Quantitative liquid chromatographic-tandem mass spectrometric determination of reserpine in FVB/N mouse plasma using a "chelating" agent (disodium EDTA) for releasing protein-bound analytes during 96-well liquid-liquid extraction

Comparison of colorimetric, fluorometric, and liquid chromatography-mass spectrometry assays for acetyl-coenzyme A

Acetyl-Coenzyme A is a central metabolite in catabolic and anabolic pathways as well as the acyl donor for acetylation reactions. Multiple quantitative measurement techniques for acetyl-CoA have been reported, including commercially available kits. Comparisons between techniques for acetyl-CoA measurement have not been reported. This lack of comparability between assays makes context-specific assay selection and interpretation of results reporting changes in acetyl-CoA metabolism difficult. We compared commercially available colorimetric ELISA and fluorometric enzymatic-based kits to liquid chromatography-mass spectrometry-based assays using tandem mass spectrometry (LC-MS/MS) and high-resolution mass spectrometry (LC-HRMS). The colorimetric ELISA kit did not produce interpretable results even with commercially available pure standards. The fluorometric enzymatic kit produced comparable results to the LC-MS-based assays depending on matrix and extraction. LC-MS/MS and LC-HRMS assays produced well-aligned results, especially when incorporating stable isotope-labeled internal standards. In addition, we demonstrated the multiplexing capability of the LC-HRMS assay by measuring a suite of short-chain acyl-CoAs in a variety of acute myeloid leukemia cell lines and patient cells.

Current Perspective and Developments in Electrochemical Sensors Modified with Nanomaterials for Environmental and Pharmaceutical Analysis

Background:

Over the past few decades, environmental pollution has appeared to be one of the most crucial global problems. The widespread intensification of numerous hazardous pollutants in the environment need the modern researchers to develop viable, reproducible and cost-effective determination tools for the reliable environmental analysis. The beneficial, as well as perilous, biological compounds are receiving growing interest due to their variable composition which produces advantageous and toxic impacts on human and the environment. Several conventional analytical methods have been established for the pharmaceutical and environmental analysis. However, certain drawbacks limited their practices in the modern rapidly growing era of science and technology. The development of electrochemical sensors has emerged as more beneficial and promising tool as against other traditional analytical approaches, in terms of simplicity, cost-effectiveness, sensitivity, stability and reliability. Nonetheless, the over potential and low anodic/cathodic current response are both considered as bottlenecks for the determination of electroactive entities exploiting electrochemical sensors. Interestingly, these problems can be easily resolved by modifying the electrodes with a variety of conductive materials, especially nanostructures.

Objective:

This review covers different electrochemical methods, reported in the literature, for the environmental and pharmaceutical analysis through simple and cost-effective nanostructures-based sensors. The electrochemical techniques with different modes and the modification of electrodes with highly conductive and prolific polymeric and nanostructured materials used for the determination of different environmental and pharmaceutical samples are the main prominence of this review. Various kinds of nanomaterials, e.g. metal, metal oxide and their composites, have been synthesized for the fabrication of sensitive electrodes.

Conclusion:

Nanostructures played a pivotal role in the modification of electrodes, which substantially enhanced the capability and sensitivity of electrochemical sensors. The proper modification of electrodes has materialized the swift detection of electroactive compounds at very low limits and offered the feasible determination procedure without any kind of signal fluctuation and over potential. In crux, due to their enhanced surface area and excellent catalytic properties, nanomaterials recently appeared as the most promising candidates in the field of electrode modification and significantly impacted the detection protocols for various environmental pollutants, viz. pesticides, metal ions and drugs.

