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Features - Geochemistry I - Lecture Slides, Slides of Geochemistry

Bhupendra Narayan Mandal UniversityGeochemistry

In these Lecture Slides, the Lecturer has tried to illustrate he following points : Features, Improvement, Ultrasonic Nebuliser, Technique Suitable, Linear Dynamic, Range, Solution, Interferences, Background Correction, Operating Conditions

Typology: Slides

2012/2013

Uploaded on 07/23/2013

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bg1
0.22213.85Zn
0.22292.40V
522190.80Tl
1.320196.03Se
312206.83Sb
127220.35Pb
0.410231.60Ni
0.38202.03Mo
0.32324.75Cu
0.24267.71Cr
0.35228.61Co
0.22214.43Cd
0.020.3313.04Be
218193.69As
0.59396.15Al
0.32328.06Ag
U-5000AT+
Pneumatic
Nebulizer
(Cross-Flow)
Wavelength
(nm)
Element
Notes: Detection limits are based on 3 sigma,
with a 10-second integration time.
Instrument used was a Thermo Jarrell Ash
ICAP 61.
0.030.2213.857Zn
0.022290.880V
0.52190.801Tl
0.0060.2334.940Ti
0.41189.927Sn
0.53196.026Se
0.32206.836Sb
0.22220.353Pb
0.060.4231.604Ni
0.30.6202.031Mo
0.030.1257.610Mn
0.060.5285.213Mg
0.020.1238.204Fe
0.020.6324.754Cu
0.010.2267.716Cr
0.020.2228.616Co
0.020.1228.802Cd
0.032317.933Ca
0.22233.061Bi
0.0090.1313.107Be
0.010.5233.527Ba
0.73188.979As
0.062396.153Al
0.031328.068Ag
U-5000AT+
Pneumatic
Nebulizer
(GemCone)
Wavelength
(nm)
Element
Notes: Detection limits are based on 3 sigma,
with a 20-second integration time.
Instrument used was a Perkin-Elmer 4300DV
ICP-OES.
Improvement in DLs with Cetac’s ultrasonic nebuliser, U-5000AT+
ICP-ES, radial, in ppb ICP-ES, axial, in ppb
Docsity.com
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Download Features - Geochemistry I - Lecture Slides and more Slides Geochemistry in PDF only on Docsity!

Zn 213.85 2 0. V 292.40 2 0. Tl 190.80 22 5 Se 196.03 20 1. Sb 206.83 12 3 Pb 220.35 27 1 Ni 231.60 10 0. Mo 202.03 8 0. Cu 324.75 2 0. Cr 267.71 4 0. Co 228.61 5 0. Cd 214.43 2 0. Be 313.04 0.3 0. As 193.69 18 2 Al 396.15 9 0. Ag 328.06 2 0. U-5000AT+ Pneumatic Nebulizer (Cross-Flow) Wavelength Element (nm) Notes: Detection limits are based on 3 sigma, with a 10-second integration time. Instrument used was a Thermo Jarrell Ash ICAP 61. Zn 213.857 0.2 0. V 290.880 2 0. Tl 190.801 2 0. Ti 334.940 0.2 0. Sn 189.927 1 0. Se 196.026 3 0. Sb 206.836 2 0. Pb 220.353 2 0. Ni 231.604 0.4 0. Mo 202.031 0.6 0. Mn 257.610 0.1 0. Mg 285.213 0.5 0. Fe 238.204 0.1 0. Cu 324.754 0.6 0. Cr 267.716 0.2 0. Co 228.616 0.2 0. Cd 228.802 0.1 0. Ca 317.933 2 0. Bi 233.061 2 0. Be 313.107 0.1 0. Ba 233.527 0.5 0. As 188.979 3 0. Al 396.153 2 0. Ag 328.068 1 0. U-5000AT+ Pneumatic Nebulizer (GemCone) Wavelength Element (nm) Notes: Detection limits are based on 3 sigma, with a 20-second integration time. Instrument used was a Perkin-Elmer 4300DV ICP-OES. Improvement in DLs with Cetac’s ultrasonic nebuliser, U-5000AT+ ICP-ES, radial, in ppb ICP-ES, axial, in ppb

