Application of ICP-MS as a Tool for Environmental Monitoring. Bill Spence Environmental Market Specialist

Transcription

1 Application of ICP-MS as a Tool for Environmental Monitoring Bill Spence Environmental Market Specialist

2 Introduction Knowledge of the concentration of metallic species in the environment has been important for the last 35 years, since the first environmental legislation Measurements are made in materials such as drinking water, natural waters, waste waters, solid wastes, soils, sediments, and biota Various analytical techniques have been used to make these measurements Contaminated Sites Wastes Drinking Water Natural Waters 2

3 Introduction Technique Invented Characteristics Thermo AAS 1952 Single element analysis, ppbppm levels with flame or furnace, good for As, Se and Hg with vapour generation ICP-AES 1972 Fast multi-element analysis, ppb-% levels Q-ICP-MS 1981 Fast multi-element analysis, ppt-ppm levels M & S Series icap 6000 Series XSeries II HR-ICP- MS 1990 Fast multi-element analysis, ppq-ppm levels without interference Element2 3

4 Trace Element Analysis Product Range PERFORMANCE INCREASE Flame AAS, HG/CV AA GFAAS M and S Series ICP-AES icap 6000 Series Quadrupole ICP-MS X Series ICP-MS HR-ICP-MS Finnigan Element2 4

5 Water Analysis

6 Drinking Water - Requirements EU Directive 98/83/EC prescribes the following: Contaminant Parametric Value Trueness % of PV Precision % PV LoD Al Sb As B Cd Cr Cu Fe Pb Mn Hg Ni Se Na SO All concentrations in μg/l

7 Waters Sample Preparation 1. Samples taken in 125 ml HDPE bottles 2. Add 1.25 ml conc. HNO 3 with bottle-top dispenser 3. Check ph 4. Mix well by shaking 5. Add further acid as necessary until ph < Loosen lid and place in oven at 98 o C for 12 hours 7. Remove from oven and allow to cool prior to analysis 8. Filter if necessary, or decant NB: For Hg, addition of gold at ~500 ppb is required as an additional step 7

8 Waters Minimum Instrument Configuration XSeries II ICP-MS Standard glass concentric nebuliser Peltier cooled impact bead spraychamber at 3 o C Standard one-piece torch with PlasmaScreen Xt interface 8

9 Waters - Analysis Analytical parameters Analyte Mass Interferences Al 27 Sb 121 As 75 ArCl B 11 Cd 111 Cr 52 ArC, ClO, ClOH Cu 65 Fe 56 ArO, CaO Pb 208 Mn 55 Hg 202 Ni 60 CaO Se 82 Na 23 SO 4 34 (as sulphur) Internal standards added via mixing tee Internal Standards Concentration (ppb) Be (9) 150 In (115) 25 Tl (205) 25 9

10 Waters - Performance Detection Limits versus Required Detection Limits Analyte MDL Required MDL Al Sb As B Cd Cr Cu Fe 3 20 Pb Mn Hg Ni Se Na SO All concentrations in μg/l

11 Drinking Water - Performance Recoveries within 10% 11

12 River Water - Performance Recoveries within 6% 12

13 Soil Analysis

14 Soils Requirements (MCERTS UK) Element LOD Precision Bias mg/kg % % Sb As Ba Be B Cd Co Cu Cr Pb Hg Mo Ni Se V Zn

15 Soils Sample Preparation 1. Dry the sample (freeze-dry, air-dry or oven dry) 2. Crush with a ball or jaw mill and/or pass through a 25 um aperture sieve 3. Accurately weigh 1 g of the sieved material into a boiling tube 4. Add 7.5 ml HCl and 2.5 ml HNO 3 and add 2-3 acid-washed alumina anti-bumping granules 5. Allow to oxidise at room temperature for between 1 and 12 hours 6. Digest in block digestion unit with reflux condenser fitted for at least 2 hours 7. Wash down the condenser and quantitatively transfer to a 50 ml graduated tube 8. Make to 50 ml with UHP water 9. Dilute 1:10 with UHP water prior to analysis NB Add 500 ppb gold if Hg is required 15

16 Soils - Minimum Instrument Configuration XSeries II CCT ED ICP-MS Standard glass concentric nebuliser Peltier cooled impact bead spraychamber at 3 o C Standard one-piece torch with PlasmaScreen Xt interface He and H 2 cell gases 16

17 Soils - Analysis Analytical parameters Element Mass Interferences Cell Mode Sb 121 As 75 ArCl He Ba 137 Be 9 B 11 Cd 111 MoO He Co 59 CaOH, CaO He Cu 65 SO 2 He Cr 52 ArC, ClO, ClOH He Pb 208 Hg 202 Mo 98 Ni 60 CaO He Se 78 ArAr H 2 V 51 ClO He Zn 66 MgAr, SO 2 He Internal standards added via mixing tee Internal Standards Concentration (ppb) Isotopically enriched 6Li 500 Ge (72) 200 Rh (103) 10 Lu (175) 10 17

18 Soils - Performance Detection Limits versus Required Detection Limits (UK MCERTS) Analyte 5-s MDL Required MDL 9Be B V CCT Cr CCT Mn CCT Fe CCT 1-59Co CCT Ni CCT Cu CCT Zn CCT 1 5 Analyte 5-s MDL Required MDL 75As CCT Se CCT Mo Cd Sn 0.03 (0.50)* 121Sb Ba Hg Tl Pb * Specified as tetraethyl tin, measured as total tin 18 All concentrations in mg/kg dry weight

