Correction function for biased results due to matrix effects in residue analysis of beta-agonists in porcine tissues and urine with LC-MS/MS

A correction function is proposed to compensate for matrix effects in the residue analysis of nine β-agonists by liquid chromatography tandem mass spectrometry.

Quantification of co-trimoxazole in serum and plasma using MS/MS

Background: Co-trimoxazole is frequently used in the prophylaxis and treatment of Pneumocystis carinii pneumonia. High plasma concentrations of sulfamethoxazole or trimethoprim are correlated with toxicity. There is, however, a large variation in PK observed which can lead to underexposure or toxicity. Results: We developed a novel LC–MS/MS method to analyze the components of co-trimoxazole, trimethoprim and sulfamethoxazole and its metabolite sulfamethoxazole-N-acetyl. This new method is expeditious due to its limited sample preprocessing and a relatively short run-time of only 3 min. Conclusion: This new method met the US FDA requirements on linearity, selectivity, precision, accuracy, matrix effects, recovery and stability and is suitable for routine analysis and future prospective studies.

Multivariate data analysis and metabolic profiling of artemisinin and related compounds in high yielding varieties of Artemisia annua field-grown in Madagascar

An improved liquid chromatography-tandem mass spectrometry (LC-MS/MS) protocol for rapid analysis of co-metabolites of A. annua in raw extracts was developed and extensively characterized. The new method was used to analyse metabolic profiles of 13 varieties of A. annua from an in-field growth programme in Madagascar. Several multivariate data analysis techniques consistently show the association of artemisinin with dihydroartemisinic acid. These data support the hypothesis of dihydroartemisinic acid being the late stage precursor to artemisinin in its biosynthetic pathway.

Quantitative hydrophilic interaction chromatography-mass spectrometry analysis of N-acetylneuraminic acid and N-acetylmannosamine in human plasma

N-acetylneuraminic acid (Neu5Ac or NANA) is the most predominant sialic acid in mammals. As a terminal component in many glycoproteins and glycolipids, sialic acid is believed to be an important biomarker related to various diseases. Its precursor, N-acetylmannosamine (ManNAc), is being investigated as a potential treatment for GNE myopathy. In this work, we developed two highly sensitive and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods for the quantitation of ManNAc and free Neu5Ac in human plasma. A fit-for-purpose approach was adopted during method validation and sample analysis. To measure the endogenous compounds and overcome the interference from plasma samples, a surrogate matrix that contained 5% bovine serum albumin (BSA) was used for the preparation of calibration standards and certain levels of quality control (QC) samples. QC samples at higher concentrations were prepared in the authentic matrix (human plasma) to best mimic incurred samples. For both methods, an Ostro 96-well phospholipid removal plate was used for sample extraction, which efficiently removed the phospholipids from the plasma samples prior to LC injection, eliminated matrix effect, and improved sensitivity. Chromatographic separation was achieved using hydrophilic interaction chromatography (HILIC) and gradient elution in order to retain the two polar compounds. The lower limit of quantitation (LLOQ) for ManNAc and Neu5Ac was 10.0 and 25.0ng/mL, respectively. The overall accuracy of the two assays was within 100%±8.3% based on three levels of QC samples. Inter- and intra-run precision (coefficient of variation (%CV)) across three analytical runs was less than 6.7% for ManNAc and less than 10.8% for Neu5Ac. These methods have been validated to support clinical studies.

Challenges of analyzing different classes of metabolites by a single analytical method

Complex biological samples include thousands of metabolites that range widely in both physiochemical properties and concentration. Simultaneously analyzing metabolites with different properties using a single analytical method is very challenging. The analytical process for metabolites comprises multiple steps including sampling, quenching, sample preparation, separation and detection. Each step can have a significant effect on the reliability and precision of ultimate analytic results. The aim of review is a discussion of considerations and challenges for the simultaneous analysis of metabolites using LC– and GC–MS systems. The review discusses available methodology for each analytical step, and presents the limitations and advantages of each method for the large-scale targeted metabolomics analysis of human and animal biological samples.

Systematic evaluation of plasma phospholipids for reliable and precise determination of dronedarone and desbutyldronedarone by LC–MS/MS

Background: The objective of the present work was to minimize or eliminate the matrix effect due to plasma phospholipids as observed during sample preparation for accurate determination of dronedarone and its active metabolite, desbutyldronedarone by LC–ESI-MS/MS. Results: The extraction recovery and matrix factors ranged from 93.27 to 95.14% and 0.99 to 1.02, respectively, for both the analytes. A linear concentration range of 0.10 to 150 ng/ml was established for both the analytes. The analytes were efficiently resolved (Rs 2.37) on Kromasil® (AkzoNobel, Bohus, Sweden) C18 column within 3.0 min. The assay reproducibility was determined by reanalysis of 72 incurred samples with % change within ±10%. Conclusion: The optimized solid-phase extraction provided cleaner extracts with reduced matrix effect from plasma phospholipids compared with protein precipitation and liquid–liquid extraction.

