A new approach to the application of solid phase extraction disks with LC–MS/MS for the analysis of drugs on a 96-well plate format

A review of the modern principles and applications of solid-phase extraction techniques in chromatographic analysis

Analytical processes involving sample preparation, separation, and quantifying analytes in complex mixtures are indispensable in modern-day analysis. Each step is crucial to enriching correct and informative results. Therefore, sample preparation is the critical factor that determines both the accuracy and the time consumption of a sample analysis process. Recently, several promising sample preparation approaches have been made available with environmentally friendly technologies with high performance. As a result of its many advantages, solid-phase extraction (SPE) is practiced in many different fields in addition to the traditional methods. The SPE is an alternative method to liquid–liquid extraction (LLE), which eliminates several disadvantages, including many organic solvents, a lengthy operation time and numerous steps, potential sources of error, and high costs. SPE advanced sorbent technology reorients with various functions depending on the structure of extraction sorbents, including reversed-phase, normal-phase, cation exchange, anion exchange, and mixed-mode. In addition, the commercial SPE systems are disposable. Still, with the continual developments, the restricted access materials (RAM) and molecular imprinted polymers (MIP) are fabricated to be active reusable extraction cartridges. This review will discuss all the theoretical and practical principles of the SPE techniques, focusing on packing materials, different forms, and performing factors in recent and future advances. The information about novel methodological and instrumental solutions in relation to different variants of SPE techniques, solid-phase microextraction (SPME), in-tube solid-phase microextraction (IT-SPME), and magnetic solid-phase extraction (MSPE) is presented. The integration of SPE with analytical chromatographic techniques such as LC and GC is also indicated. Furthermore, the applications of these techniques are discussed in detail along with their advantages in analyzing pharmaceuticals, biological samples, natural compounds, pesticides, and environmental pollutants, as well as foods and beverages.

Bract as a novel extraction phase in thin-film SPME combined with 96-well plate system for the high-throughput determination of estrogens in human urine by liquid chromatography coupled to fluorescence detection

In this study, an environmentally friendly and high-throughput method was developed for the determination of estrone (E1), 17β-estradiol (E2), 17α-ethinylestradiol (EE2) and estriol (E3) in human urine by liquid chromatography-fluorescence detector (HPLC-FLD). A biosorbent (bract) was proposed as extraction phase for Thin-Film SPME combined with 96-well system. The characterization of the biosorbent was performed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The optimizations were carried out through univariate and multivariate approaches with optimal conditions comprised of urine samples diluted 40-fold, liquid desorption performed in methanol and addition of 20% (w/v) of NaCl in the sample. Considering an extraction/desorption cycle using the 96-well plate system, the sample preparation time was 1.7 min per sample, which contributes to the high-throughput of the method proposed. The analytical parameters of merit were determined and satisfactory results were achieved, including limits of detection ranging from 0.3 μg L^-1 for estradiol to 3 μg L^-1 for estrone, while limits of quantification varied from 1 μg L^-1 for estradiol to 10 μg L^-1 for estrone. The correlation coefficients ranged from 0.9947 for estrone to 0.9999 for estriol. The accuracy and intra-assay and intermediate precisions (RSD) were evaluated through extractions in diluted urine samples (40-fold) spiked with each analyte (1, 200 and 400 μg L^-1 for E3; 0.1, 200 and 400 μg L^-1 for E2; 0.5, 200 and 400 μg L^-1 for EE2 and 10, 200 and 400 μg L^-1 for E1). The relative recoveries (n = 3) ranged from 71 to 105%, intra-assay precision (n = 3) varied from 1 to 17% and intermediate precision (n = 9) ranged from 2 to 19%. The method developed can be successfully used for the quantification of estrogens in human urine samples.

Magnetic and electric field assisted electrospun polyamide nanofibers for on-line μ-solid phase extraction and HPLC

The effects of applied magnetic and electric fields on electrospinning were investigated to produce more efficient nanofibers.

