Atomic Absorption Spectrometric Determination of Aluminium

Al-AAS determination, introduced the method of determination, determination of the interference and elimination of interference, atomization mechanism of aluminum, as well as various areas of development and application of measuring method.

　　Due to the widespread presence of aluminum in nature and it is in agriculture, metallurgy, electronics, pharmaceutical and environmental industries universal applications, rapid and sensitive detection of aluminum is very important. Determination of large amounts of aluminum is the most important analytical method of EDTA complexometric titration and determination of trace aluminium and trace of the most important and widely used method of analysis is a Spectrophotometric method. In addition, chromatography and inductively coupled plasma spectroscopy and infrared spectroscopy, also won. Due to atomic absorption spectrometric determination of aluminium has the advantage of simple, fast, so it’s in the determination of trace aluminium and trace gaining increasingly wide range of applications, it is necessary to study atomic absorption spectrometry for the determination of aluminum. Atomic absorption spectrometric determination of aluminum in this article for a summary.

　　By flame atomic absorption spectrometry

　　(A) air-acetylene flame atomic absorption spectrometry

　　1 ordinary air-acetylene flame method

　　Air-acetylene flame atomic absorption method is the most widely used method of atomization. Aluminum heat resistant alumina formed in the flame, its melting point is 2045 ° c, boiling point is 2,980 ℃, it generally cannot direct determination of aluminum in this flame. Deng Shi-Lin [1] with direct air-acetylene flame atomic absorption spectrometry determination of aluminum in soil. Also added 0.05mol/L determination of water soluble organic compounds tetramethyl ammonium chloride to make aluminum sensitivity about 7 times times, its characteristic concentration of 43 ㎍/ml/1%. While investigation of HCL, HNO3, HCLO4, H2SO4 on aluminium determination of impact, minimal amount of HNO3, HCLO4, H2SO4 all have a great effect on absorbance of aluminum, aluminum or suppression of signal. In 2mol/L does not affect the determination of aluminum in HCL concentration. Therefore, in determining treatment and samples shall be made in HCL for the media. In addition, coexistence and ion K+, Ca2+, Fe3+, Mn2+ add tetramethyl ammonium chloride case, basically do not interfere with the determination of the aluminum.

　　2 oxygen air-acetylene flame shield method

　　Shi Zaixin, “2″ oxygen determination of aluminium in steel by air-acetylene flame shield (0.1~10%), the method is relatively simple. Results show that slightly sensitization of HNO3 to aluminum, slightly inhibitory effect of HCL. Determination of coexisting elements on aluminum also affecting: Fe, and slightly inhibitory effect of Mo, Ni, Mn slightly sensitizing effect; absorption of titanium to aluminum trichloride with sensitization, and other elements of interference suppression, improved stability. But this method of gas consumption, high noise, has a strong flame emission.

　　3 by enriched oxygen air-acetylene flame

　　Weng Yong and “3″ by enriched oxygen air-acetylene flame method for the determination of aluminium, comparison of different organic reagents on enhancing effect of aluminum in this flame. When organic reagents in the benzene ring of o is the structure of aluminum containing hydroxyl and carboxyl functional groups, such as chrome azurol s aluminium reagents, tiron, sulfosalicylic acid and potassium hydrogen phthalate isochronous, and Max with a similar enhancing effect, its multiples sensitization about 2, characteristics of concentration of up to 1.2 ㎍/mL. Compared with the oxygen mask air-acetylene flame method, this method result low gas consumption, low noise, flame, and difficult to temper.

　　4 indirect air-acetylene flame atomic absorption spectrometry

　　Aluminium in air-acetylene flame dissociation heat resistant alumina formed easily in difficult, low sensitivity. With the method of oxygen-rich, characteristic concentration of 1.2 ㎍/mL “3″. Lu Jiushao “4″ by flame atomic absorption spectrometric method for indirect determination of aluminum in water and wastewater, according to the Cu2+-EDTA and Al3+, PAN quantitative Exchange reaction, chloroform extraction of Cu2+-PAN can be generated, with air-acetylene flame method for determination of residual copper in aqueous and indirect determination of aluminium, aluminium concentrations in the range 0.1~1.0mg/L has good linear relationship. PH range at the time of PH3.8~5.0 curve is a straight line, so select PH4.5. Cu2+, Ni2+ on experimental jamming serious, but before joining Cu2+-EDTA, joined the PAN first, then 1.0mg/L Cu2+ 0.1 Ni2+ on experimental and non-interference. Fe3+ serious interference, adding Ascorbic acid can eliminate Fe3+ interference. F-on determination of interference, adding boric acid can be eliminated. This indirect method for measuring the aluminum concentration range in 0.05~100 ㎎/L.

