Instrumental analytical chemistry

Accurate and specific, both qualitative and quantitative, measurement that involve any chemical scheme falls in the domain of analytical chemistry. Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP) is a replicate system and very precise examinational method that can suit all types of diluted and solid samples. Spectroscopy can be defined as the interaction of both matter and light with the application of analytical and physical. Physical spectroscopists use emitted light, absorbed light, or scattered light in order to understand the mechanics of a chemical system.

Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP) can stimulate many dissimilar elements, which can produce effective multi-element source. Atomization and excitation occur in an inert argon atmosphere. “Emission spectroscopy requires identification and selection of suitable analysis lines (wavelengths). This choice is fairly complicated for ICP-AES as usually many different emission lines of neutral atoms (10%) or ions (90%) can be used for quantitative analysis”. (Tyler, 1992) But, these vary in somewhat relative intensity.

Spectral interferences can also happen. During the five decades Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP) very often demonstrates linear calibration curvatures, which really make it impossible to determine both high and (very) low concentrations. “The average relative standard deviations for real samples are usually about 1 to 10%. The accuracy of the analysis can be optimized by using Blanc solutions with a similar matrix as the samples to be determined”. (Date & Gray, 1989) The surroundings alteration will then produce high-quality results.

But, the detection limits of the ICP-AES may vary from 1 to 100 ppb. Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP) though gives the lowest detection limit s for many of the high melting components. Atomic-Absorption Spectroscopy (AA) Atomic-absorption (AA) spectroscopy employs the amalgamation of light to calculate the absorption of gas-phase atoms. “Since samples are usually liquids or solids, the analyte atoms or ions must be vaporized in a flame or graphite furnace. The atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels”.

(Jarvis, Gray and Houk, 1992) The concentration of analyte can be established from the amount of absorption. It is hard to apply the Beer-Lambert law directly in Atomic-Absorption Spectroscopy (AA) because it may experience variations in the atomization efficiency from the sample matrix, and non-uniformity of concentration and path length of analyte atoms. “Concentration measurements are usually determined from a working curve after calibrating the instrument with standards of known concentration”.

(Thompson & Walsh 1993) The light source is usually a hollow-cathode lamp of the element that is being measured. Lasers are also used in research instruments. Since lasers are intense enough to excite atoms to higher energy levels, they allow AA and atomic fluorescence measurements in a single instrument. The disadvantage of these narrow-band light sources is that only one element is measurable at a time. AA spectroscopy requires that the analyte atoms be in the gas phase.

Ions or atoms in a sample must undergo desolvation and vaporization in a high-temperature source such as a flame or graphite furnace. Flame AA can only analyze solutions, while graphite furnace AA can accept solutions, slurries, or solid samples. Flame AA uses a slot type burner to increase the path length, and therefore to increase the total absorbance (see Beer-Lambert law). Sample solutions are usually aspirated with the gas flow into a nebulizing/mixing chamber to form small droplets before entering the flame. ICP-AES vs AA: a Comparison

The good looks and magnetism of the Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) has forced many of the analysts to think whether it is intelligent to purchase an ICP-AES or to remain with their trusted Atomic Absorption Technique (AAS). In the recent past, a new system Inductively Coupled Plasma Mass Spectrometry (ICP-MS), has been getting the attention of the analysts. Most of the analysts are in agreement that Atomic Absorption Spectrometry (AAS) is a well-established and implicit technique.

However, even though Inductively Coupled Plasma Emission Spectrometry (ICP-EAS) instrumentation has been widely available in the market for along period of time, but it is the technique that has proven to be more complicated. “The basic difference between the two techniques is that one relies upon an atomic absorption process while the other is an atomic/ionic emission spectroscopic technique. The next essential difference is the means by which the atomic or ionic species are generated. A combustion flame or graphite furnace is typically used for AA while ICP-ES uses a plasma.

The typical maximum temperature for an air/acetylene flame is 2 300 °C while for nitrous oxide acetylene, it is 2 900 °C. Temperatures as high as 10 000 K can be reached in an argon plasma”. (Thompson & Walsh, 1993) Detection limits • Furnace AA detection limits are generally better in all cases where the element can be atomized. • Detection limits for Group I elements (e. g. Na, K) are generally better by flame AAS than by ICP. • Detection limits for refractory elements (e. g. B, Ti, V, Al) are better by ICP than by flame AAS.

• Non metals such as sulfur, nitrogen, carbon, and the halogens (e.g. I, Cl, Br) can only be determined by ICP. References Date, A. R. and Gray, A. L. (1989), Applications of ICPMS, Blackie, Glasgow, UK. Jarvis, K. E. , Gray, A. L. and Houk, R. S. (1992), Handbook of ICP-MS, Blackie, Glasgow, UK Olesik, J. (1991), Elemental Analysis Using ICP-OES and ICP-MS, Anal. Chem. Vol 63 No 1, pp 12A-21A. Thompson, M. , Walsh, J. N. (1993), Handbook of Inductively Coupled Plasma Spectroscopy, Blackie, Glasgow, UK. Tyler, G. (1992), AA or ICP – which do you choose? Chemistry in Australia, Vol 59, No 4, pp 150-152.

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