Atomic emission spectrometry elemental analysis

Plasma sources were developed for emission spectrometric analysis in the late-1960s. Commercial inductively coupled and d.c. plasma spectrometers were introduced in the mid-1970s. By comparison with AAS, atomic plasma emission spectroscopy (APES) can achieve simultaneous multi-element measurement, while maintaining a wide dynamic measurement range and high sensitivities and selectivities over background elements. As a result of the wide variety of radiation sources, optical atomic emission spectrometry is very suitable for multi-element trace determinations. With several techniques, absolute detection limits are below the ng level. 

Applications Atomic emission spectrometry has been used for polymer/additive analysis in various forms, such as flame emission spectrometry (Section 8.3.2.1), spark source spectrometry (Section 8.3.2.2), GD-AES (Section 8.3.2.3), ICP-AES (Section 8.3.2.4), MIP-AES (Section 8.3.2.6) and LIBS. Only ICP-AES applications are significant. In hyphenated form, the use of element-specific detectors in GC-AED (Section 4.2) and PyGC-AED deserves mentioning. 

Que Hee SS, Boyle JR. 1988. Simultaneous multi-elemental analysis of some environmental and biological samples by inductively coupled plasma atomic emission spectrometry. Anal Chem 60 1033-1042. 

Owing to their superior fluorescent yield, heavy elements ordinarily yield considerably more intense XRF bands than the light elements. This feature can be exploited to determine the concentration of inorganic species in a sample, or the concentration of a compound that contains a heavy element in some matrix. Many potential XRF applications have never been developed owing to the rise of atomic spectroscopic methods, particularly inductively coupled plasma atomic emission spectrometry [74]. Nevertheless, under the right set of circumstances, XRF analysis can be profitably employed. 

Hoffmann and Lieser [112] used XFS to determine a range of elements in leaves and grass and compared this technique with neutron activation analysis, AAS, ICP-atomic emission spectrometry, polarography and voltammetry. 

Dreetz CD, Lund W. 1992. Air-intake filters used for multi-element analysis of airborne particulate matter by inductively coupled plasma atomic emission spectrometry. Anal Chim Acta 262 299-305. 

The EPA mobile lab analyzed soil samples for lead, zinc, copper, and nickel by XRF. Because arsenic had been identified as the element that presents the greatest risk to human health at the Cos Cob site, samples from the 0—1 ft (0—0.3 m) to 1—2 ft (0.3-0.6 m) intervals were sent off-site for analysis by inductively coupled plasma/ atomic emission spectrometry. If the off-site analysis showed arsenic concentrations greater than 10 ppm (the Connecticut direct exposure criterion for soil), the field investigators progressively analyzed samples in 1 -ft (0.3 m) intervals below and surrounding the sample, delineating hot spots, until the remaining contamination was lower than 5 ppm. 

S. P. Dolan, G. C. Capar, Multi-element analysis of food by microwave digestion and inductively coupled plasma-atomic emission spectrometry, J. Food Comp. Anal., 15 (2002), 593-615. 

The most important analytical techniques which are used in multielement trace analysis are ICP-MS, atomic absorption spectrometry (AAS) and ICP atomic emission spectrometry (AES). NAA is applied as reference method in order to establish certibed values. The regular atomic spectrometry update on clinical and biological materials, foods and beverages (ASU review) gives an overview of the recent developments in elemental analysis of food and beverages [81]. 

A. A. Momen, G. A. Zachariadis, A. N. Anthemidis, J. A. Stratis, Development and validation of routine analysis methods for the determination of essential, nonessential, and toxic minor and trace elements in cereal and cereal flour samples by inductively coupled plasma atomic emission spectrometry, Int. J. Assoc. Off. Anal. Chem., 88 (2005), 1797-1810. 

For instance, those elements present at relatively high concentration levels in milk are usually determined by FAAS or flame atomic emission spectrometry (FAES). On the other hand, if better LoDs are needed (e.g., ng g-1), the technique of choice would be ET-AAS. For multielemental analysis plasma-based techniques are recommended, such as AES for major elements and trace elements, or, as described below, mass spectrometry (MS) for major, trace, and ultratrace elements. The most relevant applications of these atomic techniques for elemental analysis in milk samples are summarized in Table 13.7. 

Inductively Coupled Plasma Atomic Emission Spectrometry ICP-AES is a technique half-way between FAAS and ET-AAS in terms of detection power. Among all ICP-AES features its robustness against matrix effects and its ability to carry out multielemental analysis predominate as the most advantageous [76-80], Multielemental analysis has also been successfully used to establish reference values [6, 76, 81-84] for many major and trace essential elements in different matrices of biological and nutritional interest, particularly in milk samples [81-83], Reference values for minor and trace element in human milk are collected in Table 13.8. 

P. L. Fernandez, F. Pablos, M. J. Martin, Multi-element analysis of tea beverages by inductively coupled plasma atomic emission spectrometry, Food Chem., 76 (2002), 483-489. 

For clcmcnt-speciPc detection in GC, a number of dedicated spectrometric detection techniques can be used, for example, quartz furnace AAS or atomic Bu-orescence spectrometry (AFS) for Hg, or microwave-induced plasma atomic emission spectrometry (MIP-AES) for Pb or Sn. However, ICP-MS is virtually the only technique capable of coping, in the on-line mode, with the trace element concentrations in liquid chromatography (LC) and capillary electrophoresis (CE) efBuents. The femtogram level absolute LoDs may still turn out to be insufficient if an element present at the nanogram per milliliter level splits into a number of species, or when the actual amount of sample analyzed is limited to some nanoliters as in the case of CE or nanoBow HPLC. The isotope spcciPcity of ICP-MS offers a still underexploited potential for tracer studies and for improved accuracy via isotope dilution analysis. 