(B) nitrous oxide-acetylene flame atomic absorption spectrometry

　　Determination of aluminum with air-acetylene flame, flame temperatures high enough to lower sensitivity. Most of the current determination of aluminium with nitrous oxide-acetylene flame. Reported in “5″ with nitrous oxide-acetylene flame method for the determination of aluminum in acidic waste water, be this through the whole program blank test-and-drop method to minimal detected concentration of 0.006 ㎎/L. Used nitrous oxide-acetylene flame temperature high, can prompted dissociation can large of compounds solutions away from, while its rich burning flame in the apart from c, and CO, and CH, not decomposition products zhiwai also like CN, and NH, components, they has strongly of restore sexual, can more effective to snatch metal oxides in the of oxygen, thus makes many high temperature difficult solutions away from of metal oxides Atomic of, makes Be, and b, and Si, and w, and Mo, and Ba, and rare earth, difficult melt sexual oxides of element on determination has interference. However, because such a high temperature of the flame can eliminate many chemical interference. Added a large number of alkali metals in the test solution (1mL/mL~2 mL/mL) can reduce the ionization interference.

　　Another reported “6″ measuring 7715D with nitrous oxide-acetylene flame of aluminium in titanium alloys at high temperature, concentration of nitrous oxide-acetylene flame characteristics for 1 ㎎/L · 1%, check out limit is 0.03 ㎍/mL in solution. Alkali metal content increases to 100 ㎍/mL AL 309.3nm interference. According to the value of ionization potential, alkali metals of caesium is most suitable for this purpose. Hydrochloric acid is the ideal acid decomposition 7715D high-temperature titanium alloy samples. Fe is one of the most common form of coexisting elements must be eliminated, using several elements such as lithium phosphate can eliminate Fe coexistence interference, and to obtain a higher sensitivity and accuracy.

　　-Graphite furnace atomic absorption method

　　Flame atomic absorption spectrometry with fast, accurate, and other advantages, in particular application of nitrous oxide-acetylene flame to increasing determination of sensitivity to aluminum, but still advance determination of trace aluminium concentration. In recent years of research on aluminium by graphite furnace atomic absorption spectrometry with more, but cannot yet meet on some sample direct analysis of the sensitivity, but there is a spectrum of non-interference in the determination, its degree of interference depends on the chemical properties of graphite surface and carrier gas used by “7″. Graphite furnace atomic absorption of matrix interference is serious, for the reduction and elimination of matrix interference, ultimately, interference-free measurement, people do a lot of research, more effective method is the combined platforms, matrix modifier and surface coatings, deduction of Zeeman effect background, gradients and precise automatic sample introduction techniques of warming.

　　(A) by graphite furnace atomic absorption

　　Shaw and Ottaway[8] with normal graphite tube 2 ㎎/L aluminum, the relative standard deviation of 7%. Due to the interference of chloride ions, using only nitric acid to dissolve the sample, this limits the application of this law. Sample dissolved in nitric acid and hydrochloric acid chloride interference must seek to eliminate, you can join such as sulfuric acid, ammonia and ammonium sulfate form volatile chloride to eliminate interference. Addition of ammonium sulfate in particular, you will get the best reproducibility. Presence of sodium sulfate and sodium sulfide also interfere with the determination of the aluminum “7″, through the work with analog matrix curves to eliminate interference. In addition, because of the different graphite tube can also cause changes in sensitivity, so before using, each graphite tube to empty firing three times. Halls, “9″ in the determination of aluminium in the dialysate, examining the effects of acidity in the substrate, and graphite furnace. Experiments show that join allows the recovery of a significant increase in nitric acid, 1% (V/V) HNO3 matrix effect can be improved, 2% (V/V) HNO3 is completely inhibit matrix effects. Sulfuric acid also has such a role, but for routine analysis, HNO3 than H2SO4, because sulfate viscosity, difficult to transfer. And the 2%HNO3 of ash may be appropriate to reduce the time. At the time of determination of aluminum in serum, to enable the graphite tube produces no carbon fouling, overcoming the high serum matrix background, He Shiyu, “10″ made by dilution. With high water made thinner, and deuterium lamps without using matrix modifier agent background correction and feature content of 18pg, relative standard deviation of 5%, good reproducibility. High purity water for thinner, blank value is low, it is this law the most favourable conditions. Yu Jinrun “11″ based sports schools are methods used, may not background correction device, substrate without separation and preconcentration of sample solution case, direct determination of low alloy steel and pure iron of 0.0005~0.01% and 0.0002~0.01% of acid-soluble aluminum in acid insoluble aluminium. Background absorption of iron and sample the same substrate solution for correction.

