Gas Chromatography-selected Ion Monitoring-mass Spectrometry Research Articles

Determination of 24 Pesticides Residues in Leather Products by Solid-Phase Microextraction Coupled with Gas Chromatography–Mass Spectrometry

Considering the high content of oil and complex residual additives in leather samples, a new analytical method based on the solid-phase extraction technique and gas chromatography-selected ion monitoring mass spectrometry (GC-SIM-MS) was developed to determine 24 organic compounds involving the organochlorine pesticides (OCPs), organophosphorous pesticides (OPPs) and pyrethroids pesticides residues in leather. The extraction conditions (such as the extraction solution, purification procedure and solid-phase extraction column) were optimized using the positive leather samples based on the recovery rates of the pesticides. The best extraction solution, solid-phase extraction column and chromatography column were n-hexane and ethyl acetate (1+1, volume) mixed solution, Carb-PSA (1.0 g, 6mL) and DB-1701 (length: 30 m, inside diameter: 0.25 mm, film thickness: 0.25 μm). The optimized extraction time and temperature were 20 min and 25°C, respectively. The detection limits of 24 pesticide residues range from 0.05 to 0.10 mg/kg, and the recoveries range from 74% to 116%. The relative standard deviations (RSD, n=6) range from 5.42% to 12.00%. The developed method presented a simple, rapid, sensitive, and inexpensive method to detect 24 pesticides in skin and leather and was successfully applied to the detect them in leather products (cowhide, sheep leather and pig leather).

Quantitative Determination of H2 in Human Blood by 22Ne-aided Gas Chromatography-Mass Spectrometry Using a Single Quadrupole Instrument.

Here, we present a quantitative method for H2 detection by gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS) using a single quadrupole instrument. Additionally, the developed method was applied to the detection of H2 in human blood by GC-SIM-MS analysis using the existing 22Ne in air as an internal standard (IS). H2 was analyzed by GC-SIM-MS using a single quadrupole instrument with double TC-Molsieve 5A capillary columns for the separation of permanent gases. The detections of H2 (analyte) and 22Ne (IS) were performed at m/z 2 and 22, respectively, by GC-SIM-MS. The analyte and IS were separated using He as the carrier gas. The ratio of the peak area of H2 to 22Ne was employed to obtain a calibration curve for H2 determination in the gas phase. The proposed GC-SIM-MS method exhibited high sensitivity in terms of the limits of detection (LOD) (1.7 ppm) and quantitation (LOQ) (5.8 ppm) for H2 analysis. The developed quantitative assay of H2 in the headspace of blood samples achieved high repeatability with a relative standard deviation (RSD) of 1.4 - 4.7%. We successfully detected and quantified H2 in the headspaces of vacuum blood-collection tubes containing whole blood from 11 deceased individuals with several causes of death by employing the developed GC-SIM-MS method. The quantitative value of H2 ranged from 5 to 905 ppm. The proposed GC-SIM-MS method was applicable to the quantitative assay of H2 in biological samples without tedious pretreatment requirements.

A metabolomics study delineating geographical location-associated primary metabolic changes in the leaves of growing tobacco plants by GC-MS and CE-MS.

Ecological conditions and developmental senescence significantly affect the physiological metabolism of plants, yet relatively little is known about the influence of geographical location on dynamic changes in plant leaves during growth. Pseudotargeted gas chromatography-selected ion monitoring-mass spectrometry and capillary electrophoresis-mass spectrometry were used to investigate a time course of the metabolic responses of tobacco leaves to geographical location. Principal component analysis revealed obvious metabolic discrimination between growing districts relative to cultivars. A complex carbon and nitrogen metabolic network was modulated by environmental factors during growth. When the Xuchang and Dali Districts in China were compared, the results indicated that higher rates of photosynthesis, photorespiration and respiration were utilized in Xuchang District to generate the energy and carbon skeletons needed for the biosynthesis of nitrogen-containing metabolites. The increased abundance of defense-associated metabolites generated from the shikimate-phenylpropanoid pathway in Xuchang relative to Dali was implicated in protection against stress.

