A new approach to evaluate regression models during validation of bioanalytical assays

A linear validation method of analytical procedures based on the double logarithm function linear fitting

BACKGROUND

The ICH Q2(R1) guideline defines linearity as its ability to obtain test results which are directly proportional to the concentration of the analyte. However, the coefficient of determination typically used is limited to evaluating the response function rather than the linearity of results, the current guidelines fail to provide a method for assessing the linearity of results.

RESULTS

The paper presents a data analysis method to validate the linearity of results. The method demonstrates the degree of data proportionality by applying double logarithm function linear fitting and solves the problem of setting the acceptance criterion by investigating the relationship between the slope, working range ratio, and maximum error ratio. In principle, this method has advantages over the coefficient of variation and recovery rate recommended by the ICH M10 guideline. Moreover, the relative error data show that the double logarithm function is more effective in overcoming heteroscedasticity than straight-line fitting.

SIGNIFICANCE

This method is more consistent with the linear definition outlined in ICH Q2 guidelines and has the potential to further clarify the concept and validation method of linearity in the future.

Can plant hormonomics be built on simple analysis? A review

The field of plant hormonomics focuses on the qualitative and quantitative analysis of the hormone complement in plant samples, akin to other omics sciences. Plant hormones, alongside primary and secondary metabolites, govern vital processes throughout a plant's lifecycle. While active hormones have received significant attention, studying all related compounds provides valuable insights into internal processes. Conventional single-class plant hormone analysis employs thorough sample purification, short analysis and triple quadrupole tandem mass spectrometry. Conversely, comprehensive hormonomics analysis necessitates minimal purification, robust and efficient separation and better-performing mass spectrometry instruments. This review summarizes the current status of plant hormone analysis methods, focusing on sample preparation, advances in chromatographic separation and mass spectrometric detection, including a discussion on internal standard selection and the potential of derivatization. Moreover, current approaches for assessing the spatiotemporal distribution are evaluated. The review touches on the legitimacy of the term plant hormonomics by exploring the current status of methods and outlining possible future trends.

A Validated HPLC-UV-ESI-IT-MS Method for the Quantification of Carnosol in Lepechinia mutica, a Medicinal Plant Endemic to Ecuador

The diphenolic diterpene carnosol was isolated from several species of the family Lamiaceae, including Lepechinia mutica, a medicinal plant endemic to Ecuador. The compound has exhibited high antioxidant, anti-inflammatory, antimicrobial, neuroprotective, and antifungal properties, as well as promising cytotoxicity against prostate, breast, skin, leukemia, and human colon cancer cell lines. In this paper, we developed and validated a simple, accurate, and reliable analytical HPLC-UV-ESI-IT-MS method, carried out on a C18 column, which is potentially suitable to quantify carnosol in plant extracts. The procedure complied with the established ICH validation parameters of analytical range (linearity in the range of 0.19-5.64 μg/g dried leaves; REAVERGE = 4.9%; R2 = 0.99907), analysis repeatability (RSD = 2.8-3.6%), intermediate precision (RSD = 1.9-3.6%), accuracy (estimated as % carnosol recovery in the range of 81 to 108%), and robustness. Finally, the LOD (0.04 µg/mg) and LOQ (0.19 μg/mg) values of carnosol/dried leaves were determined. Using this validated method, the content of carnosol in L. mutica was estimated to be 0.81 ± 0.04 mg/g of dried leaves (0.081%).

An alternative approach to validation of liquid chromatography-mass spectrometry methods for the quantification of endogenous compounds

Despite the progress in the quantification of xenobiotics, the development and validation of methods designed for endogenous substances still remain challenging due to the natural presence of the analytes in a biological matrix, leading to the inability to obtain a blank sample. Several generally recognized procedures are described to solve this issue, like using surrogate or analyte-depleted matrices or surrogate analytes. However, the workflows used do not always meet the requirements for developing a reliable analytical method or are cost-intensive. This study aimed to design an alternative approach for preparing validation reference samples using authentic analytical standards while preserving the nature of the biological matrix and solving the problem with the inherent presence of analyzed compounds in a studied matrix. The methodology used is based on the standard-addition type procedure. However, unlike the original method, the addition is modified according to a previously measured basal concentration of monitored substances in the pooled biological sample to obtain a predefined concentration in reference samples according to the European Medicines Agency (EMA) validation guideline. The study shows the advantages of described approach on an example of LC-MS/MS analysis of 15 bile acids in human plasma and compares it with other methods commonly used in this field. The method was successfully validated according to the EMA guideline with lower limit of quantification of 5 nmol/L and linearity in the range of 5 - 2000 nmol/L. Finally, the method was used in a metabolomic study on a cohort of pregnant women (n = 28) to confirm intrahepatic cholestasis, the major liver disease observed in pregnancy.