　　(B) improvement of graphite furnace atomic absorption spectrometry

　　1 matrix modifier

　　Graphite furnace atomic absorption spectrometry using matrix modifier agent reduction and elimination of matrix interference is often an effective method of. Measurement of aluminum using graphite furnace can usually not matrix modifiers, because aluminum has allowed ashing temperature high enough. Nevertheless, xiaoleqin “12″ aluminum as aluminum magnesium nitrate matrix modifier agent to become volatile compound, appropriately improve the ashing temperature, can make the background interference matter volatile before the Atomic drop, when magnesium content in 100-200 ㎎/L, absorbance is ideal. Ashing temperature of 1500 ° c, atomic transition temperature at 2,300 with good accuracy and precision. But Jiang Yongqing “13″ raised with Ca (NO3) 2 for aluminum matrix modifiers to further improve the ashing temperature, was better than the Mg (NO3) 2 results. Ca (NO3) 2 Al sensitization not only, but also increased the maximum allowed ashing temperature of aluminum, reducing atomization temperature, enhance anti-interference ability. Cai Yanrong “14″ 1.0 mL10.0%Ca (NO3) 2 ﹢ 2.5% Ascorbic acid as matrix modifier agent of this experiment, good stability and sensitization on aluminum absorption signal stronger. While on acid of species and the dosage on suction photometric of effect for has comparison, dang with hydrochloride and sulfate acidification solution Shi, as joined volume of increased, aluminum of suction photometric also as increased, but increased range is small, so General without hydrochloride and sulfate to acidification solution, and nitric acid on aluminum of increased sense role large, and as acid concentration of increased, suction photometric almost is line significantly rose. Considering the appropriate solution acidity greater sensitivity and shorter the service life of graphite tube and other factors, nitric acid for acidification with choice of volume fraction of 5%. Zhu Li, “15″ to establish a new determination of aluminum in drinking water by graphite furnace atomic absorption spectrometry. Compare K2Cr2O7, acetylacetone and K2Cr2O7-effect of acetylacetone, which K2Cr2O7-acetyl acetone mixed matrix modifiers work best. This is because K2Cr2O7 gaseous molecular compounds reduce or eliminate the generation of ALO and AL2C2, and both gaseous molecules generated will make aluminum atoms of incomplete; acetylacetone and formation of liquid aluminum-aluminum acetylacetone chelate, block aluminium carbide formation. K2Cr2O7-acetyl acetone mixed matrix modifiers enhancing effect stronger than single K2Cr2O7 or acetyl acetone as a matrix modifier agent better responsiveness and stability. Matsusaki “16″ study of graphite furnace aluminum chloride and elimination of interference when logging. They put the chlorides (concentration of 10-5~10-1mol/L) on the interference of aluminum in acidic media is divided into three types: HCI, NH4Cl, MgCl2 minor interference; NaCl, KCl the medium interference; CaCl2, SrCl2, BaCl2, CuCl2, FeCl3 is a serious interference. NaCl, KCl has relatively low volatile temperature, ashing temperature 1000 ℃ can be to get rid of their interference. Addition of other compounds also have an inhibitory effect on interference of NaCl, inhibitory effect of the size of the order is: CH3COONH4>HNO3>EDTA (NH4) 4>H2SO4. The author of “16″ pointed out that with ammonium and nitrate to acetate to remove interference effects of NaCl and KCl is better. CaCl2, SrCl2, BaCl2, CuCl2, volatile temperatures higher by FeCl3, difficult by controlling the conditions to overcome the interference of ash. Join EDTA ammonium removal CuCl2 can greatly disturb, also has similar effects to other chlorides. EDTA ammonium salt to eliminate causes of interference, not only because it has the ability of metal ion complexation and metal ion in the NH4+ replace the corresponding chloride in solution, forming volatile NH4Cl would be removed. Also found in old eliminate interference effects of graphite tube than a new properly, possibly because tubes use increased, degree of matrix interference is reduced.
Wang Chengbo “17″ replacing graphite tube coated tantalum with tungsten and tantalum substrate, using direct determination of aluminum in water by graphite furnace atomic absorption, overcome tantalum coating graphite synthesis of red tape and fewer defects and determination of results less high sensitivity, matrix interference, stable and accurate, detection limits are up to 1 ㎍/L. The author of “17″ increasing the substrate concentration, determination of aluminium in selected conditions of absorbance, discovery of tungsten and tantalum substrate solution concentration determination does not affect the result. Since joining after drying and ashing and tungsten, and tantalum substrate after atomization in graphite furnace operation, equivalent of graphite tube of a refractory coating of carbide layer formed on the surface, it’s improvement for determination of aluminium. In addition, when coated graphite tube aluminum tantalum, tantalum coated graphite tube fabrication of complex, and uses fewer because of tantalum coating layer after atomization in high temperature burning on several occasions, easy loss. After matrix modifiers instead of tungsten and tantalum, as each sample can form a layer of carbide refractory coating, significantly extend the life of a graphite tube. In addition, as the pyrolytic graphite tube than graphite tube with relatively small pores, graphite tube sample easy penetration into the tube, so that evaporation of the sample includes particles inside the tube to the surface of surface diffusion and evaporation of the sample into two parts, so as to affect the analysis results. Choice of graphite tube atomic transition temperatures of the elements should be considered high or low, forming refractory carbides and graphite tube heating rate requirements influence of several factors. In General, the element Atomic high temperature of the choice of pyrolytic graphite tube, Atom should use low temperature graphite tube can only get better sensitivity. The author of “17″ also studied Ca2+, Mg2+, Fe2+, Cu2+, chloride, sulfate, and other coexistence interference of ions on the determination of aluminum. Results show that matrix modifiers when graphite tube with tungsten and tantalum, determination of coexistent ions on Al-there is no significant interference; when using Ta-coated graphite tube, using a coating that is eroded after more than 10 times, a higher proportion of chloride remains in the grey phase, therefore in atomization phase, increasing chlorides of aluminum vapor phase interference, producing inhibitory effect on the determination of aluminum.
2 improved graphite tube

