Determination of Lead in High Purity Graphite by Graphite Furnace Atomic Absorption Spectrometry with Ultrasonic Extraction

In order to solve the time-consuming problem of high-temperature ashing (4-10 h) in the pre-treatment of high purity graphite samples, a method mentioned by title was proposed. The high purity graphite sample (0.300 0 g) was taken and placed into a 50 mL-polypropylene sample tube, and 15 mL of 10% (volume fraction) aqua regia (a mixture of hydrochloric acid and nitric acid at a volume ratio of 3∶1) solution was added for ultrasonic extraction for 20 min. Some graphite floated on the liquid surface in extraction process, so 3 mL of the extraction solution was sucked from the middle of the sample tube with a syringe, and passed through 0.45 μm water system filter membrane. The filtrate was collected into a sample tube and determined by graphite furnace atomic absorption spectrometry under the conditions such as ashing temperature at 900 ℃ and atomization temperature at 2 000 ℃. As shown by the results, ultrasonic extraction shortened the sample processing time (only 20 min). Linear relationship between the corresponding absorbance and mass concentration of Pb was found in the range of 5-50 μg·L^-1, with detection limit (3s/k) of 0.11 mg·kg^-1. The same sample was analyzed 7 times, with RSDs of the determined values of 4.6%. Test for recovery was made by standard addition method, giving results in the range of 91.0%-94.0%.