Flame methods

Data for the several flame methods assume an acetylene-nitrous oxide flame residing on a 5- or 10-cm slot burner. The sample is nebulized into a spray chamber placed immediately ahead of the burner. Detection limits are quite dependent on instrument and operating variables, particularly the detector, the fuel and oxidant gases, the slit width, and the method used for background correction and data smoothing. 

Atomic Absorption/Emission Spectrometry. Atomic absorption or emission spectrometric methods are commonly used for inorganic elements in a variety of matrices. The general principles and appHcations have been reviewed (43). Flame-emission spectrometry allows detection at low levels (10 g). It has been claimed that flame methods give better reproducibiHty than electrical excitation methods, owing to better control of several variables involved in flame excitation. Detection limits for selected elements by flame-emission spectrometry given in Table 4. Inductively coupled plasma emission spectrometry may also be employed. 

The sample, usually in the form of a solution, is carried into the hot plasma by a nebuliser system similar to that employed for flame methods (see Section 21.5) although for ICP a much slower flow rate of 1 mLmin-1 is used. 

Instead of employing the high temperature of a flame to bring about the production of atoms from the sample, it is possible in some cases to make use of either (a) non-flame methods involving the use of electrically heated graphite tubes or rods, or (b) vapour techniques. Procedures (a) and (b) both find applications in atomic absorption spectroscopy and in atomic fluorescence spectroscopy. 

Air (particulate lead) Collection of particulate matter onto membrane filter wet ashing with HN03 AAS flame (Method 7082) 50 pg/m3 82-103 NIOSH 1984... 

Park, H., Neppolian, B., Jie, H.S., Ahn,J.-P., Park, J.-K., Anpo, M. and Lee,D.-K. (2007) Preparation of bimetal incorporated Ti02 photocatalytic nanopowders by flame method and their photocatalytic reactivity for the degradation of diluted 2-propanol. Current Applied Physics, 7, 118-123. 

Element Spectral line/nm Flame Method Detection lin... 

C Extraction/Air-Acetylene Flame Method (Metals)... 

Rhodium may be analyzed by flame atomic absorption spectrophotometry using the direct air-acetylene flame method. The metal, its oxide and insoluble salts may be solubilized by digesting with sulfuric acid—hydrochloric acid mixture. Rhodium also may by analyzed by ICP-AES and ICP/MS techniques. ICP/MS is the most sensitive method. Also, it may be analyzed by neutron activation analysis. 

This applies solely to mercury as it is the only analyte that has an appreciable atomic vapour pressure at room temperature. The 253.7 nm line is usually used for mercury atomic absorption, but the transition is spin forbidden, and relatively insensitive. The 184.9 nm line is potentially 20-40 times more sensitive, but at this wavelength most flame gases and the atmosphere absorb strongly. Thus, flame methods for mercury are not noted for their sensitivity (typical flame defection limits are in the range 1-0.1 pg ml-i). If chemical reduction is employed, mercury can be brought into the vapour phase without the need to use a flame, and defection limits are dramatically improved. 

Polyethylene parts are decorated by silk screening, hot stamping, or dry offset printing. For satisfactory printing, the surface must be oxidized by hot air, flame, chlorination, sulfunc acid-dichromate solution, or electronic bombardment. Hot air or flame methods are used with molded parts flame or electronic methods with films. Inks specially made for polyethylene give best results. Roll-leaf hot stamping does not require pretreatment of the suifaoe. 

APHA. 1989a. Metals-Flame atomic absorption spectrometry, 3111B. Direct air-acetylene flame method. In Standard methods for the examination of water and wastewater. 17th Edition. Washington, DC American Public Health Association, 3-20-3-23. 

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 ... 

The first command use opens on disk drive A the database file flame which contains the characteristics for the flame method. Then the element Tl and the concentration (0.02 micro g/ml) one wants to analyze are stored in two memory variables melem and mconc , respectively. 

Before one can examine whether or not the detection limit is reached one has to move the record pointer to the record for thallium, which is done with the locate command. dBASE compares whether the concentration one wants to analyze is lower than the determination limit for the element (which is stored in concen , a field of the flame database file). dBASE then checks whether the equation (the last statement in the above set of commands) is. T. (True) or. F. (False). In case it is False, the concentration to be analyzed exceeds the determination limit and one can obtain the conditions for the flame method by typing the command display. However, if the concentration is lower than specified, the flameless method must be used. To obtain the conditions for the flameless method, one then has to open the database file containing the characteristics for the flameless method and use the display command. 

The cone, you want to analyze is bellow the limit for the flame method. You will have to use the flameless method. ... 

Barium is present at very low concentrations in most environmental samples. Thus, in spite of the availability of a detection limit of only a few ng ml 1 by flame AES, the element is rarely determined by flame methods AAS with electrothermal atomization or ICP-AES is more commonly used. A notable exception is in the determination of the element in barium-rich geological deposits.8 Another exception is in the analysis of formation waters from offshore oil wells.9 However, in this matrix, inter-element interferences are encountered from alkali and alkali-earth elements. These could be effectively eliminated by the addition of 5 g 1 1 magnesium and 3 g 1 1 sodium as a modifier.9... 

Flame methods are the conventional atomization sources used in MS for industrial hygiene (Table I). Air/acetylene at 2150-2400°C is used for the easily atomized elements like lead, cadmium, and zinc. Refractory metals such as tungsten or vanadium require hotter nitrous oxide/acetylene atomization at 2600-2800 C. The need for greater sensitivity and multielement analysis from a single filter has increased the use of electrothermal atomization for tin, vanadium, nickel, and other difficult elements. Formation of hydrides combined with flame atomization has been used in some cases to increase sensitivity. 

Collection of metal complexes of the analytes on suitable adsorbing materials is often employed as an enrichment step in combination with flame methods. In a procedure proposed by Solyak et al. [20], five metals [Co(II), Cu(II), Cr(III), Fe(III), and Pb(II)] were complexed with calmagite 3-hydroxy-4-[(6-hydroxy-m-tolyl)azo]-naphthalenesulfonic acid and subsequently collected on a soluble cellulose nitrate membrane filter. In this way an effective separation from alkaline and alkaline earth metals was achieved, based on the differences in their complex formation constants and those of the transition elements. The experimental parameters were optimized for the quantitative recovery of the elements. After hot dissolution of the filter with HNO3, the analytes were determined by FAAS. Minimum detectable concentrations ranged from 0.06 pg l-1 for Cu to 2.5 pg l-1 for Cr. 

The limits of quantifications (LoQs) achieved by flame methods are often sufficient to characterize the composition of tea raw materials. By employing FAAS... 

Substantially less sample solution (1—100 pi) is required for each element measured by ETA. This feature may make ETA an attractive alternative to flame methods when multielement studies are planned. The automatic sample injectors and improved power supply modules available with the current generation of NFAA devices have combined to make ETA less of an art than it was previously. 

The few articles currently available regarding trace analysis without preconcentration, use in general the graphite furnace technique [102,120, 138] with sample sizes of the order of microliters, and deal with the elements Sb [47, 83], Pb and Bi [48-50], As, Sb, Bi, Sn, Cd, Pb [10, 57, 116] as well as Al, Cr, Sn [6, 62], Co, and Mg [104]. Alkaline earths can be determined directly with the flame method [122, 147], Further techniques of atomic absorption by flame use concentration methods, for example for the determination of small concentrations of tin [17], Te [26], Co, Pb, and Bi [104], and W [106]. From the analytical viewpoint, it is only useful to remove the iron matrix. The extraction of the elements to be determined from the matrix always carries with it the danger of losses and therefore results showing concentrations that are too low. 

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