Maichin B, Kettisch P, Knapp G
Institute for Analytical Chemistry, Micro- and Radiochemistry, Technical University Graz, Austria.
Fresenius J Anal Chem. 2000 Jan;366(1):26-9. doi: 10.1007/s002160050006.
Investigations of microwave assisted drying of sample materials and microwave assisted evaporation of aqueous sample solutions and acidic digestion residues were accomplished by means of special rotors for the microwave digestion system MULTIWAVE. To check the results obtained by microwave assisted drying, the samples were also conventionally dried at 105 degrees C in an oven. The following samples have been dried: 10 g each of meat, fish, apple, cucumber, potato, mustard, yogurt, clay and marl; 1 g each of certified reference material TORT 2 (lobster hepatopancreas), BCR 278 (mussel tissue) and BCR 422 (cod muscle); 500 g garden mould. Microwave assisted drying takes 40 min for organic samples and 30 min for inorganic material. Important is a slow increase of microwave power during the first 20 min. The results agree well with conventional drying at 105 degrees C. Losses of As, Se and Hg have been investigated for 3 CRMs. Only Se shows losses in the range of 20%. Losses of As, Be, Cd, Co, Cr, Cu, Fe, Hg, Li, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sr, Ti, Tl, V and Zn after evaporation of aqueous samples and acidic solutions after wet digestion, respectively, have been investigated. 50 mL aqueous solution was evaporated almost to dryness within 25 min. The recovery of Hg is 40-50%, of Se 90-95% and of the other elements 97-102%. 0.2 g each of TORT 2, BCR 278 and BCR 422 have been digested with 4 mL nitric acid and 1 mL hydrochloric acid by means of the microwave digestion system MULTIWAVE. The digestion residue was evaporated almost to dryness and dissolved again in 10 mL diluted nitric acid. In this case no element losses have been observed. The measured concentration of As, Cd, Cu, Fe, Mn, Hg, Pb, Mo, Ni, Se, Sr, V and Zn agree very well with the certified values. An important prerequisite for good recoveries is not to evaporate the solutions to complete dryness.
借助微波消解系统MULTIWAVE的特殊转子，对样品材料的微波辅助干燥、水性样品溶液和酸性消解残渣的微波辅助蒸发进行了研究。为检验微波辅助干燥所得结果，还将样品在烘箱中于105℃进行常规干燥。已干燥的样品如下：各10克的肉、鱼、苹果、黄瓜、土豆、芥末、酸奶、黏土和泥灰岩；各1克的有证标准物质TORT 2（龙虾肝胰腺）、BCR 278（贻贝组织）和BCR 422（鳕鱼肌肉）；500克园土。有机样品的微波辅助干燥需40分钟，无机材料需30分钟。重要的是在最初20分钟内微波功率缓慢增加。结果与在105℃的常规干燥结果吻合良好。对3种有证标准物质研究了砷、硒和汞的损失情况。只有硒的损失在20%范围内。分别研究了湿法消解后水性样品和酸性溶液蒸发后砷、铍、镉、钴、铬、铜、铁、汞、锂、镁、锰、钼、镍、铅、锑、硒、锶、钛、铊、钒和锌的损失。50毫升水性溶液在25分钟内几乎蒸发至干。汞的回收率为40 - 50%，硒为90 - 95%，其他元素为97 - 102%。借助微波消解系统MULTIWAVE，将各0.2克的TORT 2、BCR 278和BCR 422与4毫升硝酸和1毫升盐酸进行消解。将消解残渣几乎蒸发至干，然后再次溶解于10毫升稀硝酸中。在这种情况下未观察到元素损失。测得的砷、镉、铜、铁、锰、汞、铅、钼、镍、硒、锶、钒和锌的浓度与认定值非常吻合。良好回收率的一个重要前提是不要将溶液蒸发至完全干燥。
