Rapid headspace gas chromatographic method for the determination of liquid/gas partition coefficients

A rapid, efficient and low-cost headspace technique useful for the determination of liquid/gas partition coefficients of gases and volatile substances of low and intermediate solubility is described. The equilibration step is carried out at constant pressure using glass syringes, with a ratio of liquid/gas phase volumes of ca. 1:3; after 30 min at the desired temperature, the headspace is recovered by transfer into another syringe and analyzed by gas chromatography. A study of the partition coefficients in water at 37 degrees C of 27 volatile compounds demonstrated that the method is fully applicable for all gases, with exception of those with a partition coefficient higher than 300.     

A pyrolysis/gas chromatographic method for the determination of hydrogen in solid samples

A method is described for the determination of hydrogen in solid samples. The sample is heated under vacuum after which the evolved gases are separated by gas chromatography with a helium ionization detector. The system is calibrated by injecting known amounts of hydrogen, as determined manometrically. The method, which is rapid and reliable, was checked for a variety of lunar soils; the limit of detection is about 10 ng of hydrogen.     

Simultaneous determination of tebuconazole,trifloxystrobin, and its metabolite trifloxystrobin acid residues in gherkin under field conditions

A rapid, simple, and selective analytical method for the simultaneous determination of tebuconazole, trifloxystrobin, and its metabolite trifloxystrobin acid residues in gherkin and soil was developed and validated by gas chromatography coupled with mass spectrometry. The samples were extracted with acetonitrile and cleaned up by dispersive solid‐phase extraction with primary secondary amine sorbent. The limit of quantification of the method was 0.05 mg/kg for all three compounds. The method was validated using blank samples spiked at three levels and recoveries ranged from 83.5 to 103.8% with a relative standard deviation of 1.2 to 4.8%. The developed method was validated and applied for the analysis of a degradation study sample. The residues of trifloxystrobin and tebuconazole were found to dissipate following first‐order kinetics with half‐life ranging between 3.31–3.38 and 3.0–3.04 days, respectively, for two different dosages. Pesticide residues were below the European Union maximum residue level after seven days for trifloxystrobin (0.2 mg/kg) and ten days for tebuconazole (0.05 mg/kg), which suggested the use of this fungicide mixture to be safe to humans. These results can be utilized in formulating the spray schedule and safety evaluation on trifloxystrobin and tebuconazole in gherkin crop.     

Dissipation and gas chromatographic method for the determination of profenofos residues in/on green pea and cucumber

Herein we report a novel, accurate and cost-effective gas chromatography method for the determination of average deposits of profenofos on green pea and cucumber following good agricultural practices. Additionally the risk assessment, dissipation and waiting period for profenofos were determined. The average initial deposits (2 h after spraying) of profenofos in/on green pea and cucumber were 3.41 and 3.62 mg kg⁻¹ respectively following two applications at a 10 day interval of profenofos 50EC formulation. Profenofos residues on both of the substrates were below the detection limit of 0.05 mg kg⁻¹ after 20 days at the recommended dosage. For risk assessment studies, the 20th day will be safe for consumers for consumption of green peas. The gas chromatography method was validated according to the SANTE guidelines using the various analytical parameters: linearity, accuracy, detection and quantification limits. The developed method is simple, selective and repeatable and can be extended for profenofos-based standardization of pesticide formulations for green pea/cucumber and their use as pesticides.     

Reversed-phase liquid chromatographic method for the determination of ochratoxin A in wine

In this paper, we propose a new, rapid, highly sensitive and reproducible RP-HPLC-FLD method for the detection of ochratoxin A (OTA) in wine, by directly injecting the liquid in the chromatographic system without any extraction or clean-up. An alkaline mobile phase (NH4Cl:CH-CN 85:15 (v/v), 20 mM, pH 9.8) was used to obtain a distinct fluorescence enhancement. This improvement allows to reach, without an immunoaffinity clean-up or concentration, a detection limit of 0.05 ng/ml, which is similar to those commonly obtained after immunoaffinity purification and acidic elution. The method was statistically validated and directly applied to a series of wine samples.     

Microtechniques for the gas chromatographic determination of barbiturates in small blood samples

A method for the determination of therapeutic levels of barbituric acids in 25 microliter of whole blood is described. After extraction and controlled concentration of the extract to a volume of 5 microliter, the barbituric acids are N,N'-dimethylated using a microrefluxer. Of the total extract 20-100% is injected into the gas chromatograph. Low blanks, recoveries of 70--80% and peak ratios that are comparable to those in calibration experiments are obtained provided the detailed working instructions are followed strictly. In addition, barbiturates were determined (1 ng in 25 microliter blood) using column-switching devices and nitrogen-sensitive detection.     

Micellar electrokinetic chromatographic method for the dabrafenib determination in biological samples

Two different micellar electrokinetic chromatographic methods to determine dabrafenib in urine and serum, both using borate buffer (pH 9.2, 20 mM) and SDS as separation electrolyte, are developed and validated. The analyses were carried out in a fused‐silica capillary of 75 μm of internal diameter and total length of 47 and 37 cm for urine and serum determination, respectively. The detection of the target compound was performed at 227 nm in urine samples and at 251 nm in serum samples. The linearity range was from 1 to 21 mg/L of dabrafenib in urine and from 2 to 40 mg/L in serum. In all cases, inter‐ and intraday RSDs were <4%. Sample preparation of serum samples consists of an only step of 1:1 dilution with water before its injection in the electrophoretic system. These simple, sensitive, accurate, and cost‐effective methods can be used in routine clinical practice to monitor dabrafenib concentrations in urine and serum of metastatic melanoma skin cancer patients.     

Simple ion chromatographic method for the determination of chlormequat residues in pears

Current methods for quantitative determination of chlormequat residues in food crops are characterized by rather low recoveries and the need for derivatization (in case of gas chromatography, GC), or by high capital investment (in case of liquid chromatography–mass spectrometry, LC–MS). We propose a cation-exchange chromatography method for the analysis of chlormequat in pears. The method is based on extraction of the target compound with 40 mM HCl, followed by centrifugation and filtration. The filtrate is directly injected into an ion chromatograph equipped with a commercially available cation-exchange column and a suppressed conductivity detection system. While the limit of detection (LOD) (0.5 mg/kg) may not be small enough to allow dietary analysis, the method meets all validation requirements and is an alternative for the existing GC and LC–MS methods in quality control.     

New clean-up method for gas chromatographic analysis of pyrethroid residues

Summary A fast and efficient method has been developed for clean-up of fenpropathrin and fluvalinate for gas chromatographic determination of their residues in crops, grain and soil. Charcoal (Darco-G-60) was used as adsorbent and the pyrethroids recovered by washing the adsorbent with hexane-acetone (9∶1). The method provides a clear filtrate with no interfering peaks in the chromatogram. Recoveries ranged 91.00–100%.     

Rapid method for plutonium-241 determination in soil samples

A simple and rapid procedure for the determination of plutonium isotopes in the environment is presented. The procedure combines alpha spectrometry, solvent extraction and liquid scintillation measurements to ensure that both alpha- and beta-emitting isotopes are determined. Of five tested extractants, bis-(2-ethylhexyl) phosphoric acid was found to be the best choice. The procedure was applied to soil samples contaminated with Chernobyl fallout.