I am not sure if I will address your problem, but here are a couple of thoughts:
1. Deionized water such as used in DEF is not always silica-free. Silica precipitates Ca. One possibility is that silica I the DEF is precipitating and building up calcium in your system. Consider that. If your standards and QCs are not matrix matched with the DEF (no urea), then you follow them with QCs that have urea, the urea may chelate and release some calcium from precipitate in your system when the samples come through the system. Does that sound like anything consistent with what is happening?
2. If not, consider that glass and quartz spray chambers, nebulizers, and injectors are silicates and silica, respectively. Calcium can build up on their surfaces, permitting the same problem.
Clean the glass/quartz parts weekly. Use a concentrated sulfuric acid (not fuming) or phosphoric acid instead of 10% nitric, and of course, be very careful with concentrated acids, especially with sulfuric acid. Phosphoric acid and sulfuric acid will compete to some degree with silicic acid for calcium.
Alternative: put the glass/quartz ware in an EDTA diammonium salt solution and heat to maybe 60 degrees C.
Rinse thoroughly with ultrapure water with eye protection, considering that rinsing a vessel that has been immersed in sulfuric acid could cause spattering. Maybe slowly immerse in the water before rinsing further. Rinse really well, especially if you have other analytes besides calcium. Phosphoric acid, if not a very high purity grade, often has a low arsenic impurity.
If I missed the problem entirely, hey, at least I gave it a shot.
R. Steven Pappas, Ph.D.
Team Lead, Tobacco Inorganics Group
Centers for Disease Control & Prevention
4770 Buford Highway, NE
M.S. F44, Building 110
Atlanta, GA 30341-3717, USA
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of Sean Thomas
Sent: Tuesday, August 7, 2018 11:53 AM
To: [log in to unmask]
Subject: Erratic PE 4300 Behavior
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