GC-MS analysis of organic acids in human urine in clinical settings: a study of derivatization and other analytical parameters.

In the current paper the analytical conditions for the determination of ten free organic acids by GC-MS are studied with the aim to establish a method for organic acid profiling in human urine to be used as a tool for the detection of metabolic or other health disorders. Studies included the GC-MS method development, the derivatization (trimethylsilylation) reaction conditions, the stability of the standard solutions during storage in the freezer, and the stability of the formed trimethylsilyl derivatives. Best results were obtained at a derivatization temperature of 50°C, and a reaction time of 30 min. Standard solutions were stable for 22 days, derivatized samples were stable at least for 30 h when stored at -24°C. GC-MS analysis achieved sensitive determination of the organic acids under study with limits of detection ranging from 0.03 mmol/mol creatinine for glutaric acid, to 0.34 mmol/mol creatinine for glycolic acid. Within-day and day-to-day assay imprecision was found satisfactory with relative standard deviations being below 10%. The developed method was successfully applied to the quantitative analysis of free organic acids in urine samples obtained from hospitalized children. Creatinine-corrected excretion rates of all analyzed organic acids were within reference intervals.

Flow injection on-line displacement/solid phase extraction system coupled with flame atomic absorption spectrometry for selective trace silver determination in water samples.

A novel flow injection (FI) on-line displacement solid phase extraction preconcentration and/or separation method coupled with FAAS in order to minimize interference from other metals was developed for trace silver determination. The proposed method involved the on-line formation and subsequently pre-sorption of lead diethyldithiocarbamate (Pb-DDTC) into a column packed with PTFE-turnings. The preconcentration and/or separation of the Ag(I) took place through a displacement reaction between Ag(I) and Pb(II) of the pre-sorbed Pb-DDTC. Finally, the retained analyte was eluted with isobutyl methyl ketone (IBMK) and delivered directly to nebulizer for measuring. Interference from co-existing ions with lower DDTC complex stability in comparison with Pb-DDTC, was eliminated without need for any masking reagent. With 120 s of preconcentration time at a sample flow rate of 7.6 mL min(-1), an enhancement factor of 110 and a detection limit (3s) of 0.2 microg L(-1) were obtained. The precision (RSD, n=10) was 3.1% at the 10 mug L(-1) level. The developed method was successfully applied to trace silver determination in a variety of environmental water samples and certified reference material.