Burners total consumption

Cd in 0.6A HC1 partial-consumption burner total-consumption burner 22 5 5 5... 

Flame Sources Atomization and excitation in flame atomic emission is accomplished using the same nebulization and spray chamber assembly used in atomic absorption (see Figure 10.38). The burner head consists of single or multiple slots or a Meker-style burner. Older atomic emission instruments often used a total consumption burner in which the sample is drawn through a capillary tube and injected directly into the flame. 

The total consumption type of burner consists of three concentric tubes as shown in Fig. 21.5. The sample solution is carried by a fine capillary tube A directly into the flame. The fuel gas and the oxidant gas are carried along separate tubes so that they only mix at the tip of the burner. Since all the liquid sample which is aspirated by the capillary tube reaches the flame, it would appear that this type of burner should be more efficient that the pre-mix type of burner. However, the total consumption burner gives a flame of relatively short path length, and hence such burners are predominantly used for flame emission studies. This type of burner has the advantages that (1) it is simple to manufacture, (2) it allows a totally representative sample to reach the flame, and (3) it is free from explosion hazards arising from unbumt gas mixtures. Its disadvantages are that (1) the aspiration rate varies with different solvents, and (2) there is a tendency for incrustations to form at the tip of the burner which can lead to variations in the signal recorded. 

Two basic types of flame atomising systems have been used for atomic absorption. Firstly, the total consumption or turbulent burner system in which the total sample aerosol in the oxidant stream and the fuel gas are fed separately through concentric tubes to the burner jet, where the flame is burned. Considerable turbulence, both optical and acoustic, takes place. On the positive side these burner systems are very simple in construction and thus were cheap to manufacture, did not flash-back and could handle virtually any mixture of gases. However, this system is now obsolete. 

B.D. Merkle, R.N. Knisely, FA. Schmidt, and l.E. Anderson, Superconducting Yttrium Barium Copper Oxide (YBa CUjO ) Particulate Produced By Total Consumption Burner Processing, Materials Science and Engineering, V01.A124, No.l, 1990, pp.31-38. 

R7. Robinson, J. W., and Harris, R. J., Mechanical feed burner with total consumption for flame photometry and atomic absorption spectroscopy. Anal. Chim. Arto 26, 439-445 (1962). 

W18. Winefordner, J. D., Mansfield, C. T., and Vickers, T. J., Atomization efficiency of total consumption atomizer-burners in flame photometry. Anal. Chem. 35, 1607-1610 (1963). 

LEI spectrometry using the total consumption burner, with greater sample throughput and a wider range of usable fuel-oxidant combinations, expands the possibilities for development of a more sensitive and versatile detection system for atomic spectrometry. In addition to furthering the analytical methodology, these results demonstrate that high-sensitivity LEI measurements are possible in adverse sample environments where traditional methods of optical spectrometry have proven inadequate. 

Scatter will be greater for "total consumption" burners which produce larger sample droplets, for solutions of higher dissolved matter, and for hght below 250 nm. 

Two basic types of burners have been used for atomic absorption. The one is the total consumption or diflFusion burner, of the type long used by Beckman and others for flame emission work. The other is the premix type, in a variety of designs, in which sample, fuel, and oxidant are mixed in a chamber before entering the flame. 

The total consumption burner is too well known to need much description. In essence, the fuel, oxidant, and sample are all passed through separate channels to a single opening from which the flame... 

For atomic absorption, many workers recognized the deficiencies of the total consumption burner from the beginning. The Australians almost immediately went over to a premix burner. At the present time, only a rapidly diminishing number of workers are continuing to use the total consumption burner for atomic absorption. (Recently, persuasive evidence has come to light indicating that the premix burner is also superior for flame emission.)... 

Despite the high eflBciency implied by the name of the total consumption burner, both it and most of the premix burners are only about 5% eflBcient. In the total consumption burner, the entire sample passes into the flame, but in the rapid transit of the droplets through the hot region only the smallest droplets have time to be dried and burned. In the premix burner, shown in Figure 10, the large droplets in the mixing chamber are collected on the walls and pass down the drain, while only the small droplets travel to the flame. 

The design of the premix burner shown in Figure 10 also presents a number of other advantages and disadvantages as compared with the total consumption type. The flame is not very luminous, and flicker and turbulence are quite low, so that for many elements the flame contributes no apparent noise to the output (Figure 8). Furthermore, there is rather little dependence of absorption upon sample flow rate. This is of benefit in two ways. First, the length of sample capillary, and its depth of immersion in the solution, are not very critical, so that samples can be aspirated from any vessel. For total consumption burners, by contrast, Petri dishes or very small sample containers are often recommended. Second, viscosity interferences caused by variations in sample concentration are minimized, though not eliminated. In the Perkin-Elmer burner, when the sample flow rate is cut by a factor of 2, absorption is reduced by approximately 4%. 

The total consumption burner has the advantage of having, in principle, a faster response time, a lower memory effect, and a greater versa-... 

With the premix burner it is possible to obtain better linearity of working curves, fewer interferences, and the ability to determine more metals, than with the total consumption burner. These differences stem from the fact that the premix flame is laminar and contains no large, unbumable sample droplets, while the total consumption flame is turbulent and includes large droplets. 

