Liquid chromatography/tandem mass spectrometry sensitivity enhancement via online sample dilution and trapping: applications in microdosing and dried blood spot (DBS) bioanalysis

Applications of Tandem Mass Spectrometry (MS/MS) in Protein Analysis for Biomedical Research

Mass Spectrometry (MS) allows the analysis of proteins and peptides through a variety of methods, such as Electrospray Ionization-Mass Spectrometry (ESI-MS) or Matrix-Assisted Laser Desorption Ionization-Mass Spectrometry (MALDI-MS). These methods allow identification of the mass of a protein or a peptide as intact molecules or the identification of a protein through peptide-mass fingerprinting generated upon enzymatic digestion. Tandem mass spectrometry (MS/MS) allows the fragmentation of proteins and peptides to determine the amino acid sequence of proteins (top-down and middle-down proteomics) and peptides (bottom-up proteomics). Furthermore, tandem mass spectrometry also allows the identification of post-translational modifications (PTMs) of proteins and peptides. Here, we discuss the application of MS/MS in biomedical research, indicating specific examples for the identification of proteins or peptides and their PTMs as relevant biomarkers for diagnostic and therapy.

Optimizing oxytocin LC-MS/MS sensitivity by choosing the right column

Objective

Sensitivity is often an issue in bioanalytical LC-MS/MS applications. Commonly investigated parameters to improve it include additives to mobile phase, derivatization and sample-preparation. The nature of the column, however, is not frequently evaluated.

Design and Methods

The sensitivity is compared for 18 different reversed phase and 2 different HILIC columns using 2 different mobile phase compositions. Sensitivity was evaluated in terms of S/N for 1,5 pg oxytocin on column, using a scouting gradient.

Results

The measured signal to noise ranged from 55 to 1473, indicating a substantial difference in sensitivity. The most sensitive columns were the Synergi Hydro RP (reversed phase) and the Atlantis HILIC (HILIC).

Conclusions

This study shows that choosing the right column contributes to the sensitivity of the method.

The use of mass spectrometry to analyze dried blood spots

Dried blood spots (DBS) typically consist in the deposition of small volumes of capillary blood onto dedicated paper cards. Comparatively to whole blood or plasma samples, their benefits rely in the fact that sample collection is easier and that logistic aspects related to sample storage and shipment can be relatively limited, respectively, without the need of a refrigerator or dry ice. Originally, this approach has been developed in the sixties to support the analysis of phenylalanine for the detection of phenylketonuria in newborns using bacterial inhibition test. In the nineties tandem mass spectrometry was established as the detection technique for phenylalanine and tyrosine. DBS became rapidly recognized for their clinical value: they were widely implemented in pediatric settings with mass spectrometric detection, and were closely associated to the debut of newborn screening (NBS) programs, as a part of public health policies. Since then, sample collection on paper cards has been explored with various analytical techniques in other areas more or less successfully regarding large-scale applications. Moreover, in the last 5 years a regain of interest for DBS was observed and originated from the bioanalytical community to support drug development (e.g., PK studies) or therapeutic drug monitoring mainly. Those recent applications were essentially driven by improved sensitivity of triple quadrupole mass spectrometers. This review presents an overall view of all instrumental and methodological developments for DBS analysis with mass spectrometric detection, with and without separation techniques. A general introduction to DBS will describe their advantages and historical aspects of their emergence. A second section will focus on blood collection, with a strong emphasis on specific parameters that can impact quantitative analysis, including chromatographic effects, hematocrit effects, blood effects, and analyte stability. A third part of the review is dedicated to sample preparation and will consider off-line and on-line extractions; in particular, instrumental designs that have been developed so far for DBS extraction will be detailed. Flow injection analysis and applications will be discussed in section IV. The application of surface analysis mass spectrometry (DESI, paper spray, DART, APTDCI, MALDI, LDTD-APCI, and ICP) to DBS is described in section V, while applications based on separation techniques (e.g., liquid or gas chromatography) are presented in section VI. To conclude this review, the current status of DBS analysis is summarized, and future perspectives are provided.

