Sensitive determination of glyoxal, methylglyoxal and hydroxyacetaldehyde in environmental water samples by using dansylacetamidooxyamine derivatization and liquid chromatography/fluorescence

Abstract

In this study we improved the dansylacetamidooxyamine (DNSAOA)–LC–fluorescence method for the determination of aqueous-phase glyoxal (GL), methylglyoxal (MG) and hydroxyacetaldehyde (HA). As derivatization of dicarbonyls can potentially lead to complex mixtures, a thorough study of the reaction patterns of GL and MG with DNSAOA was carried out. Derivatization of GL and MG was shown to follow the kinetics of successive reactions, yielding predominantly doubly derivatized compounds. We verified that the bis-DNSAOA structure of these adducts exerted only minor influence on their fluorescence properties. Contrary to observations made with formaldehyde, derivatization of GL, MG and, to a lesser extent of HA, was shown to be faster in acidic (H 2SO 4) medium with a maximum of efficiency for acid concentrations of ca. 2.5 mM. Concomitant separation of GL, MG, HA and of single carbonyls was achieved within 20 min by using C 18 chromatography and a gradient of CH 3CN in water. Detection limits of 0.27, 0.17 and 0.12 nM were determined for GL, MG and HA, respectively. Consequently, low sample volumes are sufficient and, unlike numerous published methods, neither preconcentration nor large injection volumes are necessary to monitor trace-level samples. The method shows relative measurement uncertainties better than ±15% at the 95% level of confidence and good dynamic ranges ( R 2 > 0.99) from 0.01 to 1.5 μM for all carbonyls. GL, MG and HA were identified for the first time in polar snow samples, but also in saline frost flowers for which unexpected levels of 0.1–0.6 μM were measured. Concentrations in the 0.02–2.3 μM range were also measured in cloud water. In most samples, a predominance of HA over GL and MG was observed.