An Alternate Spectrophotometric Method of Aluminum Estimation in some Daily Use Products

By Syed Raashid¹, Masood Ahmad Rizvi and Badruddin Khan
February 2011

The Authors are Research Scholars at the Department of Chemistry, University of Kashmir, in Hazratbal, Srinagar, Jammu & Kashmir, India.
¹ Corresponding Author

Aluminum due to its high terrestrial abundance, poses a risk of toxicity. In human beings a good number of renal, skeletal and neural disorders like Alzheimer’s disease have been shown to be linked to aluminium toxicity. Thus a need to quantify time bound exposure to this metal in human beings is obvious. Unlike most of the transition metal ions, aluminium estimation by bench top methods like potentiometry, spectrophotometry is less explored due to its non redox, less complexing, colorless, and easy hydrolysable nature. Reported spectrophotometric methods using Aluminon and 8 hydroxyquinoline have limitations of accuracy and long procedural scheme involving solvent extraction step. The work presented is an optimized alternate spectrophotometric method of aluminium estimation. The reliability of proposed method is established by verifying the results against standard methods of aluminium estimation by EDTA and Atomic Absorption Spectroscopy (AAS). The proposed method is novel in terms of accuracy, less procedural steps, no solvent extraction and quick estimation.

Keywords: Spectrophotometry, Aluminum, Xylenol Orange, Quantitative Estimation, Daily Use Products


A serious threat of aluminium toxicity to human beings arises from high levels of exposure to aluminium both from surroundings and many daily use items1,2, like tea, coffee3 antacids, canned foods and deodorants4. Agricultural toxicity due to higher concentration of solution phase aluminium is well reported and is supposed to be the main reason to limit crop productivity in acidic soils5. Although early biochemical studies did not categorize aluminium as a toxic metal in human beings, advanced medical research has shown high levels of aluminium in a number of renal6, neural7 and skeletal disorders8. Aluminum toxicity is thus a concern in modern times and quantifying human exposure along with design of simple methods to estimate aluminium in daily use items becomes inevitable.

A high electropositive character, poor coordination behavior and unavailability of variable oxidation states9 in aluminium limit its analysis by the common analytical techniques based on coordination or redox. Unlike most of the transition and many non transition metal ions spectrophotometric estimation of aluminium is less explored & reported. The two reported methods are: i) using aluminon10 and ii) using 8 hydroxyquinoline11. However both the methods have limitations in terms of accuracy and involved steps in procedural scheme, thus limiting their wide applicability. The work presented describes an alternate optimized spectrophotometric method of aluminium estimation in some products of daily use. The reliability of proposed method is established by result comparison with standard methods of aluminium estimation involving EDTA and Atomic Absorption Spectroscopy (AAS). The novelty of proposed method is in terms of accuracy, less procedural steps, no solvent extraction and quick estimation.


An appropriately designed experimental setup was used to avoid any determinate error. The solutions required were prepared in double distilled water from analytical grade chemicals of Thomas Baker make. A common strategy was adopted to obtain solution of daily use products from commercial samples for analysis. This involved taking 1 g of each sample as fine powder and dissolving in 25mL of 2N nitric acid over 24 hours at room temperature, after which the solutions were filtered and initially diluted to 100 mL with distilled water to make stock solution. Analysis was done over Perkin Elmer Atomic Absorption Spectrophotometer, Shamadzu 1650 PC UV- Visible spectrophotometer and using conventional EDTA back titrations. Two brands of antacid and tea and one brand of deodorant with the specification given in Table 1 were taken.

