Dear all
Im trying to validate an analitical method for traces detection in rinsing samples by NPOC in a TOC-VCSH Shimadzu. Overall, the method seems to be good, since it had already shown adequability and linearity.
But, when performing the residues recovery studies there is a problem, the “blank” samples always show an higher NPOC result than the spiked samples themselves. I can even imagine how can this be posible, since the blank isnt even prepared in a diferent way than the samples, and the rinse water is practically the same, and Im using inyectable grade water. I ve tried to do a lot of experiments to discart bad sampling methods on my part, or dirty glassware, but nothing like that seems to be the reason.
I think that maybe the problem is the product. Im using very dilute soltions of an ophtalmic that contains polimixine, neomicin and gramidicine. Its any of that component hard to read in TOC?.
I also think that it can be the water I use for the rinsing, since the NPOC present in those samples is always higher than the NPOC in the samples taken by the quality assurance department, being the only diference is that they purge the point by a lot more time than me, but even the NPOC results are around 0.2 ppm TOC for me, against 0.01 ppm for the quality assurance samples. Also, I know that theyre using the NPOC method becuase they had “unsolved problems” with a TC-IC method.
So, what do you think, the results are this way becuase the product, the water or me.
Thanks in advance