Method 314.0 Perchlorate

[dbush87]

I am running method 314.0 for Perchlorate on an ICS 5000. The parameters are:

ICS 5000
Eluent: KOH 45 mM
Column: AS 20
Injection Volume: 500 uL
Retention time: 14.5 min (16.5 min when new)

We run samples from a groundwater treatment system containing Perchlorate. We run Effluent samples (treated groundwater) which are almost always non detect, but lately a peak shows up at where Perchlorate's retention time. These samples have always been run at a temperature of around 24-25 degrees C. I've been getting 5-13 ppb of Perchlorate showing up. After being chilled in the refrigerator for several hours I ran the samples again and then the same samples came out non detect.

We always have a small peak showing up to the left of where Perchlorate comes out, but in this situation a peak comes out right at where Perchlorate is and the peak disappears when running the samples at a cold temperature (5 degrees C). I have never seen this before. I composite the samples (7 days' worth) and run at 24-25 degrees C and the result is non detect.

There is some organic matter in the Effluent samples but can't think of anything that would cause this. Our treatment system uses Ethanol, Ferric Chloride, and Hydrogen Peroxide.

[anionman]

What happens when you run low level standards that are at room temperature and then chilled? What is your column temperature set to?

[eja85]

It sounds like retention time shift. When you perform matrix spikes, are you getting a detectable peak, or does that shift as well?