Simultaneous determination of ornidazole and its main metabolites in human plasma by LC–MS/MS: application to a pharmacokinetic study

Background: Ornidazole is a 5-nitroimidazole antimicrobial agent used for almost 40 years. A novel LC–MS/MS assay was developed and validated for the simultaneous determination of ornidazole and its main metabolites (M3, M6, M16–1, and M16–2) in human plasma. Results: After extraction from 100 μl of plasma by protein precipitation with acetonitrile, all the analytes were separated on a Capcell PAK MG C18 column (100 × 4.6 mm, 5 μm) within 5.0 min and detected by ESI-MS/MS in the positive mode. The validation results met the acceptance criteria as per the US FDA and EMA guidelines. Conclusion: The validated method was successfully applied to a pharmacokinetic study after oral administration of 1000 mg ornidazole to six healthy Chinese volunteers.

Drug confirmation by mass spectrometry: Identification criteria and complicating factors

Drug confirmation by mass spectrometry coupled with chromatography is essential to toxicology, doping control, pain management, and workplace drug testing. High confidence in this technology is due to its superior specificity and sensitivity. However, there are challenges associated with drug confirmation, and proper setup and validation of these assays are important in assuring high-quality results. In this article, assay parameters required for drug confirmation are summarized based on recent scientific publications, various established guidelines, and our own practical experience. Factors affecting the result quality and correct results interpretation are critically reviewed. Several emerging technologies and their potential applications are briefly explored.

Development and analytical comparison of microflow and nanoflow liquid chromatography/mass spectrometry procedures for quantification of cardiac troponin T in mouse hearts

Three procedures for the quantification of cardiac troponin T (cTnT) based on liquid chromatography/mass spectrometry (LC/MS) were developed, validated and compared. The procedures were applied to estimate the cTnT content in the hearts of wild type mice C57BL/6J (WT) and double knock-outs for apolipoprotein E and receptor for LDL (AL KO). Three variants of the procedure proposed include microflow, direct injection nanoflow and preconcentration nanoflow LC/MS. Troponin T tryptic peptide YEINVLR and its analog (internal standard) were monitored in a multiple reaction monitoring mode using triple quadrupole mass detector with electrospray (ESI) ion sources. The preconcentration nanoflow LC/MS method offered the best sensitivity with a lower limit of quantification (LLOQ) of 0.25 fg µL(-1) and a minimal matrix effect. The LLOQ value was 8 times better, compared with that in direct injection nanoflow LC/MS and 200 times better than in microflow LC/MS. The accuracy or precision for all three methods were not different. Separation time in the direct injection nanoflow (8 min) was equivalent to the microflow method (6 min). The cTnT contents in the mice hearts measured by the methods developed by the present authors were not different between the WT and AL KO. We conclude that nanoflow LC/MS based quantitative proteomics offers fundamentally better sensitivities while maintaining analytical quality and separation times equivalent to microflow procedures.

Impact of electrospray ion source platforms on matrix effect due to plasma phospholipids in the determination of rivastigmine by LC–MS/MS

Background: This study evaluates the performance of three electrospray ionization source designs to monitor the interference of plasma phospholipids for reliable estimation of rivastigmine by LC–MS/MS for method ruggedness. The variation in the area response due to matrix effects was assessed by post-column infusion, post-extraction spiking and standard-line slope methods. Results: The observed interference due to coeluting phospholipids (m/z: 524.0/184.0) at the retention time of rivastigmine was 39.5, 12.9 and 0.4% using angular spray, orthogonal spray and dual orthogonal ion source spray design, respectively. Similarly, %CV for standard line slopes was 6.9, 4.6 and 2.0, respectively. Conclusion: Z-spray source design provided better and efficient transfer of gas phase ions into the mass analyzer compared with angular and orthogonal spray. The study showed that Z-spray ion source provided minimum interference from phospholipids compared with other ion source designs.

