the context of efforts to standardize and harmonize therapeutic drug monitoring of this compound using routine assays. METHODS: Sample preparation was based on protein precipitation followed by ultrafiltration. In order to minimize differential modulation of ionization by matrix constituents extended chromatographic separation was applied leading to a retention time of 9.8 min for the analyte. Measurement was done by HPLC-ESI-MS/MS. For internal standardization the derivative vancomycin-glycin (ISTD) prepared by chemical synthesis was used, HPLC conditions ensured coelution of ISTD with the analyte. RESULTS: In a bi-center validation total CVs of <4% were observed for quality control material ranging from 5.3 mg/L to 79.4 mg/L; accuracy was ±4%. No relevant ion suppression was observed. Comparative measurement of aliquots from 70 samples at the two validation sites demonstrated close agreement. CONCLUSIONS: Employing a closely related homologue molecule for internal standardization and the use of MS/MS following highly efficient sample pre-fractionation by HPLC, the method described here can be considered to offer the highest level of analytical reliability realized so far for the quantification of vancomycin in human serum. Thus, the method is suitable to be used in a comprehensive reference measurement system for vancomycin.

Rapid detection and quantification of 35 benzodiazepines in urine by GC-TOF-MS.

A rapid and sensitive method for the screening and quantification of 35 benzodiazepines in human urine by gas chromatography/time-of-flight mass spectrometry was developed and validated. Target analytes were isolated from 1 ml urine by solid-phase extraction using Oasis MCX extraction columns (extraction recovery between 35 and 99%). With a supported liquid-liquid extraction method, a new modification of conventional liquid-liquid-extraction, a less time intensive alternative for benzodiazepine extraction is presented. The sample pretreatment entails the derivatization of the benzodiazepines with N,O-bis(trimethylsilyl)trifluoroacetamide plus 1% trimethylchlorosilane. Separation of all benzodiazepines was done within 9.5 min, and detection was based on full mass spectra for each analyte. A deconvolution algorithm was used for unresolved chromatographic peaks to identify coeluted substances. The subsequent quantification was done using significant masses. The limit of quantification is 10 ng/ml for most of the compounds. Linearity is in the range between 10 and 350 ng/ml. Reproducibility was observed with coefficients of variation below 2% at concentrations of 50 and 200 ng/ml. The accuracy is between 88 and 108% depending on the respective analyte and the concentration.

Chili pepper fruits: presumed precursors of fatty acids characteristic for capsaicinoids.

Capsaicin is a molecule unique to fruits from the genus Capsicum. It is responsible for the pungent sensation and displays valuable pharmacological properties. Despite the fruits' economic importance and decades of research, the regulation of the content of capsaicinoids in individual fruits is not completely elucidated, and no agricultural cultivation of chili of defined pungency is assured. Precursor candidates of the fatty acid moiety of the capsaicinoids, especially for the unique 8-methyl- trans-6-nonenoic acid, were examined. Thioesters, acyl-ACP and acyl-CoA, were isolated from the placenta of Capsicum fruits by means of DEAE-Sepharose chromatography, selectively converted to the corresponding N-butylamides, and analyzed by GC-MS. Fatty acid moieties characteristic for capsaicinoids were identified. In two different varieties ( Capsicum chinense var. Habanero orange and Capsicum annuum var. Jalapeno) it was shown that the fatty acid pattern corresponds to the distribution pattern of the capsaicinoids formed up to this time. The acyl-thioester fractions contained already the 8-methyl- trans-6-nonenoic acid.

An LC-MS/MS based candidate reference method for the quantification of carbamazepine in human serum.

A validated LC-MS/MS-based candidate reference measurement procedure for the quantification of carbamazepine is presented in order to be used for standardization and harmonization of routine assays applied for therapeutic drug monitoring. Sample preparation was based on protein precipitation using acetonitrile followed by sample dilution. Since the previously listed certified reference material (CRM) SRM 1599 (anticonvulsant drug level assay standard) is no longer available, an ISO certified calibration material was used in this assay. As internal standards deuterated analyte congeners were applied. The method allows the measurement of carbamazepine, carbamazepine-10,11-epoxide and 10-hydroxy-10,11-dihydrocarbamazepine in the concentration range of 0.1 to 22.0µg/ml with LODs and LOQs of <0.1µg/ml and 0.1µg/ml, respectively. Comparative measurement of 105 native patient samples using the here presented method showed a good agreement between two independent laboratories with a mean bias of 0.6%.

