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Syringe filter units used in sample preparation Analyzing Drinking Water by ICP-MS for Heavy Metal Detection

Author / Editor: Klaus Schöne* / Dr. Ilka Ottleben

Extremely sensitive analytical instruments capable of assaying analytes in the femtogram range have meanwhile become standard equipment in many laboratories. But their accuracy in analysis of drinking water is decisively influenced by the right choice of syringe filter unit, as described in this article.

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The Minisart syringe filter units are suitable for use in analysis of drinking water.
The Minisart syringe filter units are suitable for use in analysis of drinking water.
(Source: Sartorius AG)

Drinking water is a nutrient essentially required for life. Therefore, its purity is the basic prerequisite for healthy nutrition. Depending on their concentration, individual substances dissolved in water can be toxic and even irreversibly impair people’s health. Very slight concentrations are all it takes for a number of heavy metals to have a toxic effect. For instance, when ingested and absorbed by the blood in concentrations as little as 100 µg/L, lead, a common heavy metal, can result in neurophysiological disorders in children, such as persistent intelligence deficits as well as motoric and mental problems [1]. Legislators and health organizations, such as the WHO [2], have therefore issued recommendations and limits for the presence of metals in water. For Europe, the limits given by the Drinking Water Directive 98/83/EC [3] apply.

Regular monitoring of drinking water required

Water treated for use as drinking water is regularly analyzed to monitor the limits established for metals. A basic step in drinking water analysis is preparation of samples during which undissolved constituents are removed from each sample by filtration through a 0.45 µm filter [4]. For this purpose, syringe filter units are used. To prevent distorting the analytical results, such filters may not release any quantities of metal ions relevant for drinking water analysis into the samples to be tested. Afterwards, the metal elements are quantitatively assayed by ICP-AES or by the more sensitive method of ICP-MS. Sampled drinking water is considered safe for consumption if its metal values are below the legal limits.

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The analytical results obtained in this study are intended to demonstrate that the Minisart syringe filter units tested have a very high degree of purity and the metal ions extracted from them are below the detection limit or considerably lower than the limits established by regulatory requirements. This study is also designed to determine whether Minisart syringe filter units are suitable for use in analysis of drinking water. In this study, ICP-MS technology was selected as the method for analysis of metal ions. Inductively coupled plasma mass spectroscopy (ICP-MS) is a highly sophisticated multi-element analytical technology that is increasingly being used in the pharmaceutical industry, the food and beverage sector and in environmental protection for analysis of trace elements. This technology enables analyses to be performed down into the sub-ppt detection limit range (parts per trillion = one particle per trillion or µg/L).

How does ICP-MS technology work?

ICP-MS technology is based on the principles of atomic emission spectroscopy. In high-temperature argon plasma, elements present in the sample are dissociated into positively charged ions and detected based on their mass-to-charge ratios as they subsequently pass through a mass spectrometer. In principle, ICP-MS consists of the following steps: sample preparation and introduction; aerosol generation; ionization by an argon plasma source; mass discrimination; and identification by the detection system, including data analysis (based on Worley and Kvech [5]). Figure 1 shows a schematic diagram of the steps in the ICP-MS process.

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