Metrohm 746 VA Trace Analyzer - Manual (Page 413)

5.7 Program instructions
746 VA Trace Analyzer / 747 VA Stand
5-262
Comments • The electrode type RDE or HMDE must be entered before the PSAMODE
measurement mode.
• With mercury film electrodes on the basis of the RDE, it is advisable
to deposit the substances with stirring on the electrodes. As in the
PSWEEP instruction, only an enrichment without stirring is possible (no
stirring is allowed during measurement), the MEAS instruction must be
inserted. The enrichment time with stirring is defined by its line time,
in general
U.meas = U.start is selected for the measurement volt-
age.
Examples PSA determination of lead in wine at a glassy carbon electrode:
Method PSA_wine.mth OPERATION SEQUENCE
Title Potentiometric Stripping Analysis of Pb
================================================================================
Instructions t/s Main parameters Auxiliary parameters
––––––––––––– ––––– ––––––––––––––––––––––––– –––––––––––––––––––––––––
1 SMPL>M V.fraction mL V.total L
2 RDE Rot.speed 2000 /min
3 DCTMODE t.step 0.30 s t.meas 40.0 ms
4 MEAS U.meas -200 mV
5 DOS>M Soln.name HCl 30% V.add 1.000 mL
6 DOS>M Soln.name Hg 1g/L V.add 0.200 mL
7 PURGE
8 CONDC U.start -1200 mV Rate 1 1000 mV/s
U.end -100 mV Rate 2 10000 mV/s
Cycles 100
9 SEGMENT Segm.name Prp-800
10 CONDC U.start -1200 mV Rate 1 1000 mV/s
U.end -100 mV Rate 2 10000 mV/s
Cycles 10
11 SEGMENT Segm.name Prp-800
12 CONDC U.start -1200 mV Rate 1 1000 mV/s
U.end -100 mV Rate 2 10000 mV/s
Cycles 10
13 ØPURGE
14 (ADD
15 (REP
16 STIR Rot speed 2000 /min
17 CONDC U.start -1200 mV Rate 1 1000 mV/s
U.end -100 mV Rate 2 10000 mV/s
Cycles 10
18 SEGMENT Segm.name Pb
19 REP)1
20 MEAS U.meas -200 mV
21 ADD>M Soln.name Pb-Std V.add 0.020 mL
22 ADD)2
23 END
Method PSA_wine SEGMENT
Prp-800
================================================================================
Instructions t/s Main parameters Auxiliary parameters
––––––––––––– ––––– ––––––––––––––––––––––––– –––––––––––––––––––––––––
1 STIR Rot.speed 2000 /min
2 DCTMODE t.step 0.30 s t.meas 40.0 ms
3 MEAS 30.0 U.meas -800 mV
4 ØSTIR
5 ØMEAS 6.0 U.standby mV
6 END