Thin-film microextraction coupled to LC-ESI-MS/MS for determination of quaternary ammonium compounds in water samples

The dual nature of the quaternary ammonium compounds, having permanently charged hydrophilic quaternary ammonium heads and long-chain hydrophobic tails, makes the sample preparation step and analysis of these compounds challenging. A high-throughput method based on thin-film solid-phase microextraction (SPME) and liquid chromatography mass spectrometry was developed for simultaneous quantitative analysis of nine benzylic and aliphatic quaternary ammonium compounds. Chromatographic separation and detection of analytes were obtained in reverse-phase mode in 8 min using a triple quadrupole mass spectrometer. Hydrophilic lipophilic balance particle-coated blades were found to be the most suitable among the different coatings tested in terms of recoveries and carryover on the blades. For desorption solvents, 70/30, v/v (A/B) with 0.1 % formic acid (where A is 10 mM ammonium acetate in acetonitrile/water (95/5 , v/v) and B is 0.1 %  (v/v) formic acid in isopropyl alcohol) was shown to be the most efficient solvent for the desorption of the analytes from the SPME sorbent. The SPME method was optimised in terms of extraction, pH, and preconditioning, as well as extraction and desorption times. Optimum conditions were 45 min of extraction time and 15 min of desorption time, all with agitation. The extraction was found to be optimum in a range of pH 6.0 to 8.0, which is consistent with the natural pH of water samples. Wide linear dynamic ranges with the developed method were obtained for each compound, enabling the application of the method for a wide range of concentrations. The developed method was validated according to the Food and Drug Administration criteria. The proposed method is the first SPME-based approach describing the applicability of the high-throughput thin-film SPME in a 96-well system for analysis of such challenging compounds.

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

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

Automated determination of phenolic compounds in wine, berry, and grape samples using 96-blade solid phase microextraction system coupled with liquid chromatography-tandem mass spectrometry

An automated 96-thin-film solid phase microextraction system was optimized for high throughput analysis of phenolic compounds in wine, berry, and grape samples. Liquid chromatography and tandem mass spectrometry methods were optimized and applied for separation and detection of compounds. Evaluation of five different stationary phases showed that polystyrene-divinylbenzene-polyacrylonitrile (PS-DVB-PAN) is the optimum extraction phase for the extraction of phenolic compounds under study. The thin-film PS-DVB-PAN SPME coating provided almost exhaustive extraction recovery for all phenolics compounds under study, except for naringenin with 80% recovery. Extraction efficiency, inter- and intra-day reproducibility, sensitivity, linearity, limit of detection and quantitation, and matrix effect were evaluated. Intra-day and inter-day reproducibility were in the respective range of 4-8 and 7-13% relative standard deviation (RSD) for all eight phenolic compounds. Limits of detection and quantitation of the proposed SPME-LC-MS/MS system for the analysis of analytes under study were found in the range of 0.2-3 and 0.5-10 ng/mL, respectively. Standard addition calibration was applied for the quantitative determination of unknown phenolic compounds from wine, berry, and grape samples. The assessment of matrix effect showed significant reduction of ion suppression/enhancement using SPME method in comparison with that of solvent extraction technique.

Thin-film octadecyl-silica glass coating for automated 96-blade solid-phase microextraction coupled with liquid chromatography-tandem mass spectrometry for analysis of benzodiazepines

A thin-film octadecyl (C18)-silica glass coating was developed as the extraction phase for an automated 96-blade solid-phase microextraction (SPME) system coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Various factors (e.g., sol-gel composition and aging time, coating preparation speed, coating thickness, and drying conditions) affecting the quality of C18-silica glass thin-film coating were studied and optimized. The results showed that the stability and durability of the coating are functions of the coating thickness and drying conditions. Coating thickness is controlled by sol-gel composition, aging time and the withdrawal speed in the dipping method. Automated sample preparation was achieved using a robotic autosampler that enabled simultaneous preparation of 96 samples in a 96-well plate format. Under the optimum SPME conditions the proposed system requires a total of 140 min for preparation of all 96 samples (i.e., 30 min preconditioning, 40 min equilibrium extraction, 40 min desorption and 30 min carry over step). The performance of the C18-silica glass 96-blade SPME system was evaluated for high-throughput analysis of benzodiazepines from phosphate-buffered saline solution (PBS) and human plasma, and the reusability, repeatability, and validity of the system were evaluated. When analysing spiked PBS and human plasma, the inter-blade reproducibility for four benzodiazepines was obtained in the ranges of 4-8% and 9-11% RSD (relative standard deviation), respectively, and intra-blade reproducibility were in the ranges of 3-9% and 8-13% RSD, respectively. The limits of detection and quantitation for plasma analysis were in the ranges of 0.4-0.7 ng/mL and 1.5-2.5 ng/mL for all four analytes.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Dispersive liquid-liquid microextraction combined with high-performance liquid chromatography for the determination of clozapine and chlorpromazine in urine

