Developing ICP-MS-based methods for regulatory purposes: One example from a contract laboratory

Transcription

1 Developing ICP-MS-based methods for regulatory purposes: One example from a contract laboratory Douglas C. Baxter, Emma Engström, Dieke Sörlin, Ilia Rodushkin ALS Scandinavia AB, SE Luleå, Sweden Right Solutions Right Partner 1 Right Solutions Right Partner

2 U and Th isotopes in water Why (develop a method for U and Th isotopes in water)? Is there a market? Is there a standard method? Are there reference materials available? Is there legislation? What could possibly go wrong? 2 Right Solutions Right Partner

3 U and Th isotopes in water Why? Customer enquiries Is there a market? Yes, if legislation exists or customers ask for a service Is there a standard method? Yes, ISO :2016 Are there reference materials available? Yes, available from IRMM Is there legislation? Yes, 2013/51/EURATOM What could possibly go wrong? 3 Right Solutions Right Partner

4 Is there legislation? 2013/51/EURATOM 4 Right Solutions Right Partner

5 Is there legislation? 2013/51/EURATOM 240 µg/l 0,12 µg/l Detection limits not too challenging 1,6 µg/l 0,00086 µg/l 5 Right Solutions Right Partner

6 Are there reference materials available? U and Th reference materials Costs 520 EUR 1900 EUR 6 Right Solutions Right Partner

7 Is there a standard method? 7 Right Solutions Right Partner

8 Is there a standard method? Spectral interferences Isobaric (none tabulated for U or Th) Polyatomic (none tabulated for U or Th; hydrides mentioned) Note that complicated polyatomic interferences exist Taylor et al., Int. J. Mass Spectrom., 243 (2005) 71 8 Right Solutions Right Partner

9 Is there a standard method? Spectral interferences Suggested solutions (few details given) Sector field instruments (correct some polyatomic interf.) Hydride interferences cannot be resolved unless resolution is improved 5-fold 9 Right Solutions Right Partner

10 Is there a standard method? Spectral interferences Suggested solutions (few details given) Sector field instruments Mathematical corrections (none mentioned for U or Th) Does that mean that none are needed? 10 Right Solutions Right Partner

11 Is there a standard method? Spectral interferences Suggested solutions (few details given) Sector field instruments Mathematical corrections Collision and reaction cell technology No interferences? Don t need these! 11 Right Solutions Right Partner

12 Is there a standard method? Non-spectral interferences (ISO ) Suggested solutions to non-spectral interferences Matrix matching or sample dilution Dilution of samples will eliminate non-spectral interferences. Detection limits needed to fulfill requirements in legislation are easily met even after samples are diluted 10- or even 100-fold. 12 Right Solutions Right Partner

13 Is there a standard method? Non-spectral interferences (ISO ) Suggested solutions to non-spectral interferences Matrix matching or sample dilution Internal standards 18 Avoid internal standards that are present in the sample or that may cause spectral interferences. 204 Tl is interfered by 204 Pb and 204 Hg. 13 Right Solutions Right Partner

14 Is there a standard method? Non-spectral interferences (ISO ) Suggested solutions to non-spectral interferences Matrix matching or sample dilution Internal standards Inclusion of a suitable internal standard in the method will allow correction for non-spectral interferences and correction for instrumental drift. 14 Right Solutions Right Partner

15 Is there a standard method? Non-spectral interferences (ISO ) Suggested solutions to non-spectral interferences Matrix matching or sample dilution Internal standards Plasma condition optimization Optimize instrumental conditions during method validation stage. Study effects of e.g. nebulizer gas flow on U and Th isotopes as well as on the chosen internal standard in both the standards and in real samples. Vanhaecke et al., J. Anal. At. Spectrom., 8 (1993) Right Solutions Right Partner

16 Is there a standard method? Non-spectral interferences (ISO ) Suggested solutions to non-spectral interferences Matrix matching or sample dilution Internal standards Plasma condition optimization 16 Right Solutions Right Partner

17 Is there a standard method? Non-spectral interferences (ISO ) Suggested solutions to non-spectral interferences Matrix matching or sample dilution Internal standards Plasma condition optimization Standard addition technique Should never be needed if the method: (i) is based on correctly-optimized instrumental conditions; (ii) includes a suitable internal standard. Remember that standard additions will not correct for spectral interferences. 17 Right Solutions Right Partner

18 Is there a standard method? Non-spectral interferences (ISO ) Suggested solutions to non-spectral interferences Matrix matching or sample dilution Internal standards Plasma condition optimization Standard addition technique Isotope dilution (costs, purity issues) 18 Right Solutions Right Partner

19 What could possibly go wrong? 2013/51/EURATOM Only mentions 234 U and 238 U Customers may require 235 U and even 236 U, as well 19 Right Solutions Right Partner

20 What could possibly go wrong? The reference materials Price does not include delivery Many carriers will not handle radioactive material Register materials with national radiation safety authority Complete inventory change documents Log all uses of material Be prepared for radiation safety authority audit 20 Right Solutions Right Partner

21 What could possibly go wrong? Look into other resources E.g. ref. [15] in ISO What is abundance sensitivity? Pourcelot et al., J. Environ. Monitor., 13 (2011) Right Solutions Right Partner

22 What could possibly go wrong? Google abundance sensitivity icp ms 22 Right Solutions Right Partner

23 What could possibly go wrong? The standard ISO No mention of abundance sensitivity ( 234 U, 236 U) No info on how to correct for hydrides ( 235 U 1 H on 236 U) Mathematical correction for abundance sensitivity and hydrides is needed Abundance sensitivity correction requires measurement of tailing on low- and highmass sides of a single isotope. Hydride correction is element specific. 23 Right Solutions Right Partner

24 What could possibly go wrong? Everything Remember to be critical Be prepared for paperwork 24 Right Solutions Right Partner