Global Journal of Science Frontier Research, H: Environment & Earth Science, Volume 22 Issue 5

1 Global Journal of Science Frontier Research Volume XXII Issue V Year 2022 45 ( H ) Version I © 2022 Global Journals Validation of X-Ray Fluorescence Spectrometer Technique to Determine Heavy Metal Concentrations in Soil Samples was prepared using the sample cup preparation. The sample cup was assembled using a 3.6 µm SpectroMembrane® Mylar® Thin-film. Each round consisted of around fourteen samples, where an average of 12 minutes was taken for each sample to be analysed. Each of the five samples was tested three times ensuring that the EDXRF was calibrated and provided reliable results. The data produced was semi- quantitative, and the elemental concentrations were then established by using a fitting method supplied by Bruker. The second batch was tested at an accredited lab situated in Germany, using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The laboratory used was accredited according to DIN EN ISO/IEC 17025:2005 notification under the Deutsche Akkreditierungsstelle (DAkkS), the national accreditation body of the Federal Republic of Germany for testing. The standard ISO/IEC 17025:2005 stipulates, in both English and German, the general prerequisites for the competence to perform tests and/or calibrations, carried out using standard methods, laboratory-developed methods and non-standard methods[21]. The laboratory was (D-PL-14081-01-00) accredited. DIN EN 13657: 2003-01 standard was used for the aqua regia digestion which is the ‘characterisation of waste - digestion for subsequent determination of aqua regia soluble portion of elements in waste’[22]. Statistical analysis was determined using the software package IBM® SPSS® Statistics 26 by comparing the results obtained by the two equipment. The data were compared by using the binomial test to calculate the ρ -value and its level of significance, and the Spearman correlation coefficient test which measured the strength of the relationship. III. R esults and D iscussion The five samples were analysed using both the XRF and ICP-MS. The quantification of the XRF data was attained by using the automatic Bruker S2 Ranger XFlash® technology which was equipped with an X-ray tube anode made of Palladium. Using tube voltages of 10 kV, 20 kV, 40 kV and 50 kV, for 180 seconds, at each voltage with a helium atmosphere, a current of 2 mA, and having a silicon drift detector. The elements detected in the soil samples were expressed as oxides. Calcium carbonate was used as a matrix to calculate the heavy metal oxides, while using the instrument’s software, Spectra EDX Launcher, to read the data. The XRF method provided a simultaneous result of 44 elements, though only As, Pb, Cd, Cu, Ni and Zn were used to compare the results with the same elements as those given in the ICP-MS report. Table 1 shows the comparison of the mean values between the XRF and the ICP-MS which were used to statistically test the data. The binomial test confirmed that the XRF data are positively related to the ICP-MS as all the ρ -values exceeded the 0.05 level of significance as seen in table 2. The Spearman correlation coefficient used to compare the relationship can be seen in figures 2-5 where figure 2 and 3 display a strong positive relationship close to 1 for arsenic (R 2 = 0.646) copper (R 2 = 0.888), cadmium (R 2 = 0.202), lead (R 2 =0.837), nickel (R 2 = 0.513) and zinc (R 2 = 0.699), whilst figure 4 displays no relationship of 0 for chromium and mercury. The overall correlation was a strong positive relationship where R 2 = 0.811. The results indicated that the XRF and ICP-MS are comparable and that the XRF produces good results when compared to an accredited instrument. The ICP- MS when compared to the XRF can be seen to be a very reliable instrument that can accomplish limits of detections at many orders of degree lower. Although it has excellent accuracy, the ICP-MS has a disadvantage that the sample needs to be in a liquid form when being tested, thus requiring acid digestion and long preparation times, when comparing it to the other instrument. The ICP-MS also has a higher cost including the consumables. On the other hand, the XRF spectrometer is cheaper to use, easier, and uses a rapid technique when comparing it to other methods of analysis. It has the advantage of reading both the solid and liquid form [23]. The ICP-MS is a quantitative instrument and has been increasing in popularity compared to the other instruments. Its detection limits can reach below the single part per trillion of any element, and it can also achieve isotopic analysis. Determination of each element’s concentrations in the sample is brought about by relating the counts measured of a definite isotope with an external calibration curve that was formerly created for that specific element [24,25]. The XRF is a semi-quantitative instrument. The data given ascertains the relative element concentrations between the samples though it does not give absolute concentration amounts. The results are calculated by analysing the area under the peak of interest. This proves why the results of both instruments are non-identical and not similar to the elements being tested as seen in Table 1[26]. When comparing the mean concentration of the elements (table 3), to the Government Decree on the Assessment of Soil Contamination and Remediation Needs the threshold limits for soil contamination [27]as seen in table 4, As, Pb and Cd proved to have a higher level than the threshold. These three heavy metals are used in everyday life and cause a number of adverse effects when present in high concentrations as in the study. Anthropogenic pollution of As could be caused through the preservation of wood, certain insecticide formulations, particular glass manufacturing, doping agent in semiconductors like gallium arsenide which