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Trace Elements and Sulfur in Pharmaceuticals

Speciation Analysis
Analytical Methods
Dynamic Reaction
Arsenic Speciation
Selenium Speciation
Chromium Speciation
Trace Metals
Metal Cyanide Complexes
Stable Isotope Ratios


LINK: Total Arsenic and Arsenic Speciation in Human Biological Samples (pdf)

LINK: Trace (ppt level) Total Arsenic and Selenium Analysis (pdf)

LINK: Arsenic Speciation in Blood


During synthesis of a pharmaceutical drug, many catalysts are used which may result in higher concentrations of certain elements in the final product. Inductively Coupled Plasma Mass Spectrometry is the ideal tool to determine trace elements in a variety of matrices including pharmaceuticals/neutraceuticals. Since ICP-MS requires samples to be in liquid form, solid samples need to be digested in acid before introduction into the instrument. Different pharmaceutical samples usually need different types of acid to solubilize and stabilize the trace elements.

While ICP-MS can provide ng/L (ppt) detection limits for most trace metals, its performance for sulfur quantification is less than optimal due to the elevated background from oxygen and higher first ionization potential for sulfur (10.36 kJ/mol). Lower sensitivity and higher background usually means many orders of magnitude higher detection limits. In order to overcome all these issues, we have developed a method that utilizes a reaction cell-based instrument to remove the interferences and provide lower detection limits.


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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This brief study confirms that the ICP-DRC-MS analytical platform is capable of delivering excellent trace metals and total sulfur detection limits for pharmaceutical materials. These detection limits would not be available without the application of ultra clean reagents and materials. The importance of experienced analysts to identify appropriate procedures and instrument settings cannot be understated. Therefore, the ability of any laboratory to provide tace elements and sulfur quantitation at such low levels is directly attributed to their facility, protocols, and qualifications of personnel/analysts.


Our scientists have tremendous experience with trace analysis. If you have any questions or would like a quotation, please feel free to email us at info@appliedspeciation.com or call (425) 483-3300.

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