SW-846 Methods 3015 and 3051 specify that the sample is to be discarded when weight loss exceeds 10%. Methods 3015A and 3051A specify that the sample is to be discarded when weight loss exceeds 1%. This seems to be a rather dramatic reduction, what is the basis for this?
When Methods 3015 and 3051 were drafted, the state of the art for vessel technology was different than it is today. At that time, it was determined that some loss of mass was inevitable, since the sealing and pressure relief components were largely composed of PTFE, which is somewhat soft and tends to flow under compression. Ten percent loss was a compromise between the ability to maintain integrity of the seal and the number of individual vessels that would fail to meet the maximum loss criterion in any individual run. Microwave technology was less advanced as well; even with rotating carousels the homogeneity of microwave energy in the cavity absorbed by individual vessels varied and resulted in uneven heating.
Advances in technology have resulted in improved sealing mechanisms and improved microwave performance. In reviewing performance data generated for Methods 3015A and 3051A, the ORCR Workgroup likely determined that a 1‐percent mass loss represented an acceptable upper bound when comparing analyte recoveries with digestion throughput.
Other Category: Inorganic