Biological sample preparation: attempts on productivity increasing in bioanalysis

Sample preparation is an important step of any biomedical analysis. Development and validation of fast, reproducible and reliable sample preparation methods would be very helpful in increasing productivity. Except for a few direct injection methods, almost all biological samples should at least be diluted before any analysis. Sometimes dilution is not possible because of the low concentration of the target analyte in the sample, and alternative pretreatments, such as filtration, precipitation and sample clean up using different extraction methods, are needed. This review focuses on the recent achievements in the pretreatment of biological samples and investigates them in six categories (i.e., dilution, filtration/dialysis, precipitation, extraction [solid-phase extraction, liquid–liquid extraction], novel techniques [turbulent flow chromatography, immunoaffinity method, electromembrane extraction] and combined methods). Each category will be discussed according to its productivity rate and suitability for routine analysis, and the discussed methods will be compared according to the mentioned indices.

HILIC UHPLC-MS/MS for fast and sensitive bioanalysis: accounting for matrix effects in method development

BACKGROUND

Matrix effects are considered to be a main obstacle of quantitative bioanalytical LC-MS/MS methods. Therefore it is often required to minimize them in order to increase method reliability. HILIC has been referenced as one of possible approaches. However, there is a lack of experimental evidence in scientific literature so far.

METHODOLOGY

Matrix effects were evaluated using spiked serum samples after SPE and protein precipitation prior to UHPLC-ESI-MS/MS. Chromatography was performed in both HILIC and reversed-phase mode. The influence of the matrix effects on the signal response was assessed using a set of 34 compounds of pharmaceutical interest and post-extraction addition approach.

RESULTS

The advantages and drawbacks of the HILIC and reversed-phase chromatographic modes were compared and discussed in detail.

CONCLUSION

HILIC demonstrated the potential to reduce the occurrence of matrix effects when a more thorough sample pretreatment procedure such as SPE was applied.

Introduction of solid-phase microextraction as a high-throughput sample preparation tool in laboratory analysis of prohibited substances

A fully automated, high-throughput method based on thin-film solid-phase microextraction (SPME) and liquid chromatography-mass spectrometry was developed for simultaneous quantitative analysis of 110 doping compounds, selected from ten classes and varying in physical and chemical properties. Among four tested extraction phases, C18 blades were chosen, as they provided optimum recoveries and the lowest carryover effect. The SPME method was optimized in terms of extraction pH, ionic strength of the sample, washing solution, extraction and desorption times for analysis of urine samples. Chromatographic separation was obtained in reversed-phase model; for detection, two mass spectrometers were used: triple quadrupole and full scan orbitrap. These combinations allowed for selective analysis of targeted compounds, as well as a retrospective study for known and unknown compounds. The developed method was validated according to the Food and Drug Administration (FDA) criteria, taking into account Minimum Required Performance Level (MRPL) values required by the World Anti-Doping Agency (WADA). In addition to analysis of free substances, it was also shown that the proposed method is able to extract the glucuronated forms of the compounds. The developed assay offers fast and reliable analysis of various prohibited substances, an attractive alternative to the standard methods that are currently used in anti-doping laboratories.

Mobile phase pH and organic modifier in reversed-phase LC–ESI-MS bioanalytical methods: assessment of sensitivity, chromatography and correlation of retention time with in silico logD predictions

Background: The aim of the work described herein was to undertake a systematic investigation of the effect of mobile phase pH and organic modifier in typical reversed-phase LC–MS methods with regard to ESI-MS response, chromatographic performance and correlation of retention time with in silico logD predictions. Results: For the test set of pharmaceutical analytes investigated, ESI-MS response was generally greater when employing methanol rather than acetonitrile as the organic modifier, and increases of up to tenfold were observed dependent on the pH-buffered mobile phase employed. Deleterious effects on chromatographic performance of protonated basic analyte were observed under conditions of neutral to weakly basic pH. A qualitative correlation between plots of predicted logD and observed retention time against pH was demonstrated. Conclusion: In the absence of a simple and/or predictive dependence of analyte ESI-MS response on the mobile phase pH, a practical evaluation should be undertaken when absolute sensitivity is paramount. The use of in silico predictions of analyte logD to direct the development of bioanalytical assays is broadly valid, but further scrutiny is recommended in predicting the retention of ionized analyte.

Impact of organic solvent additive on the integrity of plasma samples in bioanalysis by LC–MS/MS

Background: Matrix effects are one of the major drawbacks of ESI–MS/MS. It is majorly caused by lipids in plasma, which can be overcome by using different extraction techniques. Results: In this investigation, a major matrix effect was observed in samples containing a co-administered drug. Unknown compounds appeared over time in the human plasma samples spiked with co-administered drug creating major ion suppression. The changes in matrix integrity were associated with the organic solvent content in the plasma samples. Conclusion: The amount and type of organic solvent added to human plasma along with the storage conditions must be carefully determined during method development in order not to impact quantitation.

