I was wondering if you could explain how your certified values are calculated. Are they calculated based on aggregate and statistical analyses? If so, how many data points are used? I am specifically interested in phenolic, total cyanide, and soil/sludge metals. I am interested in the procedure(s) and statistical model(s) used.
Thank you for contacting us. We will be more than happy to answer your questions concerning total cyanide (QCP-CN) and phenolics (QCP-PHEN) to the best of our ability. Can you please confirm the product referenced by “soil/sludge metals”. Once we have this information we can address this one as well.
The last lot of QCP-CN purchased according to our records is, H2-CN01039. The certified value for Free Cyanide is based on a wet titrimetric assay performed in our lab using a modified version of Standard Methods 4500-CN D. We also based the certified value for Cyanide Amenable to Chlorination on this assay, because the value is assumed to be the same as Free Cyanide. However, the certified value for Total Cyanide is calculated based on the purity of the starting materials used in our manufacturing process. The last lot of QCP-PHEN purchased according to our records is, G2-PHEN01028. The certified value is calculated based on the purity of the starting material used during our manufacturing process. This value was verified using an ISO 17025 accredited outside laboratory. Their testing was performed in accordance with EPA Method 420.1.
The acceptance limits are calculated based on statistical information provided by the specific NELAC table referenced on the certificate of analysis:
- QCP-CN: NELAC PT for Accreditation: Fields of Proficiency Testing with PTRLs – Non-Potable Water 07/01/2013
- QCP-PHEN: NELAC PT for Accreditation Fields of Proficiency Testing with PTRLs (Non-Potable Water) October 3, 2011
To the best of our knowledge, NELAC collects data from multiple laboratories participating in round robin proficiency testing studies. The exact statistical methods used would be better supplied by NELAC themselves. I have attached their published SOP concerning these tables. You can find additional documents on their website http://www.nelac-institute.org/.
Serving you in chemistry,
Paul R. Gaines, Ph.D.
CEO of Inorganic Ventures & Fellow Chemist
DISCLAIMER: Advice offered by the chemists at Inorganic Ventures is intended for the individual posing the question. Feel free to contact us to verify whether these suggestions apply to your unique circumstances.