Comparison of tetraethylborate and tetraphenylborate for selenite determination in human urine by gas chromatography mass spectrometry, after headspace solid phase microextraction

Two different derivatizing reagents were tested for the development of a fast and sensitive method for the determination of selenites (Se^IV) in human urine. The reagents were sodium tetraethylborate (NaBEt₄) and tetraphenylborate (NaBPh₄), respectively, and the procedure is based on in situ derivatization of selenites in aqueous medium. Selenite ions are converted to diethylselenide (DESe) or diphenylselenide (DPhSe) and subsequently collected from the headspace by solid phase microextraction using a silica fiber coated with polydimethylsiloxane (HS-SPME). Finally, they are quantitated by GC/MS in SIM mode. Ethylation over phenylation was proved preferable for the headspace extraction because of the higher volatility of the diethyl-derivative of selenites. The optimization of the HS-SPME conditions was performed both in aqueous and urinary solutions. Under the optimum conditions for HS-SPME, the gas chromatographic conditions were also optimized. Between the two alkylation reagents tetraethylborate was proved more efficient and the quantitation was satisfactory. Aqueous certified reference materials were analyzed to evaluate the accuracy of the method. The precision of the method was 4.2% and the calculated detection limit was 0.05 μg L⁻¹ for human urine.     

Liquid‐phase microextraction by solidification of floating organic microdrop and GC‐MS detection of trihalomethanes in drinking water

A simple and sensitive methodology based on liquid‐phase microextraction (LPME) followed by GC‐MS, was developed for the determination of trihalomethanes (THMs) in drinking water. A microdrop of organic solvent was floated on the surface of the aqueous sample and it was agitated for a desired time. Then, the sample vial was cooled by inserting it into an ice bath for 4 min. The solidified solvent was transferred into a suitable vial and immediately melted. The extract was directly injected into the GC. Microextraction efficiency factors were investigated and optimized: 7 μL 1‐undecanol microdrop exposed for 15 min floated on the surface of a 10.0 mL aqueous sample with the temperature of 60°C containing 3 M of NaCl and stirred at 750 rpm. Under the selected conditions, enrichment factors (EFs) up to 482‐fold, LOD of 0.03–0.08 μg/L (S/N = 3) and dynamic linear ranges of 0.10–100 μg/L were obtained. A reasonable repeatability (RSD < 8.6%, n = 8) with satisfactory linearity (r² ? 0.9947) of results illustrated a good performance of the present method. The protocol proved to be rapid, cost‐effective, and is a green procedure for the screening purposes.     

Elimination of Matrix Interferences in GC‐MS Analysis of Pesticides by Entropy Minimization

Gas chromatography‐mass spectrometry (GC‐MS ) is an important analytical technique for the analysis of organophosphorus pesticides in food products. Because of the complex matrices of food products, multiple preprocessing steps are required prior to performing the GC‐MS analysis. Despite that, it is difficult to totally eliminate the interference of complex matrix background. In this work, we introduce an entropy minimization technique that can eliminate the need for comprehensive preprocessing steps to detect organophosphorus pesticides in a fortified orange juice sample. The pure mass spectra and extracted‐ion chromatograms of the pesticides were extracted and reconstructed. The results achieved higher National Institute of Standard and Technology (NIST ) match scores in comparison to the conventional background subtraction technique. Taken together, the entropy minimization technique is capable of providing rapid qualitative and quantitative analyses of complex GC‐MS data. This technique is expected to have great potential for natural products and food analysis applications.     

Rapid determination of bisphenol A in drinking water using dispersive liquid‐phase microextraction with in situ derivatization prior to GC‐MS