Simultaneous determination of reserpine, rescinnamine, and yohimbine in human plasma by ultraperformance liquid chromatography tandem mass spectrometry

A sensitive and selective UPLC-MS/MS method was developed and validated for the determination of three indolic alkaloids (reserpine, rescinnamine, and yohimbine) in human plasma using papaverine as internal standard (IS). After a one step protein precipitation with acetonitrile, separation was carried out using C18 column (50 × 2.1 mm, i.d. 1.7  μ m) and mobile phase consisting of acetonitrile : water : formic acid (60 : 40 : 0.1%, v/v/v) pumped at a flow rate of 0.2 mL/min. The mass spectrometric determination was carried out using an electrospray interface operated in the positive mode with multiple reaction monitoring (MRM) mode. The precursor to product ion transitions of m/z 609.32 > 195.01, m/z 635.34 > 221.03, m/z 355.19 > 144, and m/z 340.15 > 202.02 were selected for the quantification of reserpine, rescinnamine, yohimbine, and IS, respectively. The analytical response was found to be linear in the range of 0.36-400, 0.27-300, and 0.23-250 ng/mL with lower limit of quantification of 0.36, 0.27, and 0.23 ng/mL for reserpine, rescinnamine, and yohimbine, respectively. Validation was made following official guidelines. The proposed method enabled reproducible results and hence could be reliable for pharmacokinetic and toxicological analysis.

Revealing interaction between sulfobutylether-β-cyclodextrin and reserpine by chemiluminescence and site-directed molecular docking

The host-guest interaction between sulfobutylether-β-cyclodextrin (SBE-β-CD) and reserpine (RSP) is described using flow injection-chemiluminescence (FI-CL) and site-directed molecular docking methods. It was found that RSP could inhibit the CL intensity produced by a luminol/SBE-β-CD system. The decrease in CL intensity was logarithmic over an RSP concentration range of 0.03 to 700.0 nM, giving a regression equation of ∆I = 107.1lgCRES  + 186.1 with a detection limit of 10 pM (3σ). The CL assay was successfully applied in the determination of RSP in injection, saliva and urine samples with recoveries in the range 93.5-106.1%. Using the proposed CL model, the binding constant (KCD-R ) and the stoichiometric ratio of SBE-β-CD/RSP were calculated to be 7.4 × 10(6)  M(-1) and 1 : 1, respectively. Using molecular docking, it was confirmed that luminol binds to the small cavity of SBE-β-CD with a nonpolar interaction, while RSP targeted the larger cavity of SBE-β-CD and formed a 1 : 1 complex with hydrogen bonds. The proposed new CL method has the potential to become a powerful tool for revealing the host-guest interaction between CDs and drugs, as well as monitoring drugs with high sensitivity.

High resolution LC-MS(n) fragmentation pattern of palytoxin as template to gain new insights into ovatoxin-a structure. The key role of calcium in MS behavior of palytoxins

Palytoxin is a potent marine toxin and one of the most complex natural compounds ever described. A number of compounds identified as palytoxin congeners (e.g., ovatoxins, mascarenotoxins, ostreocins, etc.) have not been yet structurally elucidated due to lack of pure material in quantities sufficient to an NMR-based structural investigation. In this study, the complex fragmentation pattern of palytoxin in its positive high resolution liquid chromatography tandem mass spectra (HR LC-MS(n)) was interpreted. Under the used conditions, the molecule underwent fragmentation at many sites of its backbone, and a large number of diagnostic fragment ions were identified. The natural product itself was used with no need for derivatization. Interestingly, most of the fragments contained calcium in their elemental formula. Evidence for palytoxin tendency to form adduct ions with calcium and other divalent cations in its mass spectra was obtained. Fragmentation pattern of palytoxin was used as template to gain detailed structural information on ovatoxin-a, the main toxin produced by Ostreopsis ovata, (observe correct font) a benthic dinoflagellate that currently represents the major harmful algal bloom threat in the Mediterranean area. Either the regions or the specific sites where ovatoxin-a and palytoxin structurally differ have been identified.