Aging of biological matrices and its effect on bioanalytical method performance

Apart from the well-known matrix effects that can occur in ESI LC–MS, biological matrices may have other effects influencing the quantitative reliability of bioanalytical methods. In this paper, six case studies are presented that show the effect that aging, that is the change in properties and composition of biological matrices over time, can have on the performance of bioanalytical methods. It is shown that selectivity can be affected due to the formation or disappearance of endogenous compounds. Stability can be influenced because of the decrease (or increase) of enzyme activities and recovery can be impacted if the extractability from binding sites in the matrix is enhanced or decreased. A general discussion on the importance of these matrix effects is provided as well as a perspective on how to properly address them in the method-development and validation stages of regulated bioanalysis.

Case studies: the impact of nonanalyte components on LC–MS/MS-based bioanalysis: strategies for identifying and overcoming matrix effects

Achieving sufficient selectivity in bioanalysis is critical to ensure accurate quantitation of drugs and metabolites in biological matrices. Matrix effects most classically refer to modification of ionization efficiency of an analyte in the presence of matrix components. However, nonanalyte or matrix components present in samples can adversely impact the performance of a bioanalytical method and are broadly considered as matrix effects. For the current manuscript, we expand the scope to include matrix elements that contribute to isobaric interference and measurement bias. These three categories of matrix effects are illustrated with real examples encountered. The causes, symptoms, and suggested strategies and resolutions for each form of matrix effects are discussed. Each case is presented in the format of situation/action/result to facilitate reading.

Tracing and separating plasma components causing matrix effects in hydrophilic interaction chromatography-electrospray ionization mass spectrometry

Matrix effects on electrospray ionization were investigated for plasma samples analysed by hydrophilic interaction chromatography (HILIC) in gradient elution mode, and HILIC columns of different chemistries were tested for separation of plasma components and model analytes. By combining mass spectral data with post-column infusion traces, the following components of protein-precipitated plasma were identified and found to have significant effect on ionization: urea, creatinine, phosphocholine, lysophosphocholine, sphingomyelin, sodium ion, chloride ion, choline and proline betaine. The observed effect on ionization was both matrix-component and analyte dependent. The separation of identified plasma components and model analytes on eight columns was compared, using pair-wise linear correlation analysis and principal component analysis (PCA). Large changes in selectivity could be obtained by change of column, while smaller changes were seen when the mobile phase buffer was changed from ammonium formate pH 3.0 to ammonium acetate pH 4.5. While results from PCA and linear correlation analysis were largely in accord, linear correlation analysis was judged to be more straight-forward in terms of conduction and interpretation.

Simultaneous determination of three phenylethanoid glycosides from Callicarpae Caulis et Folium in rat plasma by LC–MS/MS and its application to PK study

Background:Callicarpae Caulis et Folium (CCF) is a traditional Chinese medicine usually used for hemostasis in clinics. In this study, a novel LC–MS/MS method was developed and validated for the simultaneous quantification of three phenylethanoid glycosides in rat plasma (verbascoside, forsythoside B and poliumoside), which are the major bioactive compounds of CCF; MS was operated in negative mode. Results: This method was linear between 5.2 and 1010 ng/ml for poliumoside, 7.0 and 420 ng/ml for forsythoside B and 2.60 and 260.0 ng/ml for verbascoside. The MS/MS ion transitions monitored were m/z 769.4→160.5, m/z 755.3→593.3, m/z 623.1→160.5 and m/z 179.0→133.6 for poliumoside, forsythoside B, verbascoside and caffeic acid (IS), respectively. Linearity, accuracy, precision and extraction recovery of three analytes were all satisfactory. Conclusion: The method developed was sensitive, specific and rapid. It has been successfully applied in a PK study of three phenylethanoid glycosides after a single oral administration of CCF extract to rats.

Quantitative mapping of glycoprotein micro-heterogeneity and macro-heterogeneity: an evaluation of mass spectrometry signal strengths using synthetic peptides and glycopeptides

Mass spectrometry (MS) is used to quantify the relative distribution of glycans attached to particular protein glycosylation sites (micro-heterogeneity) and evaluate the molar site occupancy (macro-heterogeneity) in glycoproteomics. However, the accuracy of MS for such quantitative measurements remains to be clarified. As a key step towards this goal, a panel of related tryptic peptides with and without complex, biantennary, disialylated N-glycans was chemically synthesised by solid-phase peptide synthesis. Peptides mimicking those resulting from enzymatic deglycosylation using PNGase F/A and endo D/F/H were synthetically produced, carrying aspartic acid and N-acetylglucosamine-linked asparagine residues, respectively, at the glycosylation site. The MS ionisation/detection strengths of these pure, well-defined and quantified compounds were investigated using various MS ionisation techniques and mass analysers (ESI-IT, ESI-Q-TOF, MALDI-TOF, ESI/MALDI-FT-ICR-MS). Depending on the ion source/mass analyser, glycopeptides carrying complex-type N-glycans exhibited clearly lower signal strengths (10-50% of an unglycosylated peptide) when equimolar amounts were analysed. Less ionisation/detection bias was observed when the glycopeptides were analysed by nano-ESI and medium-pressure MALDI. The position of the glycosylation site within the tryptic peptides also influenced the signal response, in particular if detected as singly or doubly charged signals. This is the first study to systematically and quantitatively address and determine MS glycopeptide ionisation/detection strengths to evaluate glycoprotein micro-heterogeneity and macro-heterogeneity by label-free approaches. These data form a much needed knowledge base for accurate quantitative glycoproteomics.

