Metrohm 746 VA Trace Analyzer - Manual (Page 535)

7 Safety, Errors, Troubleshooting, Diagnosis, GLP
746 VA Trace Analyzer / 747 VA Stand
7-36
Peak displacement
• Check and adjust the pH of the solution.
• Check electrolyte composition and correct if necessary. Use a buffer solution
instead of an acid.
• Carry out a standard addition to check whether the correct peak has been
evaluated.
• Organic components interfere with the analysis: carry out a UV digestion or
other suitable sample preparation.
• Enter a new half-wave potential in the instrument and recalculate the results.
• Check reference electrode (see section 3.6).
No peak found
• The peak is only displaced: adjust the half-wave potential and recalculate the
results.
• The sample concentration is too low: increase the sample volume or the
amount of sample.
• The concentration of the ion to be determined is too low: use HMDE (inverse
voltammetry) instead of DME or SMDE.
• Are the initial and final potentials correct?
Peak is in the highest µ A range
• The concentration of the ion to be determined is too high: reduce the sample
volume and carry out the analysis again.
• The preconcentration time under MEAS is too high, reduce it and try the
analysis again.
Double peak
• Check MME. If necessary, change capillary (see section 3.4.8) or replace
sealing needle (see section 3.4.9).
• Organic components interfere with the analysis: carry out a UV digestion or
other suitable sample preparation.
• If a second element is present at the same potential: add this element to the
sample and carry out the analysis again. If the second peak has become
higher then the second element is present.
• Has any substance been precipitated out in the measuring vessel (e.g. lead
perchlorate standard with KCl as electrolyte)?
• Try out eluents with different compositions (addition of complex formers).
• Check analysis parameters.
• Try another measurement mode like AC1. If one substance is reversible and
the second one irreversible, only the reversible substance is detected by
AC1.
Standard addition peaks displaced
• Standard solutions have been made too acidic.
• Buffering capacity of the electrolyte is not sufficient: increase electrolyte vol-
ume.