Hi, this is question pertaining accrediation of test methods.
I'm trying to validate TOC analysis according to ISO 8245:1999 (revised and approved in 2015). The water used for dilutions of samples and preparation of calibration standards is required to have maximum TOC levels which are about an order of magnitude or two below those intended for measurement (0,3 mg / L for measurement below 10 mg / L): trying to comply with this specification I run into a chicken-and-egg problem:
I can't use my typical calibration standards to confirm the absense of TOC in my dilution water since they have been prepared with that very water and in theory I can't use my calibration standards for measurement purposes since the dilution water is not verified.
Are there suppliers of water with purity specifications who satisfy these requirements? As far as I know low TOC water is supposed to be used as soon as it is prepared.
How do people comply with this requirement in practice?