Rapid sample preparation with multi-channel focused infrared micro-ashing prior to determination of chromium in gelatin capsules by electrothermal atomic absorption spectrometry

Abstract

A novel multi-channel micro-ashing method for gelatin capsules based on focused infrared radiation prior to trace chromium determination by electrothermal atomic absorption spectrometry (ETAAS) was proposed. Currently, almost all the official analytical methods (i.e. the European, British, and Chinese Pharmacopeias) for chromium in gelatin recommend the use of ETAAS, with the difference that the sample preparation method is either wet digestion or ashing in muffle furnaces. The proposed method was based on dry ashing with infrared radiation-based heating. Infrared light was focused through a gold-plated mirror to the micro-zone of a sample, and then the sample was heated quickly. In addition, by using a flow-through ashing tube with the aid of argon-assisted charring and oxygen-assisted ashing, the entire ashing process could simultaneously treat 12 samples in 15 min. The method detection limit was 0.023 μg g⁻¹. The relative standard deviations (RSD) were 3.6%, 2.4%, and 1.2% (n = 5) for 5, 10, and 20 ng mL⁻¹ chromium, respectively. Two gelatin certified reference standards were used to verify the method accuracy with recoveries of 98% and 105%, respectively. The proposed method was also applied to the analysis of real samples. The results were compared with the ones from microwave digestion and the ones obtained by conventional ashing, and they showed no significant difference. Compared with wet acid digestion and muffle furnace ashing, the proposed method was environmentally friendly and more efficient. The volume of the entire infrared ashing device was only one-fifth of the volume of a common muffle furnace. This method was more suitable for routine high throughput sample analysis in food and drug quality supervision.