Metrohm 746 VA Trace Analyzer User Manual

Page 120

4.3 Lead determination with calibration curve

746 VA Trace Analyzer / 747 VA Stand

4-35

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 25

25 and press the key.

Measurement of the 1

calibration solution

•

Measurement of the 1

calibration runs as follows (see also section

4.3.3):

−

Purging and stirring for 180 s.

−

Call-up of the segment

DPASV

for measured value recording. The

lead present in the solution is enriched at the hanging mercury

drop with stirring at a measurement voltage of –600 mV and then

determined anodically without stirring from –600

…

–200 mV. The

selected measurement mode DP leads to a current peak whose

maximum lies at ca. –400 mV.

−

The

DPASV

segment is then repeated twice. The three single

measurements are allocated the VR numbers

and

•

After the 3

measurement, the program is interrupted. The screen shows

the prompt to change the measuring vessel:

Empty the measuring vessel

•

Empty the measuring vessel, rinse it thoroughly with dist. water and

replace it in the 747 VA Stand.

The measuring vessel contains mercury, which must be disposed of in

the proper manner (see section 7.2.3).

Measurement of the 2

calibration solution

•

Repeat steps 5

…

8 with 10 mL of calibration solution

Pb-2

with a

mass concentration of 5

µµg/L. You obtain three single measurements

with the VR numbers

and

10 Measurement of the 3

calibration solution

•

Repeat steps 5

…

8 with 10 mL of calibration solution

Pb-3

with a

mass concentration of 10

µµg/L. You obtain three single measurements

with the VR numbers

and

ЪДДД

ДДД MEAS.TASK MESSAGE ДДДДДДДДДДДДДДДДДД

ДДДДДДДДДДДДДДДДДД¿

DOS Acetate 1.000 mL > M

press to break

АДДД

ДДД : continue ДДДДДДДДДДДДДДДДДД

ДДДДДДДДДДДДДДДДДДЩ

ЪДДД

ДДД MEAS.TASK MESSAGE ДДДДДДДДДДДДДДДДДД

ДДДДДДДДДДДДДДДДДД¿

Change measuring vessel

АДДД

ДДД : continue ДДДДДДДДДДДДДДДДДД

ДДДДДДДДДДДДДДДДДДЩ