Determination of Diacetonegulonic acid DAG in Water Samples

DAG (10) is the penultimate intermediate in the synthesis of ascorbic acid (vitamin C) and for many years was discharged in waste surface waters. This led to contamination of groundwaters and, although it is not toxic to humans, it has an inhibitory effect on the growth of grasses. Current European drinking water regulations restrict its concentration to 0.1 | g L_1. A fast and efficient HPTLC method has been described.

escent areas which were visible under UV light (366 nm) and quantified with a TLC scanner. Two-dimensional development was advocated for samples with less than 5 igL-1 DAG, while for higher concentrations, one-dimensional development was adequate. The calibration of peak area/weight DAG was linear within the range 0.125-1.5 |g. It was found that for the determination of higher concentrations it was essential to apply DAG as streaks to preserve linearity over the range of concentrations and it was then established that from 0.25 to 250 | g could be analysed with consistent accuracy.

The SPE procedure followed by TLC appears to be superior to derivatization followed by GC-MS and it was considered that very small concentrations of DAG could even be estimated visually without any instrumentation, thus generally giving an inexpensive procedure. Other application of quantitative TLC to the analysis of humic acids in natural waters, 6-aminocaproic acid (12), s-caprolactam in polyamide-6(11) and to uric acid (13), creatine (14) and creatinine (15) mixtures in biological materials have been described.

Due to the low concentration of DAG, SPE is used for sample preparation. Because of the sensitivity of DAG to silica gel and, more particularly to acidic solutions, it was found necessary to adjust the water sample for analysis to no less than pH 4 and to effect SPE with Polyspher RP-18 (a 35 |im poly-styrene-divinylbenzene polymer with C18 side chains) which gave a 100% recovery. For the extraction a cartridge (0.2 g) was first conditioned successively with ethyl acetate, methanol and water at pH 4 (1 cm3 of each), after which the water sample for analysis adjusted to pH 4 (20 cm3) was aspirated through the cartridge. The cartridge was dried in a stream of nitrogen and then eluted with ethyl acetate (2 x 1 cm3) and the eluate after treatment with one drop of ammonia evaporated at less than 40°C to leave 0.5 cm3, an aliquot of which was applied to an PTLC silica gel 60 F254 pre-coated plate (10 x 20 cm). In the case of original concentrations of less than 5 | g L-1, the total eluate was used for TLC.

For analysis of sample volumes up to 20 | L, multiple development one-dimensionally with solvent A, chloroform-methanol (80: 20) to 8 cm and then after drying, solvent B (chloroform-methanol-glacial acetic acid, 80:20:2) for 6.5 cm was carried out. Alternatively, two-dimensional development was carried out with the same two solvents, distances and drying. Spots or streaks were detected by immersion of the plate in an ethanolic solution of 4-methoxybenz-aldehyde containing sulfuric acid, followed by drying and heating at 130°C for 2-3 min to form red fluor-

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