![Internal Standard Procedure
Prepare a set of standard solutions for analyte (A) as with the
calibration curve method, but add a constant amount of a
second species (B called internal standard) to each solution.
Add the same amount of IS to the blank and sample solution.
Prepare a plot of SA/SB versus [A].](https://image.slidesharecdn.com/atomicemissionspectroscopychapter10-230417211330-4eaec79b/85/Atomic-Emission-Spectroscopy-Chapter10-pptx-9-320.jpg)
![Example: Pb by ICP Emission
Each Pb solution contains 100 ppm Cu as IS
[Pb]
(ppm) Pb Cu Pb/Cu
20 112 1347 0.083
40 243 1527 0.159
60 326 1383 0.236
80 355 1135 0.313
100 558 1440 0.388
Signal](https://image.slidesharecdn.com/atomicemissionspectroscopychapter10-230417211330-4eaec79b/85/Atomic-Emission-Spectroscopy-Chapter10-pptx-10-320.jpg)
Atomic Emission Spectroscopy (Chapter10.pptx
- 2. ATOMIC EMISSION SPECTROSCOPY The sample is converted into excited gaseous atoms and ions which emit light at characteristic wavelengths (wavenumbers). The analyte is identified by emission at a known wavelength (qual. analysis) and its concentration is determined from the intensity of the emission at that wavelength (quant. analysis). Atoms or ions in the gas phase can be excited by high temperatures or by light absorption. A fraction of the atoms or ions lose their excitation energy by giving off a photon. The most intense emission line for a neutral atom is the resonance line (same line for absorption and emission e.g. 589nm for Na atom).
- 3. Atomic Emission Spectrometers. Emission sources: The source must a. vaporize the sample, b. break down all compounds to atoms and ions, c. and excite the atoms and ions. • Very high temperatures are required, much higher than in atomic absorption Methods to atomize and excite the analytes: a. electrical arcs (low voltage, high current) b. electrical sparks (high voltage, low current c. flames have been used .
- 4. Monochromators/ Polychromators A polychromator has multiple exit slits with multiple detectors PMT Because there are many emission lines from the plasma, often separated by only a few Angstroms, high resolution is required in monochromators and polychromators. Designs are based on an echelle grating operating at high orders combined with an order-sorting prism
- 5. Detectors • Usually a PMT (multiple PMT’s in a polychromator) • Both the polychromator + multiple PMTs and the echelle can monitor concentrations of 10 or more elements from one sample within a few minutes. • These devices are used heavily by the metallurgy industry to monitor composition of alloys.
- 6. Internal Standard vs. external standard method • Because AES can easily perform multi-element analysis, an internal standard (an element not naturally found in the samples) is often incorporated at a constant concentration into each sample. • To compensate for fluctuation of plasma emission intensity (caused by fluctuations in plasma temperature), the emission intensity of each element line is divided by the emission intensity of an internal standard.
- 7. Internal standard Method An Internal Standard is a substance that is added in a constant amount to all samples, blanks and calibration standards in an analysis. Calibration involves plotting the ratio of the analyte signal to the internal standard signal as a function of analyte concentration of the standards. This ratio for the samples is then used to obtain their analyte concentrations from a calibration curve. Internal standard can compensate for several types of both random and systematic errors.
- 8. Internal Standard Method Most convenient when variations in analytical sample size, position, or matrix limit the precision of a technique. Or when the sensitivity of instrument changes with time
- 9. Internal Standard Procedure Prepare a set of standard solutions for analyte (A) as with the calibration curve method, but add a constant amount of a second species (B called internal standard) to each solution. Add the same amount of IS to the blank and sample solution. Prepare a plot of SA/SB versus [A].
- 10. Example: Pb by ICP Emission Each Pb solution contains 100 ppm Cu as IS [Pb] (ppm) Pb Cu Pb/Cu 20 112 1347 0.083 40 243 1527 0.159 60 326 1383 0.236 80 355 1135 0.313 100 558 1440 0.388 Signal
- 12. No Internal Standard Correction y = 5.02x + 17.6 R² = 0.9413 0 100 200 300 400 500 600 0 20 40 60 80 100 120
- 13. Internal Standard Correction y = 0.0038x + 0.0066 R² = 1 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0 20 40 60 80 100 120
- 14. unknown sample of Pb (containing100 ppm Cu as IS) gives a ratio of 0.241. Conc. of Pb in the unknown = 78.3 ppm
- 15. Back to sources: flame
- 16. Flame photometer: flame emission spectrometry is used for the quantitative determination of small amounts of metal salts in solution. Flam emission is commonly used in clinical labs for determination the concentration of Na or K ions in blood. In this method: A. sample solution sprayed or aspirated as fine mist into flame; B. conversion of sample solution into an aerosol by atomizer (scent spray)
- 17. principle. Then Heat of the flame vaporizes sample constituents. Still no chemical change. By heat of the flame + action of the reducing gas (fuel), molecules & ions of the sample species are decomposed and reduced to give ATOMS. Na+ + e- --> Na Heat of the flame causes excitation of some atoms into higher electronic states. Excited atoms revert to ground state by emission of light energy, h, of characteristic wavelength; measured by detector. The reading that the instrument gives is used to calculate the concentration of the element to be determined.
- 18. The Sherwood Model 41O
- 19. Experimental Aspects of Flame Photometry • Propane-air or natural gas-air gives good flame - strong heat, minimal background light emission. • But always need to run a solvent blank for setting zero emission. • Solutions diluted to fall within linear part of emission curve. • Anion and cation interference effects can cause errors (enhancement or suppression). "Radiation buffer" for dilution of standards and samples to swamp out inconsistencies. • Internal standard (lithium) useful to counter random flame instability and random dilution errors.
- 23. Plasma not flame • ICP torch is the most important. • Like the flame AA experiment, the sample is introduced into the instrument as a solution fed into a nebulizer, creating a fine spray of droplets in a flowing gas stream
- 26. Inductively coupled plasma (ICP): • A plasma (partially ionized gas) of argon is formed and sustained by intense electric and magnetic fields inside a coiled radio antenna (27 MHz, 1-2 kW power). A triple-tube quartz torch is used to: • (a) generate annular plasma, • (b) introduce the sample as droplets in an Ar gas stream. • Temperatures are about 10,000 K at hottest part of plasma. Observation is made 1-3 cm above hottest part; local temperatures are still high (ca. 6000 K).
- 27. Advantages: (a) a very wide dynamic range (3 to 6 orders-of-magnitude) on calibration curves; (b) stable operation over long periods of time, (c) almost no chemical interferences due to the very high temperatures. Disadvantages: (a) expensive to buy and operate; (b) rapid consumption of high purity Ar gas (several L/min).