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Aim: Determination of plasma protein binding ( PPB) is considered vital for better understanding of pharmacokinetic and pharmacodynamic activities of drugs due to the role of free concentration in pharmacological response. Methodology & results: Solid-phase microextraction (SPME) was investigated for measurement of PPB from biological matrices and compared with a gold standard approach (rapid equilibrium dialysis [RED]). Discussion & conclusion: SPME-derived values of PPB correlated well with literature values, and those determined by RED. Respectively, average protein binding across three concentrations by RED and SPME was 33.1 and 31.7% for metoprolol, 89.0 and 86.6% for propranolol and 99.2 and 99.0% for diclofenac. This study generates some evidence for SPME as an alternative platform for the determination of PPB.

Background: The hemaPEN is a liquid microsampling device for the reproducible collection and storage of blood samples as dried blood spots, for subsequent quantitative analysis. Materials & methods: We examined the device’s ability to collect accurate and precise blood volumes, at different hematocrit levels, via in vitro studies using acetaminophen in human blood. We also investigated the impact of different user training approaches on device performance. Results: The hemaPEN demonstrated acceptable volumetric accuracy and precision, regardless of the training medium used. Issues with apparent hematocrit-dependent bias were found to be associated with the extraction process, rather than the volumetric performance of the device. Conclusion: The hemaPEN is capable of readily producing high quality blood microsamples for reproducible and accurate quantitative bioanalysis.

There is growing interest in the implementation of microsampling approaches for the quantitation of circulating concentrations of analytes in biological samples derived from nonclinical and clinical studies involved in drug development. This interest is partly due to the ethical advantages of taking smaller blood volumes, particularly for studies in rodents, children and the critically ill. In addition, these technologies facilitate sampling to be performed in previously intractable locations and occasions. Further, they enable the collection of samples for additional purposes (extra time points, biomarkers, sampling during a clinical event, etc). This article gives a comprehensive insight to the utilization of these approaches in drug discovery and development, and provides recommendations for best practice for nonclinical, clinical and bioanalytical aspects.

A previous Senior Editor, and the present Senior Editor of Bioanalysis reflect on their journeys in the field of bioanalysis, and with the journal. They discuss the evolution and progress of journal since its launch 10 years ago, and where they would like to see it heading in the future.

There is continuing interest in the development and application of various microsampling technologies for drug development. The AAPS bioanalytical community microsampling subgroup and the European Bioanalysis Forum conducted a survey of their members (39 individual organizations). This gives a snapshot of current practices and demonstrates that implementation of microsampling approaches is becoming increasingly commonplace, but not universal. Greater adoption was observed for nonclinical studies, particularly nonregulatory. A number of respondents reported that they have included microsampling data in regulatory submissions. Another important observation was that where microsampling is employed for clinical studies, dried blood approaches predominate, reflecting the interest in their use where they enable sample collection which is not feasible with standard approaches or to derive richer data sets.

[ ]of writing, it is unclear whether this will result in a permanent change in how blood sampling for clinical trials and routine healthcare are performed, although it seems unlikely that the progression of these sampling technologies will be slowed by the current situation Many of the early publications in this area had a primary focus on the development of blood sampling technologies, validation of bioanalytical methods and were limited to applications supporting nonclinical and clinical studies for pharmaceutical drug development Bioanalysis 7(16) (2015) https://www future-science com/toc/bio/7/16 Neil Spooner: Spooner Bioanalytical Solutions Ltd, Hertford, UK and School of Life and Medical Sciences, University of Hertfordshire, UK Melanie Anderson: Merck and Co , Inc , West Point, PA 19486, USA Enaksha R Wickremsinhe: Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, IN 46285, USA

Aim: Collection and quantitative analysis in dry blood using volumetric absorptive microsampling (VAMS™) potentially offers significant advantages over conventional wet whole blood analysis. This manuscript explores their use for pediatric sampling and explores additional considerations for the validation of the bioanalytical method. Results: HPLC–MS/MS methods for the determination of midazolam and its major metabolite 1-OH midazolam in both whole wet blood, and dry blood collected on VAMS were developed, validated, and used to support an observational clinical study to compare pharmacokinetic parameters in pediatric patients. Conclusion: Validation data met internationally accepted guideline criteria. A strong correlation was observed in calculated concentrations between wet and dry test samples, indicating that VAMS is a suitable technique for use in pediatric clinical studies.