Ultrasensitive sub-pg/ml determination of tiotropium bromide in human plasma by 2D-UHPLC–MS/MS: challenges and solutions

Background: To adequately support pharmacokinetic evaluations of tiotropium bromide in planned clinical studies. It was desirable to measure it with a LLOQ of sub pg/ml. Results: A sensitive bioanalytical method for the determination of tiotropium in human plasma sample was successfully developed and validated in the range of 0.2–100 pg/ml. The method was successfully applied to support two clinical studies of over 3000 samples. The overall incurred sample reanalysis passing rate was 93.7%. Conclusion: The combination of a dual stage liquid–liquid extraction and a 2D ultra-HPLC greatly reduced matrix effects and increased assay sensitivity. When developing effective ultrasensitive assays, it is imperative to balance the aspects related to sensitivity with those that will ensure assay ruggedness.

Performance and storage integrity of dried blood spots for PCB, BFR and pesticide measurements

Dried blood spots (DBSs) can provide accurate and valuable estimates of exposure to environmental toxicants, and the use of information derived from archived newborn DBSs has enormous potential to open up new research on the impacts of early chemical exposure on disease. Broad application of DBS for the purpose of quantitative exposure estimation requires robust and validated methods. This study investigates the suitability of DBS analyses for population studies of exposure to three chemical groups: polychlorinated biphenyls (PCBs), brominated flame retardants (BFRs), and chlorinated pesticides. It examines background (matrix) contamination, recovery and extraction variability, sensitivity, and storage stability. DBS samples prepared using 50 μL of adult blood were analyzed by GC/MS, and method performance was confirmed by using certified materials and paired DBS-blood samples from six volunteers. Several of the target compounds and their degradation products have not been previously measured in DBSs. All target compounds were detected in DBS samples collected from the volunteers. Sample DBS cards showed background contamination of several compounds. When stored at room temperature, target compounds, excluding PBDEs, were stable for up to one month. When refrigerated or frozen, stability was acceptable for all compounds up to one year, and multiyear storage appears acceptable at colder (e.g., -80°C) temperatures. Multicompartment models may be used to estimate or correct for storage losses. Considering concentrations of contaminants for adults and children reported in the literature, and experimental values of detection limits and background contamination, DBS samples are suitable for quantifying exposures to many PCBs, BFRs and persistent pesticides.

Alternative strategies for mass spectrometer-based sample dilution of bioanalytical samples, with particular reference to DBS and plasma analysis

Background: The analysis of bioanalytical samples has required a physical dilution of high-concentration samples to bring concentrations into the validated calibration range of an assay. Results: A reversed phase ultra-high performance liquid chromatography–tandem mass spectrometry method for the quantitative analysis of pioglitazone in dried blood spots has been used to partially validate two novel techniques to analyze sample concentrations that lie above a particular calibration range. The first of the two techniques is mass spectrometer signal dilution, which consists of lowering the signal that reaches the detector. The second technique designated isotope signal ratio monitoring looks at [M+2]+1 ions (caused by naturally occurring isotopes) for samples above the upper limit of quantification. Conclusions: The newly developed methods have the potential to simplify the analysis of bioanalytical samples for which previously a physical dilution of the sample was required to bring analytes within the calibration range of an assay.

Perforated dried blood spot accurate microsampling: the concept and its applications in toxicokinetic sample collection

Dried blood spot (DBS) sampling has gained considerable interest as a microsampling technique to support drug discovery and development owing to its enormous ethical and practical benefits. Quantitative determinations of drugs and/or their metabolites collected in DBS matrix in its current format, however, have encountered technical challenges and regulatory uncertainty. The challenges of DBS bioanalysis are largely ascribed to the way how samples are collected and analyzed. Currently, an uncontrolled amount of a blood sample, e.g. 20 µl, is collected per time point per sample and spotted onto cellulose paper. Quantitation is based on removal of a fixed area of the DBS sample, resulting in sample waste, a need for mechanical punching and concomitant potential punching carryover, uncertainty in recovery assessment and the adverse impact of hematocrit on accurate quantitation. Here, we describe the concept and applications of a novel concept, namely perforated dried blood spot (PDBS), for accurate microsampling that addresses previous challenges. Advantages of PDBS are enumerated and compared with conventional DBS in the context of microsampling and liquid chromatography tandem mass spectrometry bioanalysis. Two approaches for accurate microsampling of a small volume of blood (5 µl) are proposed and demonstrated, i.e. Microsafe® pipettes and the Drummond incremental pipette. Two online sample enrichment techniques to enhance liquid chromatography tandem mass spectrometry sensitivity for microsampling bioanalysis are discussed. The PDBS concept was successfully applied for accurate sample collection (5 µl) in a toxicokinetic study in rats given a single oral gavage dose of acetaminophen. Perspectives on bioanalytical method validation for regulated DBS/PDBS microsampling are also presented.