Table 1 · List and specification of commercial products analyzed for the presence of aluminium
Sample Sample Brand Make Product Specifications
1. Antacid (A) Digene (chewable tab) Abbott pharma B-339, 7/12/2008
2. Antacid (B) Gelousil (Suspension) ----
3. Tea ( A) Darjeeling (green tea) Asia tea company M 227,
4. Tea (B) Taj Mahal (Blunded tea) Hindustan Unilever V 07 A- 01/2009
5. Deodorant Rexona (Deo... Roll-on) Hindustan Unilever 01/07,B.007

For AAS analysis test solutions were made by diluting the stock solution to ppm level with double distilled water and directly analyzing using Aluminium Hollow Cathode Lamp over NO acetylene flame. AAS data of test samples was taken as a reference to test the validity of estimation by the proposed spectrophotometric method involving aluminium xylenol complex.

Xylenol orange is reported to form a pink colored complex in 1:2 and 1:3 molar ratios to aluminum depending on temperature and pH12. Shift in λmax for free xylenol and complexed form was observed by adding aluminium to the solution at pH 5 and 35°C. All the spectrophometric absorbances were measured at a λcorresponding to λmax of aluminum xylenol complex the analyte solutions were maintained at pH5 using 0.1M acetate buffer and 35°C. The composition of the complex was established by mole fraction and continuous variation method. Molar absorbtivety coefficient (εmax) was calculated from the calibration line from the plot of known Aluminium ion concentrations versus absorbance.

In EDTA complexometric method a fixed volume of sample solution was taken in different titration flasks to which 15mL of 10-2M EDTA was added13. The solutions were maintained at a constant pH of 5 with 10 mL of 1M acetate buffer. Few drops of xylenol orange were added as indicator. The reaction mixture was kept as such for ten minutes. The excess of EDTA was back titrated with 2.0x10-2M standardized Zn2+ solution to pinkish red end point.

Figure 1

Results and Discussion

Xylenol orange shows its absorbance maximum at 476 nm, on complexation with aluminium λmax shifts from 476nm to 555.6 nm. This shift is clearly observed in absorbance curves of free xylenol and complexed one shown in Figure 1.

Figure 1 : λmax shifting for Xylenol solution, in presence of aluminium and in absence of aluminium.

The sample solutions were diluted to ppm level and analyzed for the presence of aluminium by AAS, the results of which are given in Table 2:

Table 2 · Amount of aluminium present in the sample solutions as determined by AAS analysis
Sample solution Concentration of Al as determined by AAS (ppm) Amount of Al(III) per gram of sample (mg)
1. Antacid (A) 111. 0 44.4
2. Antacid (B) 110.0 44.00
3. Tea (A) 12.5 5.00
4. Tea (B) 10.7 4.28
5. Deodorant 108.3 43.33

A series of aluminum ion solutions of known concentrations were complexed with a required (1:3 molar ratio) concentration of xylenol orange. Absorbances at the obtained λmax of aluminum xylenol complex of all the solutions were recorded and are reported Table 3.

Table 3 · Amax (Absorbance at λmax) for the known concentrations of Al3+ ion
Sample content( x mL of 10-4 M Al (III) Concentration of the solution on diluting to 25mL mol lit -1 Absorbance at λmax
1 2 8.0 x 10-6 0.698
2 4 1.6 x 10-5 0.735
3 6 2.4 x 10-5 0.803
4 8 3.2 x 10-5 0.867
5 10 4.0 x 10-5 0.897
6 12 4.8 x 10-5 0.936

Figure 2

From these recorded absorbances, molar absorbance coefficient εmax for the complex was calculated using Beer Lambert law. The Absorbance versus concentration calibration curve of aluminium solution is shown in Figure 2. From the slope of this curve molar absorptivity coefficient εmax of the complex is calculated.

Figure 2 : Absorbance of aluminum xylenol complex Vs concentration of Al(III) at λmax, [Correlation factor = 0.9857]

The value of εmax i.e. Molar abortively coefficient for aluminium xylenol complex as calculated from the slope of the curves and was found to be 5950 LCm-1mole-1. under similar experimental setup absorbance of sample solutions was recorded and Amax (Absorbance at λmax ) values obtained from which concentration of Al(III) ions in each sample was calculated and given in Table 4.