Simultaneous Determination of Hydrochlorothiazide and Reserpine in Human Urine by LC with a Simple Pre-Treatment

A simple, selective and sensitive reversed-phase high performance liquid chromatography method for simultaneous analysis of hydrochlorothiazide and reserpine in human urine was developed and subjected to primary pharmacokinetic study. After a simple protein precipitation using methanol and extraction with ethyl acetate, the analytes were separated on an Elite C(18) column at a flow rate of 0.8 mL min(-1). The mobile phase was composed of acetonitrile (A) and 0.2% ammonium chloride solution (B) for a gradient elution starting at A:B at 30:70, v/v for 0~6 min, linearly raising the percent of A from 30% to 50% (6~9 min) and ending at 50:50, v/v (9~25 min). The standard curves were linear over the range of 0.05-20 µg mL(-1) for hydrochlorothiazide and 0.02-5.0 µg mL(-1) for reserpine, respectively (r > 0.999). The limit of detection (LOD) and the limit of quantification (LOQ) were 5.5 ng mL(-1) and 18.2 ng mL(-1) for hydrochlorothiazide, and 7.1 ng mL(-1) and 23.6 ng mL(-1) for reserpine, respectively. The recoveries for both analytes were above 89.0±1.35%. The intra-day and inter-day precision for hydrochlorothiazide were less than 1.91% and 1.38%, and those for reserpine were below 1.61% and 2.64%, respectively. The method indicated good performance in terms of specificity, linearity, detection and quantification limits, precision and accuracy, and it was employed successfully for the simultaneous determination of hydrochlorothiazide and reserpine in human urine samples.

Liquid chromatography/tandem mass spectrometry method for the quantification of deserpidine in human plasma: Application to a pharmacokinetic study

A sensitive and rapid liquid chromatography/tandem mass spectrometric (LC/MS/MS) method was developed and validated for the determination of deserpidine in human plasma. The plasma samples were prepared using liquid-liquid extraction (LLE) with ethyl ether-dichloromethane (3:2, v/v). Chromatographic separation was accomplished on an Ultimate XB-C18 column. The mobile phase consisted of methanol-5mM ammonium acetate-formic acid (72:28:0.036, v/v/v). Detection of deserpidine and the internal standard tropisetron was achieved by tandem mass spectrometry with an electrospray ionization interface in positive ion mode. The lower limit of quantification was 4.0pg/ml. The linear range of the method was from 4.0 to 2000pg/ml. The intra- and inter-day precisions were lower than 14.7% in terms of relative standard deviation (RSD), and the accuracy was within +/-8.7% in terms of relative error (RE). This validated method was successfully applied for the evaluation of pharmacokinetics of deserpidine after a single oral administration dose of 0.25mg deserpidine to 22 healthy volunteers.

Simultaneous determination of seven phthalates and four parabens in cosmetic products using HPLC-DAD and GC-MS methods

Studies on the determination of seven kinds of phthalates, i.e. diethyl phthalate, dipropyl phthalate, dibutyl phthalate, benzyl butyl phthalate, dicyclohexyl phthalate, di-(2-ethylhexyl) phthalate, and dioctyl phthalate, and four parabens, i.e. methylparaben, ethylparaben, propylparaben, and butylparaben, in 15 kinds of cosmetic products, including hair sprays, perfumes, deodorants, cream, lotion, etc., by HPLC with diode array detection and GC-MS in electron impact ionization mode with selected-ion monitoring have been carried out. Methods have been developed for both qualitative and quantitative detection of phthalates and parabens. Extraction, clean-up, and analysis procedures have been optimized. HPLC and GC-MS determinations were performed after sonication-assisted extraction with methanol and clean-up with C18 SPE. These techniques permit detection of phthalates at a level of 10.0-100.0 microg/kg and of parabens at a level of 20.0-200.0 microg/kg. Overall recoveries were 85-108% with RSD values of 4.2-8.8%. Only one of the 15 examined samples was free from phthalates and parabens. The remaining 14 samples were found to contain at least three or more of these phthalates and/or parabens. The predominant phthalates and parabens detected in the studied samples were methylparaben, propylparaben, diethyl phthalate, dibutyl phthalate, dicyclohexyl phthalate, and di-(2-ethylhexyl) phthalate. The residue level is at 1.22-5289 mg/kg.

