Aluminium concentration

Determine aluminium (present as its acetylacetonate) in the sample solution by injecting 0.30 L into the column. Record the peak area obtained and read off the aluminium concentration from the calibration graph (see Note). 

Figure 2 Interactions polymer aluminium concentration of bound aluminium ions for AlCl3 (27 ppin ) and AD27 (0.25 g/1 ) Full line Calculated curve Dotted line NMR results...

Spencer and Sachs [29] determined particulate aluminium in seawater by atomic absorption spectrometry. The suspended matter was collected from seawater (at least 2 litres) on a 0.45 tm membrane filter, the filter was ashed, and the residue was heated to fumes with 2 ml concentrated hydrofluoric acid and one drop of concentrated sulfuric acid. This residue was dissolved in 2 ml 2 M hydrochloric acid and the solution was diluted to give an aluminium concentration in the range 5-50 pg/1. Atomic absorption determination was carried out with a nitrous oxide acetylene flame. The effects of calcium, iron, sodium, and sulfate alone and in combination on the aluminium absorption were studied. 

Absorbance values at the wavelength corresponding to aluminium are found using different solutions of known aluminium concentrations. A calibration graph is then plotted. If we measure the absorbance in a sample of drinking water, then the concentration of aluminium corresponding to this absorbance can be read from the calibration graph. 

In Fig. 5b the calculated bicarbonate concentrations of the three lakes with the lowest pH were corrected considering the dissolved aluminium concentrations... 

The previously mentioned release of aluminium at low pH is particularly important because of its toxic effects on organisms. As expected from theory [9], drawing the average aluminium concentrations against the mean pH a negative exponential correlation is obtained (Fig. 6) A1 increases with decreasing pH and lakes with the lowest pH have the highest aluminium concentrations. 

The Swiss law for water protection does not indicate a concentration hmit for aluminium in surface waters. Therefore, in order to better assess the measured aluminium concentrations, we compared them with the concentration limits existing in the US. The chronic US National Ambient Water Quality Criteria [19] for total aluminium at a pH of 6.5-9 is 87 pg 1, indicating that the average value over 4 days should not exceed this value more than once every 3 years. However, since aluminium seems to be more toxic at low pH s the result is that in acidic waters the acceptable chronic value of total aluminium may be even lower. We conclude that aluminium concentrations in our three most acid lakes are probably high enough to cause toxic effects on organisms. 

Unfortunately, investigations with ionic liquids containing high amounts of AlEtCl2 showed several Hmitations, including the reductive effect of the alkylalu-minium affecting the temperature stabihty of the nickel catalyst. At very high alkyl-aluminium concentrations, precipitation of black metaUic nickel was observed even at room temperature. 

A. Sepe, S. Constantini, L. Ciaralli, M. Ciprotti, R. Giordano, Evaluation of aluminium concentrations in samples of chocolate and beverages by electrothermal atomic absorption spectrometry, Food Addit. Contam., 18 (2001), 788-796. 

NMR-characterization. 27 Corbin et al. (35) were able to show by a systematic study that Z/A1 MAS NMR gives the true Si/Al ratio with a mean error of 10 %, if two conditions are met a) The amount of paramagnetic species is less than 0.05 % and b) the sample does not contain "NMR-invisible" aluminium. Chemical analyses of the samples under study showed that condition one is fulfilled. If samples contain "NMR-invisible" aluminium a difference between the concentration determined by chemical analysis and the framework aluminium concentration determined by NMR should be observed. From the absence of such a difference we conclude that "NMR-invisible" aluminium species do not exist in our samples. Also a line at the position of about 0 ppm due to octahedrally coordinated non-framework aluminium and a broad line at about 30 ppm due to tetrahedrally coordinated nonframework aluminium (36) could not be observed. The values for the concentration of framework aluminium atoms derived from the intensities of the line at about 60 ppm (see below) are in good agreement with those corresponding to the amount of alumina used in the synthesis mixtures. In conclusion, through the Al MAS NMR measurements it was possible to show that all aluminium atoms are incorporated in tetrahedrally oxygen coordinated framework positions. 

When more experiments were considered, a good correlation could be established between the aluminium concentration and the variation of the crystal habit. Figure 6 reports data collected from seven crystallizations. Spherulites exhibiting high-index faces existed for the higher supersaturation levels. When the aluminium content became lower than 4-5 mmol/1, (001) faces appeared, while (100) faces formed only below 2-2.5 mmol/1. 

Dependence of the growth rates on the aluminium in solution. Figure 8 shows the influence of the concentration of aluminium (mmol/1) on the rate of growth (nm/h) for the (001) and (hhO) faces at 115°C (the aluminium concentration taken into account corresponds to the average value between two consecutive analyses). If the experimental data are represented in In r versus In [Al] plots, satisfactory linear correlations are found. Growth rates may then be represented as ... 

Any possible way to modify the final <001> / size ratio appeared to require that growth of crystals be conducted in an optimum range of supersaturation (corresponding to a concentration of aluminium between 2 and 4 mmol/1) without modification of the initial conditions, which determine the number of crystals nucleated. The practical way in which we realized this objective was the use of an initial synthesis medium containing only the aluminium present in the structure directing mixture. Once the nucleation occurred, an aluminate solution was injected in the autoclave in order to maintain the aluminium concentration at the desired level. The expected increase in growth surface was calculated using the above kinetic equations, and the flow rate of the injected solution was continuously adjusted in order to balance the incorporation of nutrient by the crystals. 

Figure 6. Crystal habit as a function of aluminium concentration and temperature.

The growth rates of the (001) face and of the lateral surface of the cylindrical crystals (here designed as (hkO) faces) present a different energy of activation and a different dependence on aluminium concentration. These results could support the hypothesis of different growth mechanisms on the different faces. 

Figure 9. Synthesis of zeolite omega at 115°C with external supply of aluminium. Left scale aluminium concentration in the autoclave solution. Right scale rate of aluminium supply.

Anti-acids, astringents and antiseptic agents may contain a variety of aluminium salts. Organic salts, alumina, the hydroxide and phosphates may be attacked with concentrated hydrochloric acid and diluted to bring the aluminium concentration into the range 10—50 pg ml"1. Alternative procedures for antacids using hydrochloric/nitric acid [67] and extraction with 4M hydrochloric acid [95] have been proposed. For silicates, the sample is best taken up in perchloric/hydrofluoric acid, evaporated to dryness to remove silica, and then the residue dissolved in warm hydrochloric acid [87], In each case the nitrous oxide/acetylene flame is the preferred atom cell, and the method of standard additions may be used to minimise any errors arising from lateral diffusion. 

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