V. E. Negretti de Bratter, S. Recknagel, D. Gawlik, Speciation of Se, Fe and Zn in human milk whey the use of instrumental neutron activation analysis (INAA) to corroborate element profiles measured with inductively coupled plasma atomic emission spectrometry (ICP-AES), Fresenius J. Anal. Chem., 353 (1995), 137-142. 

Maintaining the quality of food is a far more complex problem than the quality assurance of non-food products. Analytical methods are an indispensable monitoring tool for controlling levels of substances essential for health and also of toxic substances, including heavy metals. The usual techniques for detecting elements in food are flame atomic absorption spectroscopy (FAAS), graphite furnace atomic absorption spectrometry (GF AAS), hydride generation atomic absorption spectrometry (HG AAS), cold vapour atomic absorption spectrometry (CV AAS), inductively coupled plasma atomic emission spectrometry (ICP AES), inductively coupled plasma mass spectrometry (ICP MS) and neutron activation analysis (NAA). 

In addition to the cation used to prepare the polymer, other cations with differing charges, sizes, coordination numbers and/or coordination geometries are used in these selectivity quotient measurements to verify specificity. Measurements are also made using polymers prepared with no metal cation (H or NH4 ) as experimental controls. The measurements required for these studies are made using a pH meter for [H ] and elemental analysis (inductively coupled plasma atomic emission spectrometry (ICP-AES) or inductively coupled plasma mass spectrometry (ICP-MS))for [M"-"]. 

An inductively-coupled plasma (ICP) is an effective spectroscopic excitation source, which in combination with atomic emission spectrometry (AES) is important in inorganic elemental analysis. ICP was also considered as an ion source for MS. An ICP-MS system is a special type of atmospheric-pressure ion source, where the liquid is nebulized into an atmospheric-pressure spray chamber. The larger droplets are separated from the smaller droplets and drained to waste. The aerosol of small droplets is transported by means of argon to the torch, where the ICP is generated and sustained. The analytes are atomized, and ionization of the elements takes place. Ions are sampled through an orifice into an atmospheric-pressure-vacuum interface, similar to an atmospheric-pressure ionization system for LC-MS. LC-ICP-MS is extensively reviewed, e.g., [12]. 

The very low concentrations expected in the analysis of trace elements in offshore and coastal Antarctic sea water can be also detected thanks to the high detection power of spectroscopic techniques such as Electrothermal Atomic Absorption Spectrometry (ETA-AAS) and Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) or ICP-MS. However, the saline matrix which constitutes the ideal medium in which to perform electrochemical measurements poses severe problems to the direct analysis of sea water because of possible signal suppression and/or undesired matrix effects. 

Rahii-Khazen R, Henriksen H, Bolann BJ, Ulvik RJ. Validation of inductively coupled plasma atomic emission spectrometry technique (ICP-AES) for multi-element analysis of trace elements in human serum. Scand J Clin Lab Invest 2000 60 677-86. 

This new technique which shows several advantages has been introduced for heavy metal detection over the recent years. The Inductively Coupled Plasma-Atomic Emission Spectrometry allows the simultaneous determination of almost all elements in all fields of elementary analysis. This technique is not very widespread in the laboratories due to the high cost and the complicated operation. 

Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of most major and trace elements. The samples are fused in a Claisse semi-automatic fusion device in Pt-Au crucibles with lithium metaborate (4). The fusion product is dissolved in diluted HNO and brought to volume. For trace elements determination the sample is decomposed by HF, HNOg and HCIO. Scandium serves as an internal standard and is added to all samples and solutions. The instrument (product of Jobin Yvon, France)is calibrated using multi-element synthetic standards. The aqueous solutions are nebulized and injected into the heart of a plasma fire ball. A computerized multi-channel vacuum spectrometer has been programmed for multi-element analysis. 

Atomic emission spectrometry is widely used in elemental analysis. The ICP is now the most popular source for emission spectrometry, although the DCP and flames are still used in some situations. 

Knowledge of the atomic spectra is also very important so as to be able to select interference-free analysis lines for a given element in a well-defined matrix at a certain concentration level. To do this, wavelength atlases or spectral cards for the different sources can be used, as they have been published for arcs and sparks, glow discharges and inductively coupled plasma atomic emission spectrometry (see earlier). In the case of ICP-OES, for example, an atlas with spectral scans around a large number of prominent analytical lines [329] is available, as well as tables with normalized intensities and critical concentrations for atomic emission spectrometers with different spectral bandwidths for a large number of these measured ICP line intensities, and also for intensities calculated from arc and spark tables [334]. The problem of the selection of interference-free lines in any case is much more complex than in AAS or AFS work. 

The oldest of the spectroscopic radiation sources, a flame, has a low temperature (see Section 4.3.1) but therefore good spatial and temporal stability. It easily takes up wet aerosols produced by pneumatic nebulization. Flame atomic emission spectrometry [265] is still a most sensitive technique for the determination of the alkali elements, as eg. is applied for serum analysis. With the aid of hot flames such as the nitrous oxide-acetylene flame, a number of elements can be determined, however, not down to low concentrations [349]. Moreover, interferences arising from the formation of stable compounds are high. Further spectral interferences can also occur. They are due to the emission of intense rotation-vibration band spectra, including the OH (310-330 nm), NH (around 340 nm), N2 bands (around 390 nm), C2 bands (Swan bands around 450 nm, etc.) [20], Also analyte bands may occur. The S2 bands and the CS bands around 390 nm [350] can even be used for the determination of these elements while performing element-specific detection in gas chromatography. However, SiO and other bands may hamper analyses considerably. 

---