Classical wet ashing versus microwave-assisted attacks for the determination of chromium in plants

Microwave-assisted pre-treatments for the determination of Cr in plants are compared with classical wet-ashing procedures using open attacks in sand-b aths. Four certified plant reference materials were analysed: pine needles (NIST SRM 1575), rye grass (BCR CRM 281), beech leaves (BCR CRM 100) and an aquatic plant (Ti apa natans) (BCR CRM 596). The use of acidic procedures with HClO4 or H2SO4 yielded different Cr results for these materials when c lassical wet-ashing procedures were used, as the use of HClO4 caused losses of volatile chromium compounds. The shorter time of analysis required (60 min) in open-focused microwave-assisted attack allows the use of HClO4 for obtaining results very close to the certified values for GRIM plant materia ls. This type of microwave digestion also led to good reproducibility value s with relative standard deviations between 5 and 10%.