Simultaneous determination of bromide and iodide as acetone derivatives by gas chromatography and electron capture detection in natural waters and biological fluids

Oxidation of bromide and iodide ions in acidic solutions in the presence of acetone forms the corresponding acetone derivatives. Iodate was reduced with thiosulfate prior to the determination. After extraction with benzene the bromo- and iodoacetone were measured by gas chromatography using electron capture detection. The bromide and iodide contents of rainwater, drinking water, river water, seawater, oil brine, common salt, cow milk, and human blood serum were determined. The relative standard deviations for bromide at 10(-7) M and for iodide at 10(-8) M concentration were 1.9% and 3.0%, respectively, using a 10-mL sample for the determination without preconcentration.     

An ultra-high performance chromatographic method for the determination of artemisinin

Objective: The goal of this study is to develop an ultra-high performance liquid chromatographic method for the quantitative determination of artemisinin at very low concentrations using selective ion mass spectroscopic detection.

Materials and methods: Separation was conducted using a C4 100?mm×?2.1?mm column, and the mobile phase consisted of an isocratic two-component system consisting of 60% of a 0.1% aqueous solution of formic acid and 40% acetonitrile at a flow rate of 0.4?ml/min. The drug was detected by means of an electrospray mass spectrometer with selective ion monitoring of the [M-H₂O+H]⁺ with m/z of 265.3 in positive ion mode.

Results: The calibration curves of artemisinin obtained from the UPLC/MS system were linear in the three ranges analyzed, with a correlation coefficient of no less than 0.9996 for all sets of standards. The peak tailing factor for all measurements were ≤1.7. The method proved to have good repeatability and linearity.

Discussion: The described analytical method reached a LOQ of 0.010?µg/ml with an isocratic system and enables an analysis rate of 20 samples per hour. The linearity of the standards was excellent for all sets of standards analyzed.

Conclusion: The method presented in this study provides a rapid and suitable means for the determination of artemisinin at very low concentrations. This is especially significant when performing dissolution studies where, due to the low solubility of artemisinin, a method that can measure the drug at nanogram levels is necessary.     

Isotopic determination of organic keto acid pentafluorobenzyl esters in biological fluids by negative chemical ionization gas chromatography/mass spectrometry.

A rapid, single-step procedure for the extraction and derivatization of organic alpha-keto acids from microliter quantities of human plasma has been developed. The keto acids were analyzed as the pentafluorobenzyl (PFB) ester by methane negative chemical ionization gas chromatography/mass spectrometry. The PFB esters possess excellent chromatographic properties and required no further derivatization to block the keto group. They fragment to produce intense carboxylate anions, often as the sole ion in the spectrum, and offer detection limits below 1 pmol. This derivative is suitable for isotopic analysis of organic keto acids because it does not introduce any additional isotopic complexity into the target molecule. Normal human plasma 4-methyl-2-oxopentanoic acid levels were 34.9 +/- 5.3 mumol.L-1 and could be determined with 1.1% precision by isotope dilution GC/MS. We have used this procedure to study leucine and 4-methyl-2-oxopentanoic acid metabolism by using stable isotopically labeled tracers in a variety of normal and abnormal conditions.     

An analytical method for trifluoroacetic Acid in water and air samples using headspace gas chromatographic determination of the methyl ester

An analytical method has been developed for the determination of trace levels of trifluoroacetic acid (TFA), an atmospheric breakdown product of several of the hydrofluorocarbon (HFC) and hydrochlorofluorocarbon (HCFC) replacements for the chlorofluorocarbon (CFC) refrigerants, in water and air. TFA is derivatized to the volatile methyl trifluoroacetate (MTFA) and determined by automated headspace gas chromatography (HSGC) with electron-capture detection or manual HSGC using GC/MS in the selected ion monitoring (SIM) mode. The method is based on the reaction of an aqueous sample containing TFA with dimethyl sulfate (DMS) in concentrated sulfuric acid in a sealed headspace vial under conditions favoring distribution of MTFA to the vapor phase. Water samples are prepared by evaporative concentration, during which TFA is retained as the anion, followed by extraction with diethyl ether of the acidified sample and then back-extraction of TFA (as the anion) in aqueous bicarbonate solution. The extraction step is required for samples with a relatively high background of other salts and organic materials. Air samples are collected in sodium bicarbonate-glycerin-coated glass denuder tubes and prepared by rinsing the denuder contents with water to form an aqueous sample for derivatization and analysis. Recoveries of TFA from spiked water, with and without evaporative concentration, and from spiked air were quantitative, with estimated detection limits of 10 ng/mL (unconcentrated) and 25 pg/mL (concentrated 250 mL:1 mL) for water and 1 ng/m(3) (72 h at 5 L/min) for air. Several environmental air, fogwater, rainwater, and surface water samples were successfully analyzed; many showed the presence of TFA.