Spectrophotometer, atomic absorption

A successful method employs flame photometry, using an atomic absorption spectrophotometer. Basically, the sample is ashed at 800°C, converted to the chloride with HCl and diluted with ionized water to give a test solution. Calibration solutions containing 1.0, 2.5, 5.0 and 10.0 pg/cm of Na are made up from a commercially available Sodium Stock Solution (containing 1 mg/cm Na). A blank of deionized water/HCl is aspirated into an air/acetylene flame set up with the atomic absorption spectrophotometer, followed by the standard solutions and the sample. A portion of the radiation proportional to the concentration of the sodium is absorbed. The absorption is measured and the concentration can be determined. 

An alternative method is to use an ion chromatograph, where the sample is ashed for about 10 h at 750°C, the residue dissolved in HNO3, diluted with distilled water to a given volume and an aliquot eluted with 0.02% methane sulphonic acid (CH3SO3H), which forms the Na salt and the conductivity is then checked against known Na standards. 

6 Determination of the Soft Finish content in Courtelle precursor 

About 10 g of precursor fiber is weighed and placed in a weighed flask and extracted in a soxhlet with 200 cm redistilled methylene chloride for 3 h (about 9 cycles). After the last cycle, the solvent is allowed to evaporate until about 10-15 cm remains in the flask and the contents of the soxhlet are about to siphon back into the flask. The residual solution in the flask is then evaporated on a water bath in a fume cupboard and finally dried for about 2 h in an oven at 80°C in one continuous operation. After cooling the flask is weighed to determine the quantity of the soft finish. 

The absorbance values corresponding to known standard solution are recorded after necessary blank settings and a calibration curve is prepared. The absorbance of the test solution is determined and concentration read off from the calibration curve. 

Some of the established manufacturers of different types and models of atomic absorption spectrophotometer are Perkin-Elmer, Cooperation, Norwalk, Conn. USA Hitachi Instruments Co., Tokyo, Japan Atomic Absorption and Electronics Corporation, New York Bausch Laumb Inc., Rochester New York Hewlett-Packard, Dayton, Ohio and many others. 

Since AAS is one of the most sophisticated, high precision and expensive t3q)e of measuring instrument, the AAS requires very careful handling and maintenance. 

Several factors may affect the flame emission of a given element and lead to interference with the determination of the concentration of given element. The factors may be broadly classified as (a) spectral interferences and (6) chemical interferences. 

Spectral interferences in AAS arise mainly from overlap between the frequencies of a selected resonance line with lines emitted by some other element, which arises because in practice a chosen line has in fact a finite band-width . With flame emission spectroscopy, there is 

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Atomic absorption spectrophotometers (Figure 10.37) are designed using either the single-beam or double-beam optics described earlier for molecular absorption spectrophotometers (see Figures 10.25 and 10.26). There are, however, several important differences that are considered in this section. 

When the identity of the matrix interference is unknown, or when it is impossible to adjust the flame to eliminate the interference, then other means must be used to compensate for the background interference. Several methods have been developed to compensate for matrix interferences, and most atomic absorption spectrophotometers include one or more of these methods. 

Other methods of background correction have been developed, including Zee-man effect background correction and Smith-Iiieffje background correction, both of which are included in some commercially available atomic absorption spectrophotometers. Further details about these methods can be found in several of the suggested readings listed at the end of the chapter. 

Figure 8-8. Atomic absorption spectrophotometer with 16 mm cine projector in piace.

This is primarily engaged in analysis of boiler water treatment matters and involves on-site studies of various problems and the chemical examination of corrosion products, boiler scales, etc. It can also carry out certain types of metallurgical, fuel and inorganic analysis. Normal wet methods of analysis coupled with a visible ultraviolet and atomic absorption spectrophotometer are used for a wide range of analytical applications. Equipment in use by the engineering insurers providing these services can include an ion chromatograph, spectrometer equipment, atomic... 

