ICP-MS: Inductively Coupled Plasma - Mass Spectrometry for Mineral and Toxic Metal Detection and Analysis
By Felicia Mohammed, NOW Quality Control Department
Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) is an instrument used for the analytical determination of elements such as minerals and metals. The high sensitivity of the instrument allows for detection at the parts-per-trillion (ppt) level.
The operation of the ICP-MS can be simplified as follows: the sample to be tested has acids added to it and is heated in a closed vessel to 180˚C in a specialized oven. It dissolves in the acid before being introduced as an aerosol into the ICP-MS, wherein the larger droplets are removed and the smaller droplets are pulled into a plasma, which is generated in a stream of Argon gas contained in a "torch". The torch is a glass tube at the center of a cooled copper coil through which an electric current is passed. This causes an interaction between the magnetic field that is created and the argon gas to produce plasma at a temperature of around 10,000˚C. The temperature of the plasma is similar to that of the surface of the sun. The high temperature is instrumental in the breakdown of any particles to its atomic mass units, from which the elements can then be identified by the mass spectrometer (similar to matching fingerprints; each one is unique).
At NOW Foods, this is the instrument that has been selected for analysis of minerals such as chromium, selenium, calcium, and magnesium. In addition, it can test for the presence of trace amounts of toxic heavy metals such as arsenic, lead, cadmium, and mercury. Our analytical lab was remodeled last year to accommodate sample preparation and instrument installation for the ICP-MS. This has been the largest investment made on any single instrument since the analytical lab was established: about one-half million dollars. NOW's commitment to provide products that not only meet label claims, but are also safe of any harmful contaminants, has been the driving force behind this move.
This was a challenge that was taken on with great enthusiasm, even though some of the chemists felt as if this was the "great unknown". Our whole way of thinking and working had to be adjusted - with an increased focus on preventing any possible contamination of our samples due to the extreme sensitivity of the new instrument. As we started training on our sample preparation method, we became aware that the analyst prepping the sample may be the greatest source of contamination. For example, jewelry (watches, rings and bracelets) can deposit traces of iron, copper, gold, silver, platinum and chromium. Some hair dyes and shampoos contain selenium and lead. Also, the use of cosmetics can be a significant source of contamination ; lipsticks may contain zinc, iron, magnesium and manganese. So we developed appropriate Standard Operating Procedures to successfully minimize the risk of contaminating samples.
After a period of thorough method development, we will be using the ICP-MS instrument for routine analysis of minerals, as well as for heavy metals on products which are susceptible to contamination This enhanced capability will allow NOW to continue providing products that are of the highest quality, using state-of-the-art detection equipment to ensure both product strength and safety.
Update December 2012: NOW Foods now has 3 such instruments because of the high workload!!!
1 Dr Robert Richter, Clean Chemistry, Techniques for the Modern Laboratory, Milestone Press
2 Agilent Technologies, ICP-MS, A Primer