## 3 Results and Discussion
### Repeatability, Accuracy and Precision  
Spectral interferences, as described above, play an important role in trace element analysis using ICP-MS. He and H collision or reaction gas, respectively, were chosen in order to avoid relevant spectral interferences, as shown in Table 3. According to [PERSON] et al. [52], the use of standard reference material is recommended when validating a method. The element composition of the urine samples and the intra-and inter-day analysis of the samples are shown in Table 7. The values shown in Table 7 are the average of triplicate preparations within a day analysis (\(n\) = 3). The final average concentration is an average concentration of the average values of each day. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Analytic** & **Validation Range (\(\mu\)g L\({}^{-1}\))** & **R\({}^{2}\)** & **Slope** \\ \hline Al & 11.33–87.10 & 0.9925 & 1.0068 \\ V & 6.93–50.90 & 0.9954 & 0.9899 \\ Cr & 1.35–19.90 & 0.9955 & 0.9469 \\ Mn & 2.77–19.90 & 0.9953 & 0.9418 \\ Fe & 21.45–222.00 & 0.9965 & 0.9469 \\ Co & 0.68–34.30 & 0.9931 & 0.9102 \\ Cu & 18.87–111.00 & 0.9961 & 1.0062 \\ Zn & 68.67–531.00 & 0.9936 & 1.0386 \\ As & 14.50–82.30 & 0.9985 & 0.9701 \\ Se & 11.60–89.30 & 0.98 & 1.0151 \\ Mo & 7.97–99.30 & 0.9988 & 1.0077 \\ Cd & 0.82–14.30 & 0.9999 & 0.889 \\ Sn & 1.71–10.00 & 0.9982 & 0.954 \\ Ba & 3.60–51.30 & 0.9984 & 0.9716 \\ TI & 2.27–17.70 & 0.9988 & 0.8703 \\ Pb & 9.17–54.40 & 0.9926 & 0.9593 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Linearity, slope and validation range of urine analytes. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Analyte** & **LOD (ug L\({}^{-1}\))** & **LOQ (ug L\({}^{-1}\))** \\ \hline Al & 7.90 & 23.94 \\ V & 2.77 & 8.41 \\ Cr & 0.29 & 0.87 \\ Mn & 0.72 & 2.17 \\ Fe & 5.50 & 16.65 \\ Co & 2.18 & 6.60 \\ Cu & 3.83 & 11.61 \\ Zn & 10.48 & 31.75 \\ As & 2.42 & 7.34 \\ Se & 3.56 & 10.80 \\ Mo & 1.05 & 3.19 \\ Cd & 0.11 & 0.33 \\ Sn & 0.22 & 0.66 \\ Ba & 0.42 & 1.28 \\ Tl & 0.46 & 1.39 \\ Pb & 4.19 & 12.69 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Limit of detection (LOD) and limit of quantification (LOQ) of the method performed in this study. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Analyte** & \begin{tabular}{c} **Theoretical** \\ **Concentration** \\ **(ug L\({}^{-1}\))** \\ \end{tabular}  & \begin{tabular}{c} **Measured** \\ **Concentration** \\ **(ug L\({}^{-1}\))** \(\pm\) SD** \\ \end{tabular}  & \begin{tabular}{c} **Accuracy (\%)** \\ **(\%)** \\ \end{tabular}  & \ \begin{tabular}{c} **Intra-Day Cv** \\ **(\%)** \\ \end{tabular}  & \begin{tabular}{c} **Inter-Day Cv** \\ **(\%)** \\ \end{tabular}  \\ \hline Al & 11.33 & 9.49 \(\pm\) 0.58 & 119.39 \(\pm\) 7.19 & 4.28 & 6.06 \\  & 17.00 & 15.66 \(\pm\) 1.43 & 109  
Table 7 demonstrates the determination of the elements Al, V, Cr, Mn, Fe, Co, Cu, Zn, As, Se, Mo, Cd, Sn, Ba, TI and Pb with an accuracy ranging from 90.97% to 150.73%. The values (except V, Co and Se as they were close to the LOQ) were in accordance with the methods' performance criteria recommended by INMETRO (2011) [53] in which the expected accuracy must be between 80-120%. The result was consistent with similar methods in the literature. [PERSON] et al. [54] reported a recovery of 78-111% for trace elements extracted from freeze-dried urine standard reference material using a sample preparation method consisting of acidification with nitric acid and Triton X-100. In another acid digestion procedure for the determination of trace element contents in urine, recoveries of 87-116% were reported in urine reference material, respectively [55]. Moreover, trace elements in urine have been extracted and digested using a microwave system. For example, [PERSON] et al., reported recoveries of between 81-107% for Al, V, Cr, Mn, Co, Cu, Cd, Sn, Ba, TI, and Pb as determined by ICP-MS [56]. [PERSON] et al. [57] obtained Cr, Mn, Cu, As, Mo, Cd, TI, Pb accuracy and repeatability results similar to this work.