Features of ICP-ES

Advantages

  • Multi-element technique suitable for wide range of elements to ~ ppb DLs in solution; large linear dynamic range ( 4 to 10 6 )
  • Most interferences can be negated by judicious selection of line, background correction, IECs, use of internal standards and appropriate operating conditions.
  • Instruments are robust and relatively inexpensive, operation and methods are well documented.
  • Can nebulise solutions much higher in TDS than in ICP-MS (in % range).
  • Cheaper per analysis than ICP-MS

Limitations

  • Less sensitive than ICP-MS, should be used as a complementary technique for the same digested sample
  • Need sample to be in solution

Principle of XRF

  • Incident high energy photons strike the atom, dislodging an electron from one of the atom's inner orbital shells.
  • The atom regains stability, filling the vacancy left in the inner orbital shell with an electron from one of the atom's higher quantum energy orbital shells.
  • The electron drops to the lower energy state by releasing a characteristic fluorescent x-ray whose intensity is measured by a detector (e.g. NaI, proportional counter). Calibration curve is constructed using well characterised, appropriate SRMs
  • Sample is prepared by LiBO 2 fusion (majors, minors, some traces) or made into pressed pellets (traces)

Features of XRF

Advantages

  • The fusion technique minimises particle size/matrix effects that could otherwise cause problems with the measurement process. Excellent for ‘whole rock’ analysis.
  • Numerous trace elements can also be determined from the same fused disk, e.g. Y, Nb, Zr. The disks can be stored indefinitely.

Limitations

  • Fluorescent X-rays can be easily absorbed by the sample itself (self-absorption), also enhanced. Important to matrix match the calibration standards, or empirical correction factors must be applied.
  • Lighter elements are not easily determined (less sensitive).
  • With respect to the fusion, sometimes refractory minerals dissolve slowly and do not give satisfactory melts or discs.
  • Samples high in sulphide minerals do not fuse well with lithium borate.
  • Sensitivity not high for trace/ultra-trace analysis

Field-portable XRF

  • Need different sources for different combinations of analyte elements
  • Relatively new compact detectors (e.g. HgI 2 , Si-PIN, Si-DRIFT and CdZnTe) are ideal for portability but their resolution is inferior to the standard Si and Ge detectors
  • Use fundamental parameter method for calibration
  • Very fast, non-destructive but DLs are still in the ppm range and
  • Accuracy (and precision) is limited by heterogeneity, moisture content, inconsistent sampling position, spectral overlap (eg Pb on As) and absorption/enhancement effects (should be taken care of by software) Typically measure 1x1 cm to a depth of ~ 2 mm in soil, especially good for Pb in environmental surveys (EPA approved) e.g. Thermo’s Niton XL EDXRF, measures from Mg (12) to U (92)

INAA: principle and features

  • Irradiate 0.5-2 g sample in a vial with a flux of 7 x 10 12 n cm - s - for 15 min; wait a week, count with Ge detector. Flux monitored with wire on sample.
  • Simultaneous, multi-element, total, automated technique that does not require digestion and therefore there is little likelihood of contamination; interferences (not too many) are well documented; good precision and accuracy (SRMs)
  • On the negative side, there is not enough coverage of the Periodic Table at adequate detection limits and access to a reactor can be difficult! Also cost of ~ $25 for the ‘exploration’ DLs and ~$60 for the ‘research’ package (shown next)

Whole-rock analysis

• Majors oxides (inc P

2

O

5

) to 0.01%; MnO and

TiO

2

to 0.001%; by Li metaborate/tetraborate

fusion and ICP-ES or XRF

• C and S to 0.01% by IR (Leco); LOI to 0.01%

• Trace elements by fusion/ICP-MS (especially

for those in refractory minerals) and by 4-

acid ICP-MS (better DLs but not always total)

• Can combine ICP-MS, ICP-ES, INAA and XRF

for full coverage