A previous Senior Editor, and the present Senior Editor of

Aim: The quality of quantitative analytical measurements is dependent on the quality of the sample collected, and dried blood spots (DBS) are no exception. As the use of DBS has matured into late-stage clinical drug-development studies, it has become apparent that a simple and straightforward approach in a controlled single-site, first-time-into-human clinic, does not always translate into multicenter clinical studies. Using synthetic blood, a method of training and assessing clinical laboratory staff has been developed to ensure the quality of sampling. Methods: A test kit comprising of synthetic blood, a pipetting aid, blank blood spot card, drying rack and training manual was sent to each clinical site for each technician to assess and approve prior to spotting PK samples. Results: The development of a DBS training kit along with a step-by-step guide has been successfully implemented. Conclusion: The training kit has been 100% successful across three large multisite clinical studies.

Background: Control blood plasma is regularly used in bioanalysis, biomarkers and proteomics, and is often obtained from commercial sources. It has always been assumed that this plasma will be comparable to plasma drawn during a drug development study. Results: When compared using total protein concentrations, plasma from only one species (dog) demonstrated statistical comparability, plasma from all other species tested (human, rabbit, mouse and rat) shows a statistically significant difference. Conclusion: If endogenous components of blood plasma are being measured, or if an assay technique does not significantly limit matrix effects, any assay controls should be prepared using control plasma from the drug development site, or using commercial plasma that has been screened against drug development site plasma.

Background: Automated DBS direct elution systems are available that incorporate IS spray modules which, unlike conventional IS addition via the extraction solvent, apply IS prior to DBS samples prior to extraction, allowing analyte and IS to be coextracted. Results: IS spray system parameters were optimized to identify the conditions that produced the best analytical performance in quantitative bioanalytical assays, without interfering with the integrity of the DBS sample prior to extraction. Conclusion: LC–MS/MS method validations across four representative small molecule assays using the optimized IS spray conditions were demonstrated to produce analytical performance comparable to conventional methods of IS addition, demonstrating that the spray technique is a viable alternative.

Background: Automated DBS direct elution techniques eliminate the manual extraction burden of DBS bioanalysis, offer good quantitative performance, the ability to eliminate hematocrit-based assay bias, and, previous reports have demonstrated that significant increases in assay sensitivity compared with manual DBS extraction are possible. Results: An investigation into elucidating parameters for optimized generic DBS direct elution for high sample throughput quantitative bioanalytical applications is presented for the first time. Generic direct elution conditions were identified that enabled LC–MS/MS assay sensitivity to be maximized while retaining acceptable chromatographic performance. Conclusion: Compared with generic conventional DBS manual extraction, assay sensitivity was demonstrated to be increased up to 33-fold across four representative small molecule compounds, using the recommended direct elution conditions.

Aims: A cross-laboratory experiment has been performed on a novel dried blood sampler in order to investigate whether it overcomes issues associated with blood volume and hematocrit (HCT) that are observed when taking a subpunch from dried blood spot samples. Materials & methods: An average blood volume of 10.6 μl was absorbed by the samplers across the different HCTs investigated (20–65%). Results: No notable change of volume absorbed was noted across the HCT range. Furthermore, the variation in blood sample volumes across six different laboratories was within acceptable limits. Conclusion: The novel volumetric absorptive microsampling device has the potential to deliver the advantages of dried blood spot sampling while overcoming some of the issues associated with the technology.

A novel approach is described for the quantitative bioanalysis of drugs in blood samples by ionization of the analytes collected on solid-phase microextraction (SPME) fibers by mass spectrometry (MS). The technique combines the attractive features of SPME microsampling using minimal sample volumes with the speed, selectivity, and sensitivity capabilities of MS detection. The method reported in this study involved generating gas-phase ions directly from SPME fibers without the need for any additional sample preparation or chromatographic separation; the entire process was completed within 5 min. Traditionally, analytes extracted by SPME fibers are desorbed by washing with suitable solvents followed by a transfer into a sample vial and subsequent liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to quantify the amount of analyte extracted and thereby determining the analyte concentration in the matrix. These sample preparation steps are completely eliminated by inserting the SPME fiber directly into the MS. Physiologically relevant concentrations of metoprolol and propranolol in blood samples were measured over several orders of magnitude down to concentration levels of 10 ng/mL. This preliminary assessment of direct SPME-MS showed high sensitivity (ng/mL), acceptable reproducibility (

The 2014 8th Workshop on Recent Issues in Bioanalysis (8th WRIB), a 5-day full immersion in the evolving field of bioanalysis, took place in Universal City, California, USA. Close to 500 professionals from pharmaceutical and biopharmaceutical companies, contract research organizations and regulatory agencies worldwide convened to share, review, discuss and agree on approaches to address current issues of interest in bioanalysis. The topics covered included both small and large molecules, and involved LCMS, hybrid LBA/LCMS, LBA approaches and immunogenicity. From the prolific discussions held during the workshop, specific recommendations are presented in this 2014 White Paper. As with the previous years’ editions, this paper acts as a practical tool to help the bioanalytical community continue advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2014 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 1) covers the recommendations for small molecule bioanalysis using LCMS. Part 2 (Hybrid LBA/LCMS, Electronic Laboratory Notebook and Regulatory Agencies’ input) and Part 3 (Large molecules bioanalysis using LBA and Immunogenicity) will be published in the upcoming issues of Bioanalysis.

The portfolios of pharmaceutical companies have diversified substantially over recent years in recognition that monotherapies and/or small molecules are less suitable for modulating many complex disease etiologies. Furthermore, there has been increased pressure on drug-development budgets over this same period. This has placed new challenges in the path of bioanalytical scientists, both within the industry and with contract research organizations (CROs). Large pharmaceutical, biotechnology and small-medium healthcare enterprises have had to make important decisions on what internal capabilities they wish to retain and where CROs offers a significant strategic benefit to their business model. Our journey has involved asking where we believe an internal bioanalytical facility offers the greatest benefit to progressing drug candidates through the drug-development cycle and where externalization can help free up internal resources, adding flexibility to our organization in order to deal with the inevitable peaks and troughs in workload.

Background: Dried blood spot (DBS) sampling is emerging as a valuable technique in a variety of fields, including clinical and preclinical testing of pharmaceuticals. Despite this popularity, current DBS sampling and analysis processes remain laborious and time consuming. Digital microfluidics, a microscale liquid-handling technique, characterized by the manipulation of discrete droplets on open electrode arrays, offers a potential solution to these problems. Results: We report a new digital microfluidic method for multiplexed extraction and analysis of pharmaceuticals in DBS samples. In the new method, four DBS samples are extracted in microliter-sized droplets containing internal standard, and the extract is delivered to dedicated nanoelectrospray ionization emitters for direct analysis by tandem mass spectometry and selected reaction monitoring. Conclusion: The new method allows for an order of magnitude reduction in processing time and approximately three-times reduction in extraction solvent relative to conventional techniques, while maintaining acceptable analytical performance for most drugs tested.

