Quantification and application of a liquid chromatography–tandem mass spectrometric method for the determination of WKYMVm peptide in rat using solid‐phase extraction

A liquid chromatographic–electrospray ionization–time‐of‐flight/mass spectrometric (LC‐ESI‐TOF/MS) method was developed and applied for the determination of WKYMVm peptide in rat plasma to support preclinical pharmacokinetics studies. The method consisted of micro‐elution solid‐phase extraction (SPE) for sample preparation and LC‐ESI‐TOF/MS in the positive ion mode for analysis. Phenanthroline (10 mg/mL) was added to rat blood immediately for plasma preparation followed by addition of trace amount of 2 m hydrogen chloride to plasma before SPE for stability of WKYMVm peptide. Then sample preparation using micro‐elution SPE was performed with verapamil as an internal standard. A quadratic regression (weighted 1/concentration²), with the equation y = ax² + bx + c was used to fit calibration curves over the concentration range of 3.02–2200 ng/mL for WKYMVm peptide. The quantification run met the acceptance criteria of ±25% accuracy and precision values. For quality control samples at 15, 165 and 1820 ng/mL from the quantification experiment, the within‐run and the between‐run accuracy ranged from 92.5 to 123.4% with precision values ≤15.1% for WKYMVm peptide from the nominal values. This novel LC‐ESI‐TOF/MS method was successfully applied to evaluate the pharmacokinetics of WKYMVm peptide in rat plasma.     

A sensitive and selective method for the quantitative analysis of miglitol in rat plasma using unique solid‐phase extraction coupled with liquid chromatography–tandem mass spectrometry

A sensitive, selective and robust liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed for the quantification of miglitol in rat plasma. The sample preparation procedures involved protein precipitation and unique solid‐phase extraction, which efficiently removed sources of ion suppression and column degradation interference present in the plasma. Chromatographic separation was achieved on an amide column using 10 mmol/L CH₃COONH₄ and CH₃CN:CH₃OH (90:10, v/v) as the mobile phase under gradient conditions. Detection was performed using tandem mass spectrometry equipped with an electrospray ionization interface in positive ion mode.The selected reaction monitoring transitions for miglitol and a stable isotope‐labeled internal standard were m/z 208 → m/z 146 and m/z 212 → m/z 176, respectively. The correlation coefficients of the calibration curves ranged from 0.9984 to 0.9993 over a concentration range of 0.5–100 ng/mL plasma. The quantification limit of the proposed method was more than 10 times lower than those of previously reported LC‐MS/MS methods. The novel method was successfully validated and applied to a pharmacokinetic study in rats. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly sensitive determination of tetrabromobisphenol A and bisphenol A in environmental water samples by solid‐phase extraction and liquid chromatography‐tandem mass spectrometry

Using bamboo‐activated charcoal as SPE adsorbent, a novel SPE method was developed for the sensitive determination of tetrabromobisphenol A and bisphenol A in environmental water samples by rapid‐resolution LC‐ESI‐MS/MS. Important parameters influencing extraction efficiency, including type of eluent, eluent volume, sample pH, volume and flow rate, were investigated and optimized. Under the optimal extraction conditions (eluent: 8 mL methanol, pH: 7; flow rate: 4 mL/min; sample volume: 100 mL), low LODs (0.01–0.02 ng/mL), good repeatability (6.2–8.3%) and wide linearity range (0.10–10 ng/mL) were obtained. Satisfied results were achieved when the proposed method was applied to determine the two target compounds in real‐world environmental water samples with spiked recoveries over the range of 80.5–119.8%. All these facts indicate that trace determination of tetrabromobisphenol A and bisphenol A in real‐world environmental water samples can be realized by bamboo‐activated charcoal SPE‐rapid resolution‐LC‐ESI‐MS/MS.     