Exploring metabolic syndrome serum free fatty acid profiles based on GC–SIM–MS combined with random forests and canonical correlation analysis

Metabolic syndrome (MetS) is a cluster of metabolic abnormalities associated with an increased risk of developing cardiovascular diseases or type II diabetes. Till now, the etiology of MetS is complex and still unknown. Metabolic profiling is a powerful tool for exploring metabolic perturbations and potential biomarkers, thus may shed light on the pathophysiological mechanism of diseases. In this study, fatty acid profiling was employed to exploit the metabolic disturbances and discover potential biomarkers of MetS. Fatty acid profiles of serum samples from metabolic syndrome patients and healthy controls were first analyzed by gas chromatography–selected ion monitoring–mass spectrometry (GC–SIM–MS), a robust method for quantitation of fatty acids. Then, the supervised multivariate statistical method of random forests (RF) was used to establish a classification and prediction model for MetS, which could assist the diagnosis of MetS. Furthermore, canonical correlation analysis (CCA) was employed to investigate the relationships between free fatty acids (FFAs) and clinical parameters. As a result, several FFAs, including C16:1n-9c, C20:1n-9c and C22:4n-6c, were identified as potential biomarkers of MetS. The results also indicated that high density lipoprotein-cholesterol (HDL-C), triglycerides (TG) and fasting blood glucose (FBG) were the most important parameters which were closely correlated with FFAs disturbances of MetS, thus they should be paid more attention in clinical practice for monitoring FFAs disturbances of MetS than waist circumference (WC) and systolic blood pressure/diastolic blood pressure (SBP/DBP). The results have demonstrated that metabolic profiling by GC–SIM–MS combined with RF and CCA may be a useful tool for discovering the perturbations of serum FFAs and possible biomarkers for MetS.

Determination and Validation of a Solid-phase Extraction Gas Chromatography-mass Spectrometry for the Quantification of Methadone and Its Principal Metabolite in Human Plasma.

This study aimed to develop a solid-phase extraction gas chromatography-selected ion monitoring-mass spectrometry method for the determination of methadone (MDN) and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in human plasma. The linear response was obtained over the concentration range from 10 to 2000 ng/mL for MDN and EDDP. The absolute recoveries of MDN and EDDP were 95.9%–98.9% and 94.8%–102.4%, with relative standard deviation (RSD) ranging from 1.8% to 2.7% and 1.8% to 3.9%, respectively. The intra- and interday precisions were found to be less than 5% for both analytes. The limits of detection of MDN and EDDP were 4 and 5 ng/mL, respectively. The presented method was convenient for therapeutic drug monitoring and pharmacokinetic studies in patients on heroin-assisted MDN therapy.

Comparison of different modifications on QuEChERS sample preparation method for PAHs determination in black, green, red and white tea

The aim of this work was the evaluation of QuEChERS extraction method for polycyclic aromatic hydrocarbon (PAH) determination in various types of tea. In the experiment, different kinds of extraction solvents, sorbents and a final method of sample preparation were compared. The final extracts were analysed by gas chromatography-selected ion monitoring-mass spectrometry. The results suggest that acetonitrile extraction, clean up with SAX and final liquid–liquid extraction was the best combination giving the most purified extracts and acceptable compound recoveries for different types of teas. In the study of real samples, compounds belonging to light PAHs were mostly detected, and heavy polycyclic aromatic hydrocarbons, including benzo[a]pyrene, were not identified in any of samples.

Cork as a new (green) coating for solid-phase microextraction: Determination of polycyclic aromatic hydrocarbons in water samples by gas chromatography–mass spectrometry

A new fiber for solid-phase microextraction (SPME) was prepared employing cork as a coating. The morphology and composition of the cork fiber was evaluated by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The proposed fiber was used for the determination of polycyclic aromatic hydrocarbons (PAHs) in river water samples by gas chromatography–selected ion monitoring–mass spectrometry (GC–SIM–MS). A central composite design was used for optimization of the variables involved in the extraction of PAHs from water samples. The optimal extraction conditions were extraction time and temperature of 60min and 80°C, respectively. The detection and quantification limits were 0.03 and 0.1μgL−1, respectively. The recovery values were between 70.2 and 103.2% and the RSD was ≤15.7 (n=3). The linear range was 0.1–10μgL−1 with r≥0.96 and the fiber-to-fiber reproducibility showed RSD≤18.6% (n=5). The efficiency of the cork fiber was compared with commercially available fibers and good results were achieved, demonstrating the applicability and great potential of cork as a coating for SPME.