Simultaneous quantification of digoxin, digitoxin, and their metabolites in serum using high performance liquid chromatography-tandem mass spectrometry.

The study describes an LC-MS/MS method for simultaneous quantification of the cardiac glycosidic drugs digoxin and digitoxin and several of their metabolites. The assay represents a useful reference method for immunoassay-based tests, which are easily biased by the presence of metabolites of the target analytes or structurally similar substances.

Magnetic beads as an extraction medium for simultaneous quantification of acetaminophen and structurally related compounds in human serum.

This paper describes a sample preparation method that complements a previously published liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for acetaminophen and eight structurally-related compounds in human serum (C. Bylda, R. Thiele, U. Kobold, D.A. Volmer. Drug Test. Anal. 2014, 6, 451). The analytes (acetaminophen [APAP] + metabolites acetaminophen-glucuronide [APG], -cysteine [APC], -mercapturate [APM] and -cysteine [APC], structurally similar analogues phenacetin and p-phenetidine, as well as tricyclic antidepressants imipramine and amitryptiline) were extracted from serum using magnetized hyper-crosslinked polystyrene particles. The sample preparation protocol was developed by means of a design of experiments (DoE) statistical approach. Using three representative compounds from the analyte panel with different polarities (high, medium, and low), two screening designs were used to identify factors that exhibited significant impact on recovery of the analytes. These parameters were then optimized to permit extraction of the complete target panel exhibiting a broad range of chemical polarities. Liquid chromatographic separations were achieved by gradient elution using a pentafluorphenyl column with subsequent detection by electrospray ionization-triple quadrupole mass spectrometry in multiple reaction monitoring (MRM) mode. The method was linear over the range 0.1-100 µg/mL for APAP, APG, p-phenetidine and phenacetin, 0.03-50 µg/mL for APS, and 0.01-10 µg/mL for APM, APC, imipramine and amitriptyline, with R(2) > 0.99. The assay exhibited good precision with CVs ranging from 2 to 9% for all analytes; the accuracy was assessed by comparing two LC-MS/MS methods using a set of 68 patient samples.

Simultaneous quantification of acetaminophen and structurally related compounds in human serum and plasma.

The method described in this study allows the simultaneous quantification of acetaminophen (APAP) and nine structurally related compounds, namely acetaminophen metabolites and structurally similar analogs (acetaminophen-glucuronide [APG], -sulfate [APS], mercapturate [APM], -cysteine [APC], p-phenetidine, phenacetin), antidote (N-acetylcysteine, NAC), and two tricyclic antidepressants (imipramine and amitryptiline). Due to the relatively high serum concentration levels in the µg/ml range, matrix effects were simply minimized by dilution. The samples were diluted with water and disulfide bonds between serum proteins and analytes reduced using tris(2-carboxyethyl)phosphine. Chromatographic separation of the analytes was achieved by gradient elution using a pentafluorphenyl (PFP) column with subsequent detection by electrospray ionization (ESI) triple quadrupole mass spectrometry in positive and negative ionization multiple reaction monitoring (MRM) modes. Quantification was performed by means of deuterated analogues of the analytes as internal standards. Total run time of the assay was 19 min. The method was fully validated and allowed quantification of the analytes with lower limits of quantification between 50 and 0.5 ng/ml. The calibration curves were linear over the range 0.1-100 µg/ml for APAP, APG, NAC, p-phenetidine and phenacetin, 0.03-50 µg/ml for APS, and 0.01-10 µg/ml for APM, APC, imipramine and amitriptyline with correlation coefficients r(2) > 0.99. The intra-assay precision was ≤5% for all analytes except NAC (CV < 10%). The inter-day precision was ≤10% for all analytes except NAC (inter-assay precision <11%). This method was used to analyze 77 patient and spiked samples and results were consistent with expected values from a round robin test.