Background: The aim of the work was to evaluate the sensitivity and reproducibility of real-time reverse transcriptase PCR for quantitative analysis of an oligonucleotide in a biological matrix. A novel approach for the identification of outliers when assessing the suitability of calibration standards and QC samples is investigated. Results: A suitable assay was established for the determination of the oligonucleotide in human plasma over a range of 0.5–100 ng/ml. Conclusion: In these preliminary investigations, the precision and accuracy of the method was established for the quantification of the oligonucleotide in human plasma. It was established that the method was precise and accurate for quantification of the oligonucleotide in human plasma. The acceptability of the data was assessed using a novel three-step process to identify any outliers, involving the use of the Grubbs’ test. The analytical method only requires a small sample volume (

This article discusses the benefits of dried blood spot sampling and the recent issues that have emerged when this technique is used in the regulated quantitative bioanalytical environment. The author explores what the way forward might be for this important technique and what some of the unexpected benefits of this change in sampling methodologies have been.

Aims Dried blood spots (DBS) alongside micro-analytical techniques are a potential solution to the challenges of performing pharmacokinetic (PK) studies in children. However, DBS methods have received little formal evaluation in clinical settings relevant to children. The aim of the present study was to determine a PK model for caffeine using a ‘DBS/microvolume platform’ in preterm infants. Methods DBS samples were collected prospectively from premature babies receiving caffeine for treatment of apnoea of prematurity. A non-linear mixed effects approach was used to develop a population PK model from measured DBS caffeine concentrations. Caffeine PK parameter estimates based on DBS data were then compared with plasma estimates for agreement. Results Three hundred and thirty-eight DBS cards for caffeine measurement were collected from 67 preterm infants (birth weight 0.6–2.11 kg). 88% of cards obtained were of acceptable quality and no child had more than 10 DBS samples or more than 0.5 ml of blood taken over the study period. There was good agreement between PK parameters estimated using caffeine concentrations from DBS samples (CL = 7.3 ml h−1 kg−1; V = 593 ml kg−1; t1/2 = 57 h) and historical caffeine PK parameter estimates based on plasma samples (CL = 4.9–7.9 ml h−1 kg−1; V = 640–970 ml kg−1; t1/2 = 101–144 h). We also found that changes in blood haematocrit may significantly confound estimates of caffeine PK parameters based on DBS data. Conclusions This study demonstrates that DBS methods can be applied to PK studies in a vulnerable population group and are a practical alternative to wet matrix sampling techniques.

Circulating drug concentrations (clinical or preclinical) underly many interactions between industry and regulators; expressing safety coverage, pharmacokinetic-pharmacodynamic relationships or defining bioequivalence and dosing regimens. Accurate and precise measurement of these circulating concentrations is pivotal to the evolution and validation of any bioanalytical method that supports regulatory interactions. Since the bioanalyst is presented with a sub-aliquot of sampled biological matrix, how do they ensure this aliquot reflects the concentration in the subject at the time of collection? Here we share experiences from project support (internal and at CROs) that suggests we need to be ever vigilant translating the needs of bioanalysis with those of project teams. The simple mantra is for bioanalytical measurements to be physiologically relevant to the patient.

21st International Reid Bioanalytical Forum, University of Surrey, Guildford, UK, 7–10 September 2015 The 21st International Reid Bioanalytical Forum held between 7 and 10 September 2015, brought together over 100 scientists from around the world, representing industry, academia and vendors, for 4 days of engaging science at the University of Surrey in Guildford, UK. The scientific program consisted of 43 podium and 23 poster presentations from key opinion leaders and those just setting out on their scientific career. The latter being the focus of the meeting. One of the highlights of the forum was the debate. An expert panel helped spark off an active discussion among a passionate audience on the topic of ‘The Current Skills Gaps in Analytical Sciences are Failing Industry.’

