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ICP Methods for Consistent Trace Elemental Data. WEALA Technical Workshop - 25-Apr-2013. The Analytical Process. Scope. Sampling. Sampling - Design. Bulk Prep. Particle Size Fractions for Metals Analysis. Aquatic Sediment (< 63 um). Terrestrial Soils (< 2 mm). - PowerPoint PPT Presentation
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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
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
• Total concentrations in the whole?• Extent and boundaries of a spill?
What question is to be answered?
• Account for heterogeneity/stratificationRepresentative of the site
• Precautions against contamination• Appropriate containers• Appropriate storage conditions and time
Protect sample integrity
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 moistAir dry (60°C)
Oven dry (105°C)
Sieving
< 6mm < 2mm
< 63 um
Splitting/Subsampling
Appropriate type of subsample;
Appropriate amount of subsample;Representative
subsample
Grinding
Break up clumps;Pulverize to defined
size
Archiving
As-received;Prepped
Particle Size Fractionsfor Metals Analysis
Terrestrial Soils(< 2 mm)
Aquatic Sediment(< 63 um)
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
• 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
Saturation Extract
• 1:1 or 1:5 most commonly listed • When unable to prepare a Saturation Extract (type
or amount of sample)• Report as mg/kg(?)
Other Extraction
Ratios
Tessier Model -Metals Fractions in Sediments
• MgCl2, pH 7.0Exchangeable
• NaOAC/HOAc, pH 5.0Bound to Carbonates• NH2OH·H2O in 25% HOAc,
pH~2Bound to Fe-Mn Oxides
• H2O2/HNO3, pH~2 (+NH4OAc)Bound to Organic Matter
• HF and HClO4ResidualAnalytical Chemistry 51(7) June 1979
Tessier Model – Extension to Terrestrial Soils(?)
• WaterSoluble
• MgCl2, pH 7.0Exchangeable
• NaOAC/HOAc, pH 5.0Bound to Carbonates• NH2OH·H2O in 25% HOAc,
pH~2Bound to Fe-Mn Oxides
• H2O2/HNO3, pH~2(+NH4OAc)Bound to Organic Matter
• HF and HClO4Residual
Metals Fractionsof Environmental Significance
Soluble
Exchangeable
Bound to Carbonates
Bound to Fe-Mn Oxides
Bound to Organic Matter
Residual
‘Environmentally Available’
or‘Total Recoverable’
metals
Standard Analytical Prep Procedures for Trace Metals
EPA 200.2 EPA 3050B ICPMS/GFAA
EPA 3050B ICPAES/FLAA
EPA 3050B* ICPAES/FLAA
Nominal Sample Mass (g - dry wt.) 1 1 1 1
1st Acid Addition
HNO3 Concentration 1 + 1 1 + 1 ConcHNO3 Volume (mL) 4 10 2.5HCl Concentration 1 + 4 Conc Conc
HCl Volume (mL) 10 10 10Temperature (°C) ~95 95 ± 5 95 ± 5 95 ± 51st Heating Time (min) 10 to 15 2nd Acid Addition
HNO3 Concentration Conc HNO3 Volume (mL) 5
Reflux Time (min) 30'heat and add acid until no change in
appearance'15 15
Evaporate to (mL) ~5
Peroxide Addition
30% H2O2 (mL) 3 DIW Volume (mL) 2
Additional 30% H2O2 1-mL increments until
minimal effervescence, to maximum 10 mL total
Evaporate to (mL) ~5
First Filter Treatment
Hot Conc HCl Rinse (mL) ≤ 5Hot DIW Rinse (mL) 20
Conc. HCl Digest Acid (mL) 5
Reflux Time (min) "until the filter paper dissolves"
Final Acid Addition
Condition "If a precipitate forms"
Conc. HCl (mL) 10Final Digest Volume (mL) 100 100 100 100Remove solids (if present) after or before Final Volume adjustment? 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 MetalsEPA 200.2 EPA 3050B
ICPMS/GFAAEPA 3050B
ICPAES/FLAAAluminum (Al) X XAntimony (Sb) X XArsenic (As) X X Boron (B) X Barium (Ba) X XBeryllium (Be) X X XCadmium (Cd) X X XCalcium (Ca) X XChromium (Cr) X X XCobalt (Co) X X XCopper (Cu) X XIron (Fe) X X XLead (Pb) X X XLithium (Li) X Magnesium (Mg) X XManganese (Mn) X XMercury (Hg) X Molybdenum (Mo) X X XNickel (Ni) X XPhosphorus (P) X Potassium (K) X XSelenium (Se) X X Silica (SiO2) Silver (Ag) X XSodium (Na) X XStrontium (Sr) X Thallium (Tl) X X XThorium (Th) X Tin (Sn) X Uranium (U) X Vanadium (V) X XZinc (Zn) X X
Analytical Prep
Special Techniques
Hot-Water Extraction
Boron
Solvent Extraction
Sulphur
Fusion
Barite-Barium Silicon
Analysis
• Multi-element• Wide dynamic range
• % to sub-ppt• Manageable interferences
Why ICP?
