Metrohm 757 VA Computrace - Manual (Page 170)

7 How to ...?
757 VA Computrace – Software
160
15. Use a pipette to add 100 µL Pb ion standard solution ρ (Pb) =
1 g/L (Metrohm No. 6.2301.100) into the measuring vessel
and click the
<OK> button.
16. The sample solution spiked again with standard addition solu-
tion is measured three times. Then the END OF DETERMINA-
TION window appears.
17. Click the <OK> button. The determination is saved automati-
cally and the result report is printed out.
18. To assess the recorded lead determination, the results printed
out in the full report for the mass concentration of lead Mass
conc. and its total scatter MC.dev. are used. The limit val-
ues of these two results depend greatly on the care taken in
the preparation of the analysis solution and in the dispensing
of the standard addition solutions. When the procedure is car-
ried out properly and carefully, the following results should be
expected:
• Accuracy = 95 … 105 %
Final Results: Pb = 0.95 … 1.05 g/L
• Scatter ≤ ± 3 %
Res. dev ≤ ± 0.03 g/L (± 3 %)
19. If desired, the reproducibility can be determined by perform-
ing the Testpb method several times and comparing the
results obtained for the mass concentration Mass conc..