Analytical Prep
advertisement
ICP Methods for Consistent Trace Elemental Data WEALA Technical Workshop - 25-Apr-2013 The Analytical Process Sampling Bulk Prep Analytical Prep Analysis Calculations and Reporting 2 2 2 2 2 2 π ππ£πππππ = π ππππππππ + π π΅π’ππ ππππ + π π΄ππππ¦π‘ππππ ππππ + π π΄ππππ¦π ππ + π πΆππππ’πππ‘ππππ Scope WEALA • Focus on soil • Environmental slant (presenter’s bias) “Consistency” relates to ‘variability’ • Event-to-event consistency relies on controlling systematic variability Sampling “Sampling involves the selection from the total population of a subset of individuals upon which measurements will be made; the measurements made on this subset (or sample) will then be used to estimate the properties (or parameters) of the total population.” Carter and Gregorich, pg. 1, first sentence Sampling - Design What question is to be answered? • Total concentrations in the whole? • Extent and boundaries of a spill? Representative of the site • Account for heterogeneity/stratification Protect sample integrity • Precautions against contamination • Appropriate containers • Appropriate storage conditions and time Field sampling design and execution is the first consideration for consistency of data for a source or site Bulk Prep Preparation of field samples for laboratory use and storage Drying Field moist Air dry (60°C) Oven dry (105°C) Sieving Splitting /Subsampling Grinding Archiving < 6mm < 2mm < 63 um Appropriate type of subsample; Appropriate amount of subsample; Representative subsample Break up clumps; Pulverize to defined size As-received; Prepped Particle Size Fractions for Metals Analysis Aquatic Sediment (< 63 um) Terrestrial Soils (< 2 mm) Particle size chart from Carter, 2008; Figure 55.1 Analytical Prep Extract/Dissolve Analytes from Solid Phase into Aqueous Solution Salinity Trace Metals Special Techniques Salinity Saturation Extract • Defined in Carter, Handbook 60 and SSSA • Well-defined procedure: • Add water to saturation • Stand > 4 hr • Vacuum-filter • Saturation % = 100 * Wwater / Wsoil • Analytical results conventionally reported as mg/L Other Extraction Ratios • 1:1 or 1:5 most commonly listed • When unable to prepare a Saturation Extract (type or amount of sample) • Report as mg/kg(?) Tessier Model Metals Fractions in Sediments Exchangeable Bound to Carbonates Bound to Fe-Mn Oxides Bound to Organic Matter Residual Analytical Chemistry 51(7) June 1979 • MgCl2, pH 7.0 • NaOAC/HOAc, pH 5.0 • NH2OH·H2O in 25% HOAc, pH~2 • H2O2/HNO3, pH~2 (+NH4OAc) • HF and HClO4 Tessier Model – Extension to Terrestrial Soils(?) Soluble Exchangeable Bound to Carbonates Bound to Fe-Mn Oxides Bound to Organic Matter Residual • Water • MgCl2, pH 7.0 • NaOAC/HOAc, pH 5.0 • NH2OH·H2O in 25% HOAc, pH~2 • H2O2/HNO3, pH~2(+NH4OAc) • HF and HClO4 Metals Fractions of Environmental Significance Soluble Exchangeable ‘Environmentally Available’ Bound to Carbonates or Bound to Fe-Mn Oxides Bound to Organic Matter Residual ‘Total Recoverable’ metals Standard Analytical Prep Procedures for Trace Metals EPA 200.2 Nominal Sample Mass (g - dry wt.) HNO3 Concentration HNO3 Volume (mL) 1st Acid Addition HCl Concentration HCl Volume (mL) Temperature (°C) 1st Heating Time (min) HNO3 Concentration 2nd Acid Addition HNO3 Volume (mL) Reflux Time (min) 1 1+1 4 1+4 10 ~95 30 Evaporate to (mL) Peroxide Addition 30% H2O2 (mL) DIW Volume (mL) 95 ± 5 10 to 15 Conc 5 'heat and add acid until no change in appearance' ~5 3 2 EPA 3050B ICPAES/FLAA 1 Conc 10 95 ± 5 EPA 3050B* ICPAES/FLAA 1 Conc 2.5 Conc 10 95 ± 5 15 15 1-mL increments until minimal effervescence, to maximum 10 mL total Additional 30% H2O2 Evaporate