提出了石墨炉原子吸收光谱法测定粮食中痕量铅量时采用铱作为持久性化学改进剂.用1.000 g·L-1铱(Ⅲ)溶液50 μL涂于石墨平台上并按规定步骤处理.结果表明:经铱溶液处理后的平台经至少400次使用仍能保持较好的灵敏度和再现性.使用此平台时,最佳的灰化和原子化温度和时间分别为900 ℃,10 s和1 800 ℃,3 s.与磷酸二氢铵-硝酸镁、氯化钯常规改进剂比较,采用铱作持久性化学改进剂,石墨炉原子吸收光谱法测定粮食中铅,灵敏度高且背景信号值低.方法的检出限(3S/N)为8 pg,特征质量为30 pg.试样加标回收率在93.2%~104.5%之间,相对标准偏差(n=7)小于3.5%.

Iridium was proposed to be used as endurable chemical modifier in the ETAAS determination of trace amounts of lead in food sample.Fifty μL of 1.000 g·L-1 iridium(Ⅲ) solution was apllied to the graphite platform and treated according to the prescribed program.It was shown that the graphite platform treated with Ir kept good sensitivity and reproducibility even after its used for at least 400 times.The optimum temperature and time for ashing and atomization with this modified graphite platform were found to be 900 ℃,10 s and 1 800 ℃,3 s respectively.As shown by the results of companative study with the conventionally used modifiers,e.g.,NH4H2PO4+Mg(NO3)2 and PdCl2,lower values of background signal and detection limit were found with the Irmodified platform.In its application to the ETAAS determination of lead in food samples,values of detection limit (3S/N) and characteristic mass found were 8 pg and 30 pg respectively.Tests for recovery and precision were made by standard addition method,the results of recovery obtained were in the range of 93.2% to 104.5%,with RSD′s (n=7) less than 3.5%.