# Ensuring the Quality of the Analytical Process in a Research Laboratory
## 3 Results  
Scaling down the Standard Operating Procedure (SOP)--Sequential Extraction of Mine Tailing and Fly Ash  
BCR sequential procedure allowed the mobility of heavy metals to be estimated. In the process of valorization of industrial waste and assessment of the environmental effect, the interest in sequential extraction constantly increased. However, two main problems could be encountered during the attempts to verify the procedure in the research laboratory: (1) the volume of the used equipment was too specific for the standard operation procedure of BCR sequential extraction and could substantially differ from the available instrumentation (80-100 mL centrifuge tubes and corresponding centrifuge were needed); and (2) the available CRM was lake sediment from a highly contaminated region, whose chemical, mineralogical, and particle-size compositions could differ greatly from the target materials'. BCR sequential extraction procedure was applied to copper mine tailings from Bulgaria to study heavy metal distribution in geochemical fractions. The results are presented in Table 1. However, the BCR procedure was modified by lowering the quantity of the sample but preserving the solid-to-liquid ratio. This modification allowed for the available equipment to be used. The scaled-down procedure could be expected to influence the recovery of heavy metals in each step of the BCR procedure [4; 5]. To verify the procedure, CRM BCR 701 was analyzed along with mine tailing samples. The results are presented in Figure 2 and Tables 1 and 2. It can be seen from this figure that the total content of heavy metals corresponded to the CRM values with the uncertainty limits. The mean values in steps 1 and 2 coincided with the certified values. However, individual recoveries in some cases at steps 3 and 4 were unsatisfactory. It could be supposed that the discrepancy could be due to the modification of the BCR procedure or to the matrix effect during ICP-OES measurement [7]. The sequential extraction results were often reported as a comparison of the concentrations of heavy metals in different fractions. Thus, the heavy metal order obtained experimentally by analyzing CRM was compared with the order of the certified concentrations (Table 2). Nevertheless, judging by the discrepancy in a part of the individual recoveries, it could be seen that the abundance of heavy metal in BCR fractions based on experimental and certified concentrations followed the same trend. It could be pointed out that the BCR CRM 701 presented a lake sediment that differed in its chemical and mineralogical composition from the studied material--mine tailings. Thus, the verification of the BCR method by CRM 701 could only approximately estimate the method behavior of real samples. The results presented in Table 1 showed that iron was the most abundant metal in the studied sample, and Cd and Ni were below the method's LOD. The metals in mine tailing were arranged according to the concentration of extractable species (Table 2); CRM results were also presented for comparison. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Fraction** & **Fe** & **Cu** & **Zn** & **Mn** & **Cd** & **Ni** & **Pb** \\ \hline \multicolumn{1}{c}{} & \multicolumn{5}{c}{**mg/kg**} \\ \hline Fraction 1 (exchangeable) & 447 & 107 & 5.5 & 20.5 & \textless{}0.25 & \textless{}0.5 & 3.8 \\ \hline Fraction 2 (reducible) & 740 & 41.4 & 6.5 & 10.3 & \textless{}0.25 & \textless{}0.5 & 9.2 \\ \hline Fraction 3 (oxidizable) & 8142 & 188 & 10.3 & 40.6 & \textless{}0.25 & \textless{}0.5 & 13.7 \\ \hline F1 + F2 + F3 (total mobile) & 9329 & 337 & 22.2 & 71.4 & \textless{}0.25 & \textless{}0.5 & 26.7 \\ \hline Fraction 4 (residual) & 10,380 & 100 & 40.2 & 102 & \textless{}0.25 & \textless{}0.5 & 17.5 \\ \hline Total & 197,116 & 437 & 62.4 & 173 & \textless{}0.25 & \textless{}0.5 & 44.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Heavy metal distribution in geochemical fractions in copper mine tailing and fly ash from coal combustion.