Background: The surge in interest in switching from traditionally used wet plasma to dried matrix spot (DMS) sampling and analysis to support pharmaceutical drug development is due to the significant ethical, financial and data quality advantages on offer. Unfortunately these advantages do not extend to sample bioanalysis, as DMS extraction is more complex than the protein precipitation method typically used for wet plasma analysis. Direct elution techniques coupled to HPLC–MS/MS have been identified as a potential means to counter this additional complexity. Results: The robustness and reproducibility of DMS HPLC–MS/MS data generated using a CAMAG DBS–MS 16 prototype automated direct elution instrument has been demonstrated to meet or exceed results obtained using a conventional manual extraction methodology. Conclusion: The data generated suggest that a simple and fast direct elution method of DMS samples that does not require additional sample or extract clean-up, offers sufficiently robust performance to be compatible with high-sample-throughput quantitative analysis. Further evaluation of the technique and the development of more advanced fully automated direct elution instrumentation is fully warranted.

Background: Dried blood spot (DBS) sampling, the collection of whole blood samples on paper, is being evaluated for its use in quantitative analysis. The aim of this investigation was to evaluate the impact of sample hematocrit (HCT) and punch location on assay bias in the measurement of compounds with varying physicochemical properties, when a portion of a DBS sample is analyzed. In addition, the statistical significance of factors such as compound, card type, HCT level, spot position on a card and the location of the punch on the spot were evaluated. Results: The results of this work indicate that for quantitative analysis using a portion of the DBS, notable bias (>15%) exists due to the effect of HCT and nonhomogeneous distribution of compound across the spot. The statistical analysis of results from a split-split-plot designed study showed that the factors of compound, card type and HCT were statistically significant (p < 0.05) both individually and in complex interactions, which affect the accuracy of quantitative concentrations obtained from DBS samples for each compound on each card type. Conclusion: To achieve the acceptance criteria (±15%) for accuracy when removing a portion of the DBS spot for quantitative analysis, HCT and punch location for each selected card type will need to be assessed during validation and sample analysis.

Background: Before shipping and storage, dried blood spot (DBS) samples must be dried in order to protect the integrity of the spots. In this article, we examine the time required to dry blood spot samples and the effects of different environmental conditions on their integrity. Results: Under ambient laboratory conditions, DBS samples on Whatman 903®, FTA® and FTA® Elute substrates are dry within 90 min of spotting. An additional 5% of moisture is lost during subsequent storage with desiccant. When exposed to elevated conditions of temperature and relative humidity, the DBS samples absorb moisture. DBS samples on FTA lose this moisture on being returned to ambient conditions. DBS samples on 903 show no visible signs of deterioration when stored at elevated conditions. However, these conditions cause the DBS to diffuse through the FTA Elute substrate. Conclusion: Blood spots are dry within 90 min of spotting. However, the substrates examined behave differently when exposed to conditions of high relative humidity and temperature, in some cases resulting in the integrity of the substrate and DBS sample being compromised. It is recommended that these factors be investigated as part of method development and validation.

Background: A study was performed to evaluate the suitability of stored EDTA-treated control whole blood for use in the preparation of calibration standards and quality control samples for quantitative bioanalytical methods employing dried blood spot (DBS) samples to support pharmaceutical exposure studies. Results: It has been demonstrated that a storage time of 14 days for control human and animal blood is suitable for producing quantitative analytical results within internationally recognised acceptance criteria for two analytes. Furthermore, blood hemolysis and chill–thaw cycles have been evaluated and shown not to affect bioanalytical results notably. Aggressive mixing techniques can result in rat blood coagulation; however, this does not occur with other species tested and can be affected by the method of blood collection. Conclusion: Control whole blood handled and stored using the recommendations generated from this study will not notably affect quantitative bioanalytical results when used for the preparation of calibration standards and quality control samples for DBS assays. It was demonstrated that control human and animal blood can be stored for periods long enough to effectively eliminate wastage.

