Exfoliated Graphite as a Solid Sorbent in Ultrasound-Assisted Dispersive Micro-Solid-Phase Extraction for Determination of Chromium and Vanadium in Herbs

In this research, a preconcentration procedure was developed for the sequential determination of chromium and vanadium using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS). Due to low concentrations, chromium and vanadium were determined following preconcentration onto exfoliated graphite using ultrasound-assisted dispersive micro-solid-phase extraction (US DMSPE). The experimental parameters, including pH of the sample solution, the amount of exfoliated graphite, extraction time, elution conditions, as well as the main parameters of HR-CS GFAAS, were investigated. The calculated limits of detection for Cr and V were 0.003 µg g⁻¹ and 0.006 µg g⁻¹, respectively. The preconcentration factors obtained for Cr and V were 28 and 34, respectively. The RSD ranged from 0.3% to 3.4% for Cr and from 0.9% to 4.6% for V. The accuracy of this method was validated by analyses of INCT-MP4-2 (Mixed Polish Herbs) certified reference material. The measured chromium and vanadium contents were in satisfactory agreement with the certified values according to the t-test for a 95% confidence level. The proposed method was successfully applied for the determination of both elements in herbs such as hawthorn flower, hawthorn fruit, motherwort, white mulberry leaf, common milkweed, mistletoe, valerian root, and horse chestnut bark.