Simultaneous and enantiospecific quantification of primaquine and carboxyprimaquine in human plasma using liquid chromatography-tandem mass spectrometry

Background

The enantiomers of the 8-aminoquinoline anti-malarial primaquine have different pharmacological properties. Development of an analytical method for simultaneous quantification of the enantiomers of primaquine and its metabolite, carboxyprimaquine, will support clinical pharmacometric assessments.

Methods

A simple and sensitive method consisting of liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) was developed for simultaneous and enantiospecific determination of primaquine and its metabolite, carboxyprimaquine, in human plasma. Stable isotopes were used as internal standards to compensate for potential interference and matrix effects. Plasma samples (100 µL) were precipitated with 1% formic acid in acetonitrile followed by phospholipid removal solid phase extraction. Primaquine and carboxyprimaquine enantiomers were separated on a Chiralcel OD-3R (150 mm × 4.6 mm; I.D. 3 μm) column using a LC gradient mode. For separation of racemic primaquine and carboxyprimaquine, the LC method was modified and validated using a reverse phase column (Hypersil Gold 100 mm × 4.6 mm; I.D. 3 µm) and a mobile phase composed of 10 mM ammonium acetate buffer, pH 3.5 and acetonitrile in the isocratic mode. Method validation was performed according to regulatory guidelines.

Results

The calibration range was set to 0.571–260 ng/mL and 2.44–2,500 ng/mL for primaquine and carboxyprimaquine enantiomers, respectively, resulting in a correlation coefficient (r²) ≥ 0.0998 for all calibration curves. The intra- and inter-day assay precisions were < 10% and the accuracy was between 94.7 to 103% for all enantiomers of primaquine and carboxyprimaquine. The enantiospecific method was also modified and validated to quantify racemic primaquine and carboxyprimaquine, reducing the total run time from 30 to 8 min. The inter-, intra-day assay precision of the racemic quantification method was < 15%. The absolute recoveries of primaquine and carboxyprimaquine were between 70 and 80%. Stability was demonstrated for up to 2 years in − 80 °C. Both the enantiomeric and racemic LC–MS/MS methods were successfully implemented in pharmacokinetic studies in healthy volunteers.

Conclusions

Simple, sensitive and accurate LC–MS/MS methods for the quantification of enantiomeric and racemic primaquine and carboxyprimaquine in human plasma were validated successfully and implemented in clinical routine drug analysis.

High-throughput quantitation method for amodiaquine and desethylamodiaquine in plasma using supported liquid extraction technology

Amodiaquine is a drug used for treatment of malaria and is often used in combination with artesunate in areas where malaria parasites are still susceptible to amodiaquine. Liquid chromatography tandem-mass spectrometry was used to quantify amodiaquine and its active metabolite, desethylamodiaquine, in plasma samples. A low sample volume of 100 µl, and high-throughput extraction technique using a supported liquid extraction (SLE⁺) technique on an automated liquid handler platform for faster sample processing are some of the advantages of this method. Separation of amodiaquine from desethylamodiaquine was achieved using a reversed phase Zorbax SB-CN 50 mm × 4.6 mm, I.D. 3.5 µm column with acetonitrile and 20 mM ammonium formate with 1% formic acid pH ~ 2.6 (15-85, v/v) as mobile phase. The absolute recoveries of amodiaquine and desethylamodiaquine were 66% to 76%, and their isotope label internal standard were in the range of 73% to 85%. Validation results of the developed method demonstrated intra-batch and inter-batch precisions within the acceptance criteria range of ± 15.0%. There were no matrix or carry-over effects observed. The lower limit of quantification was 1.08 ng/ml for amodiaquine and 1.41 ng/ml for desethylamodiaquine. The method showed robust and accurate performance with high sensitivity. Thus, the validated method was successfully implemented and applied in the evaluation of a clinical trial where participants received artemether-lumefantrine plus amodiaquine twice daily for three days (amodiaquine dose of 10 mg base/kg/day).

