Metrohm 797 VA Computrace Manual do Utilizador descarregar pdf (Página 286)

9 Troubleshooting

797 VA Computrace – Software

274

If the overlapping is too large, the peak can no longer be evalua-

ted. In this case chemical or measurement technique countermea-

sures must be used to attempt to separate these peaks better. Pos-

sible measures include changing the pH value, changing the sup-

porting electrolyte concentration, changing the supporting elect-

rolyte, use of complexing agents (see

Complex formation, section

9.6), longer deposition times and modifying or changing the

measurement technique.

• Determination of lead and thallium

With a supporting electrolyte of pH = 1, Pb and Tl peaks over-

lap greatly. Changing the pH to 13 separates the two peaks.

(The separation of lead and thallium can also be achieved by

subsequent electrolysis or in acetate buffer with EDTA).

Supporting electrolyte: Supporting electrolyte:

pH = 1 pH = 13

Analysis solution: 0.5 mg/L Pb; 1 mg/L Tl

Standard addition: with 10 μg Pb and 10 μg Tl

Electrode: SMDE

Calibration with chemically non-isoformal standards

With all possible Calibration techniques, it must be ensured that the

standards used for calibration are chemically isoformal with the

analytes. The standard substances must therefore have the same

valency (e.g. with Fe, Al) or complex formation form (e.g. with As,

Cr, Se) as the substances already present in the analysis solution. If

this is not the case the calibration can produce completely wrong

results owing to the different peak voltages and sensitivities.

Results not reproducible

Voltammetric measurements (including CVS and CPVS!) strongly

depend on the temperature.

1 2 ... 281 282 283 284 285 286 287 288 289 290 291 ... 294 295

Sem comentários

Metrohm 797 VA Computrace Manual do Utilizador Página 286