Metrohm 746 VA Trace Analyzer - Manual (Page 538)

7.4 Troubleshooting
746 VA Trace Analyzer / 747 VA Stand
7-39
Peak is in the highest µ A range
• The sample volume is too large: reduce the volume. Carry out the analysis
again.
• The enrichment period (for HMDE) is too long: Reduce the time.
• If necessary use a SMDE or DME electrode instead of HMDE.
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.
• Might it be possible to selectively mask this second element with a complex
former?
• Electrolyte solution too old: make up a new one. Its working life with organic
additives may be as short as 1 day or less.
• For Cu: work without chlorides in the electrolyte or increase the chloride con-
centration massively.
• 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
• If HMDE is used potential displacements of more than 20 … 30 mV are often
normal and have to be accepted; particularly in adsorption voltammetry.
• Standard solutions have been made too acidic.
• Buffering capacity of the electrolyte is not sufficient: increase electrolyte vol-
ume.
No addition
• Has the correct standard solution been used or is the concentration of the
solution too low: increase the volume of the standard addition or use a higher
concentration or reduce the sample amount accordingly.
• If organic components are present: carry out a UV digestion or other suitable
sample preparation.
• Concentration of the analyte is too high: dilute.
• Addition solution with metal complexing solution (time reaction).