Heavy metal drugs: Atomic answers

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  • Published: Feb 15, 2018
  • Author: David Bradley
  • Channels: Atomic
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Ultrasonic

Axial viewed inductively coupled plasma atomic emission spectrometry with ultrasonic nebulization has been used to determination concentrations of various metallic and other elemental impurities in oral pharmaceutical products. Photos by David Bradley

Axial viewed inductively coupled plasma atomic emission spectrometry with ultrasonic nebulization has been used to determination concentrations of various metallic and other elemental impurities in oral pharmaceutical products.

New regulations in the USA establish guidelines for specific daily exposures to 24 heavy metals and other elemental impurities based on their specific range of toxicological properties. The guidelines then impinge on efforts to reduce the concentrations of heavy metals present in pharmaceuticals. As such, the United States Pharmacopeia (USP) and International Conference on Harmonization (ICH) have put forth new requirements. Of course, with guidelines come new demands on analytical chemists for increased sensitivity of the techniques which ensure adherence to new regulations. There are 24 elemental impurities cited in the guidelines for which testing is required.

Now, James Menoutis, Angela Parisi, and Natasha Verma of Quantum Analytics Group, based in Bridgewater, New Jersey, USA, explain how the extremely low detection limits possible with inductively coupled plasma mass spectrometry (ICP-MS) have nudged this technique to the fore in the development and evaluation of analytical methods for supporting the new safety guidelines. It can be used to determine levels of elemental impurities in finished pharmaceutical products, active pharmaceutical ingredients, as well as excipients. However, inductively coupled plasma atomic emission spectroscopy (ICP-AES) could have several advantages, such as avoiding the conventional precipitation of metal sulfides from aqueous samples, and alternatively, the visual comparison to a lead standard that has been treated in the same way.

Pharma perspective

"The use of atomic spectrometry as an analytical technique has found widespread use for the analysis of trace metals in the environment since the mid 1970s," the team writes in the Journal of Pharmaceutical and Biomedical Analysis. Flame atomic absorption spectrophotometry (AAS) and graphite furnace atomic absorption spectrophotometry (GFAAS) have been used widely in a range of contexts. The team points out that over the same period ICP-MS and ICP-AES have also been developed, so that by 2004 there were some 17000 AES instruments installed in laboratories around the world, and only 4000 ICP-MS instruments. They point out that ICP-AES is rapid and multi-element, but needs improvement when it comes to detection limits.

Ultrasonic nebulization was developed as a sample processing technique to boost sensitivity, and, over the years, several teams have developed this further for various sample types, including sea water. The technique has also been used to study heavy metals in herbal remedies, phytopharmaceuticals, and pharmaceutical derivatives. However, there is still room for innovation, and the team points out that one improvement is possible if one carries out axial, rather than radial viewing of the plasma, In radial view ICP-AES, the plasma is observed side-on whereas in axial viewed plasma ICP-AES, the spectrometer peers down through the plasma rather than across it. The team has now used this latter perspective to see whether it is suitable for analyzing metal and elemental impurities in pharmaceuticals.

The benefits of coupling

"We have shown that by coupling an ultrasonic nebulizer to an axial ICP-AES, significant improvement in detection limits can be provided for the determination of elemental impurities in oral drugs," the team reports. Given the much larger user base of ICP-AES instruments as opposed to ICP-MS, it would make sense to home in on the AES technique with ultrasonic nebulization in order to facilitate compliance with the safety guidelines for contaminants.

The team adds that "The method has been shown to be linear, precise, and accurate over the range of 50% to 200% of the target value." However, when it comes to osmium , the technique reports a value three to four times that which is actually present in the pharmaceutical sample tested, and such an anomaly would have to be taken into account in any regulatory documentation, or better still, improved through subsequent further development of the technique.

Related Links

J Pharm Biomed Anal 2018, 152, 12-16: "Study of the use of axial viewed inductively coupled plasma atomic emission spectrometry with ultrasonic nebulization for the determination of select elemental impurities in oral drug products."

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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