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Dear Ehsan,
Thank you very much for your quick answer and once again, thank you for spending time helping with this.
In the meantime I have found the article which ealier made me believe that the LOD for I, as a guide, should be found in the area around 0,6 ppm http://www.advancedaquarist.com/2003/3/chemistry" onclick="window.open(this.href);return false;
Even though this article is more than 10 years old and technology moves fast, I would not think the LOD of todays equipment has become 100 times lower. I guess the value in Mr. Farley's article must be a mistake. Eithher way, I am truly impressed that you can meassure down to around 6 ppb. I take it, this LOD is 3 times higher than the noise from a blank sample? (BTW: it could be interesting to hear your LOQ and LOR/PQL as well)
I have not at any time believed it very likely that the messasured I value was due to an error. I just did not want to totally exclude it, among other possible causes and therefore I suggested FEM64 to have this specific meassure double checked by means of another method. I maintain my point of view on that.
You did not mention which emission line you are using but with an LOD around 6 pbb it obviously must be the 178 nm line. I'm sorry but in that case I'm not convinced that emission from P does not impact your meassures in cases where I is very low and P is in the high end. Anywway, this issue is not relevant to the actual case since clearly I is not low in this case. Thus in the actual case I fullly agree that it would indeed take a very high amount of P to cause significant interference.
Yet I would not exclude an error in the I value of 1793 ppb. May I take the liberty to give you an advice / small suggestion: If I were you I would state such high I values as >100 in the report. When you state a value like 1793 it gives the clear impressiom that you have actually measured the analyte with a precission of 1 ppb, while in fact it is merely a guesstimate with a very high degree of uncerntaionty. To me it is not correct, what do you think?
One final comment, not so much to you but just to avoid that some people should interprete from above that I do not find your analyses very good. On the contrary, in my opinion Triton's ICP-OES analysis is indeed a very valuable tool to provide us with much more accurate and reliable information on quite many parameters than we can get from any hobby test. Only for halogens, like iodide and iodate, I think other means of analysis might provide a better sensitivity than ICP-OES.
All the best
Poul