Studies On Measuring Method And Technology Of Soil Heavy Metals By Using Direct Solid Sampling

Solid sampling technology by atomic absorption(AAS), atomic fluorescence has been rapidly developed in the field of analysis techniques recently, which can replace the burdensome pre-treatment of the solid samples to avoid sample contamination and loss, and effective reduction of the method detection limit, simplify the pretreatment, avoid loss of trace elements and also to protect of the operating personal.According to the demand of the rapid determination of field, in this study, working conditions of the instrument were studied and optimized by solid sampling device DLAA-5130 and DCMA-200. Pauwels formula and Homogeneity(HE) was used to estimate the minimum sample mass real samples, and verify the representation of the estimated values. The accuracy of the methods was processed by determination of soil reference materials and soil samples from different areas. The reliability of the method was tested by comparison among different instruments.1. This study used control variate method to optimize the ashing time, evaporation power, release power of the solid sampling instrument DLAA-5130 and DCMA-200. Establish the optimal conditions for determination of four elements at last. The drying and ashing powers of Cd were 230 W, ashing time was 70 s, evaporation power was 90 W, evaporation time was 20 s, release power was 50 W. The detection limit of Cd was 0.0067 mg·kg-1, relative standard deviation was less than 5%, analysis time less than ten minutes; The drying and ashing powers of Hg were 140 W, ashing time was 150 s, evaporation power was 80 W, evaporation time was 20 s, release power was 150 W. The detection limit of Cd was 0.0046 mg·kg-1, relative standard deviation was less than 5%, analysis time less than ten minutes; Atomic fluorescence total current range was 40~60 mA, auxiliary cathode current range was 20~30 mA, negative high voltage range was 240~260 V; The drying and ashing voltage of Pb were 2.9 V, ashing time was 90 s, evaporation voltage was 1.7 V, Evaporation time was 10 s, release voltage was 1.5 V, atomic fluorescence total current range was 40~60 mA, auxiliary cathode current range was 20~30 mA, negative high voltage range was 240~260 V. The detection limit of Pb was 0.00065 mg·kg-1, relative standard deviation was less than 5%, analysis time less than five minutes; The drying and ashing voltage of As were 4.4 V, ashing time was 80 s, evaporation voltage was 1.7 V, Evaporation time was 10 s, release voltage was 1.6 V, atomic fluorescence total current was 150 mA, auxiliary cathode current range was 75 mA, negative high voltage range was 280~310 V. The detection limit of As was 0.006 mg·kg-1, relative standard deviation was less than 10%, analysis time less than five minutes;2. The study discuss the effect of temperature on the pre-treatment. The results show that drying procedure below 100℃ was comparable with air-dry. It accord with the trace sampling requirements of the instrument when the minimum sample mass range was 3~6 mg and the minimum grinding particle size was less than 0.43 mm(40 mesh) estimated by the Pauwels formula, Homogeneity(HE) and Environmental quality standards for soils. The accuracy of the result was further confirmed through the continuous determination of above 10 times and eliminate outliers, and satisfactory consequence was received.