Predicting Virulence of Fusarium Oxysporum f. sp. Cubense Based on the Production of Mycotoxin Using a Linear Regression Model

Fusarium wilt caused by Fusarium oxysporum f.sp. cubense (Foc) is one of the most destructive diseases for banana. For their risk assessment and hazard characterization, it is vital to quickly determine the virulence of Foc isolates. However, this usually takes weeks or months using banana plant assays, which demands a better approach to speed up the process with reliable results. Foc produces various mycotoxins, such as fusaric acid (FSA), beauvericin (BEA), and enniatins (ENs) to facilitate their infection. In this study, we developed a linear regression model to predict Foc virulence using the production levels of the three mycotoxins. We collected data of 40 Foc isolates from 20 vegetative compatibility groups (VCGs), including their mycotoxin profiles (LC-MS) and their plant disease index (PDI) values on Pisang Awak plantlets in greenhouse. A linear regression model was trained from the collected data using FSA, BEA and ENs as predictor variables and PDI values as the response variable. Linearity test statistics showed this model meets all linearity assumptions. We used all data to predict PDI with high fitness of the model (coefficient of determination (R² = 0.906) and adjust coefficient (R²_adj = 0.898)) indicating a strong predictive power of the model. In summary, we developed a linear regression model useful for the prediction of Foc virulence on banana plants from the quantification of mycotoxins in Foc strains, which will facilitate quick determination of virulence in newly isolated Foc emerging Fusarium wilt of banana epidemics threatening banana plantations worldwide.

High sensitivity methods to quantify chloroquine and its metabolite in human blood samples using LC-MS/MS

Aim:

Chloroquine is an antimalarial drug used in the treatment of Plasmodium vivax malaria. Three methods to quantify chloroquine and its metabolite in blood matrices were developed and validated.

Methodology & results:

Different high-throughput extraction techniques were used to recover the drugs from whole blood (50 μl), plasma (100 μl) and dried blood spots (15 μl as punched discs) followed by quantification with LC–MS/MS. The intra- and inter-batch precisions were below 15%, and thus meet regulatory acceptance criteria.

Conclusion:

The developed methods demonstrated satisfactory validation performance with high sensitivity and selectivity. The assays used simple and easy to automate extraction techniques. All methods were reliable with robust performance and demonstrated to be suitable to implement into high-throughput routine analysis of clinical pharmacokinetic samples.

Quantitation of paracetamol by liquid chromatography-mass spectrometry in human plasma in support of clinical trial

Aim:

Paracetamol is a well-tolerated antipyretic widely used in severe malaria management. The study aimed to develop and validate a rapid LC–MS/MS assay to quantify paracetamol in plasma from patients with severe malaria.

Materials & methods:

Plasma sample was precipitated by organic solvent containing isotope-labeled paracetamol internal standard. Supernatant was isolated, diluted with water, followed by LC–MS/MS analysis.

Results:

Plasma samples were extracted and assayed in less than 5.5 min. The assay response was linear (0.125–50 mg/l) with total intra- and interassay imprecision of <1.4%, which were considerably lower than most published reports.

Conclusion:

We developed, validated and applied a rapid and small volume LC–MS/MS assay with high precision and accuracy for plasma paracetamol quantitation in 989 samples from 62 patients with severe malaria. The simple and high-throughput quality could facilitate assay automation for future clinical studies.

Paracetamol is a commonly prescribed antipyretic in severe malaria management. Here, a rapid quantitative assay was developed to measure the plasma level of paracetamol. The developed method required levels as low as 20 μl plasma, and was highly precise, with a short analysis time of 5.5 min. The developed method is particularly suitable for clinical trial application and potentially for clinical use.

Validation and Automation of a High-Throughput Multitargeted Method for Semiquantification of Endogenous Metabolites from Different Biological Matrices Using Tandem Mass Spectrometry

The use of metabolomics profiling to understand the metabolism under different physiological states has increased in recent years, which created the need for robust analytical platforms. Here, we present a validated method for targeted and semiquantitative analysis of 102 polar metabolites that cover major metabolic pathways from 24 classes in a single 17.5-min assay. The method has been optimized for a wide range of biological matrices from various organisms, and involves automated sample preparation and data processing using an inhouse developed R-package. To ensure reliability, the method was validated for accuracy, precision, selectivity, specificity, linearity, recovery, and stability according to European Medicines Agency guidelines. We demonstrated an excellent repeatability of retention times (CV < 4%), calibration curves (R² ≥ 0.980) in their respective wide dynamic concentration ranges (CV < 3%), and concentrations (CV < 25%) of quality control samples interspersed within 25 batches analyzed over a period of one year. The robustness was demonstrated through a high correlation between metabolite concentrations measured using our method and the NIST reference values (R² = 0.967), including cross-platform comparability against the BIOCRATES AbsoluteIDQp180 kit (R² = 0.975) and NMR analyses (R² = 0.884). We have shown that our method can be successfully applied in many biomedical research fields and clinical trials, including epidemiological studies for biomarker discovery. In summary, a thorough validation demonstrated that our method is reproducible, robust, reliable, and suitable for metabolomics studies.