A simple method has been proposed for the determination of clozapine (CLZ) and chlorpromazine (CPZ) in human urine by dispersive liquid-liquid microextraction (DLLME) in combination with high-performance liquid chromatography-ultraviolet detector (HPLC-UV). All important variables influencing the extraction efficiency, such as pH, types of the extraction solvent and the disperser solvent and their volume, ionic strength and centrifugation time were investigated and optimized. Under the optimal conditions, the limit of detection (LODs) and quantification (LOQs) of the method were 13 and 39 ng/mL for CLZ, and 2 and 6 ng/mL for CPZ, respectively. The relative standard deviations (RSDs) of the targets were less than 5.1% (C=0.100 μg/mL, n=9). Good linear behaviors over the tested concentration ranges were obtained with the values of R (2)>0.999 for the targets. The absolute extraction efficiencies of CLZ and CPZ from the spiked blank urine samples were 98.3% and 97.8%, respectively. The applicability of the technique was validated by analyzing urine samples and the mean recoveries for spiked urine samples ranged from 93.3% to 105.0%. The method was successfully applied for the determination of CLZ and CPZ in real human urine.

Chromatography with higher pressure, smaller particles and higher temperature: a bioanalytical perspective

Recent years have seen widespread use of ultra-high-pressure liquid chromatography (UHPLC) in biological fluids. Most commonly the emphasis is on developing high throughput assay methods to reduce the analysis time and cost. Particle size and temperature are chromatographic parameters that can be changed to improve efficiency and obtain rapid separations. UHPLC and high-temperature liquid chromatography (HTLC) are two techniques that reduce the analysis time by decreasing the size of the column packing material and increasing the column temperature, respectively. Both of these techniques have advantages and limitations. In this article we have summarized the history, theoretical background of UHPLC and HTLC and the various advantages and limitations of sample preparation techniques and the detection systems (mass spectrometry and ultraviolet) used for the bioanalytical assays. In addition, selected bioanalytical applications of the two techniques have been reviewed and tabulated.

Investigation of the effect of the extraction phase geometry on the performance of automated solid-phase microextraction

A new configuration of C(18) thin film extraction phase designed for high sample throughput has been developed and applied to the analysis of benzodiazepines in spiked urine samples using high performance liquid chromatography coupled with tandem mass spectrometry. The high throughput analysis was achieved with the use of a robotic autosampler which enabled parallel analyte extraction in a 96-well plate format. Factors affecting data reproducibility, extraction kinetics, sample throughput, and reliability of the system were investigated and optimized. The intrawell reproducibility was 4.5-7.3%, while interwell reproducibility was 7.0-11% in urine and PBS samples. The limits of detection and quantitation were 0.05-0.15 ng/mL and 0.2-2.0 ng/mL for all analytes, respectively. By comparison with optimized automated multifiber SPME relying on rod geometry, the C(18) thin films showed higher extraction rates (approximate 2-fold increase) and hence higher sample throughput because of the improved configuration and more effective agitation/mass transfer. In addition, this new configuration provided an extraction phase with greater surface area to volume ratio and greater extraction phase volume, which resulted in approximately 2-fold increase in the extraction capacity for diazepam compared with the extractions with automated multifiber SPME rod geometry. The results of this investigation demonstrated the advantages of using thin films to improve extraction kinetics and sensitivity of automated SPME methods for high performance liquid chromatography.