Flame and flameless atomic

Numerous procedures, by a variety of different instruments, are available to quantify the amount of thallium present in hair, blood, tissue, saliva, and urine (for reviews, see [9,81]). Instrumentation used includes emission spectrography, flame and flameless atomic absorption spectroscopy (AAS), voltammetry, neutron activation analysis, and field desorption mass spectroscopy [13,17,82-90]. Field desorption mass spectroscopy when combined with stable isotope dilution can detect fentomole quantities and has value in that no tissue preparation (other than homogenization) is required [65,82,89], The use of these two methods, however, is restricted to specialized laboratories. 

As compromises between flame and flameless atomization techniques the Delves cup and sample boat methods have been developed (Fig.6.63). In the first of these two techniques the sample is kept in a small cup made of nickel. It is introduced into the flame of an ordinary atomic absorption slit burner. The sample is vaporized and passes through a hole into a nickel... 

The most utilized methods include X-ray fluorescence (XRF), atomic absorption spectroscopy (AAS), activation analysis (AA), optical emission spectroscopy (OES) and inductively coupled plasma (ICP), mass spectroscopy (MS). Less frequently used techniques include ion-selective electrode (ISE), proton induced X-ray emission (PIXE), and ion chromatography (IC). In different laboratories each of these methods may be practiced by using one of several optional approaches or techniques. For instance, activation analysis may involve conventional thermal neutron activation analyses, fast neutron activation analysis, photon activation analysis, prompt gamma activation analysis, or activation analysis with radio chemical separations. X-ray fluorescence options include both wave-length and/or energy dispersive techniques. Atomic absorption spectroscopy options include both conventional flame and flameless graphite tube techniques. 

A variety of techniques are available for the determination of trace elements in crude oils, and chemical methods of analysis have been summarized by Milner and McCoy. Most geochemical studies of metals in petroleum have used emission spectrography of petroleum ashes because of the multielement nature of the method. " In recent years techniques such as polarograplWfcolorimetric analysis, X-r fluorescence, ESR, flame atomic absorption, and flameless atomic absorption have been used for the analysis of crude oils. Many of the techniques require preconcentration of the metals, usually by ashing techniques and consequently involve the risk of loss of volatile compounds or contamination by reagents. For many elements at very low concentrations (<1 ug/g) the risk of contamination is very high. Most of the applications cited above involve the determination of one or a few specific elements and are not suitable for multielement analysis. 

Tikhomirova et al. [685] developed a procedure for simultaneous concentration of mercury, lead, and cadmium from seawater by coprecipitation with copper sulfide. The isolation yield is 99% for mercury and lead, and 89% for cadmium. Mercury is determined by flameless atomic absorption spectrophotometry, and lead and cadmium by flame atomic absorption spectrophotometry. 

Conventional flame techniques present problems when dealing with either small or solid samples and in order to overcome these problems the electrothermal atomization technique was developed. Electrothermal, or flameless, atomizers are electrically heated devices which produce an atomic vapour (Figure 2.36). One type of cuvette consists of a graphite tube which has a small injection port drilled in the top surface. The tube is held between electrodes, which supply the current for heating and are also water-cooled to return the tube rapidly to an ambient temperature after atomization. 

A microsampling system known as the Delve s cup is a hybrid of flameless and flame techniques. The sample is placed in a small crucible, which is held in the flame by means of a wire loop. The sample is ashed in a cooler part of the flame and then moved to the hotter part in order to cause the rapid vaporization of the element. The cup is held beneath an opening in a nickel or aluminium tube which is in the light path of the instrument. The atomic vapour... 

If refers to flame atomic absorption spectrometry and NF to flameless atomic absorption spectrometry (e.g. carbon rod). 

Trace levels (10 to 10 g/g of sample) of silver can be accurately determined in biological samples by several different analytical techniques, provided that the analyst is well acquainted with the specific problems associated with the chosen method. These methods include high frequency plasma torch-atomic emission spectroscopy (HFP-AES), neutron activation analysis (NAA), graphite furnace (flameless) atomic absorption spectroscopy (GFAAS), flame atomic absorption spectroscopy (FAAS), and micro-cup atomic absorption spectroscopy (MCAAS). 

Until now we have used the database for a very simple purpose, namely to extract information from a single file. However, it is also possible to connect several files. Let us suppose that we want to use dBASE for the following problem. In atomic absorption spectroscopy (AAS), one has to choose between the flame and the (flameless) graphite tube methods. The flame methods does not have such a low detection limit as the graphite tube, but it is easier to handle, less prone to interferences and more robust. For that reason the user s strategy will often be to apply the flame method above a certain concentration limit and the flameless method below it. The flame method has its own experimental characteristics and we suppose that we have another database file in which the characteristics for flame methods are given per element. In that case, we would like the consultation to go like this ... 

