GC–ECD Method for Determination of Glucosidically Bound Aroma Precursors in Fresh Tea Leaves

The possibility of using GC–ECD to determine glucosidically bound aroma precursors was investigated. Five β-d-glucopyranosides were derivatized with N-methyl-bis(trifluoroacetamide) (MBTFA) and then determined by GC-ECD, which showed these mono-glycosides (glucosides) could be separated and identified by GC. Repeatability, sensitivity and stability were tested, relative standard deviation (RSD) was in the range of 0.55–5.9%, the limit of detection (LOD) was lower than 10^?3 μg mL^?1, and the standard mixture was stable within 3 days (stored at 4 °C, peak areas RSD < 3%). Application of the developed derivatization and determination method to the fresh tea leaves showed that the glucosides could be accurately quantified (using phenyl β-d-glucopyranoside as internal standard). Because of its high sensitivity, the developed method was suitable for the determination of glucosides in fresh tea leaves.     

Detection of Benzo[a]pyrene in Fried Food by Ultrasound-Assisted Matrix Solid-Phase Dispersion and Isotope Dilution GC–MS

A simple, sensitive and reliable analytical method was developed for the detection of benzo[a]pyrene in fried food using gas chromatography-mass spectrometry with an isotope-labelled internal standard. Samples were directly extracted and purified by the ultrasound-assisted matrix solid-phase dispersion (MSPD) procedure. The simple pretreatment procedures were tested with different absorbents (C18, NH₂, Oasis, and SiO₂). The optimal ultrasonication-assisted MSPD was achieved by MSPD-SiO₂ and sonication for 10 min in an ultrasonic bath. The samples were quantified using benzo[a]pyrene-d₁₂ as the internal standard. An analysis of the samples spiked with different levels of benzo[a]pyrene showed recoveries ranging from 84.6 to 103.2 %, with an RSD of 3.21–8.32 %, depending on the spiking level. This method was thus shown to be suitable for the detection of benzo[a]pyrene in fried food.     

A Validated LC Method for Simultaneous Determination of Three Major Components in Entada phaseoloides

A high performance liquid chromatography method was developed for the simultaneous determination of three major active constituents in Entada phaseoloides, namely phaseoloidin (1), entadamide A (2), entadamide A-β-d-glucopyranoside (3), respectively. The samples were separated on an Aglient Eclipse XDB-C₁₈ column with gradient elution of acetonitrile and 0.3% phosphoric acid (v/v) at a flow rate of 1.0 mL min^?1 and detected at 280 nm. The three target compounds were completely separated within 10 min. All calibration curves showed good linearity (r > 0.9999) within test ranges. The reproducibility was evaluated by intra- and inter-day assays and RSD values were less than 1.04%. The recoveries were between 97.15 and 101.95%. The method was successfully applied to the analysis of three compounds in 22 commercial samples of E. phaseoloides. The results indicated that the developed LC assay was readily utilized as a quality control method for E. phaseoloides.     

Gas Chromatographic Determination of Guanidino Compounds Using Hexafluoroacetylacetone and Ethyl Chloroformate as Derivatizing Reagents

Guanidino compounds guanidine, methylguanidine, guanidinoacetic acid, guanidinobutyric acid, guanidinopropionic acid, and guanidinosuccinic acid after derivatization with hexafluoroacetylacetone and ethyl chloroformate at pH 9 in aqueous phase, eluted, and separated from gas chromatographic column HP-5 (30 m × 0.32 mm id) with film thickness of 0.25 μm at an initial column temperature 90 °C for 2 min, followed by heating rate of 10 °C min^?1 up to 220 °C with nitrogen flow rate of 1 mL min^?1. The detection was by flame ionization detector. The linear calibration ranges of each of guanidino compounds were obtained within 1–10 μg mL^?1, and the limit of detection was within 0.014–0.19 μg mL^?1. The derivatization and gas chromatography elution and separation were repeatable in terms of retention time and peak height/peak area with relative standard deviation (RSD) (n = 4) within 1.7–2.9 % and 1.4–2.8 %, respectively. The method was applied for the determination of guanidino compounds from deproteinized serum of uremic patients and healthy volunteers, and was found in the range below the limit of quantitation (BLOQ) to 1.25 μg mL^?1 with RSD within 1.4–3.6 %, and BLOQ to 0.4 μg mL^?1 with RSD 1.3–3.4 %, respectively. A number of pharmaceutical additives did not effect the determination with RSD within ±3.1 %.     