Simultaneous determination of cotinine and trans‐3‐hydroxycotinine in urine by automated solid‐phase extraction using gas chromatography–mass spectrometry

A gas chromatography–mass spectrometry method was developed and validated for the simultaneous automated solid‐phase extraction and quantification of cotinine and trans‐3‐hydroxycotinine in human urine. Good linearity was observed over the concentration ranges studied (R² > 0.99). The limit of quantification was 10 ng/mL for both analytes. The limits of detection were 0.06 ng/mL for cotinine (COT) and 0.02 ng/mL for trans‐3‐hydroxycotinine (OH‐COT). Accuracy for COT ranged from 0.98 to 5.28% and the precision ranged from 1.24 to 8.78%. Accuracy for OH‐COT ranged from ?2.66 to 3.72% and the precision ranged from 3.15 to 7.07%. Mean recoveries for cotinine and trans‐3‐hydroxycotinine ranged from 77.7 to 89.1%, and from 75.4 to 90.2%, respectively. This analytical method for the simultaneous measurement of cotinine and trans‐3‐hydroxycotinine in urine will be used to monitor tobacco smoking in pregnant women and will permit the usefulness of trans‐3‐hydroxycotinine as a specific biomarker of tobacco exposure to be determined. © 2014 The Authors. Biomedical Chromatography published by John Wiley & Sons Ltd.     

Determination of chemotherapeutic agents in fish and shellfish by matrix solid‐phase dispersion and liquid chromatography‐tandem mass spectrometry

Chemicals are widely used in aquaculture and one of the main recipients of these analytes is the aquatic environment. The aim of this work was to develop and validate a simple and sensitive method for the determination of multiclass chemotherapeutic agents in farmed fish and shellfish using matrix solid‐phase dispersion and liquid chromatography‐tandem mass spectrometry. Residues of azamethiphos, three avermectins, two carbamates, and two benzoylureas were extracted from samples using silica gel as clean‐up adsorbent and 0.5% acetic acid in acetonitrile as elution solvent. The extraction conditions were investigated and optimized using an experimental design. Mass spectrometry detection was carried out in positive electrospray ionization mode with multiple‐reaction monitoring scan (except for benzoylurea family). Matrix‐matched standards were used for the drugs quantification. Good linearity (R² ≥ 0.996) was observed in the range of 5–500 μg kg^?1. Limits of detection were in the range of 1.5–3.7 μg kg^?1. Recoveries from salmon samples spiked with veterinary drugs were in the range 84.9–118%. Precision was satisfactory since relative standard deviations were lower than 10.6%. The method can be successfully applied for the analysis of fish and shellfish from aquaculture.     

Simultaneous determination of peimine and peiminine in rat plasma by LC‐ESI‐MS employing solid‐phase extraction

A simple and reliable LC‐ESI‐MS method for the determination of peimine and peiminine in rat plasma was developed for the first time. The method was proven to be specific and sensitive by carrying out validation. The analytes were extracted from rat plasma via solid‐phase extraction on Waters Oasis MCX cartridges. Chromatography separation was achieved on a C₁₈ column using 10 mM ammonium acetate (adjusted to pH 3.0 with glacial acetic acid)–acetonitrile (85:15, v/v) as mobile phase. The linear range was 1–100 ng/mL for peimine and peiminine. Intra‐ and inter‐day precisiond were less than 10%. Accuracies were within 85–115% of their nominal concentrations. The limit of quantification was 1 ng/mL for both analytes. The developed assay was successfully applied to pharmacokinetic study of peimine and peiminine in rats orally administered the alkaloids extracts from Bulbus Fritillariae, demonstrating a possible broader spectrum of applications of this method. Copyright © 2009 John Wiley & Sons, Ltd.     

Magnetic dispersive solid‐phase extraction based on modified magnetic nanoparticles for the detection of cocaine and cocaine metabolites in human urine by high‐performance liquid chromatography–mass spectrometry