Flameless atomic absorption using an electrothermal atomiser is essentially a non-routine technique requiring specialist expertise. It is slower than flame analysis only 10—20 samples can be analysed in an hour furthermore, the precision is poorer (1—10%) than that for conventional flame atomic absorption (1%). The main advantage of the method, however, is its superior sensitivity for any metal the sensitivity is 100—1000 times greater when measured by the flameless as opposed to the flame technique. For this reason flameless atomic absorption is employed in the analysis of water samples where the flame techniques have insufficient sensitivity. An example of this is with the elements barium, beryllium, chromium, cobalt, copper, manganese, nickel and vanadium, all of which are required for public health reasons to be measured in raw and potable waters (section I.B). Because these elements are generally at the lOOjugl-1 level and less in water, their concentration is below the detection limit when determined by flame atomic absorption as a result, an electrothermal atomisation (ETA) technique is often employed for their determination. 

Some of the physical and chemical constraints on the flame atomization process — which usually precluded application to solid samples — were overcome with the advent of flameless atomization, initially accomplished with the pyrolytic coated graphite tube (or carbon rod-type) furnace atomizer. The graphite tube is a confined furnace chamber where pulsed vaporization and subsequent atomization of the sample is achieved by raising the temperature with a programmed sequence of electrical power. A dense population of ground state atoms is produced as a result for an extended interval in relation to the low atom density and short residence time of the flame. The earliest use of furnace devices in analytical atomic spectroscopy is credited to a simultaneous development by Lvov [15] and Massmann [16] however, the first application of one such device to a... 

The first requirement can be easily fulfilled by the preconcentration of the analyte before the analysis. Preconcentration has been applied to sample preparation for flame atomic absorption (25) and, more recently, for ICP (79,80) spectroscopy. However, preconcentration is not completely satisfactory, because of the increased analysis time (which may be critical in clinical analysis) and the increased chance of contamination or sample loss. Most important, however, a larger initial sample size is necessary. The apparent solution is a more sensitive technique. Table 2 lists concentrations of various metals in whole blood or serum (81,82) in comparison to limits of detection for the various atomic spectroscopy techniques. In many cases, especially for the toxic heavy metals, only flameless atomic absorption using a graphite furnace can provide the necessary sensitivity and accommodate a sample of only a few microliters (Table 1). The determination of therapeutic gold in urine and serum (83,84), chromium in serum (85), skin (86) and liver (87), copper in semen (88), arsenic in urine (89), manganese in animal tissues (90), and lead in blood (91) are but a few examples in analyses which have utilized the flameless atomic absorption technique. 

Some selected references are by Lindstrbm (1959) (Rapid microdetermination of mercury by spectrophotometric flame combustion) Thomas et al. (1972) (Rapid pyrolytic method to determine total mercury in fish) and Okuno et al. (1972) (Determination of mercury in biological samples by flameless atomic absorption after combustion and mercury-silver amalgamation). 

Recommended Air Volume 960 L Recommended Sampling Rate 2.0 L/min Analytical Procedure Air filter samples are digested with nitric acid. After digestion, a small amount of hydrochloric acid is added. The samples are then diluted to volume with deionized water and analyzed by either flame atomic absorption spectroscopy (AAS) or flameless atomic absorption spectroscopy using a heated graphite furnace atomizer (AAS-HGA). 

As indicated above, this method is extremely popular because of its low cost and ease and rapidity of use. The simplest form of AAS is the flame technique which is of rather limited sensitivity. This may often prove suitable for analysis of lead in air and soils, but is insufficiently sensitive to analyse natural waters or most vegetation samples without a prior preconcentration. For these latter samples, or for short-term air samples flameless atomic absorption is required. Flame techniques are relatively free of interference and matrix effects, but in many applications the method of standard additions [1, 2] is necessary to minimize matrix interferences. Flameless AAS is more subject to interference by background absorption and matrix effects than the flame method, and the use of both deuterium background correction and the standard additions method is usually advisable. 

A surface pretreated with KC1 would make the reaction of O atoms with hydrocarbons flameless. As it was suggested that hydroxyl was formed in the flame, the vessel was coated with KC1. Selective disappearance of hydroxyl in great amounts was known to occur on a surface coated with KC1.18 As a result, the reaction chain terminated and the reaction became flameless. However, this result was not immediate. 

Atomic Absorption Spectroscopy. One of the more sensitive instruments used to detect metal-containing toxicants is the AA spectrophotometer. Samples are vaporized either by aspiration into an acetylene flame or by carbon rod atomization in a graphite cup or tube (flameless AA). The atomic vapor formed contains free atoms of an element in their ground state, and when illuminated by a light source that radiates light of a... 

To avoid problems previously encountered with flame atomic absorption spectrometry of arsenic, and also with flameless methods such as that in which the dementis converted to arsine, Ohta and Suzuki [25] proposed an alternative method based on electrothermal ionisation with a metal microtube atomiser. Effective atomisation can be achieved by the addition of thiourea to the arsenic solution or by preliminary extraction of the arsenic-thionalide complex. The second method is recommended for soil samples so as to avoid interference due to the presence of trace elements. 

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