Comparative Analysis of the Major Constituents in the Traditional Tibetan Medicinal Plants Saussurea laniceps and S. medusa by LC–DAD–MS

Liquid chromatography coupled with diode array detector and electrospray ionization mass spectrometry was developed for the qualitative and quantitative comparison of the main constituents in Saussurea laniceps (SL) and S. medusa (SM), two species of plants used under the name “Xuelianhua” in traditional Tibetan medicine. A method validation including linearity, limit of detection, precision and recovery was performed. The results showed that a good linearity with R ² > 0.99 was achieved, and the limit of detection of the quantified constituents was reported to be between 0.8 and 3.3 ng. The relative standard deviation value was below 3.82% for repeatability, and recovery studies for the quantified compounds were found to be within the range 90.92–103.12%. The unique properties of the present method were evaluated by analyzing twelve related herbal samples including five S. laniceps samples and seven S. medusa samples. Twenty-two compounds including phenolic acids, cumarins, lignanoids and flavonoids were identified by online ESI–MS and by comparison with literature data and standard compounds, and seven of them were quantified by LC–DAD simultaneously. The results demonstrated that the common constituents in the two herbs were protocatechuic acid, syringoside, chlorogenic acid, isoquercitroside, 1,5-dicaffeoylquinic acid, apigenin 7-O-β-d-glucoside, chrysoeriol 7-O-β-d-glucoside, acacetin 7-O-β-d-glucoside, apigenin and chrysoeriol. In the present study, it was found that the characteristic constituents were umbelliferone, scopoletin and their glucosides in S. laniceps, as well as arctiin and arctigenin in S. medusa. It was feasible to choose these characteristic compounds for the quality evaluation as well as chemical authentication of the two related herbs. The results also support discrimination between the two species when using them in folk medicine.     

Activated Carbon Modified with Sodium Dodecyl Sulfonate as a Solid Phase Sorbent for the Separation and Preconcentration of Trace Cadmium in Water Samples with Detection by Electrothermal Atomic Absorption Spectrometry

A novel absorbent was prepared by sodium dodecyl sulfonate (SDS)-modified activated carbon (SDS-AC) and was employed as the microcolumn packing material for separation/preconcentration of trace Cd(II). The method based on Cd(II) was quantitatively retained by SDS-AC sorbent, which entailed cation exchange nature and negative charged surface, facilitating favorable retention of positively charged ions. The retained Cd(II) was effectively recovered with elution by 1 mol · L^?1 HNO₃, and the eluent was quantified by electrothermal atomic absorption spectrometry (ET-AAS). Under the optimized conditions, the limit of detection (LOD) for Cd(II) was 3 ng · L^?1 with the consumption of 20.0 mL sample solution. The relative standard deviation (RSD) for ten replicate measurements of 50 ng · L^?1 Cd(II) was 2.9%. The developed technique was demonstrated for the determination of trace Cd(II) in water samples and the recoveries for spiked samples were found to be in the range of 94.9–107.2%. For validation, two certified reference materials of water samples (GBW08607 and GBW08608) were analyzed, and the results obtained were in good agreement with the certified values.     

