Evaluation of Data Quality on the Detection of Heavy Metals in Soils by Atomic Absorption Spectrometry or Atomic Fluorescence Spectrometry and X-ray Fluorescence Spectrometry in Ecological Environment Monitoring

BACKGROUNDIn current ecological environmental monitoring, the standard methods used to determine the total contents of inorganic elements, such as heavy metals in soil, include atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS) and wavelength dispersive X-ray fluorescence spectrometry (WDXRF).

OBJECTIVESTo evaluate the quality, validity and mutual comparability of the results obtained by different analytical methods.

METHODSTwenty actual soil samples of different types from different regions in China were selected and inserted into the national soil environmental monitoring sample batch blind, and sent to 3-5 laboratories. AAS/AFS, WDXRF and portable X-ray fluorescence spectrometry (p-XRF) were used to determine the total amount of Cr, Ni, Cu, Zn, As, Hg, Cd, Pb, V and Mn in parallel.

RESULTSThe content of these elements was equally distributed at levels of ≤ 1.0, 1.0-2.0, 2.0-10.0, and 10.0. The results show that 85% samples had better inter-laboratory relative deviation (RD) of the WDXRF method in terms of Cr, Ni, Cu, Zn and Pb. On the other hand, 60% samples had better RD using AFS method for the As determination. Element content had more obvious effect on RD for WDXRF method. Generally, the inter-laboratory precision control was good for both AAS/AFS and WDXRF methods, and the WDXRF method was more desirable. Through further analysis of the parallelism between AAS/AFS and WDXRF methods (evaluated as the relative deviation RD' of the analytical results of these two methods), it showed that almost all the RD' of Cr, Ni, Cu and Zn was less than 20%, and more than eighty percent RD' of As and Pb was less than 20%. The results of Pearson correlation and linear relationship analysis also show that the analytical results of two methods were highly comparable. Additionally, there was also good comparability between the results of AAS/AFS and p-XRF methods for determination of Cr, Ni, Cu, Zn, Pb and As.

CONCLUSIONSAAS/AFS method and WDXRF method have equivalent test results. In actual monitoring task, the determination of Cd and Hg with lower contents should be determined by AAS/AFS which have lower detection limits. WDXRF should be chosen for the analysis large quantities of soil. Under specific experimental conditions, the p-XRF method also can obtain an acceptable quantitative results.