Inductively coupled plasma mass spectrometry (ICP-MS) instruments and their capabilities have come a long way since the method was first used in analysis. According to Jenny Nelson, application scientist at Agilent Technologies, “ICP-MS instruments today can handle almost any sample type, measure nearly every element, and report accurate concentrations from parts per quadrillion to percent levels.” She notes that there is no other metals analysis technique that comes close.
However, Nelson remarks that this means expectations of these units and their capabilities are higher than ever. Instead of simply analyzing a few heavy metals in drinking water, for example, ICP-MS instruments are expected to measure major and trace elements in one run.
Of course, these capabilities increase the cost of a unit. So, how do you decide which one to choose based on your budget? Here, we take a look at key factors to consider when purchasing an ICP-MS instrument, including how each feature impacts cost.
Interference removal as a crucial factor
Interference removal ensures that accurate results can be consistently achieved. Shona McSheehy Ducos, Qtegra ISDS Software senior product manager, Trace Elemental Analysis, Thermo Fisher Scientific, explains that spectral interferences are often the most troublesome. These occur when a polyatomic analyte or an analyte with multiple charges has the same mass to charge ratio as the analyte that is to be measured.
There are two main types of interference removal systems, either utilizing collision reaction cell (CRC) technology or high resolution (HR) technology. CRC is the predominant technique in quadrupole ICP-MS. Within this, there are two key categories: single quadrupole and triple quadrupole (TQ). The former traditionally uses CRC with an inert gas such as hydrogen. These systems are more common and come with a lower price tag. TQ-ICP-MS units usually use reactive gases in a process that offers more specific interference removal. This offers lower limits of detection (LODs), but often commands a higher price.
A different approach entirely is HR technology. McSheehy Ducos explains that this utilizes small differences in nominal mass between the analyte of interest and the interference to physically separate them. It is more transparent than CRC technology, but comes at a cost and is most likely to be used in metrology and exacting applications that require ultralow detection limits.
The importance of signal-to-noise ratio and speed
ICP-MS systems are extremely sensitive due to the use of advanced ion optics technology and a high-energy plasma source. McSheehy Ducos explains that this high sensitivity enables the measurement of very low elemental concentrations. She also reveals that equally important is the analyte background in ICP-MS, and this must be minimized to enable the best LODs.
Low LODs are more difficult (and costly) to achieve, but are often dictated by regulatory methods. “Purchasing an ICP-MS with the best signal (sensitivity) to noise (background) ratio is key to successfully meeting or exceeding regulatory requirements,” says McSheehy Ducos.
Another central factor she mentions is speed, as high throughput often translates to cost savings. ICP-MS systems are fast, with typical sample analysis times of two to three minutes. But features such as a single mode kinetic energy discrimination and discrete sampling valves can result in sample analysis times of one to two minutes.