This week you used a technique called Absorption Spectroscopy to analyze the con

Question

This week you used a technique called Absorption Spectroscopy to analyze the concentration of copper ion in solutions.

-Describe how this technique, or another form of quantitative analysis, is used in industrial/commercial/government labs (such as a semiconductor facility) to analyze concentrations of metals or other substances in solution.

-Your description should include a brief explanation of how the technique works.

-Describe the level of precision involved in the technique (concentration levels).

-Your post should be substantive and approximately 150-200 words.

Explanation / Answer

Atomic Absorption Spectroscopy (AAS) is used mostly as an analytical tool to determine which atoms are present in compounds. The compounds are dissociated into its atoms (and ions) and then light, usually optical, allows identification of atoms by their spectrum. About 70 elements can be identified this way.
Principle
The technique makes use of absorption spectrometry to assess the concentration of an analyte in a sample. It requires standards with known analyte content to establish the relation between the measured absorbance and the analyte concentration and relies therefore on the Beer-Lambert Law.

In short, the electrons of the atoms in the atomizer can be promoted to higher orbitals (excited state) for a short period of time (nanoseconds) by absorbing a defined quantity of energy (radiation of a given wavelength). This amount of energy, i.e., wavelength, is specific to a particular electron transition in a particular element. In general, each wavelength corresponds to only one element, and the width of an absorption line is only of the order of a few picometers (pm), which gives the technique its elemental selectivity. The radiation flux without a sample and with a sample in the atomizer is measured using a detector, and the ratio between the two values (the absorbance) is converted to analyte concentration or mass using the Beer-Lambert Law.

Main Components of the Atomic Absorption Spectrophotometer

The basic components of any type or brand of atomic absorption include the following:

A- Light Source

B- Burner/Nebulizer
C- Monochromator
D- Photomultiplier Detector

E- Output Device

The primary sources of radiation in atomic absorption are hollow cathode lamps. These lamps are composed of a cathode and an anode sealed in a tube with an inert gas (argon or neon). The cathode is made of the element to be determined. When a high voltage is applied the atoms of the inert gas are ionized and attracted by the cathode. These ions hit the cathode and excite the atoms of the elements used to make the cathode. Once the atoms are excited radiation is emitted at the characteristic wavelength of the element. The light from the hollow cathode lamp passes through the flame (Burner/nebulizer) where the sample is atomized. This fine mist of the sample is sprayed into the nebulizer. Atoms of the elements are formed from the sample mist and are able to absorb some of the light from the lamp at the wavelength set for that particular element. The light passed through the flame is received by the monochromator, which is set to accept and transmit radiation at the specified wavelength. The light emerges from the monochromator exit slit and falls on the photomultiplier detector. At this point an output current, proportional to the incident light, is intensified, amplified, processed electronically and finally presented to a readout device (i.e. printer, digital display).
Accuracy of AAS
If spectral and chemical interferences are minimized, an accuracy of 0.5–5% is routinely attainable. When the calibration curve is nonlinear, accuracy may be improved by using a pair of standards whose absorbances closely bracket the sample’s absorbance and assuming that the change in absorbance is linear over this limited concentration range. Determinate errors for electrothermal atomization are often greater than that obtained with flame atomization due to more serious matrix interferences.

Precision
For absorbance values greater than 0.1–0.2, the relative standard deviation for atomic absorption is 0.3–1% for flame atomization and 1–5% for electrothermal atomization. The principle limitation is the variation in the concentration of free analyte atoms resulting from variations in the rate of aspiration, nebulization, and atomization when using a flame atomizer, and the consistency of injecting samples when using electrothermal atomization.

Applications of atomic absorption spectroscopy
Biological Samples
A wide range of the samples of biological origin are subjected to analytical procedures for the determination of the elements present in them. These may include plant leaves, fruits, vegetables, blood, urine, muscle tissue, hair, etc. The major difficulty in the analysis of these materials is their complex nature. More so, these samples cannot be analysed directly but require dry ashing followed by wet digestion with oxidising acids such as HNO3and HClO4
. In case of blood analysis, plasma or serum is generally preferred because of the presence of significant amounts of clinically significant elements in them.
Determination of lead
As you know, lead is another highly toxic element which is an environmental contaminant. It enters into biological systems like plants and animals and reaches blood, urine, teeth, bones, hair, plant and animal tissues, etc. These materials need to be analytically assessed for the amount of lead so that its damage potential can be ascertained. From the viewpoint of occupational and environmental toxicology the determination of lead in blood is the most important since the concentration of lead in whole blood is considered to be the best indicator of current lead exposure in humans. It enters into human blood because of inhalation of polluted air, food and water though these are less relevant for assessing health hazards for humans than the amount of lead actually absorbed. In a typical lead determination, after adding heparin, a natural anticoagulant, the blood is treated with trichloroacetic acid to precipitate proteins. These are then separated bycentrifugation. In order to avoid interferences, lead is extracted in an organic solvent methyl isobutylketone (MIBK) after adding ammonium pyrrolidinedithiocarbamate (APDC) at pH 3. The lead is extracted as Pb (APCO)2
. The organic phase is then aspirated into air-acetylene flame for the determination of lead. The detection limit of lead in blood is 0.1 µg/mL. Most values of lead in blood are in the range 0.3– 0.4 µg/mL with 0.6 µg/mL as the upper limit. It is essential that internal and external quality control should be used for the determination of lead in blood
other applications
Groundwater sampling
Evaluation of bore water samples
Determination of the amount of contamination from mines
Evaluation of specific elements in food or pharmaceuticals
Evaluation of specific elements in petrochemicals
Use in medicine for biological monitoring
Use in evaluating nanomaterials
Use in patholog

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