Sample Preparation - Poor Mn recovery for soil standards

There are a number of possibilities to explain your results, but we will assume that sample inhomogeneity and/or poor characterization of the soil standards are not the cause. These assumptions are reasonable for standards, but ultimately may not be appropriate in the case of your high results. The first consideration is that 3051 is not intended as a total sample decomposition method, so are you seeking to quantify only extractable metals? With that in mind, what other metals are you measuring for, are you using only HNO3 or the general 3:1 ratio of HNO3 to HCl, and do you observe clear solutions free of particulates following digestion? If some sample material remains, so you filter or centrifuge prior to analysis? If the soil standards are homogenous and accurate with respect to their stated values, then the sample preparation is the most likely cause for your results, and modifying details of that method might help, e.g., greater acid-to-sample ratio, different acid combinations, or longer digestion times. If a single digested sample does not give repeatable results over several different ICP measurements, then the analysis itself is likely part of the problem. It might be helpful to start there; can a single digested sample generate the same ICP results over multiple runs over several days. These are general considerations as there are many potential causes for your unusual Mn results. If you could provide any additional information, it’s possible we could offer more specific recommendations.