Interferences. One study of relative interferences is shown in Figure 12. Here the effect of fluoride concentration on the absorption of barium is measured, both when a total consumption burner and a Perkin-Elmer premix burner are used. It will be seen that the effects are negligible with the premix burner, and immediate and severe with total consumption (J). In another study, it was found that the presence of phosphate interferes seriously with the absorption of magnesium with a total consumption burner (9). With a well-designed premix unit, there is no such effect (2). 

Figure 12, Total consumption and premix burners are compared for interferences of fluoride with the determination of barium (Ref, 1)...

Linearity. In Figures 13 and 14, the absorption for calcium in water solution is given for two different instrumental arrangements. In Figure 13, a premix burner is used, and the sample beam is passed once through the flame (21), In Figure 14, a total consumption burner is employed. 

Figure 14. Working curves for calcium, with total consumption burners and five passes through the flame (Ref. 15)...

Element Versatility. A considerable number of elements require temperatures higher than those of the air-acetylene flame to dissociate them from their chemical compounds. In atomic absorption, these elements are known generally, though somewhat inaccurately, as "refractory elements. These elements, of which sihcon, titanium, and vanadium are examples, are diflBcult and in some cases impossible to determine with the total consumption burner, although they are quite readily determined with a properly designed and used premix system. The reason is believed to be that the turbulence of the total consumption flame causes entrained air to penetrate throughout the cone, thereby lowering the eflFective flame temperature (12). 

For premix burners, the most common supply gases are air and acetylene, while the total consumption burners generally use air and hydrogen. All detection limits are usually given in water solution. 

Fuel economy is also on the side of acetylene, since a 300 cu. ft. tank lasts approximately three working weeks. A similar tank of hydrogen, required by the total consumption burner, is consumed in about three hours. Ordinary welding-grade acetylene is adequate for atomic absorption. The air supply must be free from dust and oil. 

The high burning speed and explosive potential of oxy-acetylene flames made it difficult to produce a usable premix oxy-acetylene burner. The total consumption burner, on the other hand, while capable of burning such a fuel combination, produced such a brilliant and turbulent flame that it was difficult to obtain analytical results with it. Various eflForts to modify the total consumption burner met with only moderate success. 

The Long Tube. As first reported by Fuwa and Vallee (5), the fiame from a total consumption burner is so tilted as to pass down a horizontal ceramic tube, which is typically up to 90 cm. long and about 1 cm. in diameter. This tube lies along the optical path of the spectrophotometer. The atoms in the flame therefore spend a considerably longer time in the optical path than they do with a conventional burner. For elements whose compounds are dissociated at relatively low temperatures, such as zinc, very notable increases in absorption are obtained. 

Flame emission has traditionally been performed with total consumption burners. However, it has recently been shown that the premix burner, with a nitrous oxide head, is an excellent source for flame emission measurements, and is in many cases superior. In Figure 26, a flame emission scan is shown for aluminum in ethanol, with a premix nitrous oxide burner as a source. 

Several elements (Zn, Pb, Cuy Ni, Ca, Mg, Fe, and Mn) are determined routinely in water samples using atomic absorption spectroscopy. Sodium and potassium are determined by flame emission. The preparation of the samples the analytical methody the detection limits and the analytical precisions are presented. The analytical precision is calculated on the basis of a sizable amount of statistical data and exemplifies the effect on the analytical determination of such factors as the hollow cathode sourcey the ffamey and the detection system. The changes in precision and limit of detection with recent developments in sources and burners are discussed. A precision of 3 to 5% standard deviation is attainable with the Hetco total consumption and the Perkin-Elmer laminar flow burners. 

To carry out the analysis in the best manner possible, a study was conducted on the various hollow cathode lamps, burners, and optical systems to assess them as to their advantages and disadvantages in the analysis of water. Particular emphasis was given to the comparison of the total consumption and premix burners (6, 7). The results are presented here in the form of conservative values attainable of sensitivity and precision, and a discussion of the differences noted. 

The analyses were performed on a Jarrell-Ash Model No. 32-360 multipass atomic absorption spectrophotometer equipped with a Beckman total consumption three burner set operated on a hydrogen-air mixture, and Westinghouse single element hollow cathode lamps. 

To investigate this matter of precision further, as well as the limit of detection, two other types of burners and various hollow cathode lamps were tested under similar conditions. The primary objective was to compare a new single flame total consumption burner, operated on a hydrogen-air fuel mixture, with a premix burner using acetylene and air for fuel. The total consumption burner is the Hetco type, and was used with the Jarrell-Ash spectrophotometer. The premix burner is the Perkin-Elmer type and it was tested as a part of the Perkin-Elmer Model 290 Atomic Absorption Spectrophotometer. Synthetic standards for Ca, Mg, Fe, Pb, and Cu were analyzed in varying concentrations. The data was assessed on both a short-term (daily) basis, where new standard curves were prepared daily, and on a long-term basis, where the shift in the calibration curve was included in the data. 

---