Perforated dried blood spots: a novel format for accurate microsampling

Dried blood spots (DBS) in their current format encounter challenges in bioanalysis using fixed areas, including but not limited to, waste of DBS samples (only a fraction is used for analysis), the need for sample punching leading to concerns of sample carryover, uncertainty for accurate recovery assessments and hematocrit (HCT) effects. Here we describe a novel concept, namely perforated dried blood spots (PDBS), for accurate microsampling that addresses previous challenges. PDBS discs were prepared from regular filter paper, with a diameter of 6.35 mm and a thickness of 0.83 mm. An accurate amount of blood sample (5–10 µl), was deposited, dried and stored on the PDBS discs. Upon sample analysis, PDBS samples are simply pushed by single-use pipette tips into 96-well plates. The proof-of-concept study was carried out on a PDBS LC–MS/MS assay development and validation under GLP criteria for the quantitation of lansoprazole in human whole-blood (K3EDTA). Particularly, the effect of HCT on the accuracy of quantitation was found to be related to recovery from PDBS samples. In all, PDBS was proved to be a viable alternative to conventional DBS, offering additional advantages of complete sample utilization, no requirement for punching, ease of recovery assessments, and elimination of sampling influence due to HCT levels.

LC–MS/MS bioanalytical challenge: ultra-high sensitivity assays

Anne-Françoise Aubry is Director of Bioanalytical Sciences at Bristol-Myers Squibb Co., leading a team in developing bioanalytical methods for early development drug candidates in support of toxicology and clinical studies. Her main research interests are high-speed, high-resolution LC and new approaches for LC–MS/MS drug bioanalysis in regulated laboratories. Anne Aubry is on the executive board of the Eastern Analytical Symposium and on the organizing committee of the Applied Pharmaceutical Analysis and Chemical and Pharmaceutical Structure Analysis (Shanghai 2011) conferences.

The challenges of developing and running low pg/ml LC–MS/MS bioanalytical assays in a regulated laboratory are reviewed. The practical problems encountered in implementing ultrasensitive assays are less in reaching a suitable sensitivity on the instrument than in implementing procedures to control losses and contamination, eliminate matrix interferences and ensure assay robustness so that the assay can be validated to industry standards. Solutions to these problems can be found in each of the three facets of the bioanalytical assay: the sample preparation, the chromatographic separation and the mass spectrometric detection. The key to developing an ultrasensitive assay is to optimize each of these elements. Progress in MS instrumentation has been essential in our ability to reach the low pg/ml limits.

LC–MS/MS sensitivity enhancement using 2D-SCX/RPLC and its application in the assessment of pharmacokinetics of clonidine in dried blood spots

Background: Dried blood spot (DBS) technology offers distinctive preclinical and clinical advantages primarily ascribed to microscale sampling (e.g., 40–80 µl per time point), and the nature of solid-state samples in filter papers. Logistic benefits in sample collection, storage and shipping also result. However, the effective DBS samples available for bioanalysis are finite, that is, in the order of approximately 1 µl equivalent of plasma (3-mm punch) from a DBS of approximately 15–20 µl whole blood samples. This represents 20- to 100-times fewer samples for bioanalysis compared with a typical plasma assay. It is critical to increase LC–MS/MS sensitivity to accommodate DBS bioanalysis. Results: We developed a 2D strong cation exchange reversed-phase LC–MS/MS (2D-SCX/RPLC–MS/MS) for online enrichment, separation and detection of basic polar compounds, using clonidine hydrochloride as a model compound. Positively charged clonidine was retained and enriched in the first dimensional SCX column even in large volumes, eluted to a second dimensional RP column with ammonium acetate, de-salted with highly aqueous solvent and separated in an analytical RP column. Injection of 100 µl clonidine extract exhibited essentially the same peak shape as that from 1 µl and the response of clonidine increased quantitatively in the range of 1–100 µl. Conclusion: The method was successfully employed to analyze clonidine DBS samples from an in-house toxicology study, where clonidine hydrochloride was administered to cynomolgus monkeys to produce hypotensive effects. Of 55 DBS samples collected post-dose, a total of 52 samples were within the curve range of 0.1–50 ng/ml, where valid clonidine PK profiles were obtained. The PK parameters agreed well with the onset of hemodynamic changes measured with implanted miniature telemetry blood pressure transmitters. In comparison, only 21 samples were within the curve range of 2 to 1000 ng/ml from a HILIC–MS/MS method, which limited useful injection volume to 5 µl.