This paper described a novel approach for the determination of bisphenol A by dispersive liquid‐phase microextraction with in situ acetylation prior to GC‐MS. In this derivatization/extraction method, 500 μL acetone (disperser solvent) containing 30.0 μL chlorobenzene (extraction solvent) and 30.0 μL acetic anhydride (derivatization reagent) was rapidly injected into 5.00 mL aqueous sample containing bisphenol A and K₂CO₃ (0.5% w/v). Within a few seconds the analyte was derivatized and extracted at the same time. After centrifugation, 1.0 μL of sedimented phase containing enriched analyte was determined by GC‐MS. Some important parameters, such as type and volume of extraction and disperser solvent, volume of acetic anhydride, derivatization and extraction time, amount of K₂CO₃, and salt addition were studied and optimized. Under the optimum conditions, the LOD and the LOQ were 0.01, 0.1 μg/L, respectively. The experimental results indicated that there was linearity over the range 0.1–50 μg/L with coefficient of correlation 0.9997, and good reproducibility with RSD 3.8% (n = 5). The proposed method has been applied for the analysis of drinking water samples, and satisfactory results were achieved.     

Differentiation between weathered kerosene and diesel fuel using automatic thermal desorption‐GC‐MS analysis and the likelihood ratio approach

The identification of various petroleum products, which can be used to set a fire, is one of the tasks of a forensic examination. One of the analytical problems is differentiation of weathered kerosene and diesel fuel samples, analysed with automatic thermal desorption‐GC‐MS technique, because there are only small quantitative differences in their chemical compositions. The presented research showed that the observed differences in the analysed samples of kerosene and a diesel fuel, which were weathered at the time of burning, were systematic and significant. Therefore, it was possible to distinguish them on the basis of information about the relative content of n‐alkanes (C₁₁H₂₄–C₁₅H₃₂) when statistical methods (cluster analysis and likelihood ratio approach) were applied.     

Combined quantification of paclitaxel,docetaxel and ritonavir in human feces and urine using LC‐MS/MS

A combined assay for the determination of paclitaxel, docetaxel and ritonavir in human feces and urine is described. The drugs were extracted from 200 μL urine or 50 mg feces followed by high‐performance liquid chromatography analysis coupled with positive ionization electrospray tandem mass spectrometry. The validation program included calibration model, accuracy and precision, carry‐over, dilution test, specificity and selectivity, matrix effect, recovery and stability. Acceptance criteria were according to US Food and Drug Administration guidelines on bioanalytical method validation. The validated range was 0.5–500 ng/mL for paclitaxel and docetaxel, 2–2000 ng/mL for ritonavir in urine, 2–2000 ng/mg for paclitaxel and docetaxel, and 8–8000 ng/mg for ritonavir in feces. Inter‐assay accuracy and precision were tested for all analytes at four concentration levels and were within 8.5% and <10.2%, respectively, in both matrices. Recovery at three concentration levels was between 77 and 94% in feces samples and between 69 and 85% in urine samples. Method development, including feces homogenization and spiking blank urine samples, are discussed. We demonstrated that each of the applied drugs could be quantified successfully in urine and feces using the described assay. The method was successfully applied for quantification of the analytes in feces and urine samples of patients. Copyright © 2013 John Wiley & Sons, Ltd.     

Rapid determination of natural and synthetic hormones in biosolids and poultry manure by isotope dilution GC–MS/MS

The release of hormones into the environment due to land application of biosolids and manure is a cause of concern for their potential impacts. This paper presents the development of a rapid and sensitive method, based on extraction, for the analysis of 13 hormones in biosolids and poultry manure. A simultaneous derivatization of hydroxyl and ketone groups was carried out for the determination of hormones by GC–MS/MS. The method was validated in three matrices (sewage sludge, manure, and broiler litter). Recoveries from spiked samples at three concentration levels (50, 25, and 10 ng/g) ranged from 76 to 124% with relative SDs ≤ 16%. Method detection limits for the three matrices were in the range of 0.5–3.0 ng/g dry weight. The optimized method was applied to biosolid and poultry manure samples collected in Spain. Only seven of the 13 studied hormones were detected in the different samples. trans‐Androsterone was detected at high levels (up to 3.1 μg/g in biosolid samples). Estrone and estradiol were the two hormones detected at higher levels in layer manure, whereas estrone and 4‐androstene‐3,17‐dione presented the highest levels in broiler litter.     

