Determination of Aluminum at Trace Level in Water Samples by Visible Absorption Spectroscopy with a Laser Diode

Abstract

KeywordsVisible-laser diode spectrometer, aluminum, water sample , Eriochrome Cyanine R, cetylpyridinium chlorideVarious studies on visible (VIS-LD) and near infrared laser diodes (NIR-LD) have shown their advantage as light sources for several spectrometers.'-4 Visible and near infrared laser diodes have superior great advantages over the conventional sources. They have relatively large output power, narrow spectral linewidth and are inexpensive. The spectrometers constructed with the laser diodes provide detection limits as good as or better than those of conventional spectrophotometers.Eriochrome Cyanine R (ECR) is a triphenylmethane reagent like Chrome Azurol S and is used for the determination of aluminum in various matrices.5-' This reagent gives various complexes at pH 6 -7.5 and at ca. 620 nm in ternary systems with cationic surfactans like Zephiramine, cetyltrimethylammonium chloride (CTA), etc. To our knowledge, no publication has described the determination of aluminum with Eriochrome Cyanine R (ECR)-cetylpyridinium chloride (CPC) ternary complex using VIS-LD absorption spectrometer.In the present paper, we report on the use of a spectrometer constructed with a 3 mW VIS-LD (635±20 nm) and without a monochromator to determine aluminum in water samples by the ECR-CPC ternary complex method. Experimental Reagents and solutionsAll chemicals obtained from commercial sources were of analytical grade unless otherwise stated. All aqueous solutions were prepared using doubly distilled water. The aluminum stock solution, 1000 µg l-' was prepared from Al(N03)39H20 in 10.3 M HCl and standardized compleximetrically with EDTA. Portions were diluted daily for obtaining reference and working solutions.Eriochrome Cyanine R (Sigma Chem. Co., St. Louis) solution (0.2%(w/v)) was prepared daily by dissolving in water and adjusting final acid concentration to 10.3 M with HCI. Cetylpyridinium chloride (Sigma Chem. Co., St. Louis) solution (0.2%(w/v)) was prepared in water. Acetate buffer solutions were used to adjust pH to 6.0. ApparatusA spectrometer has been designed and constructed in our laboratory using VIS-LD as a light source. The semiconductor laser diode (Philips Model CQL-840 No : 9341013) used was operated at 3 mW. The wavelength at 635 nm was locked by a sensitive temperature controller (Peltier element, TEC 1-12705 Melcor Model Bi-Te) and a constant current laser diode power supply. The sample cell was a 1-cm standard optical glass cell. The light intensity was measured by a Hitachi HR-8101 (Si-P/N) photodiode (550-950 nm).A Hitachi Model 150-20 UV-VIS spectrophotometer with a to mm optical path cell was used for the verification of the results obtained with the VIS-LD absorption spectrometer. The measurements were performed at 635 nm. SamplingWater samples for aluminum determinations were collected from the municipal water supplies of Erciyes University and Bozanti Street and in the Mersin Bay at the Mediterranean Sea and in the Izmir Bay at the Aegean Sea in March 1996. The samples were filtered through a cel...

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