Extraction and on-fiber derivatization of chlorophenols in leather by internally cooled solid phase microextraction

This study proposes a new analytical procedure based on an internally cooled solid phase microextraction technique (CF-SPME) combined with on-fiber derivatization and gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS) for the determination of phenols extracted directly from leather samples. The extraction and derivatization conditions were optimized using experimental designs, such as: extraction time and sample temperature of 5 min and 170 ºC, fiber recoat temperature of 20 ºC, and exposing the fiber to the headspace of 70 µL of bis(trimethylsylyl)trifluoro-acetamide derivatizing agent for 23 min. Detection limits ranging from 1.03 to 2.68 µg g-1 and relative standard deviation (RSD) lower than 15% (n = 5) were obtained. The recovery was studied at three concentration levels and excellent recoveries ranging from 64.5 to 92.3% were obtained.

Application of solid‐phase microextraction and gas chromatography‐mass spectrometry for the determination of chlorophenols in leather

This paper proposes a new analytical procedure based on the headspace solid-phase microextraction (HS-SPME) technique and gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS) for the determination of 16 phenols extracted from leather samples. The optimized conditions for the HS-SPME were obtained through two experimental designs - a two-level fractional factorial design followed by a central composite design - using the commercial SPME fiber polyacrylate 85 μm (PA). The best extraction conditions were as follows: 200 μL of derivatizing agent (acetic anhydride), 20 mL of saturated aqueous NaCl solution and extraction time and temperature of 50 min and 75°C, respectively. All optimized conditions were obtained with fixed leather sample mass (250 mg), vial volume (40 mL) and phosphate buffer pH (12) and concentration (50 mmol/L). Detection limits ranging from 0.03 to 0.20 ng/g, and relative standard deviation (RSD) lower than 10.23% (n=6) for a concentration of 800 ng/g (chlorophenols) and 1325 ng/g (2-phenylphenol) in the splitless mode were obtained. The recovery was studied at three concentration levels by adding different amounts of phenols to the leather sample and excellent recoveries ranging from 90.0 to 107.2% were obtained. The validated method was shown to be suitable for the quantification of phenols in leather samples, as it is simple, relatively fast and sensitive.

Metabolite target analysis of isoprenoid pathway in Saccharomyces cerevisiae in response to genetic modification by GC-SIM-MS coupled with chemometrics

A highly selective, sensitive and nonradioactive analytical method for identification and quantification of intracellular metabolites involved in isoprenoid pathway has been developed by means of gas chromatography-selected ion-monitoring mass spectrometry (GC-SIM-MS). These metabolites are classified into two groups: sterols (squalene, ergosterol, lanosterol) and phosphorylated compounds (geranyl diphosphate, farnesyl pyrophosphate, geranylgeranyl pyrophosphate) based on their physicochemical properties. To quantify both groups in a single analytical run, GPP, FPP and GGPP were cleaved to the parent alcohols, geraniol, farnesol, geranylgeraniol by pyrophosphatase followed by alkaline phosphatase before extraction, separation and detection. This study evaluated several extraction procedures and determined the effects of the type of extraction solvent, times used for extraction. Under optimized GC/EI-MS conditions, six compounds were separated with high efficiency in the selected-ion monitoring (SIM) mode. Linearity of the method was good with correlation coefficients (r 2) in the range of 0.9953–0.9999 and detection limits were 1.53–151.88 ng/ml. The intra-day and inter-day precision of the method, as RSD, were less than 5.31 and 6.04%, respectively. The accuracy of six compounds varied between 87.7 and 110.8%. This assay was successfully applied to the determination of six major metabolites in the pathway for isoprenoid biosynthesis in S. cerevisiae and is sensitive to detect changes following genetic modification. By isolating statistically significant differences among metabolite levels from four biological conditions, we observed discriminatory metabolic features that hinted that the role of erg9 and coq1gene was involved in isoprenoid pathway. Integrating this analytical approach with statistical strategies, we can determine the influence of erg9 and coq1gene on isoprenoid levels of S. cerevisiae, thus leading to improved understanding of the pathway in a multitude of biological systems.

Routine method for the simultaneous quantification of 17α-hydroxyprogesterone, testosterone, dehydroepiandrosterone, androstenedione, cortisol, and pregnenolone in human serum of neonates using gas chromatography–mass spectrometry

Steroid determination by immunoassays results in significant interferences and inaccurate results. This study describes the development and validation of a new gas chromatographic–mass spectrometric method for the simultaneous quantification of 17α-hydroxyprogesterone (17αOHP), testosterone ( T), dehydroepiandrosterone (DHEA), androstenedione (Δ4-A), cortisol ( F) and pregnenolone (Preg) in serum of neonates. Steroids were extracted and purified from 0.5 mL serum using diethyl ether and Extrelut mini NT1 column. The extracts were derivatized with N-methyl- N-trimethylsilyl-trifluoroacetamide (MSTFA)/trimethylsilyl iodide (TMSI)/dithioerythritol (DTE) and the resulting trimethylsilyl derivatives were quantified by gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS). The detection limit for all steroids was lower than 0.1 ng/mL. The limit of quantification was 0.1 ng/mL for all steroids except cortisol which was at 0.25 ng/mL. d 3-Testosterone and methyltestosterone served as internal standards. Precision for all compounds at the concentrations of 0.5, 1, 5 and 10 ng/mL ( n = 10) in fortified steroid-free serum samples ranged from 0.8% to 16.6%. Accuracy was calculated at the concentrations of 0.5, 1, 5 and 10 ng/mL and ranged from −9.2% to 10.6% ( n = 10). Linear calibration equations were obtained for all five steroids (0.125–31.25 ng/mL) and for cortisol (0.125–200 ng/mL). Relative recoveries at concentrations 1.0 and 12.5 ng/mL ranged from 70.5% to 97.5%. Absolute recoveries at the same concentrations ranged from 73.2% to 96.6%. Reference intervals were estimated for infants aged from 9 to 40 days. The proposed steroid profile is suitable for routine analysis and provides meaningful data for samples within normal range as well as those with elevated levels.

Simultaneous determination of dehydroepiandrosterone and its 7-oxygenated metabolites in human serum by high-resolution gas chromatography–mass spectrometry

A highly sensitive and specific method has been developed for the simultaneous measurement of free (unconjugated) or sulfate-conjugated forms of dehydroepiandrosterone (DHEA), 7α-hydroxy-DHEA (7α-OH-DHEA), 7β-hydroxy-DHEA (7β-OH-DHEA), and 7-oxo-DHEA (7-oxo-DHEA) in human serum. This method is based upon a stable isotope-dilution technique by gas chromatography–selected-ion monitoring mass spectrometry. Free steroids were extracted from serum with an organic solvent and the sulfate-conjugated steroids remained in aqueous phase. Free steroids were purified by solid-phase extraction, while sulfate-conjugated steroids were hydrolyzed by sulfatase and deconjugated steroids were purified by solid-phase extractions. The extracts were treated with O-methylhydroxylamine hydrochloride and were subsequently dimethylisopropylsilylated. The resulting methyloxime-dimethylisopropylsilyl (MO-DMIPS) ether derivatives were quantified by gas chromatography–selected-ion monitoring mass spectrometry in a high-resolution mode. The detection limits of MO-DMIPS ether derivatives of DHEA, 7α-OH-DHEA, 7β-OH-DHEA and 7-oxo-DHEA were 1.0, 0.5, 0.5 and 2.0 pg, respectively. Coefficients of variation between samples ranged from 10.6 to 22.9% for free 7-oxygenated DHEA to less than 10% for DHEA and sulfate-conjugated 7-oxygenated DHEA. The concentrations of these steroids were measured in 18 sera samples from healthy volunteers (9 males and 9 females; aged 23–78 years). Free DHEA, 7α-OH-DHEA, 7β-OH-DHEA and 7-oxo-DHEA levels ranged between 0.21–3.55, 0.001–0.194, 0.003–0.481, and 0.000–0.077 ng/ml, respectively, and the sulfate-conjugated steroid levels of these metabolites ranged between 253–4681, 0.082–3.001, 0.008–0.903, and 0.107–0.803 ng/ml, respectively. The free DHEA-related steroid concentrations were much lower than those previously measured by RIA and low-resolution GC–MS. The present method made it possible to determine simultaneously serum DHEA-related steroid levels with sufficient sensitivity and accuracy.