LC-MS/MS method for the simultaneous analysis of seven antimalarials and two active metabolites in dried blood spots for applications in field trials: Analytical and clinical validation

In epidemiological studies, antimalarials measurements in blood represent the best available marker of drugs exposure at population level, an important driver for the emergence of drug resistance. We have developed a liquid chromatography-tandem mass spectrometry method (LC-MS/MS) for the simultaneous quantification of 7 frequently used antimalarials (amodiaquine, chloroquine, quinine, sulfadoxine, pyrimethamine, mefloquine, lumefantrine) and 2 active metabolites (N-desethyl-amodiaquine, desbutyl-lumefantrine) in 10-μl dried blood spots (DBS). This sampling approach is suitable for field studies wherein blood samples processing, transportation and storage are problematic. Sample preparation included extraction from a 3 mm-disk punched out of the DBS with 100-μl of methanol + 1% formic acid containing deuterated internal standards for all drugs. Good performances were achieved in terms of trueness (-12.1 to +11.1%), precision (1.4-15.0%) and sensitivity, with lower limits of quantification comprised between 2 ng/ml (sulfadoxine) and 20 ng/ml (chloroquine, quinine, pyrimethamine, mefloquine, lumefantrine and desbutyl-lumefantrine). All analytes were stable in DBS kept for 24 h at room temperature and at 37 °C. The developed assay was applied within the frame of a pharmacokinetic study including 16 healthy volunteers who received a single dose of artemether-lumefantrine. Lumefantrine concentrations in plasma and in DBS were highly correlated (R = 0.97) at all time points, confirming the assumption that lumefantrine concentrations determined in DBS confidently reflect blood concentrations. The blood/plasma ratio of 0.56 obtained using the Bland-Altman approach (and corresponding to the slope of the linear regression) is in line with very low penetration of lumefantrine into red blood cells. This sensitive multiplex LC-MS/MS assay enabling the simultaneous analysis of antimalarials in DBS is suitable for epidemiological studies in field conditions.

A fast method for GHB-GLUC quantitation in whole blood by GC-MS/MS (TQD) for forensic purposes

γ-Hydroxybutyric acid (GHB) is an endogenous compound with a historical use, both in licit and illicit terms. Importantly, the post-mortem behavior of GHB has been studied due to the possibility of using this compound as a biomarker for estimating the post-mortem interval (PMI). However, the post-mortem behavior of the recently discovered glucuronated GHB metabolite (GHB-GLUC) has not been studied. Nevertheless, GHB-GLUC may also have potential both to assist in PMI determination and also to increase the window of detection of GHB consumption. In this work, for the first time, a reliable method using GC-MS/MS for the quantification of GHB-GLUC in whole blood samples was developed and validated, with a simple, fast and cheap sample pretreatment. The method proved to be specific, precise, linear in a work range between 200 and 5000ng/mL, with LOD and LOQ of 52.65ng/mL and 200ng/mL, respectively, and an extraction recovery of 51%. Furthermore, the method was applied to a set of real post-mortem blood samples non-related with GHB intoxication and the obtained results were also discussed.

Quantification of the antimalarial drug pyronaridine in whole blood using LC-MS/MS - Increased sensitivity resulting from reduced non-specific binding

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Sensitive and accurate method suitable for high-throughput routine analysis of pyronaridine in whole blood.

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Validated according to US FDA bioanalytical validation guidelines.

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Described impact on freeze and thaw stability using different anticoagulants.

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Described adsorption and carry-over issues and how to overcome them.

Malaria is one of the most important parasitic diseases of man. The development of drug resistance in malaria parasites is an inevitable consequence of their widespread and often unregulated use. There is an urgent need for new and effective drugs. Pyronaridine is a known antimalarial drug that has received renewed interest as a partner drug in artemisinin-based combination therapy. To study its pharmacokinetic properties, particularly in field settings, it is necessary to develop and validate a robust, highly sensitive and accurate bioanalytical method for drug measurements in biological samples. We have developed a sensitive quantification method that covers a wide range of clinically relevant concentrations (1.5 ng/mL to 882 ng/mL) using a relatively low volume sample of 100 μL of whole blood. Total run time is 5 min and precision is within ±15% at all concentration levels. Pyronaridine was extracted on a weak cation exchange solid-phase column (SPE) and separated on a HALO RP amide fused-core column using a gradient mobile phase of acetonitrile–ammonium formate and acetonitrile-methanol. Detection was performed using electrospray ionization and tandem mass spectrometry (positive ion mode with selected reaction monitoring). The developed method is suitable for implementation in high-throughput routine drug analysis, and was used to quantify pyronaridine accurately for up to 42 days after a single oral dose in a drug-drug interaction study in healthy volunteers.

