Determination of cyanide ion by ion chromatography amperomet

In May 2013, maintenance was performed at a user and the CN- in solid waste was measured using an ion chromatogram amp detector. In the determination of CN-standard samples encountered a more interesting question, the following to start some discussion and thinking.
The instrument used by the user is configured to configure the conductivity detector and amperometric detector (and use the autosampler) for the ion chromatograph. After injecting a standard sample of CN-different concentrations manually, inject the injector into the autosampler in descending order of concentration. In the morning, the 5-mg / L CN- ion chromatogram is shown below:

After measuring 5 mg / L CN- again after 4 hours interval, it was found that the peak shape of CN- was changed as shown in the figure:

Figure 2 5 mg / L CN-ion chromatogram (1: system peak; 2: CN-) for 4 hours after loading in air
It can be seen from the spectrum that when the 5 mg / L CN- is placed in the air for 4 hours and the sample is measured again, the peak of the CN- becomes shorter and becomes fat, as the freshly prepared CN-sample peak is sharp. The possible reason is that CN- is partially oxidized after 4 hours in the air to form a CN- / OCN-ion pair that changes the oxidation process of CN- on the surface of the silver electrode and thus changes in peak shape. Re-preparation of 5mg / L CN-injection spectrum is basically consistent with Figure 1, indicating the use of ion chromatography CN-samples need to be configured as soon as possible after the determination to avoid deterioration.