Determination of lead, cadmium and chromium in electrical and electronic products by AA-1800 flame atomic absorption spectrometry - Master's thesis - Dissertation

Determination of Lead, Cadmium and Chromium in Electrical and Electronic Products by AA-1800 Flame Atomic Absorption Spectrometry

Key words: flame atomic absorption method; content of lead, cadmium and chromium in electronic and electrical products; analysis instrument ; AA-1800C range This standard specifies sealed pressure tanks for lead, cadmium and chromium in electrical and electronic products. Digestion-flame atomic absorption spectrometry. This standard applies to the determination of the restricted substances lead, cadmium and chromium in the 10 categories of civil and industrial electrical and electronic products covered by the WEEE and RoHS directives. It covers all materials of electrical and electronic products such as polymers, metals and electronic products. The method is suitable for simultaneously measuring total lead, total cadmium and total chromium content in electronic and electrical products. The minimum detection concentration of the method was: lead (Pb) 0.2 μg / mL, cadmium (Cd) 0.02 μg / mL, chromium (Cr) 0.2 μg / mL. The measurement result of chromium can be used as a quantitative screening method for hexavalent chromium in electronic and electrical products. Method summary The metal components in electronic and electrical are directly treated by conventional low temperature acid digestion to make them soluble salts. The remaining electronic and electrical components are treated by a closed high temperature pressure digestion method: the split and crushed sample is placed in a Teflon tank, nitric acid and hydrogen peroxide water are added, and the stainless steel outer casing is tightened to dissolve the sample in a high temperature and closed container. . The digested liquid is introduced into the atomic absorption spectrometer, and the quantitative analysis of lead, cadmium and chromium is carried out by using the proportional relationship between the absorbance and concentration of Pb, Cd and Cr atoms at a specific wavelength. 3 equipment and reagents 3.1 equipment 3.1.1AA-1800C flame atomic absorption spectrometer (MEAS China), optional lead, cadmium and chromium hollow cathode lamps. 3.1.2 oven, can be heated to 180 ° C. 3.1.3 Teflon cans (with lid) and stainless steel cans. 3.2 Reagents and materials Unless otherwise stated, reagents that meet national or professional standards are used, either in ionized water or water of equivalent purity. 3.2.1 Nitric acid (HNO3): excellent grade pure 3.2.2 hydrogen peroxide (H2O2): analytical pure 3.2.3 hydrochloric acid (HCl): excellent grade pure 3.2.4 lead, cadmium, chromium standard solution: national standard substance, concentration is 100μg /mL or 1000 μg/mL. 4 Determination step 4.1 Sample processing 4.1.1 Wire and cable type: first wash the surface of the wire and cable (with neutral detergent, ionized water, ethanol, etc.), naturally air dry and cut with a tool to a size of no more than 2mm × 2mm sample. 4.1.2 Circuit board type, plastic case, etc.: saw it into a powder sample with a chainsaw, or mechanically crush it and then grind it into a powder sample with a grinder. Small electronic devices such as capacitors and resistors, glass components, etc.: mechanically broken into samples up to 2 mm × 2 mm in size. 4.1.3 Battery type: Metal components (such as casing, electrode, etc.) are returned to category 5.1.4, and non-metallic components (such as battery filling) can be directly sampled after being uniformly mixed. 4.1.4 Metal components: processed into thin strips or powder samples by metal cutting machine or machine tool. 4.2 Sample digestion 4.2.1 High temperature pressure digestion method: Suitable for samples of 4.1.1 to 4.1.3. Weigh 0.2g~0.5g sample into the Teflon tank correctly, add 8mL HNO3 (3.2.1), 5mLH2O2 (3.2.2), cover with Teflon cap, tighten the stainless steel jacket, and put it into the oven. Heat at 180 ± 5 ° C for 4 hours. Cool to room temperature. Take out the Teflon tank. At this time, the organic matter contained in the sample should be completely digested, the solution is clear, transfer the solution carefully to a 100 mL volumetric flask, wash the Teflon tank and cover 3-4 times with water, and wash the solution. In the volumetric flask, make up to the mark. If the solution is not clear or precipitated, filter it with filter paper or filter and store the filtrate for testing. At the same time, do the reagent vacancy experiment. 4.2.2 Conventional low temperature acid digestion method: suitable for 4.1.4 samples. Weigh 0.5g sample into beaker or conical flask, add 3mL water, 3mL HNO3 (3.2.1), cover the surface dish, wait for the reaction to calm down. . If the sample still has a residue, warm it on the hot plate. Add 1~2mL HNO3 (3.2.1) depending on the degree of dissolution until the sample is completely dissolved. A metal or alloy that cannot be dissolved in nitric acid may be supplemented with 5-10 mL of HCl (3.2.3) and dissolved at low temperature. After the dissolution was complete, it was cooled and transferred to a 100 mL volumetric flask, washed with water and brought to volume. At the same time, do the reagent vacancy experiment. 4.3 Determination of 4.3.1 atomic absorption spectrometer parameters using flame atomic absorption spectrometry, according to the instrument manual requirements to choose their own test conditions, the general instrument use conditions are: elemental measurement wavelength, nm other optional wavelength, nm passband width, nm flame background Calibration Pb217.0283.31.0C2H2-air open Cd228.8326.20.5C2H2-air open Cr357.9429.00.2C2H2-air open 4.3.2 calibration curve using lead, cadmium, chromium standard solution (4.6), diluted with water, with the following Standard solution (containing 2% HNO3 medium, single standard and mixing standard): Pb (μg/mL): 0,1,2,3,5,10; Cd (μg/mL): 0,0.1,0.2, 0.3, 0.5, 1; Cr (μg/mL): 0, 1, 2, 3, 5, 10. This standard solution series can be stored at 4 ° C for 1 month. The absorbance of the standard solution is measured, the calibration curve is plotted with the corresponding concentration of the absorbance value, and the fitting curve parameters (slope, intercept, linear coefficient, characteristic concentration, etc.) are calculated. 4.3.3 Sample measurement and results The absorbance values ​​of the digestion solution (4.2) were measured while measuring the calibration curve, and the concentrations of Pb, Cd and Cr in the digestion solution were calculated from the calibration curve. If the concentration of Pb, Cd and Cr in the digestion solution exceeds the concentration value at the highest point of the calibration curve, the digestion solution should be appropriately diluted before measurement. The Pb, Cd and Cr contents in the sample are calculated according to formula (1): C=(AB)×V×N/W........................(1) where: C——Pb, Cd or Content, μg / g; A - the concentration of the sample calculated from the calibration curve, μg / mL; B - the concentration of the vacancy solution calculated from the calibration curve, μg / mL; V - the volume of the digested solution , mL; N - digestion factor dilution factor; W - sample sample quality, g. 5 Precision The absolute difference between two independent determinations obtained under repeated conditions shall not exceed 15% of the arithmetic mean.