Improvement of GC‐MS Analysis of Shahrbabak Ziziphora tenuior Essential Oil by Using Multivariate Curve Resolution Approaches

Essential oil of aerial parts of Ziziphora tenuior growing in Shahrbabak in central Iran are isolated by hydrodistillation. Due to complexity of essential oils, there are fundamental problems such as co‐elution in their direct gas chromatography‐mass spectrometry analysis. These problems can result in low similarity matches in MS library search, so that true identification and determination of individual components may fail. In the present work, each component was identified and determined using GC‐MS coupled with multivariate curve resolution (MCR) techniques. In this way, more information along with higher accuracy and precision can be extracted from pure experimental GC‐MS data. The number of identified components found increased from 37 in direct similarity search to 80 in GC‐MS/MCR method. To identify each individual component, similarity search and Kovat's retention index comparison were implemented. The results found showed that pulegone (38.3%), 3′,5′‐dihydroxyacetophenone (22.83%), isomenthone (7.06%), 2‐methyl‐5‐(1‐methylethyl)‐phenol (3.41%), limonene (2.59%) and 2‐acetyl‐4,4‐dimethyl‐cyclopent‐2‐enone (2.49%) were the most abundant components. The reported compounds accounted for 94.39% of total content of the essential oil. A characteristic feature of the Iranian Ziziphora tenuior is the absence of piperitenone in its constituents compared with the oil of other Ziziphora species from Turkey.     

GC‐MS of amaryllidaceous galanthamine‐type alkaloids

Galanthamine‐type alkaloids produced by plants of the Amaryllidaceae family are potent acetylcholinesterase inhibitors. One of them, galanthamine, has been marketed as a hydrobromide salt for the treatment of Alzheimer's disease. In the present work, gas chromatography with electron impact mass spectrometry (GC‐EIMS) fragmentation of 12 reference compounds isolated from various amaryllidaceous plants and identified by spectroscopic methods (1D and 2D nuclear magnetic resonance, circular dichroism, high‐resolution MS (HRMS) and EIMS) was studied by tandem mass spectrometry (GC‐MS/MS) and accurate mass measurements (GC‐HRMS). The studied compounds showed good peak shape and efficient GC separation with a GC‐MS fragmentation pattern similar to that obtained by direct insertion probe. With the exception of galanthamine‐N‐oxide and N‐formylnorgalanthamine, the galanthamine‐type compounds showed abundant [M]^+. and [M‐H]⁺ ions. A typical fragmentation pattern was also observed, depending on the substituents of the skeleton. Based on the fragmentation pathways of reference compounds, three other galanthamine‐type alkaloids, including 3‐O‐(2′‐butenoyl)sanguinine, which possesses a previously unelucidated structure, were identified in Leucojum aestivum ssp. pulchelum, a species endemic to the Balearic islands. GC‐MS can be successfully applied to Amaryllidaceae plant samples in the routine screening for potentially new or known bioactive molecules, chemotaxonomy, biodiversity and identification of impurities in pharmaceutical substances. Copyright © 2012 John Wiley & Sons, Ltd.     

GC–MS/MS method for the quantification of α‐cedrene in rat plasma and its pharmacokinetic application

α‐Cedrene is a pharmacologically active ingredient isolated from the essential oil of cedar. A selective and sensitive GC–MS/MS method was developed for the quantification of α‐cedrene in rat plasma for the first time. α‐Cedrene was extracted from rat plasma using ethyl acetate at neutral pH. The analytes were determined in selective reaction monitoring mode using MS/MS: m/z 204.3→119.0 for α‐cedrene and m/z 146.0→111.0 for 1,4‐dichlorobenzene (internal standard). The standard curve was linear (r² ≥ 0.995) over the concentration ranges of 5–800 ng/mL. The lower limit of quantification was 5 ng/mL using 50 μL of rat plasma. The coefficient of variation and relative error for intra‐ and interassays at four quality control levels were 3.1–13.9% and ?4.0–2.6%, respectively. The stability of processing (freeze–thaw, long‐term storage at ?80°C, and short‐term storage at room temperature) and chromatography (reinjection) was shown to be of insignificant effect. The present method was applied successfully to the pharmacokinetic study of α‐cedrene after its intravenous (10 mg/kg) and oral (25 mg/kg) administration in male Sprague‐Dawley rats.     