Tracking problems and possible solutions in the quantitative determination of small molecule drugs and metabolites in biological fluids using liquid chromatography–mass spectrometry

During the last decade, quantification of low molecular weight molecules using liquid chromatography-tandem mass spectrometry in biological fluids has become a common procedure in many preclinical and clinical laboratories. This overview highlights a number of issues involving "small molecule drugs", bioanalytical liquid chromatography-tandem mass spectrometry, which are frequently encountered during assay development. In addition, possible solutions to these issues are proposed with examples in some of the case studies. Topics such as chromatographic peak shape, carry-over, cross-talk, standard curve non-linearity, internal standard selection, matrix effect, and metabolite interference are presented. Since plasma is one of the most widely adopted biological fluid in drug discovery and development, the focus of this discussion will be limited to plasma analysis. This article is not intended to be a comprehensive overview and readers are encouraged to refer to the citations herein.

Liquid–liquid extraction of strongly protein bound BMS-299897 from human plasma and cerebrospinal fluid, followed by high-performance liquid chromatography/tandem mass spectrometry

BMS-299897 is a gamma-secretase inhibitor that is being developed for the treatment of Alzheimer's disease. Liquid-liquid extraction (LLE), chromatographic/tandem mass spectrometry (LC/MS/MS) methods have been developed and validated for the quantitation of BMS-299897 in human plasma and cerebrospinal fluid (CSF). Both methods utilized (13)C6-BMS-299897, the stable label isotope analog, as the internal standard. For the human plasma extraction method, two incubation steps were required after the addition of 5 mM ammonium acetate and the internal standard in acetonitrile to release the analyte bound to proteins prior to LLE with toluene. For the human CSF extraction method, after the addition of 0.5 N HCl and the internal standard, CSF samples were extracted with toluene and no incubation was required. The organic layers obtained from both extraction methods were removed and evaporated to dryness. The residues were reconstituted and injected into the LC/MS/MS system. Chromatographic separation was achieved isocratically on a MetaChem C18 Hypersil BDS column (2.0 mm x 50 mm, 3 microm). The mobile phase contained 10 mM ammonium acetate pH 5 and acetonitrile. Detection was by negative ion electrospray tandem mass spectrometry. The standard curves ranged from 1 to 1000 ng/ml for human plasma and 0.25-100 ng/ml for human CSF. Both standard curves were fitted to a 1/x weighted quadratic regression model. For both methods, the intra-assay precision was within 8.2% CV, the inter-assay precision was within 5.4% CV, and assay accuracy was within +/-7.4% of the nominal values. The validation and sample analysis results demonstrated that both methods had acceptable precision and accuracy across the calibration ranges.

Fragmentation of trimethoprim and other compounds containing alkoxy-phenyl groups in electrospray ionisation tandem mass spectrometry

This work describes electrospray ionisation tandem mass spectrometry studies of trimethoprim and a series of structurally similar compounds containing alkoxy-phenyl groups; using accurate mass measurement to confirm the proposed fragmentations. Radical cations were observed in the spectra obtained for some of the compounds, as well as uncommon fragmentations showing losses of CH4 and C2H6, whereas other compounds showed the formation of even electron ions. Possible structures for the fragment ions have been proposed and explanations for the different types of fragmentations based on the structures of the compounds. In addition an alternate structure for a fragment ion previously reported for tandem mass spectrometry of trimethoprim has been proposed, based on accurate mass measurement.