to (mL) Hot Conc HCl Rinse (mL) Hot DIW Rinse (mL) First Filter Conc. HCl Digest Acid (mL) Treatment Reflux Time (min) Condition Final Acid Addition Conc. HCl (mL) Final Digest Volume (mL) Remove solids (if present) after or before Final Volume adjustment? EPA 3050B ICPMS/GFAA 1 1+1 10 ~5 100 100 100 ≤5 20 5 "until the filter paper dissolves" "If a precipitate forms" 10 100 after before before before * EPA 3050B states "may be used to improve the solubilities and recoveries of antimony, barium, lead, and silver when necessary. These steps are optional and are not required on a routine basis" Applicable Metals EPA 200.2 Aluminum Antimony Arsenic Boron Barium Beryllium Cadmium Calcium Chromium Cobalt Copper Iron Lead Lithium Magnesium Manganese Mercury Molybdenum Nickel Phosphorus Potassium Selenium Silica Silver Sodium Strontium Thallium Thorium Tin Uranium Vanadium Zinc (Al) (Sb) (As) (B) (Ba) (Be) (Cd) (Ca) (Cr) (Co) (Cu) (Fe) (Pb) (Li) (Mg) (Mn) (Hg) (Mo) (Ni) (P) (K) (Se) (SiO2) (Ag) (Na) (Sr) (Tl) (Th) (Sn) (U) (V) (Zn) X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X EPA 3050B ICPMS/GFAA EPA 3050B ICPAES/FLAA X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X Analytical Prep Special Techniques Hot-Water Extraction Boron Solvent Extraction Sulphur Fusion BariteBarium Silicon Analysis Why ICP? What is “ICP”? • Multi-element • Wide dynamic range • % to sub-ppt • Manageable interferences • ICP = Inductively-Coupled Plasma • For metals analysis, typically an argon plasma sustained in a radio-frequency electromagnetic field • Serves to atomize and ionize the sample • Detection of the atoms/ions define the technique (AES or OES; MS or CRC-MS; HR-MS) Anatomy of a Plasma Plasma Temperature Zones1 Plasma Formation1 Droplet Conversion in the ICP Source2 1Spectroscopy 16(6) June 2001 2Perkin-Elmer, 1997 Basic ICP Instrument Architecture Perkin-Elmer, 1997 Emission Spectroscopy Light Spectra White Light (sunlight) Emission Spectrum of Iron (Fe) Grating Equation mλ = d (sinα + sinβ), where m is the spectral order (an integer) and λ is the wavelength Palmer, C. and Loewen, E., Diffraction Grating Handbook, sixth edition; Newport Corporation, 2005. Rowland Circle Polychromator Perkin-Elmer, 1997 Spectral Overlap Palmer, C. and Loewen, E., Diffraction Grating Handbook, sixth edition; Newport Corporation, 2005. Echelle Optical Mount Perkin-Elmer, 1997 2-D Spectral Array Perkin-Elmer, 1997 Atomic Mass Spectra 40 91.22 Zr Zirconium Relative Abundance of the Natural Isotopes Spectroscopy 17(10) October 2002; Perkin-Elmer Relative Abundance of the Natural Isotopes Spectroscopy 17(10) October 2002; Perkin-Elmer Elements analyzed by ICPMS http://www.perkinelmer.ca/EN-CA/CMSResources/Images/44-74849tch_icpmsthirtyminuteguide.pdf Plasma – Mass Spectrometer Interface Spectroscopy 16(7) July 2001 Quadrupole Spectrometer Spectroscopy 16(10) October 2001 Conventional ICPMS Spectroscopy 17(2) February 2002 (edited graphic) Collision/Reaction Cell ICPMS Spectroscopy 17(2) February 2002 Collision/Reaction Cell ICPMS Spectroscopy 17(2) February 2002 Hi-Resolution ICPMS Spectroscopy 16(11) November 2001 Hi-Resolution ICPMS Name Symbol Oxygen 16O 17O 18O Chlorine 35Cl 15.994915 16.999132 17.99916 99.757 0.038 0.205 Name Symbol Iron 54Fe Mass 58Fe 5.845 91.754 2.119 0.282 75As 74.92160 100 56Fe 57Fe 75.78 24.22 40Ar 35.967546 37.962732 39.962383 0.3365 0.0632 99.6003 40Ar16O 55.957298 40Ar16O - 56Fe = 0.022356 40Ar35Cl 74.931236 40Ar35Cl - 75As = 0.009640 36Ar 38Ar Arsenic Abundance (%) 53.939615 55.934942 56.93540 57.93328 34.968853 36.96590 37Cl Argon Mass Abundance (%) Hi-Resolution ICPMS Spectroscopy 