|MadSci Network: Chemistry|
This question was a stumper, and we resorted to e-mail for further elucidation of the problem. I can't say we've solved it, but I reproduce the two key e-mail messages as a partial solution. David Kopaska-Merkel Geological Survey of Alabama First message: further information from submittor Hi David! I will give you a little background about what is going on with this nitrate test we are having trouble with. The biotechnology based pharmaceutical company I work for had some renovations done during the annual shutdown period earlier this month. This included an upgrade of the water system. We are testing nitrate levels in both Nanopure (filtered water system) and WFI (Water For Injection). The nitrate test we are running is based on both British Pharmacoepia (BP) and European Pharmacoepia (EP) methods for nitrate levels in water. I did not actually conduct the test myself but three other analysts have been trying for the last three weeks to collect some kind of data from the test. I have not read the STM (Standard Test Method) for the assay but know that it involves making up a 0ppm, 0.2ppm, and 1ppm nitrate standards (diphenylamine is the nitrate source). The test is colorimetric and involves a 15 minute incubation at 50C (122F). You are supposed to see a blue colour in the 0.2ppm standard but we get nothing. The 1ppm standard is blue but very light in appearance. The samples are supposed to be lighter than the 0.2ppm standard. We have gone so far as to run the test spectrophotometrically with no luck! When they tried this approach, with a set of calibration standards, the 0.2ppm standard gave a negative absorbance. I have performed nitrate tests in another lab I worked in and we used some kind of kit. The test was easy and always worked. I don't know if we are using EP and/or BP methods because of FDA or HPB (this is the Canadian regulatory body) requirements but a test kit is definitely out of the question in this case. Any suggestions? Thanks for your help! This test is driving everyone crazy! :) Julia Second message: Response from chemist Hi Julia, David forwarded me your comments on your analytical problem. As David mentioned, we don't use the test mentioned; we use ion chromatography or the cadmium reduction method ---- and unfortunately I doubt if our library has the BP or EP methods. It does sound to me that if you're analyzing for NO3 using diphenylamine as a standard that you may not be getting a complete oxidation of the amine to produce NO3 --- if that's any help! Robert E. Meintzer Geological Survey of Alabama
Try the links in the MadSci Library for more information on Chemistry.