19 Soils - Performance 19 All concentrations in mg/kg dry weight N = 22 RTC-CRM038 Spike Recovery Analyte Mean %RSD Cert %Rec Mean %RSD Spike Value %Rec 9Be B V CCT Cr CCT Mn CCT Fe CCT Co CCT Ni CCT Cu CCT Zn CCT As CCT Se CCT Mo Cd Sn Sb Ba Hg Tl Pb

20 Seawater Analysis

21 The Challenges Seawater is a complex matrix.. 21

22 The Challenges Instrument Drift From Deposition Polyatomic Interferences 22

23 The Challenges - Contamination Still the biggest single cause of incorrect results! Can easily be managed with Careful sample handling techniques and dedicated clean areas Use of adequate quality reagents, standards and water Pre-washing/leaching of all sample and standard containers Requires common sense and good procedures that are rigidly adhered to Normal lab conditions ppb-ppm level contamination ppq-ppt level contamination Clean room conditions 23

24 Sample Handling Wear powder-free gloves at all times Class-100 clean room is advisable Good laminar flow hood may suffice Use only PFA or FEP bottles Decontaminate bottles by soaking in 10% HNO 3 Rinse thoroughly with UPA water (5 times) 24

25 Sample Preparation Dilute samples by weight on a balance do not use a pipette Use only best quality ultrapure water (>18MΩ cm) containing trace UPA Grade HNO 3 as a diluent Dilute to produce a salinity of around 3 parts per thousand (3,000 ppm) use salinity refractometer to test this is a 1:10 dilution for an average open ocean seawater Spike all samples with a constant amount of internal standard gallium (71), rhodium (103) and iridium (193) at 1 to 5 ppb work well 25

26 Seawater - ICP-MS Instrument Configuration XSeries II CCT ED ICP-MS Standard glass concentric nebuliser Peltier cooled impact bead spraychamber at 3 o C Standard one-piece torch with PlasmaScreen Xs interface run in Xs + Mode He and H 2 cell gases 26

27 Instrument Set-up Set up for low sample uptake rate (~0.4 ml / min or less) Orange/green peri-pump tube at ~20 rpm Best not to use autosampler or probe teflon tube only Manual sample changing or special autosampler for low contamination, e.g. CETAC ASX-100 or ESI SC-2 Run standard sample introduction or use Burgener AriMist nebuliser Use PlasmaScreen Plus and standard torch Use Xs interface in Xs + Mode Use pure He (or 8% H 2 in He as cell gas) 27

28 CCT Gas Optimization He Only Log Signal Intensity (icps) ClO, ClOH, ArC Cr V Co 52Cr Unpiked 52Cr Spiked BEC BEC (ppb) Signal Intensity (icps) ClO 51V Unspiked 51V Spiked BEC BEC (ppb) Signal Intensity (icps) Co Unspiked 59Co Spiked BEC CaO, CaOH BEC (ppb) He Flow Rate (ml/min) He Gas Flow (ml/min) He Gas Flow (ml/min) Log Signal Intensity (icps) Ni CaO, CaOH 60Ni Unpiked 60Ni Spiked BEC BEC (ppb) Signal Intensity (icps) Cu NaAr 63Cu Unspiked 63Cu Spiked BEC BEC (ppb) Signal Intensity (icps) ArCl As 75As Unspiked 75As Spiked BEC BEC (ppb) He Gas Flow (ml/min) He Gas Flow (ml/min) 5.5 ml/min He removes all interferences! He Gas Flow (ml/min)

29 Calibration Take 1:10 NASS-5 and measure Spike the same bottle with 100ppt of analytes and remeasure Spike again to 200ppt and remeasure Spike again to 500ppt and remeasure 29

30 Results for Seawater Reference Materials NASS-5 1:10 Analyte Measured Known Rec% 100ppt Spike Rec% 51V Cr Mn Fe Co Ni Cu Zn As Se Cd Cd Pb

31 Results for Seawater Reference Materials CASS-4 1:10 Analyte Measured Known Rec% 100ppt Spike Rec% 51V Cr Mn Fe Co Ni Cu Zn As Se Cd Cd Pb

32 Results for Seawater Reference Materials SLEW-3 1:5 Analyte Measured Known Rec% 500ppt* Spike Rec% 51V Cr Mn Fe Co Ni Cu Zn As Se Cd Cd Pb

33 BEC in Trace HNO 3 Analyte BEC (ppt) 51V Cr Mn Co Ni Cu Zn 4 75As 2 78Se 5 111Cd Pb 1 33

34 Stability 2 Hours Continuous Aspiration V (1) 52Cr (1) Concentration (ppb) Mn (1) 56Fe (1) 59Co (1) 60Ni (1) 63Cu (1) 65Cu (1) 66Zn (1) 75As (1) 95Mo (1) 98Mo (1) 111Cd (1) 208Pb (1) 238U (1) 0 00:00:00 00:14:24 00:28:48 00:43:12 00:57:36 01:12:00 01:26:24 01:40:48 01:55:12 Time (hh:mm:ss) 34

35 Stability 2 Hours Continuous Aspiration % % Internal Standard Response (%) % % % 95.00% 90.00% 71Ga (2) 71Ga (1) 103Rh (1) 191Ir (2) 193Ir (1) 85.00% 80.00% 00:00:00 00:14:24 00:28:48 00:43:12 00:57:36 01:12:00 01:26:24 01:40:48 01:55:12 Time (hh:mm:ss) 35

36 Conclusions ICP-MS is a powerful and essential tool for environmental monitoring Ideal for trace element analysis in waters, soils, sediments, biota Advances in interface technology improve its performance and robustness for environmental applications Copes with higher TDS, gives better long-term stability Collision cell technology removes polyatomic interferences produced by sample matrix components Enables analysis of diluted seawater and soil digests 36