High-throughput pharmacokinetics screen of VLA-4 antagonists by LC/MS/MS coupled with automated solid-phase extraction sample preparation

Automation of plasma sample preparation for pharmacokinetic studies on VLA-4 antagonists has been achieved by using 96-well format solid-phase extraction operated by Beckman Coulter Biomek 2000 liquid handling system. A Biomek 2000 robot is used to perform fully automated plasma sample preparation tasks that include serial dilution of standard solutions, pipetting plasma samples, addition of standard and internal standard solutions, performing solid-phase extraction (SPE) on Waters OASIS 96-well plates. This automated sample preparation process takes less than 2 h for a typical pharmacokinetic study, including 51 samples, 24 standards, 9 quality controls, and 3-6 dose checks with minimal manual intervention. Extensive validation has been made to ensure the accuracy and reliability of this method. A two-stage vacuum pressure controller has been incorporated in the program to improve SPE efficiency. This automated SPE sample preparation approach combined with liquid chromatography coupled with the high sensitivity and selectivity of tandem mass spectrometry (LC/MS)/MS has been successfully applied on both individual and cassette dosing for pharmacokinetic screening of a large number of VLA-4 antagonists with a limit of quantitation in the range of 1-5 ng/ml. Consequently, a significant throughput increase has been achieved along with an elimination of tedious labor and its consequential tendency to produce errors.

Progress in liquid chromatography-mass spectrometry instrumentation and its impact on high-throughput screening

In the past 10 years, liquid chromatography-mass spectrometry (LC-MS) has rapidly matured to become a very powerful and useful analytical tool that is widely applied in many areas of chemistry, pharmaceutical sciences and biochemistry. In this paper, recent instrumental developments in LC-MS-related interfacing, ionization and mass analysis are reviewed from the perspective of the application of LC-MS in high-throughput screening of combinatorial libraries and the related high-throughput quantitative bioanalysis in early drug-discovery studies, such as early adsorption, distribution, metabolism and excretion studies.

High-throughput cytochrome p450 inhibition assays by ultrafast gradient liquid chromatography with tandem mass spectrometry using monolithic columns

A generic method employing ultrafast liquid chromatography with tandem mass spectrometry (LC/MS/MS) was developed and employed for routine screening of drug candidates for inhibition of five major human cytochrome p450 (CYP) isozymes, CYP3A4, CYP2D6, CYP2C9, CYP2C19, and CYP1A2. The method utilized a monolithic silica rod column to allow fast flow rates to significantly reduce chromatographic run time. The major metabolites of six CYP-specific probe substrates for the five p450 isoforms were monitored and quantified to determine IC(50) values of five drug compounds against each p450 isozyme. Human liver microsomal incubation samples at each test compound concentration were combined and analyzed simultaneously by the LC/MS/MS method. Each pooled sample containing six substrates and an internal standard was separated and detected in only 24 seconds. The combination of ultrafast chromatography and sample pooling techniques has significantly increased sample throughput and shortened assay turnaround time, allowing a large number of compounds to be screened rapidly for potential p450 inhibitory activity, to aid in compound selection and optimization in drug discovery.

Enantiomeric separation and quantification of fluoxetine (Prozac) in human plasma by liquid chromatography/tandem mass spectrometry using liquid-liquid extraction in 96-well plate format

Fluoxetine (Prozac) is currently one of the widely prescribed selective serotonin reuptake inhibitors (SSRIs) for the treatment of depression. A high-throughput sample preparation procedure using liquid-liquid extraction (LLE) in a 96-well plate format in conjunction with liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed and validated for quantification of fluoxetine enantiomers in human plasma. After addition of internal standard and ammonium hydroxide, samples were extracted with ethyl acetate. The organic extract was evaporated to dryness and reconstituted in methanol. Where possible, sample transfer and LLE steps were automated using a Tomtec Quadra 96 workstation. Adequate separation of fluoxetine enantiomeric pairs (resolution of 1.17) was achieved on a vancomycin column eluted with methanol containing 0.075% (by weight) ammonium trifluoroacetate. A triple quadrupole mass spectrometer, operated in the multiple reaction monitoring mode at m/z 310-->44 for fluoxetine enantiomeric pairs and m/z 287-->241 for oxazepam (internal standard), was used. Analysis was performed in the positive ion mode using atmospheric pressure chemical ionization (APCI). The standard curve range was 2.0-1000 ng/mL for each fluoxetine enantiomer. The intra- and inter-day precision and accuracy of the quality control (QC) samples were <12.5% (CV) and <13.6% (CV), respectively, for each fluoxetine enantiomer; the correlation coefficient was >0.990. Method ruggedness was demonstrated by the reproducible performance of the assay during a three-day validation period.