High-performance liquid chromatography with time-programmed fluorescence detection for the quantification of Levofloxacin in human plasma and cerebrospinal fluid in adults with tuberculous meningitis

An accurate and reliable high-performance liquid chromatography with time-programmed fluorescence detection was developed and validated to measure levofloxacin in human plasma and cerebrospinal fluid (CSF). After solid phase extraction process using Evolute^® ABN 96 fixed well plate; levofloxacin and internal standard-enoxacin were separated using a mobile phase consisting of phosphate buffer 10mM with 0.025% triethylamine pH 3.0 - acetonitrile (88:12, v/v) on a Purosphere RP-8e column (5μm, 125×4.0mm) at a flow rate of 1.2mL/min at 35°C. The excitation/emission wavelengths were set to 269/400nm and 294/500nm, for enoxacin and levofloxacin, respectively. The method was linear over the concentration range of 0.02 to 20.0μg/mL with a limit of detection of 0.01μg/mL. The relative standard deviation of intra-assay and inter-assay precision for levofloxacin at four quality controls concentrations (0.02, 0.06, 3.0 and 15.0μg/mL) were less than 7% and the accuracies ranged from 96.75% to 101.9% in plasma, and from 93.00% to 98.67% in CSF. The validated method was successfully applied to quantify levofloxacin in a considerable quantity of plasma (826) and CSF (477) samples collected from 232 tuberculous meningitis patients, and the preliminary intensive pharmacokinetics analysis from 14 tuberculous meningitis patients in Vietnam is described in this paper.

Simultaneous estimation of lisofylline and pentoxifylline in rat plasma by high performance liquid chromatography-photodiode array detector and its application to pharmacokinetics in rat

Lisofylline (LSF) is an anti-inflammatory and immunomodulatory agent with proven activity in serious infections associated with cancer chemotherapy, hyperoxia-induced acute lung injury, autoimmune disorders including type-1 diabetes (T1DM) and islet rejection after islet transplantation. It is also an active metabolite of another anti-inflammatory agent, Pentoxifylline (PTX). LSF bears immense therapeutic potential in multiple pharmacological activities and hence appropriate and accurate quantification of LSF is very important. Although a number of analytical methods for quantification of LSF and PTX have been reported for pharmacokinetics and metabolic studies, each of these have certain limitations in terms of large sample volume required, complex extraction procedure and/or use of highly sophisticated instruments like LC-MS/MS. The aim of current study is to develop a simple reversed-phase HPLC method in rat plasma for simultaneous determination of LSF and PTX with the major objective of ensuring minimum sample volume, ease of extraction, economy of analysis, selectivity and avoiding use of instruments like LC-MS/MS to ensure a widespread application of the method. A simple liquid-liquid extraction method using methylene chloride as extracting solvent was used for extracting LSF and PTX from rat plasma (200μL). Samples were then evaporated, reconstituted with mobile phase and injected into HPLC coupled with photo-diode detector (PDA). LSF, PTX and 3-isobutyl 1-methyl xanthine (IBMX, internal standard) were separated on Inertsil® ODS (C18) column (250×4.6mm, 5μm) with mobile phase consisting of A-methanol B-water (50:50v/v) run in isocratic mode at flow rate of 1mL/min for 15min and detection at 273nm. The method showed linearity in the concentration range of 50-5000ng/mL with LOD of 10ng/mL and LLOQ of 50ng/mL for both LSF and PTX. Weighted linear regression analysis was also performed on the calibration data. The mean absolute recoveries were found to be 80.47±3.44 and 80.89±3.73% for LSF and PTX respectively. The method was successfully applied for studying the pharmacokinetics of LSF and PTX after IV bolus administration at dose of 25mg/kg in Wistar rat. In conclusion, a simple, sensitive, accurate and precise reversed-phase HPLC-UV method was established for simultaneous determination of LSF and PTX in rat plasma.

An HPLC method with diode array detector for the simultaneous quantification of chloroquine and desethylchloroquine in plasma and whole blood samples from Plasmodium vivax patients in Vietnam, using quinine as an internal standard

A sensitive, simple method for quantification of chloroquine (CQ) and desethylchloroquine (MCQ) in whole blood and plasma from Plasmodium vivax patients has been developed using HPLC with diode array detection (DAD). Solid‐phase extraction on Isolute‐96‐CBA was employed to process 100 μL of plasma/whole blood samples. CQ, MCQ and quinine were separated using a mobile phase of phosphate buffer 25 mm, pH 2.60–acetonitrile (88:12, v/v) with 2 mm sodium perchlorate on a Zorbax SB‐CN 150 × 4.6 mm, 5 μm column at a flow rate of 1.2 mL/min, at ambient temperature in 10 min, with the DAD wavelength of 343 nm. The method was linear over the range of 10–5000 ng/mL for both CQ and MCQ in plasma and whole blood. The limit of detection was 4 ng/mL and limit of quantification was 10 ng/mL in both plasma and blood for CQ and MCQ. The intra‐, inter‐ and total assay precision were <10% for CQ and MCQ in plasma and whole blood. In plasma, the accuracies varied between 101 and 103%, whereas in whole blood, the accuracies ranged from 97.0 to 102% for CQ and MCQ. The method is an ideal technique with simple facilities and instruments, bringing about good separation in comparison with previous methods. © 2016 The Authors Biomedical Chromatography Published by John Wiley & Sons Ltd