An easy‐to‐handle magnetic dispersive solid‐phase extraction procedure was developed for preconcentration and extraction of cocaine and cocaine metabolites in human urine. Divinyl benzene and vinyl pyrrolidone functionalized silanized Fe₃O₄ nanoparticles were synthesized and used as adsorbents in this procedure. Scanning electron microscopy, vibrating sample magnetometry, and infrared spectroscopy were employed to characterize the modified adsorbents. A high‐performance liquid chromatography with mass spectrometry method for determination of cocaine and its metabolites in human urine sample has been developed with pretreatment of the samples by magnetic dispersive solid‐phase extraction. The obtained results demonstrated the higher extraction capacity of the prepared nanoparticles with recoveries between 75.1 to 105.7% and correlation coefficients higher than 0.9971. The limits of detection for the cocaine and cocaine metabolites were 0.09–1.10 ng/mL. The proposed magnetic dispersive solid‐phase extraction method provided a rapid, environmentally friendly and magnetic stuff recyclable approach and it was confirmed that the prepared adsorbents material was a kind of highly effective extraction materials for the trace cocaine and cocaine metabolites analyses in human urine.     

On‐line solid‐phase extraction for liquid chromatography–mass spectrometry analysis of pesticides

Public concern about pesticides in food and water has increased dramatically in the last two decades. In order to guarantee consumers’ health and safety, analytical methods that could provide fast and reliable answers without compromising accuracy and precision are required. Sample treatment is probably the most tedious and time‐consuming step in many analytical procedures and, despite the significant advances in chromatographic separations and mass spectrometry techniques, sample treatment is still one of the most important parts of the analytical process for achieving good analytical results. Therefore, over the last years, considerable efforts have been made to simplify the stage and to develop fast, accurate, and robust methods that allow the determination of a wide range of pesticides without compromising the integrity of the extraction process. This review article intends to give a short overview of recently developed on‐line solid‐phase extraction, preconcentration, and clean‐up procedures for the determination of pesticides in complex matrices by liquid chromatography–mass spectrometry techniques.     

Validation and application of a liquid chromatography‐tandem mass spectrometric method for the determination of GDC‐0152 in human plasma using solid‐phase extraction

A liquid chromatography–tandem mass spectrometric (LC‐MS/MS) method was developed and validated for the determination of GDC‐0152 in human plasma to support clinical development. The method consisted of a solid‐phase extraction for sample preparation and LC‐MS/MS analysis in the positive ion mode using TurboIonSpray^TM for analysis. d₇‐GDC‐0152 was used as the internal standard. A linear regression (weighted 1/concentration²) was used to fit calibration curves over the concentration range of 0.02–10.0 ng/mL for GDC‐0152. There were no endogenous interference components in the blank human plasma tested. The accuracy at the lower limit of quantitation was 99.3% with a precision (%CV) of 13.9%. For quality control samples at 0.0600, 2.00 and 8.00 ng/mL, the between‐run %CV was ≤8.64. Between‐run percentage accuracy ranged from 98.2 to 99.6%. GDC‐0152 was stable in human plasma for 363 days at ?20°C and for 659 days at ?70°C storage. GDC‐0152 was stable in human plasma at room temperature for up to 25 h and through three freeze–thaw cycles. In whole blood, GDC‐0152 was stable for 12 h at 4°C and at ambient temperature. This validated LC‐MS/MS method for determination of GDC‐0152 was used to support clinical studies. Copyright © 2012 John Wiley & Sons, Ltd.     

On‐line microdialysis coupled solid‐phase extraction to decrease matrix interference in the HPLC analysis of urinary ketamine and its metabolites

A microdialysis sampling (MDS) on‐line SPE (MDS/SPE) has been applied to redeem the detection after dilution to decrease matrix interference in the analysis of ketamine (K) and its two main metabolites, norketamine (NK) and dehydronorketamine (DHNK) in urine by HPLC. After being filtrated, diluted and adjusting the pH, K and its metabolites in the diluted sample solution were collected through MDS and then trapped on an on‐line SPE for HPLC analysis. The optimal conditions for MDS/SPE were investigated and then applied to real sample analysis. Experimental results indicated that the MDS/SPE by using regenerated cellulose hollow fiber (8‐cm length) and 1 mM sulfuric acid as the perfusate at 20 μL/min flow‐rate to collect analytes from 100‐fold diluted urine sample (20 mL at pH 6.0), and then having been trapped in octadecyl‐modified silica phase SPE for 30 min, offered the optimum efficiency. The concentration levels of 41, 42 and 28% (m/m) for K, NK and DHNK, respectively, in urine were redeemed for determination. The detection limits were 0.38, 0.33 and 0.34 ng/mL (in 100‐fold diluted sample) for K, NK and DHNK, respectively. The method provides a very simple, inexpensive and eco‐friendly procedure to determine K, NK and DHNK in urine.     