Surface-activated chemical ionization-electrospray mass spectrometry in the analysis of urinary thiodiglycolic acid

RATIONALE

Thiodiglycolic acid (TDGA) is a urinary metabolite of the oxazaphosphorine class of chemotherapeutics, in particular of ifosfamide. Ifosfamide metabolism generates chloroacetaldehyde (CAA), a toxic compound associated with neurotoxicity, nephrotoxicity, urotoxicity and cardiotoxicity. CAA, in turn, interacts with cellular thiol groups leading to GSH depletion, cell death and generation of thiodiglycolic acid (TDGA), as a final product. TDGA is mainly excreted in the urine. The ability to accurately measure TDGA in urine, therefore, will be a useful way of monitoring exposure to ifosfamide during chemotherapy.

METHODS

TDGA in urine samples was measured with liquid chromatography coupled to mass spectrometry (LC/MS) by means of a novel Surface-Activated Chemical Ionization-Electrospray (SACI-ESI) or a classical ESI ion source alone.

RESULTS

The SACI-ESI and ESI alone based methods for analysis of urinary TDGA were optimized and compared. A strong reduction in matrix effect together with enhanced quantification performances was obtained with the SACI-ESI when compared with ESI. In particular, an increase in quantification precision (from 85 to 95%) and accuracy (from 59 to 90%) were observed, which allowed for optimal detection of TDGA.

CONCLUSIONS

The LC/SACI-ESI-MS approach provides a very sensitive and quantitative method for the analysis of TDGA. Thanks to the enhancement in sensitivity and matrix effect reduction, the SACI-ESI source enables the use of a relatively low-cost ion-trap mass spectrometer in the analysis of this toxicity biomarker in urine. Due to these characteristics, this approach would constitute an invaluable tool in the clinical laboratory, for measuring TDGA and other toxicity related biomarkers of chemotherapy with proper sensitivity and accuracy.

Silica hydride-based chromatography of LC–MS response-altering compounds native to human plasma

Background: An investigation was carried out into the chromatographic behavior, on a silica hydride-based phase and a comparator silica-based phase, of an important group of lipids endogenous to human plasma, which are associated with matrix effect and in the context of quantitative peptide analysis. Results: The propensity for aqueous normal phase (ANP) retention on the silica hydride-based phase was strong and extensive in comparison with the silica-based comparator, and the lipophilic interferences in question were readily eluted using the ANP mode, a contrast to over-retention issues with accompanying implications for method ruggedness typically found with silica-based phases. Conclusion: The silica hydride-based phase, with ANP operation, offered selectivity conducive to rapid lipophilic interferent elimination and the bimodal retention involved in suitable gradient elution was appropriate for general peptide analytical application.

Determination of dimethyltryptamine and β-carbolines (ayahuasca alkaloids) in plasma samples by LC-MS/MS

BACKGROUND

Ayahuasca is a psychoactive plant beverage originally used by indigenous people throughout the Amazon Basin, long before its modern use by syncretic religious groups established in Brazil, the USA and European countries. The objective of this study was to develop a method for quantification of dimethyltryptamine and β-carbolines in human plasma samples.

RESULTS

The analytes were extracted by means of C18 cartridges and injected into LC-MS/MS, operated in positive ion mode and multiple reaction monitoring. The LOQs obtained for all analytes were below 0.5 ng/ml. By using the weighted least squares linear regression, the accuracy of the analytical method was improved at the lower end of the calibration curve (from 0.5 to 100 ng/ml; r(2)> 0.98).

CONCLUSION

The method proved to be simple, rapid and useful to estimate administered doses for further pharmacological and toxicological investigations of ayahuasca exposure.

LC-MS/MS method for simultaneous estimation of candesartan and hydrochlorothiazide in human plasma and its use in clinical pharmacokinetics

BACKGROUND

ATACAND HCT(®) (candesartan cilexetil-hydrochlorothiazide [CAN-HCTZ]) combines an angiotensin II receptor (type AT1) antagonist and a diuretic. Quantification of CAN and HCTZ in biological matrices has traditionally been difficult - developing a single method with the desired sensitivity has been the issue.