An Optimized Ion-Pair HPLC Method for Simultaneous Analysis of Nucleoside Triphosphate Levels in Hepatoma Cell Line

An improved ion-pair HPLC method was developed for the simultaneous determination of ribonucleoside triphosphates and their corresponding deoxyribonucleoside triphosphates in HepG2 cell extracts. HPLC conditions, flow rate and column temperature were optimized and good linearity (r ²  > 0.9993) was obtained over the investigated concentration ranges. Reproducibility was evaluated by intra- and inter-day assays and RSD values were below 5.39%. Recoveries ranged from 98.2 ± 3.49% to 103.1 ± 1.75%, respectively. Finally, the method was successfully applied to the analysis of eight compounds present in HepG2 cell extracts.     

An Effective High-Performance Liquid Chromatographic–Mass Spectrometric Assay for Catecholamines, as the N(O,S)-Ethoxycarbonyl Ethyl Esters, in Human Urine

The purpose of this study was to develop a simple and accurate analytical method for determination of norepinephrine, epinephrine, and dopamine in urine. The method involves liquid–liquid extraction then liquid chromatography–mass spectrometry (LC–MS). Alkyl chloroformate derivatives were prepared, as the N(O,S)-alkoxycarbonyl alkyl esters of the analytes, in the aqueous samples. The optimum derivatizing reagent for preparation of the N(O,S)-alkoxycarbonyl alkyl esters was chosen by comparing the efficiency of LC of the derivatized analytes after liquid–liquid extraction. The optimum conditions for liquid–liquid extraction from the aqueous matrix were pH 3.0, no salt, and diethyl ether as extraction solvent. Limits of detection (LOD) were 0.5 ng mL^?1 for dopamine and epinephrine and 0.1 ng mL^?1 for norepinephrine. Limits of quantification (LOQ) for urine samples were 1.0 ng mL^?1 for all three compounds. The precision of intra- and inter-day assays was 1.65–581 and 7.17–9.73% (relative standard deviation, RSD), respectively. The range of inaccuracy for intra- and inter-day assays was ?6.47 to 11.9% and ?7.5 to 7.76% (bias) at concentrations of 5 and 50 ng mL^?1, respectively.     

Determination of Organotin Compounds in Wine by Microwave-Assisted Extraction and High Performance Liquid Chromatography–Inductively Coupled Plasma Mass Spectrometry

A new analytical procedure for the determination of five organotin compounds in several matrix wine samples is reported. The organotin compounds were extracted by microwave-assisted extraction with n-hexane. Extraction conditions, such as volume of n-hexane required, extraction temperature, and extraction time, were investigated and optimized by an orthogonal array experimental design. The determination of organotin compounds in the final extracts was carried out by liquid chromatography–inductively coupled plasma mass spectrometry. The procedure showed limits of detection between 0.029–0.049 µg · L^?1. The linearity was in the range of 0.5 to 100 µg · L^?1. The precision expressed as relative standard deviation (RSD) was below 9.43%. The developed method was successfully employed to analyze different matrix wine samples, and some analytes were detected at the level of 0.053 to 1.14 µg · L^?1.     

LC–DAD–MS Determination of the Major Constituents in Radix Angelicae sinensis

Column liquid chromatography with diode array and mass spectrometric detection was developed for the qualitative and quantitative analysis of the major constituents in Radix Angelicae sinensis. Sixteen compounds including phthalic acid, vanillic acid, ferulic acid, guaiacol, Z-6,7-epoxyligustilide, senkyunolide F, carvacrol, Z-ligustilide, Z-butylidenephthalide, E-6,7-dihydroxydihydroligustilide, senkyunolide I or senkyunolide H, coniferyl ferulate, sendanelolide, butylphthalide, E-ligustilide, E-butylidenephthalide except guaiacol and carvacrol were identified using online ESI–MS in comparisons with literature data and standard compounds. Nine compounds were quantified by LC–DAD simultaneously. For chromatographic analysis, a Merck C₁₈ column (5 μm, 250 mm × 4.6 mm) with a compatible guard column (C₁₈, 5 μm, 7.5 mm × 4.6 mm) was used. The mobile phase consisted of (A) 0.1% aqueous formic acid and (B) acetonitrile. Ten microliters of each sample solution were injected and eluted at a flow rate of 1 mL min^-1. The column temperature was maintained at 30 °C. The validation of this method proved good linear regression (r ² > 0.9992) within the test ranges, desirable repeatability with overall intra- and inter-day variations of less than 4.91% and well acceptable recoveries varied between 90.91 and 96.73% while the RSDs were below 3.23% (n = 3). The proposed method was successfully applied to the quantification of the nine components in sixteen samples from different localities in China. This assay provides a valid and an overall quality control of Radix Angelicae sinensis.     