Derivatization coupled to headspace programmed‐temperature vaporizer gas chromatography with mass spectrometry for the determination of amino acids: Application to urine samples

A new method based on headspace programmed‐temperature vaporizer gas chromatography with mass spectrometry has been developed and validated for the determination of amino acids (alanine, sarcosine, ethylglycine, valine, leucine, and proline) in human urine samples. Derivatization with ethyl chloroformate was employed successfully to determine the amino acids. The derivatization reaction conditions as well as the variables of the headspace sampling were optimized. The existence of a matrix effect was checked and the analytical characteristics of the method were determined. The limits of detection were 0.15–2.89 mg/L, and the limits of quantification were 0.46–8.67 mg/L. The instrumental repeatability was 1.6–11.5%. The quantification of the amino acids in six urine samples from healthy subjects was performed with the method developed with the one‐point standard additions protocol, with norleucine as the internal standard.     

Metabolic profile of glyburide in human liver microsomes using LC‐DAD‐Q‐TRAP‐MS/MS

The sulfonylurea urea drug glyburide (glibenclamide) is widely used for the treatment of diabetes milletus and gestational diabetes. In previous studies monohydroxylated metabolites were identified and characterized for glyburide in different species, but the metabolite owing to the loss of cyclohexyl ring was identified only in mouse. Glyburide upon incubation with hepatic microsomes resulted in 10 metabolites for human. The current study identifies new metabolites of glyburide along with the hydroxylated metabolites that were reported earlier. The newly identified drug metabolites are dihydroxylated metabolites, a metabolite owing to the loss of cyclohexyl ring and one owing to hydroxylation with dehydrogenation. Among the 10 identified metabolites, there were six monohydroxylated metabolites, one dihydroxylated metabolite, two metabolites owing to hydroxylation and dehydrogenation, and one metabolite owing to the loss of cyclohexyl ring. New metabolites of glyburide were identified and characterized using liquid chromatography–diode array detector–quadruple‐ion trap–mass spectrometry/mass spectrometry (LC‐DAD‐Q‐TRAP‐MS/MS). An enhanced mass scan–enhanced product ion scan with information‐dependent acquisition mode in a Q‐TRAP‐MS/MS system was used to characterize the metabolites. Liquid chromatography with diode array detection was used as a complimentary technique to confirm and identify the metabolites. Metabolites formed in higher amounts were detected in both diode array detection and mass spectrometry detection. Copyright © 2012 John Wiley & Sons, Ltd.     

Assessment of the matrix effect on the headspace solid-phase microextraction (HS-SPME) analysis of chlorophenols in wines

In this paper, we propose a comparative study to check the matrix effect on the extraction of three chlorophenols, 2,4,6-trichlorophenol (TCP), 2,3,4,6-tetrachlorophenol and pentachlorophenol, direct precursors of 2,4,6-trichloroanisole, in synthetic and commercial wines (white and red wines). A rapid, simple and sensitive methodology based on solid-phase microextraction (SPME) and GC with electron capture detection (GC-ECD) and mass spectrometric detection (GC-MS) was developed and the variables affecting the extraction process (temperature, time and salt content) were examined employing a factorial design at two levels. Since GC-ECD does not allow the clear identification of target analytes in white wine, owing to overlapped interferences, GC-MS/MS was used for subsequent examinations. Calibration curves were constructed in synthetic, white and red wine. Significant differences between the slopes of synthetic and red wine, with the exception of TCP, were observed. Analytical parameters were evaluated and satisfactory results were obtained, showing the usefulness of the headspace SPME (HS-SPME) method for determining chlorophenolic compounds in wines.     

Direct determination of pregabalin in human urine by nonaqueous CE‐TOF‐MS

Determination of pregabalin in urine samples was carried out by nonaqueous CE with TOF‐MS via ESI, with a mixture of 10 mM ammonium formate and 0.05% acetic acid in methanol. By using TOF‐MS, accurate mass information was obtained, thus causing a great improvement in qualitative ability. In order to avoid ionic suppression, urine samples dilution 1:10 was used. This was the only treatment to urine samples before the injection. Despite this dilution, the detection limit was as low as 0.03 μg/mL for pregabalin. The method was validated with respect to accuracy, precision, and linearity, LOD, and LOQ. This method was applied to the analysis of urine samples from seven different cancer patients undergoing treatment with pregabalin. The developed method may find wide application for the routine determination of pregabalin in biological samples in order to establish a more efficient and safe dosage.     