Procedure. Allow the whole of the sample solution (1 L) to flow through the resin column at a rate not exceeding 5 mL min . Wash the column with 250 mL of de-ionised water and reject the washings. Elute the copper(II) ions with 30 mL of 2M nitric acid, place the eluate in a small conical flask (lOOmL, preferably silica) and evaporate carefully to dryness on a hotplate (use a low temperature setting). Dissolve the residue in 1 mL of 0.1 M nitric acid introduced by pipette and then add 9 mL of acetone. Determine copper in the resulting solution using an atomic absorption spectrophotometer which has been calibrated using the standard copper(II) solutions. 

Within the confines of the present volume it is not possible to provide a detailed discussion of instrumentation for atomic fluorescence spectroscopy. An instrument for simultaneous multi-element determination described by Mitchell and Johansson53 has been developed commercially. Many atomic absorption spectrophotometers can be adapted for fluorescence measurements and details are available from the manufacturers. Detailed descriptions of atomic fluorescence spectroscopy are to be found in many of the volumes listed in the Bibliography (Section 21.27). 

Before commencing any experimental work with either a flame (emission) photometer or an atomic absorption spectrophotometer, the following guidelines on safety practices should be studied. These recommendations are a summary... 

A double-beam atomic absorption spectrophotometer should be used. Set up a vanadium hollow cathode lamp selecting the resonance line of wavelength 318.5 nm, and adjust the gas controls to give a fuel-rich acetylene-nitrous oxide flame in accordance with the instruction manual. Aspirate successively into the flame the solvent blank, the standard solutions, and finally the test solution, in each case recording the absorbance reading. Plot the calibration curve and ascertain the vanadium content of the oil. 

Anon., safety practices for atomic absorption spectrophotometers. International Laboratory, 1974, May/June, 63. International Scientific Communications Inc, Fairfield, Conn., USA... 

Na Influx Studies. Na influx was monitored according to the procedure of Owen and Villereal (34), with some modifications. Cells were seeded onto 60-mm culture dishes, grown, and serum starved as described for the assays above. The cells were washed with incubation media and incubated in 3 ml of the appropriate agent at 37 C. After incubation the cells were rapidly washed in ice cold 0.1 mM MgCL and extracted with 5% TCA/0.5% KNO3 for sodium determination or 0.2% SDS for protein determination. Sodium concentration was measured using a Varian Model 275 Atomic Absorption Spectrophotometer. Protein was determined fluorimetrically. 

Fuller, C. W. "A Simple Standards Additions Technique Using the Model 306 Atomic Absorption Spectrophotometer". 

Pekarek, R. S. and Hauer, E. C. "Direct Determination of Serum Chromium and Nickel by an Atomic Absorption Spectrophotometer with a Heated Graphite Furnace". Fed. Proc. 

The concentrates were subsequently analysed for arsenic using Varian-Techtron AAS atomic absorption spectrophotometer fitted with a Perkin-Elmer HGA 72 carbon furnace, linked to a zinc reductor column for the generation of arsine (Fig. 5.3). A continuous stream of argon was allowed to flow with the column connected into the inert gas line between the HGA 72 control unit and the inlet to the furnace. Calcium sulfate (10-20 mesh) was used as an adsorbent to prevent water vapour entering the carbon furnace. The carbon tube was of 10 mm id and had a single centrally located inlet hole. 

Soo [96] determined picogram amounts of bismuth in seawater by flameless atomic absorption spectrometry with hydride generation. The bismuth is reduced in solution by sodium borohydride to bismuthine, stripped with helium gas, and collected in situ in a modified carbon rod atomiser. The collected bismuth is subsequently atomised by increasing the atomiser temperature and detected by an atomic absorption spectrophotometer. The absolute detection limit is 3pg of bismuth. The precision of the method is 2.2% for 150 pg and 6.7% for 25 pg of bismuth. Concentrations of bismuth found in the Pacific Ocean ranged from < 0.003-0.085 (dissolved) and 0.13-0.2 ng/1 (total). 

