Technical note: The equivalency of sodium results in cheese digested by either dry ashing or microwave-accelerated digestion

Analysis of dairy products for minerals such as sodium requires mineralization of the sample, which is typically done by either dry ashing or atmospheric wet ashing; both methods are time consuming and wet ashing requires the repeated handling of hot acid. A rapid method using microwave-accelerated acid digestion before atomic absorption spectrometry to measure sodium was compared with dry ashing in 138 samples of blue cheese (in duplicate) that varied in sodium content and age. Linear regression of the results obtained within different cheese salting treatments and sampling locations over time showed that the methods were equivalent in terms of linearity and the slope of the line. A consistent bias was observed, with lower sodium concentrations being quantified during atomic absorption spectrometry for the microwave-digested samples. Evaluation of this difference by the 2 one-sided test (TOST) procedure showed that the confidence intervals of the percentage difference between the methods fell within the predetermined acceptable percentage difference. We conclude that this rapid microwave digestion procedure of blue cheese yielded equivalent results to dry ashing.