Identification of 2,5-dimethoxy-4-ethylthiophenethylamine and its metabolites in the urine of rats by gas chromatography–mass spectrometry

A simple and specific method based on gas chromatography–selected ion monitoring-mass spectrometry (GC–SIM-MS) for the analysis of in vivo metabolism of 2,5-dimethoxy-4-ethylthiophenethylamine (2C-T-2) in rats is described. Three male rats were administered 20 mg/kg of 2C-T-2 by intra-peritoneal injection, and 24 h urine fractions were collected before and after the administration for analysis. After acidic hydrolysis of the urine samples, the metabolites were liquid–liquid extraction and analyzed by a quadruple mass spectrometer in the selected ion monitoring mode. The findings show that four metabolites of 2-(4-ethylthio-2,5-dimethoxyphenyl)-ethanol ( M w: 242), 4-ethylthio-2,5-dimethoxyphenyl acetic acid ( M w: 256), 1-acetoamino-2-(2-hydroxy-4-ethylthio-5-methoxyphenyl)-ethane ( M w: 269) and 1-acetoamino-2-(2-methoxy-4-ethylthio-5-hydroxyphenyl)-ethane ( M w: 269) are present and the metabolic pathway for 2C-T-2 in the rat is proposed.

Changes in levels of endogenous plant hormones in cambial regions of stems ofLarix kaempferi at the onset of cambial activity in springtime

The total amounts of endogenous indole-3-acetic acid (IAA), cytokinins, and abscisic acid (ABA) were quantified by gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS) in cambial regions of the main stems ofLarix kaempferi during the spring season. During the sampling period, cambium in the dormant state entered the active meristematic state. The total amount of IAA did not change at the onset of cambial reactivation but increased when the active division of cambial cells became apparent. Four cytokinins —trans- andcis-ribosylzeatin (RZ),N6-isopentenyladenine (iP),N6-isopentenyladenosine (iPA) — were quantified, but no zeatin (Z) was detected. The total amount of the four cytokinins together and the total amount of isopentenyl-type cytokinins (iP and iPA) varied during the sampling period but did not appear to be specifically associated with cambial activity. The total amounts oftrans- andcis-RZ remained relatively constant during the sampling period, as did the total amount of ABA. The results suggest that there is little correlation between total amounts of endogenous plant hormones in the cambial region and reactivation of the cambium during the spring.

Naturally occurring benzodiazepines: current status of research and clinical implications.

Naturally occurring benzodiazepines (BZDs) were first detected in mammalian tissues in 1986. They comprise a variety of 1,4-benzodiazepines corresponding to drugs commercially available for the treatment of anxiety disorders, sleep disturbances and epileptic seizures. Several biosynthetic pathways leading to the formation of BZDs are currently being discussed and have led to the proposition of possible precursor molecules. For years, the identification of naturally occurring BZDs in mammalian organisms was mostly confined to post mortem CNS material for sensitivity reasons. While radioimmunoassay and radioreceptor assay techniques have been tentatively applied to quantitations of genuine BZDs from human milk and cerebrospinal fluid, accurate measurements in peripheral blood have only recently become accessible, e. g., by gas chromatography/selected ion monitoring-mass spectrometry (GC/SIM-MS). This review summarizes existing evidence of benzodiazepines' occurrence in nature and discusses implications for neuropsychiatric disorders.

Changes in cytokinin levels of Phalaenopsis leaves at high temperature

The effect of high temperatures on cytokinin levels in Phalaenopsis hybrida leaves was investigated. Endogenous cytokinins were identified and quantified in Phalaenopsis leaves grown under high temperature conditions (30/25 °C day/night) using high performance liquid chromatography, bioassay and gas chromatography-selected ion monitoring-mass spectrometry. After 5 and 20 d of low temperature (25/20 °C day/night), zeatin, zeatin riboside and dihydrozeatin levels in the leaves were higher than that in leaves subjected to high temperature treatments. When Phalaenopsis leaves were exposed to low temperatures, about 76 % of the free cytokinins detected were of the zeatin-type. Glucoside cytokinins in the leaves increased significantly 5 d following high temperatures, and the rate of increase in glucoside cytokinins corresponded to the duration of high temperatures. At the same time, zeatin riboside and dihydrozeatin declined significantly following high temperature application. A significant accumulation of glucoside cytokinins, zeatin-9-glucoside, zeatin-O-glucoside, zeatin riboside-O-glucoside, and dihydrozeatin-O-glucoside was observed 20 d following high temperatures. These results suggest that high temperatures lead to an accumulation of glucoside cytokinins and a reduction of free base and riboside cytokinins.

