Metrohm 746 VA Trace Analyzer - Manual (Page 359)

5.7 Program instructions
746 VA Trace Analyzer / 747 VA Stand
5-208
•
EV:Cd < 1e-9 (line 5)
If an evaluation value EV:Cd is found for the substance Cd that is
> 0 A and < 1 nA, the evaluation formula A02 is activated and the
sample proportionally spiked with standard addition solution Cd-Std1
(1 mg/L Cd).
•
EV:Cd >= 1e-9 (line 7)
If an evaluation value EV:Cd is found for the substance Cd that is
≥ 1 nA, the evaluation formula A02 is activated and the sample
proportionally spiked with standard addition solution Cd-Std2
(100 mg/L Cd).
The second example shows a lead determination with consideration
of the thallium content.
Method AB231_2.mth OPERATION SEQUENCE
Title Pb/Tl - AB 231
================================================================================
Instructions t/s Main parameters Auxiliary parameters
––––––––––––– ––––– ––––––––––––––––––––––––– –––––––––––––––––––––––––
1 SMPL>M V.fraction mL V.total L
2 (ADD . .
3 SEGMENT Segm.name Pb
4 ADD>M Soln.name Pb std V.add 0.100 mL
5 ADD)2 . .
6 DOS>M Soln.name EDTA V.add 0.100 mL
7 SEGMENT Segm.name Tl
8 (CASE EV:Tl > 200e-12 Calc.f. A01 A02
9 (ADD
10 SEGMENT Segm.name Tl
11 ADD>M Soln.name Tl std V.add 0.050 mL
12 ADD)2
13 CASE EV:Tl <= 200e-12 Calc.f. A03
14 CASE)
15 END . .
Method AB231_2 CALCULATION
max. 15 lines
================================================================================
Quantity Formula (R##, C##, A##) Res.unit Sig.dig.
–––––––––––– –––––––––––––––––––––––––––––––––––––––– –––––––– ––––––––
rho(Pb) A01 = MC:Pb - (MC:Tl * 1.0138 * 0.5) #g/L 3
rho(Tl) A02 = MC:Tl #g/L 3
rho(Pb) A03 = MC:Pb #g/L 3
As the half-wave potentials of the two metals are virtually identical, in the
first segment
Pb the sum of Pb and Tl is determined. After the masking
of Pb with EDTA, the segment Tl is then started that provides the
evaluation value EV:Tl . The remaining program run depends on the
testing of this value in the CASE block:
• EV:Tl > 200e-12 (line 8)
If an evaluation value EV:Tl is found for the substance Tl that is
> 200 pA, the evaluation formulae A01 and A02 are activated and
thallium is determined with the aid of the standard addition. The mass
concentrations of lead and thallium are put out as the final results
with that of lead being corrected by the proportion due to thallium.
This proportion is calculated assuming the same sensitivity by multi-
plication of the determined Tl content by the factor 1.0138 * 0.5 (ratio
of the molar masses Pb
2+ /Tl + ).