Quantification of 4‐OH‐2,6‐Xylidine and its Conjugates in Human Urine Samples Utilising Microextraction in Packed Syringe On‐line with Liquid Chromatography and Electrospray Tandem Mass Spectrometry (MEPS‐LC‐MS/MS)

Microextraction by packed sorbent

Microextraction by packed sorbent (MEPS) is a miniaturized form of SPE. MEPS can handle small sample volumes and be connected on-line with LC or GC without any modifications. In addition, the MEPS sorbent bed is integrated into an injection syringe and can be used for more than 100 extractions. The key aspect of MEPS is that the solvent volume used for the elution of the analytes is of a suitable order of magnitude to be injected directly into GC or LC systems. MEPS has been used in many research fields such as environmental, biological and food analysis. This article gives an overview of the MEPS technique, including fields of application and common formats.

Solid phase microextraction and related techniques for drugs in biological samples

In drug discovery and development, the quantification of drugs in biological samples is an important task for the determination of the physiological performance of the investigated drugs. After sampling, the next step in the analytical process is sample preparation. Because of the low concentration levels of drug in plasma and the variety of the metabolites, the selected extraction technique should be virtually exhaustive. Recent developments of sample handling techniques are directed, from one side, toward automatization and online coupling of sample preparation units. The primary objective of this review is to present the recent developments in microextraction sample preparation methods for analysis of drugs in biological fluids. Microextraction techniques allow for less consumption of solvent, reagents, and packing materials, and small sample volumes can be used. In this review the use of solid phase microextraction (SPME), microextraction in packed sorbent (MEPS), and stir-bar sorbtive extraction (SBSE) in drug analysis will be discussed. In addition, the use of new sorbents such as monoliths and molecularly imprinted polymers will be presented.

A critical review of microextraction by packed sorbent as a sample preparation approach in drug bioanalysis

Sample preparation is widely accepted as the most labor-intensive and error-prone part of the bioanalytical process. The recent advances in this field have been focused on the miniaturization and integration of sample preparation online with analytical instrumentation, in order to reduce laboratory workload and increase analytical performance. From this perspective, microextraction by packed sorbent (MEPS) has emerged in the last few years as a powerful sample preparation approach suitable to be easily automated with liquid and gas chromatographic systems applied in a variety of bioanalytical areas (pharmaceutical, clinical, toxicological, environmental and food research). This paper aims to provide an overview and a critical discussion of recent bioanalytical methods reported in literature based on MEPS, with special emphasis on those developed for the quantification of therapeutic drugs and/or metabolites in biological samples. The advantages and some limitations of MEPS, as well as its comparison with other extraction techniques, are also addressed herein.

Monolithic packed 96-tips set for high-throughput sample preparation: determination of cyclophosphamide and busulfan in whole blood samples by monolithic packed 96-tips and LC-MS

A monolithic methacrylate packed 96-tips device was used for the extraction of the busulfan and cyclophosphamide in whole blood samples. Using a packed 96-tips set, a 96-well plate could be handled in about 2 min. The key aspect of the monolithic phase is that monolithic material can offer both good extraction capacity and low-back-pressure properties. The validation of the methodology showed that the accuracy values of quality-control samples were between 99 and 113% for busulfan, and between 103 and 110% for cyclophosphamide. The inter-day precision ranged from 7.0 to 12% for busulfan and from 13 to 16% for cyclophosphamide. The standard calibration curves were obtained within the concentration range 5-2000 nm for busulfan and from 10 to 5000 nm for cyclophosphamide in blood samples. The coefficients of determination were ≥0.99.

Rapid screening of drug compounds in urine using a combination of microextraction by packed sorbent and rotating micropillar array electrospray ionization mass spectrometry

RATIONALE

Screening of drugs from urine samples can be non-selective or laborous, using either immunological, gas chromatography/mass spectrometry (GC/MS) or liquid chromatography (LC)/MS methods. Therefore, a rapid screening method for selected drugs in urine sample was developed in a proof-of-principle manner, utilizing simple and fast techniques for both sample treatment and sample analysis.