Comparison between liquid chromatography-time of-flight mass spectrometry and selected reaction monitoring liquid chromatography-mass spectrometry for quantitative determination of idoxifene in human plasma

This study compares HPLC electrospray time-of-flight mass spectrometry and selected reaction monitoring (SRM) LC-MS for high throughput quantitative determination of a small molecule drug in biological samples. A high throughput LC-MS method was developed for quantitatative determination of idoxifene in human plasma and the evaluation was accomplished with the cross-validation of the developed LC-MS method between the time-of-flight mass spectrometer, and a triple quadrupole mass spectrometer operated in the SRM mode. A simple one-step semi-automated 96-well liquid-liquid extraction procedure was used to prepare 96 samples in approximately 30 min and a rapid gradient was used to shorten the LC run time. Time-of-flight mass spectrometry provides acquisition of full-scan mass spectra and extracted ion current chromatograms, which may be extracted from the total ion current chromatogram for peak area determination. The limit of quantitation for idoxifene in human plasma obtained with the time-of-flight mass spectrometer was 5 ng/ml based on 100-microl aliquots of human plasma, and the linear dynamic range was from 5 ng/ml to 2000 ng/ml. The quantitative LC-MS results from the time-of-flight mass spectrometer demonstrated that precision did not exceed 7.1% and accuracy did not exceed 1.7% with reference to quality control samples at three concentration levels in replicates of six. In contrast, the limit of quantitation for idoxifene in human plasma using a tandem triple quadrupole mass spectrometer was 0.5 ng/ml with a linear dynamic range to 1000 ng/ml. The results from the triple quadrupole instrument show that the precision did not exceed 2.2% and accuracy did not exceed 2.9%. The overall results suggest time-of-flight mass spectrometry may be a viable technique for high throughput bioanalytical work for the quantitative determination of a representative small molecule drug in the low ng/ml range in human plasma.

High-throughput semi-automated 96-well liquid/liquid extraction and liquid chromatography/mass spectrometric analysis of everolimus (RAD 001) and cyclosporin a (CsA) in whole blood

A semi-automated high-throughput liquid/liquid extraction (LLE) assay was developed for RAD001 and cyclosporin A (CsA) in human blood. After addition of internal standard and ammonium hydroxide, samples were extracted twice with methyl tert-butyl ether (MTBE). The organic extract was evaporated to dryness and reconstituted in mobile phase. Where possible, sample transfer and LLE steps were automated using a Tomtec Quadra 96 workstation. Samples were analyzed using ESI-LC/MS/MS employing the transitions of ([M + NH(4)](+) --> [M + H](+)) for CsA and ([M + NH(4)](+) --> [M + H-(CH(3)OH + H(2)O)](+)) for RAD001, under isocratic chromatographic conditions (75:25, (v/v), acetonitrile/20 mM ammonium acetate) with a run time of 3.6 min. A lower limit of quantitation (LLOQ) of 0.368 ng/mL and 5.23 ng/mL was achieved for RAD001 and CsA, respectively, using a sample volume of 0.3 mL for the analysis. The method was validated over a 3-day period and the resulting calibration curves had a correlation coefficient >0.99 over the concentration range 0.368 to 409 ng/mL and 5.24 to 1748 ng/mL for RAD001 and CsA, respectively. The inter-day coefficient of variation (CV) was less than 15% at the LLOQ for both compounds. The method was applied to the analysis of clinical samples. Under normal working conditions four 96-well plates could be extracted and LC/MS analysis completed in less than 28 h. A marked improvement in sample throughput efficiency was realized with this LLE method when compared to existing solid phase extraction (SPE) methods which deal with both RAD001 and CsA.