Background: A clinical investigation was performed into the practicalities of the collection of blood samples for the determination of drug exposures on filter paper, known as dried blood spot (DBS) sampling using a two-period, single-dose, open-label trial conducted in 11 healthy volunteers who received a single oral dose of paracetamol. Questionnaires relating to the blood sampling and spotting process and tolerability were completed by staff and volunteers. Paracetamol concentrations in DBS samples obtained by venous cannula (DBS-Can) were compared against those from fingerprick (DBS-FP) and fresh whole blood obtained from a cannula (WB-Can). Results: The questionnaires demonstrated that FP and blood spotting was easy to perform and well tolerated and compared favorably with cannula sampling. Paracetamol concentrations in DBS-Can were greater than those in WB-Can (positive bias) except below 8000 ng/ml when both were interchangeable. When comparing DBS-FP to DBS-Can, both the bias and variability differed significantly across the five sampling time points. Conclusion: The study has shown that the DBS technique is practical in the context of a clinical trial. Interchangeability of drug concentrations between blood sampling site and mode of blood collection has to be checked and taken into account when designing pharmacokinetic studies for other compounds.

The CAMAG thin-layer chromatography mass spectrometer (TLC-MS) interface has been assessed as a tool for the direct quantitative bioanalysis of drugs from dried blood spot (DBS) samples, using an MS detector, with or without high-performance liquid chromatography (HPLC) separation. The approach gave acceptable sensitivity, linearity, accuracy, and precision data for bioanalytical validations with and without the inclusion of HPLC separation. In addition, the direct elution technique was shown to increase assay sensitivity for a range of analytes representing a wide "chemical space" for pharmaceutical-type molecules over that obtained by conventional manual extraction of samples (punching of DBS and elution with solvent prior to HPLC-MS analysis). Investigations were performed to optimize extraction time, minimize sample-to-sample carry-over, and compare chromatographic performance. On the basis of this preliminary assessment, it has been demonstrated that the TLC-MS interface has the potential to be an effective tool for the direct analysis of drugs in DBS samples at physiologically relevant concentrations, an approach that could provide significant time and cost savings and greatly simplify bioanalytical procedures compared to current manual practices. Further, the increased sensitivity compared to that of manual extraction may enable the analysis of analytes not currently amenable to DBS sampling due to limitations in assay sensitivity.

The Deep Underground Neutrino Experiment (DUNE) is a project to design, construct and operate a next-generation long-baseline neutrino detector with a liquid argon (LAr) target capable also of searching for proton decay and supernova neutrinos. It is a merger of previous efforts of the LBNE and LBNO collaborations, as well as other interested parties to pursue a broad programme with a staged 40 kt LAr detector at the Sanford Underground Research Facility (SURF) 1300 km from Fermilab. This programme includes studies of neutrino oscillations with a powerful neutrino beam from Fermilab, as well as proton decay and supernova neutrino burst searches. In this paper we will focus on the underground physics with DUNE., Comment: 5 pages, 3 figures, contribution to TAUP2015

Hematocrit (HCT)-based assay bias (composed of area and recovery bias) is an important contributing factor to the barriers that currently hinder the development and acceptance of dried blood spots (DBS) as a widely used quantitative bioanalytical sampling technique for regulatory studies. This article describes the evaluation of a practical internal standard spray addition technique, used prior to LC-MS/MS analysis, which is demonstrated to nullify the effect of recovery bias. To our knowledge, this is the first time a potential solution to HCT-based recovery bias has been investigated in detail and reported in the literature. This new technique is coupled with accurate volume DBS sampling, whole-spot extraction, and automated direct elution techniques to demonstrate a workflow that both nullifies HCT-based assay bias and the additional manual extraction burden associated with DBS analysis.

There is great interest in the development of integrated tools allowing for miniaturized sample processing, including solid phase extraction (SPE). We introduce a new format for microfluidic SPE relying on C18-functionalized magnetic beads that can be manipulated in droplets in a digital microfluidic platform. This format provides the opportunity to tune the amount (and potentially the type) of stationary phase on-the-fly, and allows the removal of beads after the extraction (to enable other operations in same device-space), maintaining device reconfigurability. Using the new method, we employed a design of experiments (DOE) operation to enable automated on-chip optimization of elution solvent composition for reversed phase SPE of a model system. Further, conditions were selected to enable on-chip fractionation of multiple analytes. Finally, the method was demonstrated to be useful for online cleanup of extracts from dried blood spot (DBS) samples. We anticipate this combination of features will prove useful for separating a wide range of analytes, from small molecules to peptides, from complex matrices.