A sensitive multidimensional method for the detection, characterization, and quantification of trace free drug species in antibody-drug conjugate samples using mass spectral detection

Conjugation processes and stability studies associated with the production and shelf life of antibody-drug conjugates (ADCs) can result in free (non-conjugated) drug species. These free drug species can increase the risk to patients and reduce the efficacy of the ADC. Despite stringent purification steps, trace levels of free drug species may be present in formulated ADCs, reducing the therapeutic window. The reduction of sample preparation steps through the incorporation of multidimensional techniques has afforded analysts more efficient methods to assess trace drug species. Multidimensional methods coupling size-exclusion and reversed phase liquid chromatography with ultra-violet detection (SEC-RPLC/UV) have been reported, but offer limited sensitivity and can limit method optimization. The current study addresses these challenges with a multidimensional method that is specific, sensitive, and enables method control in both dimensions via coupling of an on-line solid phase extraction column to RPLC with mass spectral detection (SPE-RPLC/MS). The proposed method was evaluated using an antibody-fluorophore conjugate (AFC) as an ADC surrogate to brentuximab vedotin and its associated parent maleimide-val-cit-DSEA payload and the derived N-acetylcysteine adduct formed during the conjugation process. Assay sensitivity was found to be 2 orders more sensitive using MS detection in comparison to UV-based detection with a nominal limit of quantitation of 0.30 ng/mL (1.5 pg on-column). Free-drug species were present in an unadulterated ADC surrogate sample at concentrations below 7 ng/mL, levels not detectable by UV alone. The proposed SPE-RPLC/MS method provides a high degree of specificity and sensitivity in the assessment of trace free drug species and offers improved control over each dimension, enabling straightforward integration into existing or novel workflows.

Development and validation of an ultra-high-performance liquid chromatography tandem mass spectrometric method for the simultaneous determination of free and conjugated Alternaria toxins in cereal-based foodstuffs

A UPLC-ESI^+/--MS/MS method for the simultaneous determination of free (alternariol, alternariol monomethyl ether, altenuene, tenuazonic acid, tentoxin, altertoxin-I) and conjugated (sulfates and glucosides of alternariol and alternariol monomethyl ether) Alternaria toxins in cereals and cereal products (rice, oat flakes and barley) was developed. Optimization of the sample preparation and extraction methodology was achieved through experimental design, using full factorial design for extraction solvent composition optimization and fractional factorial design to identify the critical factors in the sample preparation protocol, which were in turn subjected to optimization. Final extracts were analysed using an Waters Acquity UPLC system coupled to a Quattro Premier XE mass spectrometer equipped with an electrospray interface operated in both positive and negative ionization mode. Chromatographic separation was achieved using an Acquity UPLC HSS T3 column, and the applied gradient elution programme allowed for the simultaneous determination of 10 Alternaria toxins in a one-step chromatographic run with a total run time of only 7min. Subsequently, the method, applying isotopically labelled internal standards ([²H₄]-alternariol monomethyl ether and [¹³C₆,¹⁵N]-tenuazonic acid), was validated for several parameters such as linearity, apparent recovery, limit of detection, limit of quantification, precision, measurement uncertainty and specificity (in agreement with the criteria mentioned in Commission Regulation No. 401/2006/EC and Commission Decision No. 2002/657/EC). During validation, quality of the bioanalytical data was improved by counteracting the observed heteroscedasticity through the application of weighted least squares linear regression (WLSLR). Finally, 24 commercially available cereal-based foodstuffs were subjected to analysis, revealing the presence of tenuazonic acid in both rice and oat flake samples (<LOQ - 68±7μgkg^-1) and tentoxin in rice samples (<LOQ - 10.9±2.0μgkg^-1).

Method validation using weighted linear regression models for quantification of UV filters in water samples

This paper describes the validation of a method consisting of solid-phase extraction followed by gas chromatography-tandem mass spectrometry for the analysis of the ultraviolet (UV) filters benzophenone-3, ethylhexyl salicylate, ethylhexyl methoxycinnamate and octocrylene. The method validation criteria included evaluation of selectivity, analytical curve, trueness, precision, limits of detection and limits of quantification. The non-weighted linear regression model has traditionally been used for calibration, but it is not necessarily the optimal model in all cases. Because the assumption of homoscedasticity was not met for the analytical data in this work, a weighted least squares linear regression was used for the calibration method. The evaluated analytical parameters were satisfactory for the analytes and showed recoveries at four fortification levels between 62% and 107%, with relative standard deviations less than 14%. The detection limits ranged from 7.6 to 24.1 ng L(-1). The proposed method was used to determine the amount of UV filters in water samples from water treatment plants in Araraquara and Jau in São Paulo, Brazil.

