Flow-injection MS analysis as a simplified approach to pesticide screening in apples.

A fast and simplified method based on mass spectrometry analysis was developed for pesticide qualification in apple peel. The main feature of the method is flow-injection of the loop pre-defined sample volume directly to the MS source, with no chromatographic separation. Method performances were evaluated for five pesticides regularly used in apple orchard treatments. First, primary features of the method such as the loop injection dynamics, total analysis time, chronogramic peaks integrity and sensitivity were evaluated. Then the applicability of the method for qualitative and quantitative screening was assessed on citrate buffered QuEChERS cleaned-up apple peel samples. The developed method offers a possibility for simplified, more economic high throughput screening for pesticides in apples. The method is intended to be a tool for preliminary qualitative assessment of pesticides residues in fruit. Quantitative features of the method are analyte and sample preparation dependent, most certainly due to the lack of chromatography.

Spectroscopic and potentiometric studies on derivatized natural humic acid.

Isolated soil humic acid (HA) and commercial Aldrich HA were derivatized by esterification with methanol-thionyl and acetylation with acetic anhidride, in order to obtain derivatives with selectively blocked carboxyl and phenol groups, respectively. Results obtained by FT-IR spectroscopy and potentiometry show that the methanol-thionyl procedure is a selective, specific and efficient route for blocking carboxyl groups. The good correlation between results obtained by direct potentiometry after HA esterification and by classical calcium-acetate and baryta exchange methods suggests that esterification followed by direct acid-base potentiometric titration can be used as a method for the estimation of carboxyl and phenol group contents. Phenol groups can not be specifically identified by the acetylation method, due to the low selectivity of the acetylation method. The average values of apparent and intrinsic pK of underivatized and derivatized HAs confirm decrease in ionizable groups content due to derivatization and their values are related to the different chemical structures of the acids.