Magnetic solid‐phase extraction or dispersive liquid–liquid microextraction for pyrethroid determination in environmental samples

The determination of 15 pyrethroids in soil and water samples was carried out by gas chromatography with mass spectrometry. Compounds were extracted from the soil samples (4 g) using solid–liquid extraction and then salting‐out assisted liquid–liquid extraction. The acetonitrile phase obtained (0.8 mL) was used as a dispersant solvent, to which 75 μL of chloroform was added as an extractant solvent, submitting the mixture to dispersive liquid–liquid microextraction. For the analysis of water samples (40 mL), magnetic solid‐phase extraction was performed using nanocomposites of magnetic nanoparticles and multiwalled carbon nanotubes as sorbent material (10 mg). The mixture was shaken for 45 min at room temperature before separation with a magnet and desorption with 3 mL of acetone using ultrasounds for 5 min. The solvent was evaporated and reconstituted with 100 μL acetonitrile before injection. Matrix‐matched calibration is recommended for quantification of soil samples, while water samples can be quantified by standards calibration. The limits of detection were in the range of 0.03–0.5 ng/g (soil) and 0.09–0.24 ng/mL (water), depending on the analyte. The analyzed environmental samples did not contain the studied pyrethroids, at least above the corresponding limits of detection.     

Solid‐phase extraction and analysis of paroxetine in human plasma by ultra performance liquid chromatography–electrospray ionization mass spectrometry

A rapid, sensitive and rugged solid‐phase extraction ultra performance liquid chromatography tandem mass spectrometry (UPLC‐MS/MS) method was developed for determination of paroxetine in human plasma. The procedure for sample preparation includes simple SPE extraction procedure coupled with Hypersil Gold C₁₈ column (100 mm ? 2.1 mm, i.d., 1.9 μm) with isocratic elution at a flow‐rate of 0.350 mL/min and fluoxetine was used as the internal standard. The analysis was performed on a triple‐quadrupole tandem mass spectrometer by multiple reactions monitoring mode via electrospray ionization. Using 500 μL plasma, the methods were validated over the concentration range 0.050–16.710 ng/mL for paroxetine, with a lower limit of quantification of 0.050 ng/mL. The intra‐ and inter‐day precision and accuracy of the quality control samples were within 10.0%. The recovery was 69.2 and 74.4% for paroxetine and fluoxetine respectively. Total run time was only 1.9 min. The method was highly reproducible and gave peaks with excellent chromatography properties. Copyright © 2009 John Wiley & Sons, Ltd.     

Development of magnetic octadecylsilane particles as solid‐phase extraction adsorbent for the determination of fat‐soluble vitamins in fruit juice‐milk beverage by capillary liquid chromatography

A sensitive, fast and simple method based on magnetic octadecylsilane particles was developed for the extraction of three fat‐soluble vitamins followed by capillary LC (CLC) analysis with UV detection. Magnetic octadecylsilane particles were prepared based on three‐step reactions including co‐precipitation, sol‐gel polymerization and alkylation. The characterization of the prepared product was studied by scanning electron microscope and Fourier‐transform infrared spectrometry. The particles were used as magnetic SPE adsorbent for the extraction of fat‐soluble vitamins in fruit juice‐milk beverage. The extraction condition and efficiency of the particles for fat‐soluble vitamins were investigated. By coupling magnetic SPE with capillary LC with UV detection, low concentrations of fat‐soluble vitamins in fruit juice‐milk beverage can be detected without the interference from other substances in the sample matrix.     