RESULTS

A high-throughput bioanalytical method for the analysis of CAN and HCTZ in human plasma using liquid-liquid extraction and LC coupled to negative ion mode MS/MS has been developed and validated according to US FDA guidelines. The method uses 100 µl plasma and covers the calibration range 1-160 ng/ml for CAN and 2-160 ng/ml for HCTZ for routine pharmacokinetic studies in humans. The intra- and inter-day precision values for CAN and HCTZ met the acceptance criteria. CAN and HCTZ were stable in a battery of stability studies (benchtop, autosampler and long-term).

CONCLUSION

The advantages of the described technique included a single method with a shorter run time (2.5 min), simple extraction technique, LLOQ of 1 ng/ml for CAN and 2 ng/ml for HCTZ and lower sample volume (0.10 ml), which overcomes drawbacks of two single methods for each analyte, such as higher analysis time, LOQ and sample volume, as in previously published methods. The developed assay was applied to an oral pharmacokinetic study in humans.

Utilization of hydrophilic-interaction LC to minimize matrix effects caused by phospholipids

Background: In bioanalysis, phospholipids may affect the precision and accuracy of LC–MS/MS methods and compromise the quality of the results, especially when samples in complex biomatrices are extracted by protein precipitation techniques. Results: It was found that the retentive behavior of both common pharmaceuticals and physiologically relevant phospholipids under bare silica hydrophilic-interaction LC (HILIC) is more predictable than under reversed-phase conditions. In particular, the retention time of phospholipids was not significantly affected by varying the salt and acid modifiers in the mobile phases, but common pharmaceuticals can be shifted away from these phospholipid interferences through mobile phase modifiers. Several mass spectrometric techniques were applied to confirm this finding. Conclusion: HILIC chromatography is a valued tool in the development of robust bioanalytical assays with minimal and predictable phospholipid interferences. Furthermore, addition of a small amount of ion-pairing additives can reliably move pharmaceutical compounds away from these suppressive regions.

The influence of electrospray ion source design on matrix effects

This study investigates to which extent the design of electrospray ion sources influences the susceptibility to matrix effects (MEs) in liquid chromatography-tandem mass spectrometry (LC-MS/MS). For this purpose, MEs were measured under comparable conditions (identical sample extracts, identical LC column, same chromatographic method and always positive ion mode) on four LC-MS/MS instrument platforms. The instruments were combined with five electrospray ion sources, viz. Turbo Ion Spray, Turbo V(TM) Source, Standard ESI, Jet Stream ESI and Standard Z-Spray Source. The comparison of MEs could be made at all retention times because the method of permanent postcolumn infusion was applied. The MEs ascertained for 45 pesticides showed for each electrospray ion source the same pattern, i.e. the same number of characteristic signal suppressions at equivalent retention times in the chromatogram. The Turbo Ion Spray (off-axis geometry), Turbo V(TM) Source (orthogonal geometry) and the Standard Z-Spray Source (double orthogonal geometry) did not differ much in their susceptibility to MEs. The Jet Stream ESI (orthogonal geometry) reaches a higher sensitivity by an additional heated sheath gas, but suffers at the same time from significantly stronger signal suppressions than the comparable Standard ESI (orthogonal geometry) without sheath gas. No relation between source geometry and extent of signal suppression was found in this study.

Implication of free cholesterol in LC–MS response enhancement

Background: In the context of matrix effects in bioanalytical LC–MS/MS, a speculative link between free cholesterol, the recoveries of the compound from three common extraction procedures, and response enhancement was qualitatively investigated. Results: Injections on-column of cholesterol both in solution and extracts, in conjunction with post-column infusion of three representative drugs, reveal a direct role in pronounced response enhancement for two out of three analytes, under one set of LC–MS/MS conditions, for the majority of typical plasma extraction procedures, where electrospray-based gaseous ion generation is used. Conclusion: Cholesterol has been shown to have a strong association with LC–MS/MS response enhancement and ideally should be monitored during method development, reinforcing the reasoning behind minimizing SPE elution volumes and avoiding less selective means of sample preparation.