Magnetic Nanoparticle-Based Micro-Solid Phase Extraction and GC�CMS Determination of Oxadiargyl in Aqueous Samples

A new facile, rapid, inexpensive, and sensitive method based on magnetic micro-solid phase extraction (M-??-SPE) coupled to gas chromatography?Cmass spectrometry (GC?CMS) was developed for determination of the herbicide oxadiargyl in environmental water samples. The feasibility of employing non-modified magnetic nanoparticles (MNPs) as sorbent was examined and applied to perform the extraction process. Influential parameters affecting the extraction efficiency along with desorption conditions were investigated and optimized. The limit of detection (LOD, S/N = 3) and limit of quantification (LOQ, S/N = 10) of the method under optimized conditions were 0.005 and 0.030 ng mL^?1, respectively. The relative standard deviations (RSD) (n = 3) at a concentration of 0.10 ng mL^?1 was 11%. The calibration curve of oxadiargyl showed linearity in the range of 0.050?C0.50 ng mL^?1. The developed method was successfully applied to the extraction of oxadiargyl from spiked tap water and Zayande-Rood River water samples and the relative recoveries of 98 and 94% were obtained, respectively.     

GC Analysis of Amino Acids Using Trifluoroacetylacetone and Ethyl Chloroformate as Derivatizing Reagents in Skin Samples of Psoriatic and Arsenicosis Patients

The separation and determination of 19 amino acids were examined using two stages derivatization with trifluoroacetylacetone and ethyl chloroformate from the column HP-5 (30 m × 0.32 mm id) with film thickness 0.25 ??m at an initial column temperature 100 °C for 2 min with ramping of 20 °C min^?1 up to 250 °C with nitrogen flow rate of 3 mL min^?1. The detection was performed by flame ionization detector. Total separation time was 10 min. The separation was repeatable with relative standard deviation (RSD) (n = 5) within 1.5?C1.9 and 1.3?C1.7% in terms of retention time and peak height/peak area, respectively. The method was applied for the determination of amino acids from skin samples of psoriatic patients (n = 6), arsenicosis patients (n = 5) and normal subjects (n = 9) and variation in the contents of the amino acids was noted. The RSDs for the determination were obtained within 3%.     

Sensitive LC–ESI–MS Method for Determination of Tiopronin in Human Plasma

A sensitive liquid chromatographic–electrospray ionization–mass spectrometric (LC–MS) method has been developed for direct measurement of the concentration of tiopronin in human plasma. Hydrochloric acid solution was used to stabilize the tiopronin and prevent formation of a dimer, or reaction with endogenous thiols. The method involved liquid–liquid extraction of tiopronin from plasma samples with ethyl acetate, simple reversed-phase chromatography, and mass spectrometric detection with nanogram detection limits. Acetaminophen was used as internal standard (IS). The limit of quantification was 5 ng mL^?1 (RSD 4.3%). The method was validated within the linear range 5–500 ng mL^?1. The correlation coefficient for the calibration regression line was 0.9997 or better. Intra-day and inter-day accuracy were better than 15%. The method has been successfully used for a pharmacokinetic study with human subjects. Among the pharmacokinetic data obtained, t _1/2 was 2.37 ± 0.63 h and T _max was 4 h.     