Multivariate analysis of the volatile components in tobacco based on infrared‐assisted extraction coupled to headspace solid‐phase microextraction and gas chromatography‐mass spectrometry

A novel infrared‐assisted extraction coupled to headspace solid‐phase microextraction followed by gas chromatography with mass spectrometry method has been developed for the rapid determination of the volatile components in tobacco. The optimal extraction conditions for maximizing the extraction efficiency were as follows: 65 μm polydimethylsiloxane‐divinylbenzene fiber, extraction time of 20 min, infrared power of 175 W, and distance between the infrared lamp and the headspace vial of 2 cm. Under the optimum conditions, 50 components were found to exist in all ten tobacco samples from different geographical origins. Compared with conventional water‐bath heating and nonheating extraction methods, the extraction efficiency of infrared‐assisted extraction was greatly improved. Furthermore, multivariate analysis including principal component analysis, hierarchical cluster analysis, and similarity analysis were performed to evaluate the chemical information of these samples and divided them into three classifications, including rich, moderate, and fresh flavors. The above‐mentioned classification results were consistent with the sensory evaluation, which was pivotal and meaningful for tobacco discrimination. As a simple, fast, cost‐effective, and highly efficient method, the infrared‐assisted extraction coupled to headspace solid‐phase microextraction technique is powerful and promising for distinguishing the geographical origins of the tobacco samples coupled to suitable chemometrics.     

Determination of avoparcin in animal tissues and milk using LC‐ESI‐MS/MS and tandem‐SPE

A highly sensitive and selective method using LC‐ESI‐MS/MS and tandem‐SPE was developed to detect trace amounts of avoparcin (AV) antibiotics in animal tissues and milk. Data acquisition using MS/MS was achieved by applying multiple reaction monitoring of the product ions of [M + 3H]³⁺ and the major product ions of AV‐α and ‐β at m/z 637 → 86/113/130 and m/z 649 → 86/113/130 in ESI(+) mode. The calculated instrumental LODs were 3 ng/mL. The sample preparation was described that the extraction using 5% TFA and the tandem‐SPE with an ion‐exchange (SAX) and InertSep C18‐A cartridge clean‐up enable us to determine AV in samples. Ion suppression was decreased by concentration rates of each sample solution. These SPE concentration levels could be used to detect quantities of 5 ppb (milk), 10 ppb (beef), and 25 ppb (chicken muscle and liver). The matrix matching calibration graphs obtained for both AV‐α (r >0.996) and ‐β (r >0.998) from animal tissues and milk were linear over the calibration ranges. AV recovery from samples was higher than 73.3% and the RSD was less than 12.0% (n = 5).     

Relationships between structure,ionization profile and sensitivity of exogenous anabolic steroids under electrospray ionization and analysis in human urine using liquid chromatography–tandem mass spectrometry

The relationships between the ionization profile, sensitivity, and structures of 64 exogenous anabolic steroids (groups I–IV) was investigated under electrospray ionization (ESI) conditions. The target analytes were ionized as [M + H]⁺ or [M + H–nH₂O]⁺ in the positive mode, and these ions were used as precursor ions for selected reaction monitoring analysis. The collision energy and Q3 ions were optimized based on the sensitivity and selectivity. The limits of detection (LODs) were 0.05–20 ng/mL for the 64 steroids. The LODs for 38 compounds, 14 compounds and 12 compounds were in the range of 0.05–1, 2–5 and 10–20 ng/mL, respectively. Steroids including the conjugated keto‐functional group at C3 showed good proton affinity and stability, and generated the [M + H]⁺ ion as the most abundant precursor ion. In addition, the LODs of steroids using the [M + H]⁺ ion as the precursor ion were mostly distributed at low concentrations. In contrast, steroids containing conjugated/unconjugated hydroxyl functional groups at C3 generated [M + H ? H₂O]⁺ or [M + H ? 2H₂O]⁺ ions, and these steroids showed relatively high LODs owing to poor stability and multiple ion formation. An LC‐MS/MS method based on the present ionization profile was developed and validated for the determination of 78 steroids (groups I–V) in human urine. Copyright © 2015 John Wiley & Sons, Ltd.     