• 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)
What is
“ICP”?
Anatomy of a Plasma
1Spectroscopy 16(6) June 2001
Plasma Formation1
Plasma Temperature Zones1
2Perkin-Elmer, 1997
Droplet Conversion in the ICP Source2
Basic ICP Instrument Architecture
Perkin-Elmer, 1997
Emission Spectroscopy
Light Spectra
White Light (sunlight)
Emission Spectrum of Iron (Fe)
Grating Equation
Palmer, C. and Loewen, E., Diffraction Grating Handbook, sixth edition; Newport Corporation, 2005.
mλ = d (sinα + sinβ), where m is the spectral order (an integer) and λ is the wavelength
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
ZrZirconium
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 MassAbundance
(%) Name Symbol MassAbundance
(%)
Oxygen 16O 15.994915 99.757 Iron 54Fe 53.939615 5.84517O 16.999132 0.038 56Fe 55.934942 91.75418O 17.99916 0.205 57Fe 56.93540 2.119
58Fe 57.93328 0.282Chlorine 35Cl 34.968853 75.78
37Cl 36.96590 24.22 Arsenic 75As 74.92160 100
Argon 36Ar 35.967546 0.336538Ar 37.962732 0.063240Ar 39.962383 99.6003
40Ar16O 55.957298 40Ar16O - 56Fe = 0.022356
40Ar35Cl 74.931236 40Ar35Cl - 75As = 0.009640
Hi-Resolution ICPMS
Spectroscopy 16(11) November 2001
Interferences in ICP
• 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
Physical
• Affects the nature of the plasma or the analytes in the plasma
• Molecular compound formation; ionization; solute vaporization
Chemical
• Affects the intensity of the analyte signal reaching the detector
• Background shifts• Overlapping wavelengths/masses
Spectral
Addressing Interferences
• Matrix-matching of standards with samples• Use of internal standard(s)• Water-saturated nebulization gas (prevent salt
build-up)• Dilution
Physical
• (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
Chemical
Physical Effects in ICPMS -Space-Charge Interference
Spectroscopy 16(9) September 2001
Addressing Interferences
Spectral – AES
• Matrix-matching• Off-peak correctionBackground
• Alternate wavelength• Inter-element correctionOverlap
Correcting AES Spectral Interference
Off-peak background correction Inter-element correction
where,
determined previously from standards
http://inorganicventures.com/tech/icp-operations/spectral-interference-correction/correction-icp-oes
Types of MS Spectral Overlap
• Two isotopes of same mass• e.g. 40Ar on 40CaIsobaric
• Molecular ions formed in the plasma• e.g. 40Ar35Cl on 75AsPolyatomic
• Mass discrimination based on m/z• e.g. 136Ba++ on 68Zn+
Double-charged
ions
Addressing Interferences
Spectral – MS
• Matrix-matchingBackground
• Alternate mass• Mass equation• Collision/Reaction• Increase resolution
Overlap
Correcting MS Spectral Interference
Alternate Mass Mass equation
where,
Spectroscopy 17(10) October 2002; Perkin-Elmer
Correcting MS Spectral Interference
Collision/Reaction Increase Resolution
http://inorganicventures.com/tech/icp-operations/spectral-interference-correction/correction-icp-oes
Calculation and Reporting
• Dilutions• Alternate lines• Correction equations
Method modifications
• mg/L to mg/kg (as required)Units
• As-received• Air-dried basis• Oven-dried basis
Moisture-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
?