High Throughput Metal Analysis using a Modern ICP and Spark Ablation Accessory

1. High Throughput Metal Analysis using a Modern ICP and Spark Ablation Accessory A. Clavering, G. Buchbinder, N. Verblyudov, F. Bulman Rio Symposium, Sept 2008

2. High Purity Metals Analysis by ICP-OES with Spark Ablation • We will look at: • Background of these analyses • Some common problems with metals analysis • Analytical considerations for high purity metals (Ag and Pb) by a variety of Atomic Spectroscopy techniques • High Purity Silver and Lead Analysis by ICP-OES with Spark Ablation • Further research for the future

3. Background – where are the results from? • Pure silver analysis - Kolyma State Refinery, in the Magadan region of Russia, utilise an iCAP 6500 Duo ICP with Solid Sampling Excitation Accessory (SSEA) for the analysis of silver – the SSEA/iCAP combination replaced their DC Arc Atomcomp 2000. The silver results presented here are part of their daily routine analysis for plant control and final product evaluation. • Pure lead analysis - Thermo Cambridge was requested to undertake a short feasibility study to determine whether the iCAP with SSEA accessory was capable of determining low-levels of impurities (down to a MDL of 0.1ppm in solid, Ni and Te) in pure lead for a manufacturer.

4. Problems with metal analysis by Atomic Spectroscopy • DC Arc analysis • (solid sampling) is sensitive and can determine low-level impurities in solid silver • Matrices containing even small quantities of Se and Te in Ag may show errors • Lower grade silver also shows errors. • Pb analysis may show similar problems to Ag – elemental volatility?

5. Problems with metal analysis by Atomic Spectroscopy • Flame AA and ICP-OES are suitable for metal analysis – precious metal bullion, lower grade metals and base metals • ICP is probably most suited due to multi-element capabilities, reduced matrix effects, and better sensitivity. But… • Problems always exist – most notably with solution chemistry

6. Problems: Pb and Ag analysis by Atomic Spectroscopy • Not all impurities will dissolve in nitric acid – possible filtration and separate treatment for insolubles – more time consuming • Solubility product for chlorides and silver is very low – limited solubility for AgCl when trying to dissolve with Aqua Regia – filtering may be necessary • Some impurities may co-precipitate – either a complexing agent is required or excess Cl- addition – impurities may still be lost • In Ag and Pb, elements like Sn are a problem – quite often involve procedures with hydrofluoric acid!!

7. The Benefits of Solid Sampling By Spark Ablation • Remove most sample preparation time • Minimal sample preparation time is needed to prepare the “dip” sample • Metal sample surface only needs to be lathed – a quick and simple operation • The amount of sample consumed is small • Precious metals being expensive – minimised consumption of a sample is preferred. Spark ablation requires only small quantities of sample. • Metal CRMs are also expensive – may be reused many times over. • Spark ablation produces a much larger sampling relative to Laser ablation – thus making it ideal for bulk and solid metal sampling whereas Laser Ablation is better suited for samples which require analysis at precise locations and non-conductive samples.

8. Instrumentation Used – iCAP 6500 with SSEA ICP-OES with Spark Ablation

9. iCAP ICP coupled with SSEA • SSEA – Separate Sampling and Excitation Accessory • A spark ablation system which will ablate any conductive sample to a dry metal vapour • The aerosol is passed directly into the ICP with an argon carrier gas • Normal ICP process occurs with atomisation, excitation, emission and analysis • The iCAP 6000 Series couples and communicates through iTEVA software

10. Ag Analysis: Kolyma State Refinery, Russia Spark Ablation is an approved standard method of analysis per the Russian Standards governing body GOST

11. Sampling Quantity / Sample Prep At Kolyma, they ablate the silver sample and directly transfer the metal vapour into the base of the plasma torch – no other sample introduction components

12. SSEA Coupling to an iCAP • ICP can directly couple to the SSEA carrier gas line or a custom-built dual nebuliser chamber can be used for rapid changeover between liquids and solids

13. SSEA Schematic with optional dual port spray chamber SSEA

14. ICP-OES Plasma Viewing • Radial View of the Plasma – Robust, fewer chemical interferences • Axial View of the Plasma – best sensitivity, lowest detection limits • Do we improve signal to background ratios with complex spectra? • SSEA is commonly coupled to an iCAP Radial ICP but an iCAP Duo can also be used – radial view is useful • Silver and lead are not spectrally rich and signal to background is improved with the axial view

15. Instrumental Parameters - Ag and Pb comparison • Parameters of ICP - Pb • RF forward power – 1300 watts • Coolant gas flow – 12 L/min • Auxiliary gas flow – 1.0 L/min • Integration time – 30s maximum • Parameters of SSEA – Pb (MP 327) • Power level – 1 • Frequency – 800 Hz • Spark Gap – 2 mm • Pressure in delivery line – 18 psi • Parameters of ICP – Ag • RF forward power – 1150 watts • Coolant gas flow – 12 L/min • Auxiliary gas flow – 0.5 L/min • Integration time – 30s maximum • Parameters of SSEA – Ag (MP 961) • Power level – 3 • Frequency – 500 Hz • Spark Gap – 2 mm • Pressure in delivery line – 18 psi • Samples were lathed and ensured that the surface was smooth – the SSEA’s o-ring seal ensures no air ingress • Total Analysis time per sample < 5 mins including sample change

16. Instrumental Parameters: Ag – Calibration curves • Pd 340.458 nm calibration curve on the right (State Kolyma Refinery, Russia) shows a correlation coefficient of six 9s • Ordinarily the calibration is better than three 9s or not accepted

17. Ag Results 1 – Results and Detection Limits

18. Instrumental Parameters: Pb – Calibration curves • Bi 223.061nm (Thermo Cambridge, the wilds of England) shows a correlation coefficient of 0.9994. • Ordinarily the calibration was better than three 9s.

19. Ag Results 2 – Accuracy

20. Pb results 1 – Detection Limits (BCS 210D)

21. Pb results 2 – CRM materials results (MBH)

22. Problems and Further Research • Problems: • Lead analysis shows response or detection limits of some elements to be inconsistent with normal ICP sensitivities – Se, Cu, Na. • SSEA parameters are sometimes constrained by physical properties of the metals. • Te and Ni results comparison between OE Spark and SSEA were somewhat inconsistent on some samples. • Further work: • Categorise further materials – e.g. pure copper, “hard” alloys. • Research the effect of other carrier gases – helium, nitrogen – helium is already known to boost Laser sensitivity significantly • Alternate spray chamber conditions – using a continuous spray of a dilute acid(s) – reduces background but will it improve DLs in some applications?

23. High Throughput Metal Analysis using a Modern ICP and Spark Ablation Accessory A. Clavering, G. Buchbinder, N. Verblyudov, F. Bulman Rio Symposium, Sept 2008