Profiling phospholipid elution in reversed-phase LC–MS/MS bioanalytical methods in order to avoid matrix effects

Background: Endogenous phospholipids have a profound matrix effect in bioanalytical LC–MS methods and considerable effort is invested in strategies to minimize their impact either by removal during sample processing or chromatographic separation during the analytical run. The aim of the research presented in this article was to investigate the latter approach, under reversed-phase conditions. Results: The retention of glycerophosphocholines (GPCs) in mobile phases employing acetonitrile demonstrated a complex ‘U-shaped’ relationship with the percentage of organic. Conversely, in mobile phases employing methanol, the relationship between retention and percentage of organic was entirely predictive and unaffected by changes in the mobile phase pH. The GPC elution profile was also qualitatively equivalent irrespective of the species from which the plasma was derived. Conclusion: The predictive nature of GPC retention, under reversed-phase chromatography and with MeOH as organic modifier, is an important finding that should allow for a more streamlined and simplified strategy in the development of bioanalytical assays.

Confirmation of no impact from different anticoagulant counter ions on bioanalytical method

Background: In the past several years, the impact of changing counter ions while keeping the same anticoagulant in bioanalytical LC–MS/MS methods has become a highly discussed topic. In order to confirm that there is no impact from counter ions, matrix effect and stability evaluations were performed on bicalutamide LC–MS/MS bioanalytical methods. Results: Independently from the anticoagulant counter ion used, the matrix effect evaluation met acceptance criteria, even when using conditions expected to increase matrix effect, such as protein precipitation with an analog internal standard. Freeze–thaw along with storage stabilities, namely short- and long-term, demonstrated less than 8% deviation regardless of the counter ion used. Conclusion: Differences in the anticoagulant counter ion used has no impact on the bicalutamide bioanalytical LC–MS/MS method.

Systematic evaluation of supported liquid extraction in reducing matrix effect and improving extraction efficiency in LC-MS/MS based bioanalysis for 10 model pharmaceutical compounds

In past a few years, there has been a large increase in the application of supported liquid extraction (SLE) for LC-MS/MS based bioanalysis due to its distinct practical advantage in reduced time cost, ease of operation and the feasibility for automation. The main purpose of this study was to systematically evaluate supported liquid extraction in reducing matrix effect and improving extraction efficiency/recovery under various extraction conditions with 10 model pharmaceutical compounds in liquid chromatography coupled to electrospray tandem mass spectrometry (LC-ESI-MS/MS) analysis. Selected compounds have diverse physicochemical properties where logP ranges from 0.1 to 6.24 and pK(a) ranges from 4.0 to 11.1. The factors that may have the impact on the recovery of analytes and phospholipids (PL) were assessed. Over 75% recovery was achieved for every analyte under its respectively optimized extraction conditions where the selection of the polarity of extraction solvent and buffered pH can be critical for efficient recovery. Furthermore, the matrix effect was assessed by postextraction spike and postcolumn infusion method. The matrix effect was considerably reduced for all analytes under most extraction conditions evaluated for SLE, compared with protein precipitation (PPT) method. The correlation between matrix effect and residual phospholipids in sample extract was clearly shown. Although analyte-dependent matrix effect was observed prominently in sample extract prepared by PPT, it was minimized by SLE sample preparation process that effectively removes the majority of phospholipids. Sample extracted by ethyl acetate contained more phospholipids and demonstrated stronger matrix effect than by other organic solvents. Water-miscible organic content, such as methanol and acetonitrile in samples prior to loading has significant impact on PL recovery when eluting with methyl tert-butyl ether. However, isopropanol does not enhance the recovery of PL when adding to dichloromethane for elution. In addition, the compromise between improved extraction efficiency by SLE and reduced matrix effect is sometimes necessary to yield clean extract with acceptable recovery. The effective removal of phospholipids and reduction of matrix effect, while achieving good recovery for all pharmaceutical compounds with diverse physicochemical properties, demonstrated that SLE is a valuable alternative technique to liquid-liquid extraction (LLE) in high throughput LC-MS/MS based bioanalysis.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for monitoring drug exposure in hematopoietic stem cell transplant recipients

A liquid chromatography-tandem mass spectrometry method was developed for the quantification of circulating levels of multiple immunosuppressant drugs including cyclosporine (CsA), tacrolimus, methotrexate (Mtx), prednisone, prednisolone, methylprednisone, total and free mycophenolic acid (MPA), as well as MPA phenolic (MPAG) and acyl (AcMPAG) glucuronide metabolites. Linearity, precision and accuracy were validated within the typical therapeutic range of concentrations for each compound. The assay was linear over 0.125-25ng/mL for tacrolimus, 1-500ng/mL for prednisone/methylprednisone, 2-400ng/mL for Mtx, 2-1000ng/mL for prednisolone and from 7.5 to 1500ng/mL for CsA with the lowest limit of quantification (LLOQ) being 0.125, 1.00, 2.00, 2.00 and 7.5ng/mL, respectively. The calibration curve concentrations for MPA and MPAG ranged from 50 to 50,000ng/mL (LLOQ: 50ng/mL) and 10 to 10,000ng/mL (LLOQ: 10ng/mL) for AcMPAG. Mean recoveries in blood and plasma were 84%±5.7%. The method could measure individual drugs with high sensitivity, accuracy (bias≤14%), and reproducibility (CV≤12.8%). Its clinical application was validated by measuring levels of these drugs in samples obtained from hematopoietic stem cell transplant recipients treated with combined immunosuppressive drug therapy. Our results indicate that this approach is suitable for simultaneous determination of in vivo levels of immunosuppressive drugs commonly used in combined therapies.

Extraction methods for the removal of phospholipids and other endogenous material from a biological fluid

Background: A comparison of three different sample preparation techniques for the analysis of plasma samples has been investigated to highlight the effect that these approaches have on the removal of endogenous material. The three techniques under investigation are: SPE, support assisted liquid–liquid extraction and nonspecific solvent-based protein precipitation. Results: Comparisons are made on the practicalities of each approach and to allow a semiquantitative assessment between the effectiveness of these different techniques the relative amounts of phospholipids present within the sample are analyzed. Total ion chromatograms are also obtained to further study the effects of different extraction techniques in the removal of endogenous components from a biological matrix. Both of these approaches provide a very coarse measure of the cleanliness of the extracts and demonstrate that support assisted liquid–liquid extraction and an optimized SPE approach remove a greater amount of endogenous material. Conclusion: This study highlights the importance of sample preparation in removing endogenous material, which may have a detrimental effect on the performance of a bioanalytical assay.

Quantification of total and unbound concentrations of lorazepam, oxazepam and temazepam in human plasma by ultrafiltration and LC-MS/MS

BACKGROUND

A fast and sensitive assay for quantifying total and unbound concentrations of lorazepam (Lzp), oxazepam (Ozp) and temazepam (Tzp) in human plasma was needed for a plasma protein binding study.

RESULTS

Plasma samples were precipitated with acetonitrile for determination of total concentrations or subjected to ultrafiltration for determination of unbound concentrations. An LC-MS/MS assay was developed with an Allure® PFP propyl column and a mobile phase of 35% acetonitrile/0.1% formic acid over 4.5 min and ESI+-MS/MS detection. Matrix effects were negligible in plasma and approximately 70% in ultrafiltrate but were accounted for by the internal standards Lzp-d₄, Ozp-d₅ and Tzp-d₅. The assay was validated for total concentrations of 10-100 ng/ml Lzp, 200-2000 ng/ml Ozp and 100-1000 ng/ml Tzp, and for unbound concentrations of 1-10 ng/ml Lzp, 20-200 ng/ml Ozp and 10-100 ng/ml Tzp. Precision was <14% CV and accuracy was 96-110% throughout the calibration range. The mean precision of triplicate analysis of 60 study samples was <4% CV for total and <8% CV for unbound concentrations.

CONCLUSION

A fast and sensitive assay was developed and validated. It has been applied successfully to a protein binding study.

Development of methods to monitor ionization modification from dosing vehicles and phospholipids in study samples

Two approaches to monitor the matrix effect on ionization in study samples were described. One approach is the addition of multiple reaction monitoring transitions to the bioanalytical methods to monitor the presence of known ionization modification-causing components of the matrix, for example, m/z 184→125 (or m/z 184→184) and m/z 133→89 may be used for phospholipids and polyethylene oxide containing surfactants, respectively. This approach requires no additional equipment and can be readily adapted for most method. The approach detects only the intended interfering compounds and provides little quantitative indication if the matrix effect is within the tolerable range (±15%). The other approach requires the addition of an infusion pump and identifies an appropriate surrogate of the analyte to be infused for the determination of modification on the ionization of the analyte. The second approach detects interferences in the sample regardless of the sources (i.e., dosing vehicle components, co-administrated drugs, their metabolites, phospholipids, plasticizers and endogenous components introduced due to disease stage).

Minimizing matrix effects while preserving throughput in LC–MS/MS bioanalysis

Background: Phospholipids are known to cause matrix effects in LC–MS analysis and are not effectively removed by one of the most common method of sample preparation: organic solvent protein precipitation. The objective of this research is to minimize phospholipid interferences chromatographically. Results: In this article we examine several chromatographic approaches and highlight the method we developed that allows for the rapid gradient separation of model drug molecules from phospholipids. Conclusion: The new approach (which utilizes a mixture of methanol and acetonitrile as the organic mobile phase on a 2.1 × 20 mm C18 column) minimized phospholipids-related matrix effects in the analysis of plasma samples prepared by protein precipitation and is suitable for high-throughput bioanalysis in drug discovery.