I've got an issue with our PE 4300 that is starting to confound us.
Every three to four months, we start to see a rise in Ca concentrations
that we believe to be errant. DEF fluid (32.5% urea) makes up about 85%
of what we test on a daily basis. The rise starts slow, maybe 0.05-0.1
ppm on instrument but quickly rises to a current max of 8 ppm. We have
tested samples that came up non-detect in June and get several ppm. All
of our QC comes back great, 95-105% recovery and all blanks are
extremely low (0.002) or ND. Last time we had this issue, our service
guy blamed contamination in our rinse. However, while it may have
contributed to our issue, I don't believe it was the root cause since
our QC was good at that time as well. It seems to be an issue with our
sample intake system as the counts drop to ~100-200 without the pump
running. At this point, we have changed all tubing, cleaned all
glassware (soaked spray chamber in 10% nitric, passed 10% through the
neb and soaked the torch in aquaregia). We have also changed the vessels
for needle rinse, internal standard and calibration standards. My
chemist is in the process of rewriting our method. I have RBS-25 on
order to try to etch the spray chamber as we do get a few droplets
forming near the neck. Any thing else we can look at? I am starting to
run out of things to try. Any help is greatly appreciated.
6034 Corporate Drive
East Syracuse NY 13057
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