Table 4 · Absorbance, Concentration and corresponding amount of aluminium per gram in the samples
Sample Solution Absorbance at λmax, (556.4 nm) of Complex Concentration of Al(III) ions mol L-1 Amount of Al(III) per gram of sample (mg)
1 Antacid (A) 0.987 1.51 x10-2 40.70
2 Antacid (B) 0.889 1.49 x 10-2 40.20
3 Tea (A) 0.867 1.46 x 10-3 3.94
4 Tea (B) 0.585 1.44 x 10 -3 3.88
5 Deodorant 0.935 1.57 x 10-2 42.40

The results of complexometric back titration are given in table 6 where Vb represents the volume of Zn (II) back titrated in each case. The concentration of aluminium ions in each sample was calculated and reported in Table 5:

Table 5 · Aluminum concentrations of the sample solutions determined by the EDTA back titration
Sample Solution Volume of 0.02 M Zn(II)used in titration mL Concentration of Al (III)in sample solution mol L-1 Amount of Al(III) per gram of sample (mg)
1 Antacid (A) 3.6 1.56 x 10-2 42.11
2 Antacid (B) 3.5 1.52 x 10-2 41.00
3 Tea (A) 6.0 1.50 x 10-3 4.05
4 Tea (B) 6.1 1.40 x 10-3 3.78
5 Deodorant 3.6 1.56 x 10-2 42.11

A comparative account of aluminium estimation by three analytical techniques is as under Table 6:

Table 6 · Comparison of three analytical techniques for aluminium estimation in commercial items
Sample Solution Concentration of Al(III) mg per gm of samples
Spectrophotometry Complexometery AAS
1. Antacid (A) 40.70 42.11 44.40
2. Antacid (B) 40.20 41.00 44.00
3. Tea (A) 3.94 4.05 5.00
4. Tea (B) 3.88 3.78 4.28
5. Deodorant 42.40 42.11 43.33

The results obtained led to the conclusion that all the samples contain appreciable quantity of aluminium. The close resemblance in the amounts of aluminum estimated by three different analytical techniques viz AAS, Spectrophotometry and Complexometric titrations justify the reliability of these techniques for estimation of Aluminum. Comparing spectrophotometric and AAS data predicts that the proposed alternate method for the estimation of aluminium using xylenol orange can be a reliable aluminium estimation method. The proposed alternate spectrophotometric method is novel over other two reported spectrophotometric methods viz using Aluminon and 8-hydroxyquinoline, in terms of reliability, simple procedure and unlike 8- hydroxyquinoline method does not involve a solvent extraction step.


An alternate spectrophotometric method of aluminum estimation with novelty in terms of accuracy, reliability, simple procedure and robust estimation is proposed. Besides this alternate method, the study also hints about risk of aluminum toxicity from daily use items and predicts about the bioavailability of aluminum from such products.

Even though the amount of aluminium present in the tea is less than the amount present in antacid, the bioavailability of aluminium from tea is more than from antacids as the ingredients of milk or lemon in the tea complex with aluminum and prevent its hydrolysis to insoluble aluminum hydroxide in intestine, more over tea is often taken where as antacids are used less frequently. A high risk of aluminum toxicity can be associated with deodorants not only because of higher aluminum content but also the route of its entry in body. Deodorants contain aluminum as aluminium chlorohydrate that blocks sweat pores. Unlike the oral route (Alkaline intestinal pH) there is hardly any physiological barrier to deodorants that prevents aluminium to get to body. This direct injection of aluminium to the blood stream is much more dangerous than the oral dose.

Post Note

It is interesting and amazing to note, deodorant users most of whom are learned individuals and also self claimed sophisticated ones, try to avoid body odor by their use, they hardly care to realize the gravity and consequences of their own action in spite of being posted with the fact that they are introducing aluminum in their blood stream directly. It is thus recommended that while the production of aluminium containing deodorants should be discontinued, or else the user should be educated about its ills and consequences.


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