In my last blog (“How Valid Is Your Data? - Part 1”) we discussed what happens when samples enter the laboratory. We covered spiking of samples, control blanks and relative percent difference in sample concentrations. That discussion led me to close Part 1 with a “reality check” example from my own experience analyzing beverages. While everything looked great from the outside looking in… a hidden issue needed to be resolved: spectra did not match the control blanks and/or calibration. This indicated the existence of a kinetics issue in the online reduction reaction used to achieve elemental Hg – specifically, method timing constraints.
In Part 2 of this blog, I am happy to report that I’ve successfully analyzed brewed coffee, red wine, milk, orange juice, brewed tea and soda pop. The original method guidance I was using was written for ICP, via microwave digestion. Sometimes H2O2 is used to enhance oxidation in microwave digestion and the method did in fact use H2O2. Knowing that dissolved oxygen would interfere with the reduction used in the CVAA technique, I assumed that the digestion process would entirely consume the H2O2. Well it didn’t, hence my spectra issues which affected the results!