The LZ experiment, featuring a 7-tonne active liquid xenon target, is aimed at achieving unprecedented sensitivity to WIMPs with the background expected to be dominated by astrophysical neutrinos. To reach this goal, extensive simulations are carried out to accurately calculate the electron recoil and nuclear recoil rates in the detector. Both internal (from target material) and external (from detector components and surrounding environment) backgrounds are considered. A very efficient suppression of background rate is achieved with an outer liquid scintillator veto, liquid xenon skin and fiducialisation. Based on the current measurements of radioactivity of different materials, it is shown that LZ can achieve the reduction of a total background for a WIMP search down to about 2 events in 1000 live days for 5.6 tonne fiducial mass.

Volumetric absorptive microsampling (VAMS) is a simple intuitive technique for collecting and quantitative analysis of dried blood samples. It enables the collection of an accurate blood volume (approximately 10μL) regardless of blood hematocrit. A bioanalytical method for the determination of paracetamol in dried blood supported on VAMS samplers has been validated and used to support a toxicokinetic (TK) study in rat. The calculated TK parameters were comparable to those obtained from blood-water (1:1, v/v) samples. VAMS is demonstrated to be a robust method that simplifies both the blood sample collection and bioanalytical laboratory procedures and generates high quality quantitative data. However, problems were encountered with controlling the bleed rate during sample collection, resulting in the VAMS tips being flooded and highlighting the need for bleeding methods to be compatible with microsampling techniques to avoid wasting blood. Alternative sample collection procedures are discussed that minimize these issues.

Further to the discussions on the bioanalysis of samples generated using microsampling techniques [1–6] and more specifically the ongoing work of the European Bioanalysis Forum (EBF) Liquid Microsampling Consortium [7], this article seeks to highlight some of the ‘philosophical’ aspects around liquid microsampling and to introduce some of the experimental elements that will form part of future efforts by the Consortium. Discussion will be focused on three major areas: sample manipulation, homogeneity of samples and validation of assays. The scope of this manuscript will be liquid microsampling and will not focus on adsorption techniques such as dried blood spots (DBS) and solid phase microextraction. Different microsampling techniques have created great interest from toxicokinetic (TK) and pharmacokinetic (PK) scientists, since they offer the potential to reduce sample volumes for exposure assessment in biofluids. For preclinical studies microsampling can facilitate the generation of serial profiles in rodent exposure evaluation studies, rather than working with composite designs. Microsampling has facilitated the removal of satellite animal groups leading to substantial reductions in the number of animals required and the reduction or elimination of rodent warming. Benefits in the clinical environment include the ability to take reduced sample volumes from pediatric, elderly and critically ill patient populations. In a recent publication the NC3R group proposes the following definition of a blood microsample: the sample should ideally not contain more than 50 μl whole blood [8]. As a consequence the subsequent plasma volumes are 20 μl or lower. Another, more philosophical consideration would be the impact of sampling volume on the animal or subject; for example, 50 μl of blood may not be considered as a ‘microsample’ in the context of juvenile animals or newborn babies. Two major liquid microsampling approaches can be envisaged

Volumetric absorptive microsampling (VAMS) is a novel approach to obtaining a dried blood sample for quantitative bioanalysis that overcomes the area bias and homogeneity issues associated with conventional dried blood spot (DBS) sample when a subpunch is taken. The VAMS sampler absorbs a fixed volume of blood (∼10 μL) in 2–4 s with less than 5% volume variation across the hematocrit range of 20–70% with low tip-to-tip variability. There is no evidence of selective absorption by the tip of the plasma component over whole blood. Recommendations for best practice when collecting samples were developed based upon the results of tests examining a number of potential abuse scenarios.