　　Because aluminum matrix interference when serious measurement, Slavin, “18″ with platform furnace isotherm determination of coexistent ions in aluminum and Zeeman background correction and elimination of interference. And the most convenient and effective way is by pyrolytic-coated graphite tube “19″, because of pyrolytic-coated graphite tube than the porosity graphite tube with a relatively small, so you can avoid the infiltration of sample tubes, almost only when heating evaporation on the surface, the so-called ideal of s-shaped particles evaporation. Pyrolytic graphite tube retention in the grey phase of the interfering relative reduction will help overcome the interference of coexisting elements, by the young Apple “19″ reported after use of pyrolytic graphite tube, 17 species of coexisting elements on aluminum reduction: a determination of interference in the tungsten. And Yang Baogui “20″ and graphite furnace made of molybdenum processing platform, test signals that can be reinforced, not volatile carbon generated and possibly molybdenum carbide, caulk the pore of graphite tube surface, play the role of coatings. Taddia “21″ l ‘ VoV platform reduces encountered by graphite furnace method for determination of aluminium in Silicon interference. And noted that the pyrolytic-coated graphite tube only in l ‘ VoV platform when used in combination to obtain reliable data, without sacrificing precision matrix interference while reducing minimum. Pyrolytic-coated pyrolytic graphite and graphite tube platforms available, exist to increase the sensitivity of 60% nitrate, and that this increase does not change with the amount of nitrate, is a constant value. Use platform to eliminate the impact of HF base itself does not interfere with the determination of aluminum and Silicon. Pyrolytic graphite Guan Jiaji improved agent and l ‘ VoV platform of jiaji improver “22″ the determination of aluminum, can eliminate changes in substrate on the analysis of signal interference on the one hand, improve the sensitivity of analysis, direct determination of aluminium without matrix separation; on the other hand also to overcome the interference of coexisting elements.

　　Mechanism of three aluminum atoms

　　According to the document “23″ views of aluminium in graphite furnace atomization process can be divided into the following three conditions, namely,

　　(1) (l or s) → AlCl3 (g) → Al (g) ﹢ 3Cl (g)

　　Decomposition of volatile chlorides, so the performance loss for ashing, Atomic is not on there.

　　(2) Al2O3 (s) ﹢ 3C (s) → 2Al (s or l) ﹢ 3CO (g)

↓

2Al（g）

But Al2O3 except hard carbon can be restored, a Disproportionation reaction with carbon

2Al2O3﹢9C→Al4C3﹢6CO

Al4C3 while at 3,000 will decompose to release Atomic state aluminum, but it is the formation and decomposition of Al4C3, linear destruction of aluminium, graphite tube life shorter, measuring accuracy declining, so Slavin[18] repeatedly stressed by pyrolytic graphite tube.

　　（3） Al2O3（g）→AlO（g）﹢Al（g）﹢O2（g）

↓

Al（g）﹢O（g）

Deng Bo, “24″ believe that aluminum may only be produced by thermal decomposition of oxides, this is consistent with the results of their experiments.

　　The four closings

　　To sum up, particularly nitrous oxide-acetylene flame by flame atomic absorption method for determination of aluminium has better sensitivity, determination of aluminum in some specimens is viable; determination of sensitivity of aluminium by graphite furnace atomic absorption than nitrous oxide-acetylene flame, especially matrix modifiers and coated graphite tube, sensitivity has been significantly improved, a method is the more widely used. All in all, atomic absorption spectrometric determination of aluminum, is fast, simple characteristics, suitable for universal application.

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