Ultrapreconcentration and determination of organophosphorus pesticides in water by solid‐phase extraction combined with dispersive liquid–liquid microextraction and high‐performance liquid chromatography

Solid‐phase extraction coupled with dispersive liquid–liquid microextraction was developed as an ultra‐preconcentration method for the determination of four organophosphorus pesticides (isocarbophos, parathion‐methyl, triazophos and fenitrothion) in water samples. The analytes considered in this study were rapidly extracted and concentrated from large volumes of aqueous solutions (100 mL) by solid‐phase extraction coupled with dispersive liquid–liquid microextraction and then analyzed using high performance liquid chromatography. Experimental variables including type and volume of elution solvent, volume and flow rate of sample solution, salt concentration, type and volume of extraction solvent and sample solution pH were investigated for the solid‐phase extraction coupled with dispersive liquid–liquid microextraction with these analytes, and the best results were obtained using methanol as eluent and ethylene chloride as extraction solvent. Under the optimal conditions, an exhaustive extraction for four analytes (recoveries >86.9%) and high enrichment factors were attained. The limits of detection were between 0.021 and 0.15 μg/L. The relative standard deviations for 0.5 μg/L of the pesticides in water were in the range of 1.9–6.8% (n = 5). The proposed strategy offered the advantages of simple operation, high enrichment factor and sensitivity and was successfully applied to the determination of four organophosphorus pesticides in water samples.     

Fast determination of 14 mycotoxins in chestnut by dispersive solid‐phase extraction coupled with ultra high performance liquid chromatography‐tandem mass spectrometry

A dispersive solid‐phase extraction coupled with ultra high performance liquid chromatography with tandem mass spectrometry method was developed and validated for the simultaneous determination of T‐2 toxin, penicillic acid, fumonisins B₁, B₂, and B₃, aflatoxins B₁, B₂, G₁, and G₂, ochratoxin A, deoxynivalenol, 3‐acetyldeoxynivalenol, 15‐acetyldeoxynivalenol, and zearalenone in chestnut samples. The method was used to analyze 136 samples obtained from Shandong province in China. The mycotoxins were extracted using a dispersive solid‐phase extraction method and cleaned using an improved quick, easy, cheap, effective, rugged, and safe approach. The mycotoxins were then detected using a triple‐quadrupole mass spectrometer. The limits of detection and quantification ranged from 0.02 to 1 and 0.1 to 2 μg/kg, respectively. The recovery rates ranged from 74.2 to 109.5%, with relative standard deviations below 15%. A total of 71 samples were contaminated with seven mycotoxins at concentrations ranging from 1.2 to 105.5 μg/kg, with a number of samples exceeding the maximum limits set in the European regulations for mycotoxins in unprocessed chestnuts.     

Combination of dispersive solid‐phase extraction and salting‐out homogeneous liquid–liquid extraction for the determination of organophosphorus pesticides in cereal grains

A new analytical method for the determination of organophosphorus pesticides in cereal samples was developed by combining dispersive SPE (d‐SPE) and salting‐out homogeneous liquid–liquid extraction (SHLLE). The pesticides were first extracted from cereal grains with acetonitrile, followed by d‐SPE cleanup. A 2 mL aliquot of the extract was then added to a centrifuge tube containing 9.2 mL water and 3.3 g NaCl for SHLLE. Analysis of the extract was carried out by gas chromatography coupled with flame photometric detection. The d‐SPE procedure effectively provides the necessary cleanup of the extract while SHLLE is used as an efficient concentration technique. Experimental parameters influencing the extraction efficiency including amounts of added water and salt were investigated. Recovery studies were carried out at three fortification levels, yielding recoveries in the range of 57.7–98.1% with the RSD from 3.7 to 10.9%. The reported limits of determination obtained from this study were 1 μg/kg, which is better than the conventional methods. In the analysis of 40 wheat and corn samples taken from Beijing suburbs, only two wheat samples have chlorpyrifos residue over the limits of determination.     

