Fabrication of monolith-based solid-phase microextraction for effective extraction of total chromium in milk and tea samples prior to HPLC/DAD analysis

Abstract

A convenient, sensitive and low-cost approach for the determination of trace levels of total chromium in milk and tea samples was developed by combination of solid-phase microextraction (SPME) and HPLC/DAD. To meet the chromatographic separation and UV detection, Cr(VI) was reacted with sodium diethyldithiocarbamatetrihydrate to form Cr coordination compound. According to the chemical properties of the complex, a new sorbent based on porous monolithic material (PMM) was fabricated and employed as the extraction phase of SPME. The prepared PMM displayed satisfying enrichment ability for Cr complex. Under the most appropriate parameters, the linear ranges for chromium were 1.0–500 μg/kg and 0.5–300 μg/kg in milk and tea samples, respectively, with good correlation coefficients (R2 greater than 0.99). The limits of detection for chromium were as low as 0.11 μg/kg and 0.092 μg/kg in milk and tea samples, separately. The RSDs for method precision were in the range of 0.23–8.6%. The reliability and applicability of introduced method was successfully demonstrated by quantification of low contents of total chromium in milk and tea samples. The recoveries at three fortified levels varied from 83.4% to 112%, and the RSDs (n = 3) were in the range of 2.1% and 8.9%. Compared with existing methods, the current approach exhibited some merits such as satisfactory sensitivity, low consumption of sample and high cost effectiveness.