Metrohm 746 VA Trace Analyzer - Manual (Page 114)

4.3 Lead determination with calibration curve
746 VA Trace Analyzer / 747 VA Stand
4-29
4.3 Lead determination with calibration curve
The usual calibration procedure for the majority of the determinations
possible with the 746 VA Trace Analyzer is standard addition
(example, see section 4.2). However, the mass concentration of a
substance can also be calculated using a calibration curve deter-
mined beforehand by measurement of different reference solutions.
Result determination with the aid of a calibration curve saves time
compared with standard additions, but is admissible only when
• the matrix of all samples and calibration solutions is identi-
cal or has no influence on the measurement,
• all measurement parameters (capillary, temperature, etc.)
remain unchanged in the measurements, and
• the accuracy of the results obtained is regularly checked
using the standard addition method.
In the present example, a lead determination in drinking water is used
to show you how a method with calibration curve is programmed and
performed.
You must first prepare the 746 VA Trace Analyzer and 747 VA Stand as
described in section 4.1 before you can perform this example.
4.3.1 Reagents and accessories
To perform the method
CALCRV.mth
, the following solutions are needed:
1 Acetate buffer 1 mol/L, pH 4.6
2 Lead ion standard solution, ρρ(Pb 2+ ) = 1 g/L
Lead ion standard solution (Metrohm No. 6.2301.100) for preparation of the
following calibration solutions:
• Calibration solution Pb-1
ρ(Pb 2+ ) = 2.5 µ g/L
• Calibration solution Pb-2
ρ(Pb 2+ ) = 5 µ g/L
• Calibration solution Pb-3
ρ(Pb 2+ ) = 10 µ g/L
• Calibration solution Pb-4
ρ(Pb 2+ ) = 20 µ g/L
3 Conc. hydrochloric acid Suprapur, w(HCl) = 0.3 (30%)
4 Drinking water
• Water that has been in the supply system for a lengthy period of time
absorbs metals from the pipe and fittings materials and thus falsifies the
analysis results. Hence, before taking the water sample allow the water
to run out of the tap in a powerful stream for several minutes.