In this method, a closed vessel concentrated acid digestion was performed for all different pharmaceutical materials. Open vessel digestions are not recommended for total sulfur quantitation due to the possibility of volatile organic sulfide formations which can result in negatively biased results. Sample digests were then analyzed by an ELAN 6100 DRC plus ICP-MS. Quality control included one matrix duplicate per sample matrix, one set of matrix spike and matrix spike duplicate per sample matrix, analytical duplicates, analytical spikes, certified reference materials, and laboratory control samples (blank spikes).

The precision was represented by the relative percent differences between matrix duplicates which were consistently below 2%. The accuracy of the measurements were defined by the recoveries from the certified reference materials which were within 5% of the true value. The recoveries for the analytical and matrix spikes identified minimal matrix interferences were associated with the analytical or digestion procedures (less than 8% deviation from the true value).

The projected detection limit for total sulfur, which was generated from statistical interpretation of a low level sample), was approximately 0.3 mg/kg. The detection limits for other trace elements were well below 0.020 mg/Kg.

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