Determination of testosterone and 6β-hydroxytestosterone by gas chromatography–selected ion monitoring–mass spectrometry for the characterization of cytochrome p450 3A activity

A method for the determination of testosterone and its metabolite, 6β-hydroxytestosterone, in liver microsomal incubates employing gas chromatography with selected ion monitoring mass spectrometric detection (GC–SIM–MS) has been developed. The method is more rapid than previously reported methods. Testosterone and its metabolites are extracted from the incubation mixture in a single step with methylene chloride. The method does not require derivatization and testosterone and its metabolites are separated on a HP-5MS fused-silica capillary column in less than 15 min. The retention times of testosterone ( m/z 288), methyltestosterone ( m/z 302), and 6β-hydroxytestosterone ( m/z 304) are approximately 12.7, 12.8, and 13.4 min, respectively. There are no interferences from other known CYP450 metabolites of testosterone. In addition, the selectivity and specificity of the mass spectrometer helps eliminate possible interferences from drugs and new chemical entities evaluated using this methodology. Calibration curves for testosterone and 6β-hydroxytestosterone are linear from 0.25 to 100 μ M. Extraction recoveries are better than 92% for both analytes and the internal standard, methyltestosterone. Over the course of five separate runs, within-day and inter-day precision (expressed as relative standard deviation) was less than 5% for all concentrations of testosterone and 6β-hydroxytestosterone. Accuracies ranged from 95.8 to 105.8% for testosterone and 94.6 to 104.2% for 6β-hydroxytestosterone. The assay has been used to characterize the CYP3A metabolic activity of multiple preparations of human, rat, and dog liver microsomes.

Determination of indole-3-pyruvic acid levels in Arabidopsis thaliana by gas chromatography–selected ion monitoring-mass spectrometry

A rapid and simple method is described for the determination of indole-3-pyruvic acid (IPA) levels in Arabidopsis thaliana by gas chromatography–selected ion monitoring-mass spectrometry (GC–SIM-MS). The method includes derivatization of IPA with hydroxylamine in the crude extract, followed by ethyl acetate partitioning, solid-phase extraction with C 18 resin, reversed-phase high-performance liquid chromatography (HPLC), and GC–SIM-MS. Three derivatizing reagents were tested; these were pentafluorobenzylhydroxylamine, pentafluorophenylhydrazine, and hydroxylamine. Hydroxylamine proved to be the most useful, as the IPA-oxime was easiest to purify from plant extracts and was the most stable. IPA was quantified in Arabidopsis seedlings ranging in age from 5 to 12 days; levels varied from 4 to 13 ng/g, peaking at 7–9 days.

Red-light-regulated growth

The etiolated maize (Zea mays L.) shoot has served as a model system to study red light (R)-regulated growth. Previous studies have shown that R inhibition of maize mesocotyl elongation involves a change in the auxin economy. Shown here is that R causes an increased tension in the epidermis relative to the inner tissue indicating that the growth of the epidermis is preferentially inhibited by R irradiation. This observation, taken together with previous indirect estimates of auxin within the epidermis, has prompted the hypothesis that R mediates the inhibition of mesocotyl elongation by preferentially decreasing auxin in the epidermis, a tissue which constrains the growth of the organ. We tested this hypothesis using gas chromatography-selected ion monitoring-mass spectrometry analysis of free indole-3-acetic acid (IAA) levels in both the apical 1 cm of the mesocotyl and the corresponding epidermis of etiolated and 4-h, R-irradiated seedlings. Red light irradiation caused a 1.4-fold reduction in free IAA within the whole section of the apical mesocotyl. However, within the peeled mesocotyl epidermis, R irradiation caused at least a 1.9-fold reduction in free IAA. To determine if the nearly twofold decrease in epidermal auxin occurring after R is physiologically significant, IAA was differentially applied to opposite sides of shoots. A twofold difference in IAA application rate caused asymmetrical growth. Thus, the twofold R-induced decrease in free IAA level in the epidermis, a difference sufficient to affect growth, and the rapid R-induced change in growth rate in the epidermis are consistent with the hypothesis that R causes growth of the mesocotyl to decrease by preferentially regulating the free IAA level in the mesocotyl epidermis.

Determination of low levels of poly(ethylene glycol) 400 in plasma and urine by capillary gas chromatography-selected ion-monitoring mass spectrometry after solid-phase extraction

A convenient and sensitive method for the quantitative determination of poly(ethylene glycol) 400 in plasma and urine with capillary gas chromatography-mass spectrometry has been developed. The sample preparation involves solid-phase extraction with subsequent derivatization with heptafluorobutyric anhydride, which proved to give the most stable derivative. The derivatization procedure was optimized using experimental design, and different solid-phase extraction columns were evaluated. The limit of quantitation was 1 μmol/l (0.4 μg/ml) for both plasma and urine.