Study of 1,4-naphthoquinone as a new useful derivatization reagent for LC analysis of aliphatic thiols in dietary supplements and pharmaceuticals

The use of 1,4-naphthoquinone as an advantageous pre-column reagent for liquid chromatography analysis of aliphatic thiol compounds is proposed. The compound reacts selectively in mild conditions (5 min at room temperature; pH 7.5) with thiol function. The resulting adducts were separated under isocratic conditions by using a reversed-phase column (C-12n) with a mobile phase corresponding to methanol/triethylammonium phosphate buffer (pH 3; 0.05 mol L^?1) 65:35, v/v, at a flow rate of 0.4 mL min^?1 in presence of quercetin as internal standard. Detection was set at a wavelength of 420 nm. The effect of the derivatization reaction conditions on the N-acetylcysteine (NAC) reaction yield was investigated by a series of experiments. The yield of NAC derivative was found to be quantitative at a reagent thiol molar ratio of about 3 by comparison with an authentic specimen of synthesized NAC adduct, which was characterized by ¹?H NMR, IR, and UV. Similar linear responses were observed by standard and placebo solutions (determination coefficient, 0.9998). The within- and between-day standard deviations (RSD) were ≤0.47 %. Recovery studies showed good results (100.03 %) with RSD 0.76 %. The limit of detection was about 20 pmol. The utility of the validated method for the determination of NAC in a new dietary supplement and commercial formulations is demonstrated.     

Quantitative Analysis of Artemether and its Metabolite Dihydroartemisinin in Human Plasma by LC with Tandem Mass Spectrometry

We report the development and validation of a high-performance liquid-chromatographic–tandem mass spectrometric method for determination of artemether (ARM) and its active metabolite dihydroartemisinin (DHA) in human plasma; artemisinin was used as internal standard (IS). Chromatographic separation was performed on a 150 mm × 4.6 mm i.d., 5 μm particle, C₁₈ column coupled with a 4.0 mm × 3.0 mm i.d., 5 μm particle, C₁₈ guard column. The mobile phase was acetonitrile–0.1% formic acid solution, 80:20 (v/v), at a flow-rate of 1 mL min^?1. An atmospheric-pressure chemical-ionization (APCI) interface was used to produce sample ions, and positive ions were quantified by using the MS detector in selected-reaction-monitoring mode, using the reaction m/z 221 to 163 for determination of ARM and DHA and the reaction m/z 283 to 219 for determination of the IS. Plasma samples were prepared by extraction with methyl t-butyl ether, evaporation of the extract to dryness, and reconstitution of the residue with mobile phase. Extraction recovery for ARM and DHA ranged from 74.74 to 99.39%. High specificity and a limit of quantification of 5 ng mL^?1 were achieved for ARM and DHA. Linearity was confirmed over the concentration range 5–500 ng mL^?1; the correlation coefficients (R) were >0.99. The relative standard deviation for intra-day and inter-day assay of both compounds was <9.60% and inaccuracy was within ±10.81%. Stock solutions were stable at 4 °C for at least 720 h. Processed extracts were stable at room temperature for at least 24 h and QC samples were stable during three freeze–thaw cycles. In spiked human plasma under ambient conditions ARM was stable for at least 8 h whereas DHA was stable for 2 h only.     

Determination of Methadone in Biological Samples Using Liquid Phase Microextraction with Back Extraction Combined with LC

Liquid phase microextraction with back extraction (LPME-BE) combined with liquid chromatography-ultra violet (LC-UV) was applied for the extraction and determination of methadone in biological fluids. At the optimized conditions, an enrichment factor of 386 and detection limit (LOD) of 0.2 μg L^?1 were obtained. The calibration curve was linear (r ² = 0.989) in the concentration range of 0.6–1,000 μg L^?1. Within-day relative standard deviation RSD (S/N = 3) and between-day RSD were 2.7 and 5.9%, respectively. The feasibility of the proposed method was evaluated by extraction and determination of methadone in plasma and urine samples and satisfactory results were obtained.     