Statistical approach for selection of regression model during validation of bioanalytical method

The selection of an adequate regression model is the basis for obtaining accurate and reproducible results during the bionalytical method validation. Given the wide concentration range, frequently present in bioanalytical assays, heteroscedasticity of the data may be expected. Several weighted linear and quadratic regression models were evaluated during the selection of the adequate curve fit using nonparametric statistical tests: One sample rank test and Wilcoxon signed rank test for two independent groups of samples. The results obtained with One sample rank test could not give statistical justification for the selection of linear vs. quadratic regression models because slight differences between the error (presented through the relative residuals) were obtained. Estimation of the significance of the differences in the RR was achieved using Wilcoxon signed rank test, where linear and quadratic regression models were treated as two independent groups. The application of this simple non-parametric statistical test provides statistical confirmation of the choice of an adequate regression model.

A fast method for the quantitation of key metabolites of the methionine pathway in liver tissue by high-resolution mass spectrometry and hydrophilic interaction ultra-performance liquid chromatography

We developed an assay for the extraction and simultaneous quantitation of five key metabolites of the methionine metabolic pathway in liver tissue. The metabolites included were 5'-methylthioadenosine, methionine, homocysteine, S-adenosyl-L-homocysteine, and S-adenosyl-L-methionine. The metabolites were extracted using a bead-based homogenization method, and quantitation was carried out using hydrophilic interaction chromatography and time-of-flight mass spectrometry. The extraction procedure was optimized by testing the effect of various solvent combinations. The chromatographic method was optimized for peak shape, signal intensity, and carry-over. With a total chromatographic run time of 5 min, this assay is suitable for the analysis of large sample sets. Time-of-flight mass spectrometry provided high mass accuracy which, combined with isotope pattern matching and use of chemical standards, guarantees high specificity. Moreover, by operating the mass spectrometer in enhanced duty cycle mode the signal strength for the analytes increased three- to tenfold in comparison with the generic full-scan mode. For quantitation, a matrix-spiked calibration method was used. The lowest analyte levels detected and quantified using our method were within the range of concentrations found in the liver. The inter-day coefficients of variance for the analytes were between 5 and 15% in pooled tissue samples. Interestingly, the CVs between individual liver tissue aliquots were about twice as high. Additional experiments suggested that this higher variability was caused by uneven distribution of the analytes within the liver. In conclusion, an optimized and robust assay is now available for the extraction and quantification of key metabolites in the methionine metabolic pathway.

A pharmacokinetic study of a combination of beta adrenoreceptor antagonists - in the isolated perfused ovine eye

The treatment of posterior eye diseases, such as diabetic retinopathy and age-related macular degeneration, is of growing interest as the number of people affected by these conditions continues to rise. This study utilises the methods of cassette dosing and the perfused ovine eye model - to reduce animal usage and therefore animal time - to show that for a series of beta adrenoreceptor antagonists, lipophilicity is a key physicochemical property that governs drug distribution within the eye. Following intravitreal injection, lipophilic beta adrenoreceptor antagonists penetrate to the posterior eye, where they bind to the choroid and reside in the retina at greater concentrations than more hydrophilic beta adrenoreceptor antagonists, which preferentially penetrate to the anterior eye.

Quantification of the anti-influenza drug zanamivir in plasma using high-throughput HILIC-MS/MS

BACKGROUND

parenteral zanamivir is a promising drug for the treatment of severe influenza. However, quantification of this polar drug in biological matrices has traditionally been difficult and the methods developed have been relatively insensitive.

RESULTS

a high-throughput bioanalytical method for the analysis of zanamivir in human plasma using SPE in the 96-well plate format and LC coupled to positive MS/MS has been developed and validated according to US FDA guidelines. The method uses 50 microl of plasma and covers a large working range from 1-50, 000 ng/ml with a LOD of 0.50 ng/ml.

CONCLUSION

this new LC-MS/MS assay is more sensitive than previous methods despite using a small plasma volume sample. It is particularly suitable for clinical studies on both parenteral and inhaled zanamivir.

