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The Effect of Matrices in the Analysis of Mercury by ICP

Mercury analysis is one of the most difficult analyses by ICP and ICP/MS instrumentation.

Mercury standards are sold in nitric acid. However, nitric acid alone is not an ideal matrix for analysis. Diluted mercury standards in nitric acid matrix show a lot of variation when analyzed over a period of time. SPEX CertiPrep conducted a study on the effect of matrices in the analysis of Hg by ICP.

Solution preparation: NIST SRM 3131 was diluted to 100 mg/L in two different nitric acid concentrations, 10% HNO3 and 5% HNO3. These two solutions were further diluted to 2 mg/L on five different days in four different matrices as shown in Table 1

Solution analysis: Initial calibration was done using 2 mg/L Hg in 20% HCl/1% HNO3. Final analysis was done on all the diluted samples at the same date following completion of analysis of a given matrix diluted on different days before taking up the second matrix.

Conclusion: Results are shown in Table 2:  Concentration shown is the average of four replicates in three wavelengths, 253, 194 and 184 nanometers. Consistent analytical results are obtained when mercury is analyzed in 2% HCl + 1% HNO3 or in 20% HCl + 1% HNO3 when the different dilutions are analyzed over a period of time. Addition of gold to nitric acid matrix also produced repeatable results.  F test showed no significant difference in the standard deviations between these matrices while the standard deviation was very significantly higher for the analysis in 2% nitric acid alone. It is concluded that nitric acid alone is not an ideal matrix for the analysis of Mercury.