Development of an electrospray LC-MS/MS method for quantification of Δ(9) -tetrahydrocannabinol and its main metabolite in oral fluid.

A fast and sensitive reference method for quantification of Δ(9) -tetrahydrocannabinol (THC) and its main metabolite 11-nor-9-carboxy-Δ(9) -tetrahydrocannabinol (THCCOOH) in oral fluid is described in this study. Samples were collected using an oral specimen collection device, followed by solid-phase extraction and liquid chromatography-tandem mass spectrometry analysis. Chromatographic separation of the analytes was achieved by gradient elution on a reversed-phase column with subsequent detection by electrospray triple quadrupole mass spectrometry in positive ionization multiple reaction monitoring mode. Quantification was performed by means of deuterated analogues of the analytes as internal standards. Total run time of the assay was 12 min. The method allowed sensitive quantification of both analytes at a limit of quantification of 0.2 ng/ml. This sensitivity is essential for analysis of samples collected with the Intercept Oral Fluid Collection device (OraSure) and an assay for simultaneous quantification of THC and THCCOOH in saliva has not yet been described. The calibration curves for THC and THCCOOH were linear in the range between 0.25 and 8 ng/ml (r(2) > 0.99). Ion suppression effects from endogenous or exogenous interferences were investigated using selected model substances (albumin, ascorbic acid, bilirubin, hemoglobin, breath spray, cigarette, chewing gum, chewing tobacco, candy, tooth whitening, and Tums antacid). These substances were chosen because of the high probability of their presence in the collected samples. None of the 11 endogenous model interferences altered the accuracy of analysis, demonstrating good robustness of the method with respect to interferences in common hygiene products, medicine, tobacco and naturally occurring endogenous substances.

Simultaneous quantification of four vitamin D metabolites in human serum using high performance liquid chromatography tandem mass spectrometry for vitamin D profiling.

OBJECTIVES: For quantification of 25-hydroxyvitamin D(3) (25OH-D(3)), 25-hydroxyvitamin D(2) (25OH-D(2)), 3-epi-25-hydroxyvitamin D(3) (3-epi-25OH-D(3)) and 24R,25-dihydroxyvitamin D(3) (24R,25(OH)(2)-D(3)) in human serum a high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method was developed and validated. DESIGN AND METHODS: After protein precipitation further purification is achieved with on-line sample preparation using a reversed phase (RP) C-4 column. Chromatographic separation is realized by a RP-column with core shell material and pentafluorophenyl (PFP) selectivity. Atmospheric pressure chemical ionization in the positive ion mode with multi-reaction monitoring is used for analyte detection. RESULTS: Baseline separation of the analytes is achieved below 10 min. The method is linear over the range 4.0-265.3 nmol/L for 25OH-D(3), 3.9-183.6 nmol/L for 25OH-D(2), 2.0-133.8 nmol/L for 3-epi-25OH-D(3) and 2.8-129.9 nmol/L for 24R,25(OH)(2)-D(3) (r(2)>0.998). The limit of quantification is 4.0 nmol/L for 25OH-D(3), 3.9 nmol/L for 25OH-D(2), 2.0 nmol/L for 3-epi-25OH-D(3) and 2.8 nmol/L for 24R,25(OH)(2)-D(3). The CVs for the intra-day and inter-day precision are <5% and <4%, respectively. Metabolite levels for a set of 50 human serum samples have been determined and resulted in the detection of considerable amounts of 3-epi-25OH-D(3) and 24R,25(OH)(2)-D(3). CONCLUSIONS: This highly specific HPLC-MS/MS method is suitable for vitamin D profiling. There is a correlation between 25OH-D(3) and 24R,25(OH)(2)-D(3). Serum concentration of 24R,25(OH)(2)-D(3) increases disproportionally with increasing concentration of 25OH-D(3).