A novel liquid–liquid extraction and stable isotope dilution NCI‐GC‐MS method for quantitation of agmatine in postmortem brain cortex

The group of biologically important amines includes putrescine, spermidine and spermine, as well as agmatine, which is a guanidino‐amine. There is considerable evidence supporting a role of these amines in the etiology and pathology of mental disorders. We have previously developed a quantitative GC‐MS method for simultaneous measurement of three major polyamines to support our studies linking polyamines to mental disorders. However, a unique GC‐MS method is required for agmatine. To efficiently extract agmatine from postmortem brain tissues, we developed an isopropanol based liquid–liquid extraction protocol using potassium carbonate as a salting‐out agent which showed a much greater recovery than n‐butanol used in earlier methods. The GC‐MS analysis employed hexafluoroacetylacetone as derivatization reagent and was carried out using negative chemical ionization with total ion and selected ion monitoring. ¹⁵N₄‐Agmatine was synthesized from ¹⁵N₄‐L ‐arginine and used as internal standard in a conventional stable isotope dilution assay. This method accurately measures the level of agmatine from very small quantities (10–20 mg) of postmortem brain tissue, with a quantitation limit down to 1 ng/g of wet tissue. The limit of detection is 0.01 ng/g of wet tissue. Copyright © 2010 John Wiley & Sons, Ltd.     

Cryogenic modulation fast GC × GC–MS using a 10 m microbore column combination: Concept,method optimization,and application

The present research is based on the concept of using a 10 m × 0.1 mm id column for cryogenic‐modulation fast comprehensive two‐dimensional gas chromatography with quadrupole mass spectrometry. Specifically, an 8.9 m × 0.1 mm id low‐polarity column was used as the first dimension, and a 1.1 m × 0.1 mm id medium‐polarity column was used as the second dimension. The main scope of the investigation was to develop a high peak‐capacity method, with an analysis time of approximately 10 min. Various aspects related to method optimization are discussed, as well as separation parameters such as peak capacity (in each dimension, and as a total value), first‐dimension sample capacity, peak widths, modulation ratio, sensitivity enhancement, and number of spectra per peak. The fast approach was evaluated in applications involving a mixture of cosmetic allergens and a sample of perfume. The approach proposed enables high‐resolution separations in a short time (across the C₈–C₂₃ alkane range), as well as a considerable reduction of the consumption of gases for modulation cooling and heating.     

Development of microextraction techniques in combination with GC–MS/MS for the determination of mycotoxins and metabolites in human urine

Simple and highly efficient sample preparation procedures, namely, dispersive liquid–liquid microextraction and salting‐out liquid–liquid extraction for the analysis of ten Fusarium mycotoxins and metabolites in human urine were compared. Various parameters affecting extraction efficiency were carefully evaluated. Under optimal extraction conditions, salting‐out liquid–liquid extraction showed a better accuracy (84–96%) and precision (<14%) than dispersive liquid–liquid microextraction. Hence, a multibiomarker method based on salting‐out liquid–liquid extraction followed by gas chromatography with tandem mass spectrometry was proposed. Satisfactory results in terms of validation were achieved. The method resulted in low limits of detection and quantitation within the range of 0.12–4 and 0.25–8 μg/L, respectively. The method accuracy and precision were evaluated at three spiking levels (8, 25 and 100 μg/L) and the recoveries were in a range from 70 to 120% with relative standard deviations lower than 15%. Matrix effect was evaluated and matrix‐matched calibrations were used for quantitation purpose. The developed method was applied in 12 human urine samples as a pilot study before and after sample treatment with β‐glucuronidase before the analysis to quantify the mycotoxin conjugates. Total deoxynivalenol (free + conjugated) was found in 83% of samples at an average concentration in positive samples of 31.6 μg/L.