Determination On Trace Concentrations Of Six Hazardous Substances For RoHS Compliance

The threaten of hazardous substances contained in electronic and electrical equipment (EEE) to environment is of high concern, therefore, European Council and Parliament issued the RoHS Directive to restrict the maximal concentration value (MCV) of six substances ? lead (Pb), cadmium (Cd), mercury (Hg), hexavalent chromium (Cr6+), polybrominated biphenyls (PBBs),and polybrominated diphenylethers (PBDEs) ? contained in the new EE products put on the EU market at the trace level (100mg/kg or 1000mg/kg). To comply with the RoHS regulation, EE industries in Hong Kong and China South are facing with great challenges. In this work, GC-MS, ICP-OES, UV-Visible Spectrophotometry were employed to determine the trace concentrations of the above six hazardous substances, and a standard method system for screening primarily, extraction, qualitative and quantitative analyses of the six substances was established and their factors were analyzed. By evaluating the relative standard deviation (R.S.D), recovery, repeatability, limit of detection, linear relation etc., the optimum parameters were given and thus the precision of analysis was equal to or higher than the IEC 62321 standard, meeting the requirement of RoHS.Several methods were proposed to solve the issues in the process of the instrumental analysis on the six hazardous substances. Firstly, by means of interelement correction (IEC), multi-wavelengths, two-point correction, and SPE online flow-injection adsorption method etc., background shift and spectra overlap caused by matrix effect, ambient ion interferences, emission of non-analytes in ICP-OES analysis were eliminated. Secondly, in order to overcome the interferences from PCB, PCN, HCB in the process of determination of PBBs/PBDEs, a matrix solid-phase dispersion (MSPD) method with YMC ODS-C18 as carrier was employed, which completely removed the negative influences of the persistent organic pollutants (POPs). Thirdly, by combining GC-NICI-MS with GC-EI-MS, brominated isomers or ramifications were distinguished from other halogen compounds in which anion fragment retention peaks of [Br]-, [HBr2]- and molecule chain fragment peaks of [M+2]+,[M+4]+,[M+6]+,[M+8]+ were observed simultaneously, and thus the selectivity to brominated retardant flames was greatly improved. Besides, effects of sample shape, thickness, screening area and screening time etc. on X-ray emission intensities of analytes during EDXRF screening were discussed, and in order to eliminate secondary excitation of analytes, absorption, X-ray dispersion of coexisting ions etc., a parameter simulation regression analysis was established, the results showed that a satisfactory function curve between emission intensities and concentration of analytes was obtained. The above means can improve the precision and reliability on the determinations of six hazardous substances.The limit of detection (LOD) on the ultralow substance content is a"bottleneck"of the spectral and chromatographic technologies. The determination of the ultratrace concentration of Cr6+, Pb, Cd were studied by enriching/preconcentrating method with two adsorbents: sawdust and multi-walled carbon nanotubes (MWCNTs). The former was used to enrich Cr(VI) and separate Cr(III), the later was employed to enrich Pb2+, Cd2+ and removal the interference during Hg determination. In order to enhance enrichment efficiency, thermodynamic and dynamic parameters such asΔGο,ΔHο,ΔSοwere discussed. The result showed that the objective content in the sample solutions was concentrated about 50-100 fold, and LOD was minimized toμg·L-1, ng·L-1 level.Furthermore, an optimized imminent model based on back-propagation neural network for experimental data was programmed. The n-D internet relation of sample data can be reduced dimensionly on 2-D plane without loss of real information, and along the trend direction, an optimal point was found out. Using this model to optimize the operational condition of Cr(VI) extraction and PBBs soxhlet extraction, the error (ξ) between simulation and real value was less than 0.05%, which provided a theoretic basis of actual experimental optimization design.Pointing to the economic pressure for RoHS compliance and based on SONY green management system, a"stocking-producing-saling"tri-chain method on supervising the EE products was established, and it is meaningful to guide the green products management of electronic and electrical industries in China Mainland and Hong Kong.