16(11) November 2001 Interferences in ICP Physical • Affects how much of the sample gets to the plasma or spectrometer • Differences in viscosity, surface tension, TDS yield variations in solution transport and nebulization Chemical • Affects the nature of the plasma or the analytes in the plasma • Molecular compound formation; ionization; solute vaporization Spectral • Affects the intensity of the analyte signal reaching the detector • Background shifts • Overlapping wavelengths/masses Addressing Interferences Physical • Matrix-matching of standards with samples • Use of internal standard(s) • Water-saturated nebulization gas (prevent salt build-up) • Dilution Chemical • (Tend not to be prevalent in ICP owing to high energy) • Optimization of operating conditions • Matrix-matching of standards with samples • Use of internal standard(s) • Dilution Physical Effects in ICPMS Space-Charge Interference Spectroscopy 16(9) September 2001 Addressing Interferences Spectral – AES Background Overlap • Matrix-matching • Off-peak correction • Alternate wavelength • Inter-element correction Correcting AES Spectral Interference Off-peak background correction Inter-element correction [π]πππ‘π’ππ = [π]ππππππππ‘ − πΎππΌ [πΌ]πππ‘π’ππ where, πΎππΌ = [π]ππππππππ‘° [πΌ]πππ‘π’ππ° determined previously from standards http://inorganicventures.com/tech/icp-operations/spectral-interference-correction/correction-icp-oes Types of MS Spectral Overlap Isobaric Polyatomic Doublecharged ions • Two isotopes of same mass • e.g. 40Ar on 40Ca • Molecular ions formed in the plasma • e.g. 40Ar35Cl on 75As • Mass discrimination based on m/z • e.g. 136Ba++ on 68Zn+ Addressing Interferences Spectral – MS Background Overlap • Matrix-matching • Alternate mass • Mass equation • Collision/Reaction • Increase resolution Correcting MS Spectral Interference Alternate Mass Mass equation 82ππ = 82ππ − 1.008696 ∗ 83πΎπ where, 82 1.008696= 83 Spectroscopy 17(10) October 2002; Perkin-Elmer πΎπ πππ’ππππππ 11.6% = πΎπ πππ’ππππππ 11.5% Correcting MS Spectral Interference Collision/Reaction Increase Resolution http://inorganicventures.com/tech/icp-operations/spectral-interference-correction/correction-icp-oes Calculation and Reporting Method modifications Units Moisturebasis • Dilutions • Alternate lines • Correction equations • mg/L to mg/kg (as required) • As-received • Air-dried basis • Oven-dried basis Summary The final result of an analytical measurement depends on a series of numerous decisions for processing the sample, each of which has an influence on the magnitude of that result Consistency of results within or between sampling events depends on the consistency of the processes applied to the sample ICP-based analytical techniques are valuable tools for measuring metals in soils but require understanding of their behaviour in the given sample matrix References • Boss, C.B. and Fredeen, K.J.; Concepts, Instrumentation and Techniques in Inductively Coupled Plasma Optical Emission Spectrometry, Second Edition; The Perkin-Elmer Corporation, 1997. • Carter, M.R. and Gregorich, E.G., eds., Soil Sampling and Methods of Analysis, Second Edition; Canadian Society of Soil Science, 2008. • Palmer C. and Loewen, E., Diffraction Grating Handbook, sixth edition; Newport Corporation, 2005. • Spectroscopy magazine and www.spectroscopyonline.com • Richards, L.A., ed., Agriculture Handbook No. 60: Diagnosis and Improvement of Saline and Alkali Soils; USDA, 1954. • Tessier, A., Campbell, P.G.C., Bisson, B., Sequential Extraction Procedure for the Speciation of Particulate Trace Metals; Analytical Chemistry: 15(7), June 1979, pp. 844-851. Questions ?
