Owner manual

4.4 Lead determination with internal standard
746 VA Trace Analyzer / 747 VA Stand
4-53
• The status display in the header of the dialog page "MONITORING"
switches to * BUSY *, the start time of the measurement is entered un-
der Determination and the determination is given a standard name,
also formed from the start time. Further, during the measurement the
measurement window is superimposed which shows the current pro-
gram line being executed and the remaining line time.
• Shortly after the start of the determination, the screen shows the prompt
to add 10 mL sample to the measuring vessel.
5
Addition of sample
• Remove stopper 2525 on 747 VA Stand and use a pipette to add 10 mL of
drinking water to the measuring vessel through the pipetting opening.
Press the <ENTER> key.
• The screen shows the prompt to add 1 mL acetate buffer to the measur-
ing vessel.
6
Addition of acetate buffer
• Use a pipette to add 1 mL acetate buffer (1 mol/L, pH 4.6) to the
measuring vessel through the pipetting opening. Then close the pipet-
ting opening using stopper 2525 and press the <ENTER> key.
• The screen shows the prompt to add 100 µL of the solution CdRefSol
with the internal standard to the measuring vessel.
7
Addition of the internal standard
• Use a pipette to add 100 µµL of the cadmium standard solution with a
mass concentration of 1 mg/L to the measuring vessel through the pi-
petting opening. Then close the pipetting opening using stopper 2525 and
press the <ENTER> key.
8
Measurement of the sample solution
• Measurement of the sample solution runs as follows (see also section
4.4.3):
− Purging and stirring for 180 s.
− Call-up of the segment DPASV for measured value recording.
Lead and cadmium are enriched with stirring at the hanging mer-
cury drop at a measurement voltage of –800 mV and then deter-
mined anodically without stirring from –800 ... –200 mV. The se-
lected measurement mode DP leads to a current peak for lead
whose maximum lies at ca. –400 mV and a current peak for cad-
mium with a maximum at ca. –580 mV.
− The DPASV segment is then repeated twice. Both the three single
measurements for the substance lead and also the three single
measurements for cadmium are allocated the VR numbers 00,
01 and 02.
• On completion of the last measurement, the lead mass concentration is
calculated using the proportionality factor stored in the method. The pro-
gram is now at an end. The status display in the header of the dialog
page "MONITORING" switches back to * READY *, the instrument is
ready for a new determination.