METHODS

Sample treament of spiked urine samples was performed with microextraction by packed sorbent (MEPS). Five different sorbent materials (C(2), C(8), C(18), M1 (cation exchanger), and Sil (pure silica)) were tested for the MEPS. The sample analysis was performed using a circular microchip with 60 micropillar electrospray ionization (μPESI) tips combined with a mass spectrometer (either a triple-quadrupole or ion-trap mass spectrometer) without any chromatographic step.

RESULTS

The sample treatment/analysis setup was tested using three drug compounds at a concentration of 1  μM. We found that the C(2), C(8) and C(18) sorbents in combination with 96% alkaline methanol as an eluent worked the best. All compounds were easily detected and identified by MS/MS in spiked urine samples. The whole qualitative analytical procedure was rapid as the sample treatment together with the MS analysis took about 5  min per sample.

CONCLUSIONS

A rapid screening method for selected drugs from urine samples was developed, providing adequate selectivity and sensitivity, as well as a short total analysis cycle time. This new method can provide a new alternative for screening purposes, as both the extraction and analysis steps could be totally automatized.

Sample treatment based on extraction techniques in biological matrices

The importance of sample preparation methods as the first stage in bioanalysis is described. In this article, the sample preparation concept and strategies will be discussed, along with the requirements for good sample preparation. The most widely used sample preparation methods in the pharmaceutical industry are presented; for example, the need for same-day rotation of results from large numbers of biological samples in pharmaceutical industry makes high throughput bioanalysis more essential. In this article, high-throughput sample preparation techniques are presented; examples are given of the extraction and concentration of analytes from biological matrices, including protein precipitation, solid-phase extraction, liquid–liquid extraction and microextraction-related techniques. Finally, the potential role of selective extraction methods, including molecular imprinted phases, is considered.

Microextraction by packed sorbent (MEPS): a tutorial

This tutorial provides an overview on a new technique for sample preparation, microextraction by packed sorbent (MEPS). Not only the automation process by MEPS is the advantage but also the much smaller volumes of the samples, solvents and dead volumes in the system. Other significant advantages such as the speed and the simplicity of the sample preparation process are provided. In this tutorial the main concepts of MEPS will be elucidated. Different practical aspects in MEPS are addressed. The factors affecting MEPS performance will be discussed. The application of MEPS in clinical and pre-clinical studies for quantification of drugs and metabolites in blood, plasma and urine will be provided. A comparison between MEPS and other extraction techniques such as SPE, LLE, SPME and SBSE will be discussed.

Microextraction by packed sorbent for LC–MS/MS determination of drugs in whole blood samples

Background: Microextraction by packed sorbent (MEPS) is used as an online sample-preparation method. The determination of local anesthetics lidocaine, ropivacaine and bupivacaine directly in human blood was performed using MEPS online with LC–MS/MS. Results: The range of the calibration curves in whole blood was 10–10000 nmol/l. The lower limit of quantification was set to 10.0 nmol/l. The accuracy of the quality control samples ranged from 85 to 97%. The interday precision of the studied analytes was within the range 1–5%. The regression correlation coefficient (r2) was over 0.995 for all runs. The present method is rapid, reliable and robust and may be used for therapeutic drug monitoring of studied analytes in whole blood. Conclusion: This assay allows the analysis of drugs in human blood directly. Sample preparation is simple and automated. The assay reduced the handling time and the cost, and could handle small volumes of whole blood samples (25 µl).

Quantitative analysis of methadone in human urine samples by microextraction in packed syringe-gas chromatography-mass spectrometry (MEPS-GC-MS)

A method for the simultaneous analysis of methadone in urine samples by microextraction in a packed syringe online with GC-MS (MEPS-GC-MS) is described. The new method reduced the sample handling and the detection limit by two- to seven-fold compared to published methods. Using a quantitation method based on the calculation of analyte concentration by comparison to an internal standard, we were able to measure methadone levels consistent with values reported for healthy individuals. The intra-assay precisions (RSD) of the method using quality control (QC) samples at three different concentration levels were about 11-14% (n = 6). The interassay precisions (RSD) were 11-15% for methadone in urine samples (n = 18). The accuracy varied from 89 to 109% for intra-assay (n = 6), and 97 to 107% for inter-assay (n = 18). The regression correlation coefficients (r(2)) were over 0.99 in all experiments.