Determination of rifampicin in human plasma by high‐performance liquid chromatography coupled with ultraviolet detection after automatized solid–liquid extraction

A precise and accurate high‐performance liquid chromatography (HPLC) quantification method of rifampicin in human plasma was developed and validated using ultraviolet detection after an automatized solid‐phase extraction. The method was validated with respect to selectivity, extraction recovery, linearity, intra‐ and inter‐day precision, accuracy, lower limit of quantification and stability. Chromatographic separation was performed on a Chromolith RP₈ column using a mixture of 0.05 m acetate buffer pH 5.7–acetonitrile (35:65, v/v) as mobile phase. The compounds were detected at a wavelength of 335 nm with a lower limit of quantification of 0.05 mg/L in human plasma. Retention times for rifampicin and 6,7‐dimethyl‐2,3‐di(2‐pyridyl) quinoxaline used as internal standard were respectively 3.77 and 4.81 min. This robust and exact method was successfully applied in routine for therapeutic drug monitoring in patients treated with rifampicin.     

Salting‐out‐assisted liquid–liquid extraction with acetonitrile for the determination of trimetazidine in rat plasma using liquid chromatography–mass spectrometry

A high‐throughout bioanalytical method based on salting‐out‐assisted liquid/liquid extraction (SALLE) method with acetonitrile and mass spectrometry‐compatible salts followed by LC‐MS/MS analysis of trimetazidine in rat plasma is presented. It required only 50 μL of plasma and allows the use of minimal volumes of organic solvents. The seamless interface of SALLE and LC‐MS eliminated the drying‐down step and the extract was diluted and injected into an LC‐MS/MS system with a cycle time of 2.5 min/sample. The retention times of trimetazidine and IS were approximately 1.1 and 1.7 min, respectively. Calibration curves were linear over the concentration range of 0.1–100 ng/mL, which can be extended to 500 ng/mL by dilution. The intra‐ and inter‐batch precision, accuracy and the relative standard deviation were all <15%. This method was successfully applied to determine trimetazidine concentrations in rat plasma. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation of matrix effects in analysis of estrogen using liquid chromatography–tandem mass spectrometry

Matrix effects of different biological samples, including phosphate‐buffered saline–bovine serum albumin (PBS‐BSA), gelded horse serum, mouse serum, and mouse brain, were investigated for the determination of 17α‐ and β‐estradiol using derivatization with dansyl chloride prior to LC‐MS/MS. Matrix effects were evaluated based on the slopes of regression lines plotted from results obtained in biological matrices versus pure standard solutions. Such plots indicate the enhancement or suppression of signal based on the presence of a particular biological fluid for a particular method. The matrix effects from PBS‐BSA were similar to those of mouse serum. In contrast, analyses performed from horse serum and mouse brain yielded significant ion suppression, especially for 17β‐estradiol. Precipitation during derivatization was observed when pre‐concentrated samples were processed with ethyl acetate as an extraction solvent. This was overcome with the use of methyl tert‐butyl ether; however, matrix effects from this preparation were still present, evidenced by signal suppression and poor linearity in the standard curve. This work affirms that caution should be taken in the transfer of methods for use with different biological matrices, especially in the case where surrogate matrices are necessary for calibration purposes.     

Multiresidue analysis of glucocorticoids in milk by LC–MS/MS with low‐temperature purification and dispersive solid‐phase extraction

A multiresidue method for the determination of 12 glucocorticoids (clobetasol propionate, budesonide, triamcinolone, triamcinolone acetonide, fludrocortisone acetate, flumethasone, beclomethasone, prednisone acetate, 6‐α‐methylprednisolone, hydrocortisone, cortisone, and prednisone) in bovine milk was developed using liquid chromatography with tandem mass spectrometry. Isoflupredone was used as an internal standard. Milk samples were treated with ethyl acetate to extract glucocorticoids and were frozen at −20°C for 6 h to precipitate fat. The extract was dried under nitrogen, and residues were dissolved in an acetonitrile/water solution. A further clean‐up step was used by dispersive solid‐phase extraction, with octadecyl silica and primary secondary amine as the absorbents. The recoveries of glucocorticoids spiked at 0.5, 1.0, 10.0 μg/kg ranged from 75.7 to 117.3%, except for clobetasol propionate and budesonide (16.1–49.5%). The limits of quantification were 0.01–0.5 μg/kg in milk. This method has been successfully applied in real samples. The results demonstrated that this method is simple, robust, and suitable for identification of glucocorticoid residues in milk.