I am a beginner in ICP-MS analysis. We are analysing dissolved trace metals (Li, Be, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) in groundwater using Inductively Coupled Plasma Mass Spectrometry ICP-MS (Thermo Scientific model iCAP Qc). The total dissolved solids concentration in the groundwater ranges from 16 to 1000mg/l. I am told that a TDS up to 50 mg/ l can be analysed directly in ICP-MS. If the TDS is more than that, the samples need to be diluted. In such a case, my trace metals will be going below the detection limit. How do I beat this problem? Any tips for me? Thanks.
I am also working on groundwater contamination and have used the ICP-MS several times. The most important step during the analysis of water samples for heavy metal contamination, as you mentioned, is the element of interest (you may be interested in several elements like Fe, Cd, Ni, etc.) The second step is to check out the previous heavy metals report on the area from where you have collected the samples. It will give you an idea about the average concentration of your element(s) of interest in that area. After that, you have to see the minimum and maximum average range of heavy metals ( for example - in your area, the minimum cons. is of element Ni and is 1 ppb and maximum cons. that is of As is 80 ppb). Then you have to run the calibration standard of 0.1 ppb, 1 ppb, 20 ppb, 50 ppb, 100 ppb, 200 ppb (having element of interest) in order to find the best possible results. In order to make the data more robust, you also have to run the SRM (standard reference material). If you the standard in the range of your sample's previous results, as I mentioned, you don't need to go for dilution. Otherwise, you have to go for dilution especially if the concentration is very very Haigh for example in more than 500 ppb to 1 or 10 ppm.
Regards
Not sure where, exactly, you came up with the 50 ppm TDS number. That might be true for a really old system (Agilent 4500 series, for example), but it is certainly not true for any system that involves a collision cell or an off-axis detector.
The best way is to pass the sample through cation exchange resin to selectively remove major component such as Sodium and Calcium which are not your analyte of interest this should decrease your sample TDS.
Mark Krause Thank you, Mark. I cross-checked the ICP-MS model my collaborator has (Thermo Scientific iCAP Qc). It indeed works on collision cell technology. Therefore do you think that I can run samples having TDS about 800mg/l directly? Else let me know what is the maximum TDS the ICP-MS can take for a direct run without dilution.
Take at look at this article:
https://www.selectscience.net/application-notes/analysis-of-high-matrix-samples-using-argon-gas-dilution-with-the-thermo-scientific-icap-q-icp-ms/?artID=37714
However, it's best to dilute the samples. For some elements (e.g. Li, Be, Ti, Mn, Fe, Zn) the ICP-AES technique would be better. If the samples do not differ in terms of the hydrochemical type (proportions of the main components), then you can prepare a synthetic matrix for the calibration solution and determine the functional relationship of the recovery value of the element as the TDS changes.
If they are too different, then traditional calibration with the addition method or a newer method can be used: Virgilio A et al.- Analytical and Bioanalytical Chemistry, 2018,410,1157-62 - Multi-isotope calibration for inductively coupled plasma mass spectrometry
- Badges
- Science method
- Similar topics
- Biological Science
- Ecology