Water for ICP-MS
Impact of Water
Impact of Water Quality on ICP-MS analyses
Water is not used during the analysis step, however, sample preparation step, blank, and standard preparation require high purity water. The water selected must meet two basic features:- Avoid interferences with the metals being analyzed
- Enable the instrument to run in optimum conditions, i.e. reduce contamination of the ICP-MS
Experimental Conditions
Results expected with an ICP-MS instrument are very much dependant on the analytical conditions and environment of the laboratory. Working in a clean room versus standard laboratory will allow reaching significantly lower detection limits and background equivalent concentrations.An additional important parameter to consider in the appreciation of the water quality utilized is the analytical capability of the ICP-MS instrument itself. Over the last decades, the detection limits expected for some elements has dramatically improved. Examples given in Figure 2 demonstrate that the limiting factor of the analysis is not the reagent purity (including water) but the ICP-MS technology. While this observation remains true for some elements that are hardly naturally present in water, nowdays, the sensitivity of the instruments is such that reagent quality might interfere with trace analysis for some elements.
Figure 2: Evolution of detection over two decades.
The selection of the containers is highly important, as some containers may release ions in the water for an extended period of time. Once the best container has been selected, the preparation (rinsing, soaking and cleaning steps) of the container for high purity water sampling needs to be studied. Here is an example of procedure developed for high purity water sampling.
Figure 3: Analytical procedurefor high purity water analysis
The HNO3 utilized to stabilize the samples may also be a source of contamination of the sample. While nitric acid is useful to keep the samples for long periods of time and to increase the reproducibility of the analytical data, it may participate to the sources of contamination.
| Concentrations in ng.mL-1 | |||||
|---|---|---|---|---|---|
| Na | Ca | Fe | Zn | Pb | |
| Classical Lab | |||||
| Ultrapure Water | 3.2 | 1.9 | 2.5 | 0.20 | 0.14 |
| Ultrapure HNO3 | 5.4 | 2.2 | 2.4 | 0.45 | 0.29 |
| Clean Room | |||||
| Ultrapure Water | 0.45 | 0.27 | 0.17 | 0.025 | 0.013 |
| Ultrapure HNO3 | 0.84 | 0.8 | 1.3 | 0.051 | 0.038 |
| 1 http://www.ivstandards.com |
|||||
Water Quality Parameter
- Water free of traces of elements
Obviously any trace of metal in the water can interfere with the analysis. An 18.2 MΩ•cm resistivity is a minimum requirement, and other precautions should be taken to ensure that no ions ever leak from the water purification unit. This may include the use of a safety ion exchange cartridge to prevent release of ions upon exhaustion of the cartridges, or the use of final filters with adsorption capacities for metals. It also requires careful selection of the tubing and valves to avoid any contamination of the high purity water. - Particulates
Particulates must be removed to avoid spoilage of the nebulizer. In addition some metals also may stick to particulates and perturb the analysis. A 0.1 µm filter is used at the outlet of the purification unit to prevent particulate release from the water purification unit. - Reduced Organics
Large quantities of organics would stick on the nebulizer walls and result in more frequent cleaning. In addition, some metals form organo metallic complexes. Those include platinum, mercury, tin or palladium, that form covalent bonds with organic moieties. In order to ensure low levels of those elements in the water, it is important to break down those organo metallic complexes and removes the metals. A photooxidation process is used to degrade the organic part. The metals then liberated in the water are removed using ion exchange resins. Activated carbon adsorbs organics and is utilized as well to decrease the overall organic content in the water. - Bacteria
It is important to maintain the bacterial count as low as possible in the water. Indeed, bacteria can release ions and they also behave as particulates. Therefore, they can create interferences with the ions dosed and spoil the nebulizer as well. Various means are utilized in the purification unit to control and reduce the bacterial level. Germicidal UV (254 nm) is used in combination with end filters set at the point-of-use.
Levels of elements in high purity water delivered by a combination Milli-Q® Integral + Q-Pod® Element systems
Levels of elements in high purity water reported here were obtained in clean room conditions in order to minimize the contamination due to the laboratory. A water purification system, the Milli-Q® IQ Element set downstream a Milli-Q® Integral, specifically designed for the production of high purity water with extremely low levels of metals was utilized to obtain those data.Values obtained with an Agilent 7700s + MFN100
More Information
You may find more information related to water quality on ICP-MS analyses in the following web site:Literature
- Application Note: Ultrapure Water for Determination of Elemental Impurities per USP - Anastasia Domanova, Juhani Virkanen, Glenn Woods, Stephane Mabic - December 2017
- Application Note: Ultrapure Water for Determination of Elemental Impurities in Pharmaceuticals - Anastasia Domanova, Juhani Virkanen, Glenn Woods, Stephane Mabic - November 2017
- Mabic S., Kano I., Darbouret D. Matching purified water quality to experimental detection limits. LabPlus Internat. 16-18, April/May, 2003.
- R&D Notebook - Ultrapure water for boron and silica sensitive laboratory applications. I. Kano and D. Darbouret.
- Ultrapure water blank for boron trace analysis, D. Darbouret and I. Kano. Journal of Analytical Atomic Spectrometry, 2000, 15 : 1395-1399.
- Blank optimization for elemental analysis down to ppt levels, D. Darbouret and I. Kano. Ultrapure Water, September 1999: 53-58.
- Datasheet: Milli-Q® IQ Element Unit
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