Multiplex ultra-performance liquid chromatography-tandem mass spectrometry method for simultaneous quantification in human plasma of fluconazole, itraconazole, hydroxyitraconazole, posaconazole, voriconazole, voriconazole-N-oxide, anidulafungin, and caspofungin

Therapeutic drug monitoring (TDM) may contribute to optimizing the efficacy and safety of antifungal therapy because of the large variability in drug pharmacokinetics. Rapid, sensitive, and selective laboratory methods are needed for efficient TDM. Quantification of several antifungals in a single analytical run may best fulfill these requirements. We therefore developed a multiplex ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method requiring 100 μl of plasma for simultaneous quantification within 7 min of fluconazole, itraconazole, hydroxyitraconazole, posaconazole, voriconazole, voriconazole-N-oxide, caspofungin, and anidulafungin. Protein precipitation with acetonitrile was used in a single extraction procedure for eight analytes. After reverse-phase chromatographic separation, antifungals were quantified by electrospray ionization-triple-quadrupole mass spectrometry by selected reaction monitoring detection using the positive mode. Deuterated isotopic compounds of azole antifungals were used as internal standards. The method was validated based on FDA recommendations, including assessment of extraction yields, matrix effect variability (<9.2%), and analytical recovery (80.1 to 107%). The method is sensitive (lower limits of azole quantification, 0.01 to 0.1 μg/ml; those of echinocandin quantification, 0.06 to 0.1 μg/ml), accurate (intra- and interassay biases of -9.9 to +5% and -4.0 to +8.8%, respectively), and precise (intra- and interassay coefficients of variation of 1.2 to 11.1% and 1.2 to 8.9%, respectively) over clinical concentration ranges (upper limits of quantification, 5 to 50 μg/ml). Thus, we developed a simple, rapid, and robust multiplex UPLC-MS/MS assay for simultaneous quantification of plasma concentrations of six antifungals and two metabolites. This offers, by optimized and cost-effective lab resource utilization, an efficient tool for daily routine TDM aimed at maximizing the real-time efficacy and safety of different recommended single-drug antifungal regimens and combination salvage therapies, as well as a tool for clinical research.

Determination of eflornithine enantiomers in plasma by precolumn derivatization with o-phthalaldehyde-N-acetyl-L-cysteine and liquid chromatography with UV detection

A bioanalytical method for indirect determination of eflornithine enantiomers in 75 microL human plasma has been developed and validated. L- and D-eflornithine were derivatized with o-phthalaldehyde and N-acetyl-L-cysteine to generate diastereomers which were separated on two serially connected Chromolith Performance columns (RP-18e 100 x 4.6 mm i.d.) by a isocratic flow followed by a gradient flow for elution of endogenous compounds. The diastereomers were detected with UV (340 nm). The between-day precisions for L- and D-eflornithine in plasma were 8.4 and 2.3% at 3 microm, 4.0 and 5.1% at 400 microm, and 2.0 and 3.7% at 1000 microm. The lower limit of quantification was determined to be 1.5 microm, at which precision was 14.9 and 9.9% for L- and D-eflornithine, respectively.

Liquid chromatography and tandem mass spectrometry for the quantitative determination of ixabepilone (BMS-247550, Ixempra) in human plasma: method validation, overcoming curve splitting issues and eliminating chromatographic interferences from degradants

A sensitive method was developed and validated for the measurement of ixabepilone (BMS-247550, Ixempra) using a demethylated analogue of ixabepilone (BMS-212188) as an internal standard. A 0.050 mL portion of each plasma sample was extracted with 0.450 mL of acetonitrile containing the internal standard via protein precipitation. The supernatant was analyzed on a LC-MS/MS system. Chromatography was carried out on a 2.0 mm x 100 mm YMC ODS-AQ 3 microm column using an isocractic mobile phase consisting of acetonitrile:10 mM ammonium acetate, pH 5.0 (70:30, v/v) at a flow rate of 0.30 mL/min. The mass spectrometer was fitted with a TurboIonSpray source and operated in negative ionization mode. Detection of ixabepilone and BMS-212188 were accomplished using multiple reaction monitoring (MRM) of precursor>product ion pairs of m/z 505.2>405.2, and 492.1>392.1, respectively. The assay range was 2.00-500 ng/mL and was fitted to a 1/x(2) weighted quadratic regression model. Replicate sample analysis indicated that intra- and inter-day accuracy and precision are within +/-15.0%. The recovery of ixabepilone from 0.050 mL of plasma containing 5.00 and 400 ng/mL was greater than 94%. The method was demonstrated to be sensitive, selective and robust, and was successfully used to support clinical studies. This paper also discussed approaches used for resolving a curve splitting issue observed during quantitative analysis of ixabepilone in biological matrices. Finally, to adapt the methodology to pharmacokinetics of ixabepilone after oral administration, the potential interference of chemical degradants on the determination of ixabepilone was evaluated.