Determination of Quinoxalines and Their Two Main Metabolites in Environmental Water Samples by Liquid Chromatography–Tandem Mass Spectrometry

A sensitive high performance liquid chromatography–tandem mass spectrometry method was developed for the determination of residues of carbadox, mequindox, olaquindox, quinocetone, cyadox, quinoxaline-2-carboxylic acid, and 3-methylquinoxaline-2-carboxylic acid in environmental water samples. The samples were freeze-dried at ?80°C, re-dissolved in 1.0 mL methanol-water (5:95), then purified with N-propyl ethylenediamine. The separation of the analytes was performed on a column (150 × 2.1 mm i.d., 5.0 µm) using acetonitrile and 0.1% formic acid as mobile phases. The target compounds were confirmed and quantified by tandem mass spectrometry in multiple reaction monitoring mode. The results showed that there were linear relationships between peak area and concentrations of these compounds with correlation coefficients exceeding 0.99. The average recoveries at the spiked levels of 0.25, 0.5, 1.0, and 2.0 µ g L^?1 ranged from 68.7% to 109% with relative standard deviations less than 14% except cyadox. The limits of detection of the analytes were between 2.0 and 6.0 ng L^?1. This method meets the requirements for the determination of drug residues in environmental water samples.     

Preparation of an ionic liquid-mediated carbon nanotube-poly(dimethylsiloxane) fiber by sol–gel technique for determination of polycyclic aromatic hydrocarbons in urine samples using head-space solid-phase microextraction coupled with gas chromatography

A novel ‘ionic liquid-mediated multi-walled carbon nanotube (MWCNT)-poly(dimethylsiloxane) (PDMS)’ hybrid coating was prepared by the covalent functionalization of MWCNTs with hydroxyl-terminated PDMS using the sol–gel technique. The prepared fiber was successfully used for the separation and determination of trace amounts of polycyclic aromatic hydrocarbon compounds (PAHs) in four urine samples using head-space solid-phase microextraction coupled to gas chromatography-flame ionization detection. The proposed fiber has high thermal stability and long durability and it can be used more than 210 times without any significant change in its sorption properties. The effects of important parameters such as the exposure time, sampling temperature, sample ionic strength and stirring rate on the extraction efficiency have been studied and optimized. Under the optimal conditions, the method detection limits (S/N = 3) were in the range of 0.0005–0.004 ng mL^?1 and the limits of quantification (S/N = 10) between 0.002 and 0.01 ng mL^?1. The relative standard deviations for one fiber (repeatability, n = 5) were 4.9–7.5 % and for the fibers obtained from different batches (reproducibility, n = 3), 6.1–8.9 %. The developed method was successfully applied to determine trace levels of PAHs in real urine samples. The obtained relative recoveries for the spiked samples with 0.05 ng mL^?1 of each of the PAH compounds were 89.3–107.2 %.     

LC Determination and Pharmacokinetic Study of Gemfibrozil in Human Plasma

A simple and sensitive LC method for the quantitative determination of gemfibrozil in human plasma samples is described. Mometasone furoate was used as the internal standard. Plasma samples were pretreated by protein precipitation using methanol. Separation was performed at 40 °C on a YMC^® ODS-A reverse phase column (5 μm particle size, 150 mm × 4.6 mm i.d.) using 0.2% (v/v) triethylamine in water (adjusting to pH 4.0 with phosphoric acid) and acetonitrile (45:55, v/v) as mobile phase which was delivered at 1.5 mL min^?1. Ultraviolet detection was performed at 230 nm. The linear concentration range for gemfibrozil was 0.25–50 μg mL^?1. The detection limit of this method was 0.1 μg mL^?1. Intra- and inter-assay RSD ranged from 0.63 to 2.04% and 1.37 to 4.27%, respectively. The method was sensitive, simple and repeatable enough to be used in pharmacokinetic studies.