Olafsson [472] described a similar procedure, in which the sample (450 ml) is acidified with nitric acid, aqueous stannous chloride is added, and the mercury is entrained by a stream of argon into a silica tube wound externally with resistance wire and containing pieces of gold foil, on which the mercury is retained. The tube and its contents are then heated electrically to about 320 °C and the vaporised mercury is swept by argon into a 10 cm silica absorption cell in an atomic absorption spectrophotometer equipped with a recorder. The absorption (measured at 253.7 nm) is directly proportional to the amount of mercury in the range 0 - 24 ng per sample. 

Lee [524] described a method for the determination of nanogram or sub-nan ogram amounts of nickel in seawater. Dissolved nickel is reduced by sodium borohydride to its elemental form, which combines with carbon monoxide to form nickel carbonyl. The nickel carbonyl is stripped from solution by a helium-carbon monoxide mixed gas stream, collected in a liquid nitrogen trap, and atomised in a quartz tube burner of an atomic absorption spectrophotometer. The sensitivity of the method is 0.05 ng of nickel. The precision for 3 ng nickel is about 4%. No interference by other elements is encountered in this technique. 

The samples were analysed by injecting 25 pi aliquots into an HGA 2000 Perkin-Elmer graphite furnace attached to a Jarrell-Ash 82-800 double beam atomic absorption spectrophotometer. Graphite tubes in the furnace were replaced after 75-100 analyses. Metal concentrations were determined by comparing the peak heights of the samples to the standard curve established by the determination of at least five known standards. The detection Emits of this technique for 1% absorption were 0.9 pmol/1 (Fe), and 0.2 pmol/1 (Mn). The coefficient of variation was 11% at 6.5 pmol/1 for iron and +12% at 11.8 pmol/1 for manganese. 

A sample of stainless steel (0.320 g) was weighed out and dissolved in nitric acid. The resulting solution was made up to 1 dm3 with water. Five standards and the sample solution were analysed for nickel consecutively on a flame atomic absorption spectrophotometer with the following results ... 

Figure 14.7. An atomic absorption spectrophotometer capable of functioning in either the EM or AA mode.

The system used by these workers consisted of a Microtek 220 gas chromatograph and a Perkin-Elmer 403 atomic absorption spectrophotometer. These instruments were connected by means of a stainless steel tubing (2mm o.d.) connected from the column outlet of the gas chromatograph to the silica furnace of the atomic absorption spectrometer. The silica furnace was set at 1000°C. The gas chromatographic column was packed with 3% OV-1 supported on Chromosorb W. The column was temperature programmed at 15°C h to 150°C. 

A series of eight absorbance measurements using an atomic absorption spectrophotometer are as follows 0.855, 0.836, 0.848, 0.870, 0.859, 0.841, 0.861, and 0.852. According to the instrument manufacturer, the precision of the absorbance measurements using this instrument should not exceed 1% relative standard deviation. Does it in this case ... 

Let us dwell on Figure 6.4 for a moment. The standards and sample solutions are introduced to the instrument in a variety of ways. In the case of a pH meter and other electroanalytical instruments, the tips of one or two probes are immersed in the solution. In the case of an automatic digital Abbe refractometer (Chapter 15), a small quantity of the solution is placed on a prism at the bottom of a sample well inside the instrument. In an ordinary spectrophotometer (Chapters 7 and 8), the solution is held in a round (like a test tube) or square container called a cuvette, which fits in a holder inside the instrument. In an atomic absorption spectrophotometer (Chapter 9), or in instruments utilizing an autosampler, the solution is sucked or aspirated into the instrument from an external container. In a chromatograph (Chapters 12 and 13), the solution is injected into the instrument with the use of a small-volume syringe. Once inside, or otherwise in contact with the instrument, the instrument is designed to act on the solution. We now address the processes that occur inside the instrument in order to produce the electrical signal that is seen at the readout. 

FIGURE 9.14 An illustration of the light path for a single-beam atomic absorption spectrophotometer with a... 

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