Most of the analytical techniques used for the determination of heavy metals in solid samples require sample digestion. This way, the sample in the liquid state can be introduced into an analytical instrument. However, sample digestion can lead to loss of volatile compounds. This also leads to having partly soluble compounds present in the analysed material.
On the other hand, methods such as X-ray fluorescence that directly work with solid samples have limits of detection that are unsatisfactory. That’s why scientists have developed an analytical technique that doesn not require sample digestion while still producing satisfactory detection limits. This method is based on inductively coupled plasma – mass spectrometry (ICP-MS).
In the ICP-MS method, the sample is introduced undigested into an analytical instrument. It starts with pumping sample (mostly liquid) into nebulizer where it is turned into a fine aerosol with argon gas. From there it goes to spray chamber, after which fine particles are injected to the plasma torch. In plasma torch, ionisation of the sample occurs. The ions are then directed to mass analyser and detector.
For slurry sampling by ICP-MS, the sample should be ground and dispersed in a suitable chemical. Studies showed that sample particle size of 8 µm would act the same as liquid droplets in the nebulizer. They will undergo the same ionisation process in the plasma torch.
Slurry nebulisation ICP-MS is useful for multi-element analysis in many types of rock samples. It can also be used for sediment and soil testing. It is also an alternative technique for the determination of volatile elements such as arsenic, antimony, and tin. For the determination of low levels of uranium, thorium, niobium, and tantalum, slurry nebulisation ICP-MS is also useful. The limits of detection using this technique are less than 1 ng/g for many elements such as chromium, selenium, silver, cadmium, tin, and antimony.
Shu-feng Chen and Shiuh-jen Jiang J. Anal. At. Spectrom., 1998. 13, 1113-1117 Determination of cadmium, mercury and lead in soil samples by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry