Abstract
The nitrosamine N-nitrosoglyphosate (NNG) is present as a minor impurity in technical-grade glyphosate (GLY), which is widely used in crops worldwide. Due to their high toxicity, regulatory agencies have established as 1.0 mg kg−1 (w/w) the maximum concentration of NNG allowed in the technical standard of glyphosate to produce commercial formulations. Considering the high similarity between the structural formulas of NNG and GLY, a flow system with online photo-cleavage coupled to solid phase extraction is proposed. The NO group of NNG was cleaved by UV radiation (254 nm) and sequentially isolated in the form of NO2− at the strong anionic exchange sorbent in a mini-column. Griess reagent was used as eluent solution for the spectrophotometric determination of NO2−, which was related to NNG concentration. The extraction procedure and photo-cleavage reaction were carried out in SIA system, resulting in a linear range from 0.05 to 1.25 mg kg−1 NNG (R2 = 0.9937) with sampling rate of 5.7 det h−1. The pre-concentration factor was twelve-fold and good repeatability for the 0.05 mg kg−1 solution of NNG was observed (r.s.d = 3.7%, n = 3) after 48 successive determinations, without significant changes in the analytical figures of merit. A limit of detection (LOD) of 3.1 × 10−3 mg kg−1 was estimated and good recoveries (96.5%, n = 3) in the presence of high amount of glyphosate was obtained.
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