научная статья по теме A HIGHLY SENSITIVE SPECTROPHOTOMETRIC DETERMINATION OF ULTRA TRACE AMOUNTS OF AZIDE ION IN WATER AND BIOLOGICAL SAMPLES AFTER PRECONCENTRATION USING DISPERSIVE LIQUID–LIQUID MICROEXTRACTION TECHNIQUE Химия

Текст научной статьи на тему «A HIGHLY SENSITIVE SPECTROPHOTOMETRIC DETERMINATION OF ULTRA TRACE AMOUNTS OF AZIDE ION IN WATER AND BIOLOGICAL SAMPLES AFTER PRECONCENTRATION USING DISPERSIVE LIQUID–LIQUID MICROEXTRACTION TECHNIQUE»

ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2014, том 69, № 8, с. 880-886

ОРИГИНАЛЬНЫЕ СТАТЬИ

УДК 543

A HIGHLY SENSITIVE SPECTROPHOTOMETRIC DETERMINATION OF ULTRA TRACE AMOUNTS OF AZIDE ION IN WATER AND BIOLOGICAL SAMPLES AFTER PRECONCENTRATION USING DISPERSIVE LIQUID-LIQUID MICROEXTRACTION TECHNIQUE

© 2014 Reihaneh Hajiaghabozorgy, Ali Reza Zarei1, Shahram Ghanbari Pakdehi

Faculty of Chemistry and Chemical Engineering, Malek Ashtar University of Technology Tehran, P. O.Box 15875-1774, Iran 1E-mail: zarei1349@gmail.com Received 16.04.2012; in final form 05.12.2012

A simple and highly sensitive method developed for preconcentration and spectrophotometric determination of ultra trace amounts of azide ion (N-) in water and biological samples using dispersive liquid—liquid microextraction (DLLME) technique. The method is based on ion association formation of azide ion with malachite green and extraction of the ion pairing product using DLLME technique. Some important parameters, such as reaction conditions and the kind and volume of extraction solvent and disperser solvent were studied and optimized. The calibration curve was linear in the range of 0.5—50 ^g/L of azide ion. Also, the enrichment factor and extraction recovery obtained were 24.7 and 98.7%, respectively. The method was applied to the determination of azide ion in water and biological samples.

Keywords: azide ion, dispersive liquid—liquid microextraction, spectrophotometry, preconcentration, water and biological samples.

DOI: 10.7868/S0044450214080088

Sodium azide (NaN3) is widely used for a variety of technological applications including the production of pesticides and herbicides, biomedical sciences as preservative in diagnostic reagents, the automotive industry as a propellant for air bags, and for the production of detonators and other explosives in military purposes [1, 2]. Sodium azide is a highly toxic compound classified as a first-class poison [3]. In humans, it is rapidly absorbed through ingestion and inhalation and hydrolysis to hydrazoic acid that forms a strong complex with hemoglobin, and consequently blocks oxygen transport in the blood and prevents the cells of the body from using oxygen, when this happens, the cells die. So it is more harmful to the heart and brain than the other organs, because the heart and the brain use a lot of oxygen. The threshold limit value for sodium azide was reported 0.3 mg/m3 [4, 5].

Different methods have been reported for the determination of azide ion, such as titrimetry [6, 7], high performance liquid chromatography [8—10], gas chromatography [11], capillary electrophoresis [12, 13], ion chromatography [14—17], amperomety [18, 19], electron paramagnetic resonance [20], and spectrophotometry [21—25]. Some of these methods are time consuming and suffer from lack of sensitivity.

Azide ion is a rapidly acting potentially deadly chemical, thus, a fast and highly sensitive analytical method is necessary for determination of azide ion.

Sample preparation has a direct impact on accuracy, precision, and quantitation limits and is often the rate determining step of analytical process, especially when trace determination has been the purpose [26]. Liquid—liquid extraction (LLE) is a versatile classical sample preparation technique prescribed in many standard analytical methods. However, conventional LLE uses large amounts of potentially toxic organic solvents which are often hazardous and explosive [27]. To overcome these drawbacks, some techniques such as liquid phase microextraction and solid phase microextraction have been developed. Recent research trends involve miniaturization of the traditional liquid—liquid extraction principle.

Dispersive liquid-liquid microextraction is a new liquid phase microextraction based on ternary component solvent system that is similar to homogeneous liquid—liquid extraction method [28—30] and also cloud point extraction [31]. This method consists of two steps:

1) The injection of an appropriate mixture of extraction and disperser solvent into aqueous sample containing analytes. At this step the extraction solvent

400 pE Acetone containing 100 pE of 1,2-Dichlorobenzene

Sample solution

Injected rapidly

into sample solution using 1 mL syringe

Cloudy solution resulted from dispersion of extraction solvent

Dilution of sedimented phase with ethanol to 400 pE

Spectrophotometric determination (^max = 620 nm)

Sedimented phase

Fine droplets of 1,2-dichlorobenzene in aqueous solution

Fig. 1. Schematic diagram of dispersive liquid—liquid microextraction technique.

was dispersed into the aqueous sample as very ne droplets and analytes were enriched into it. Because of a large surface area between extraction solvent and aqueous sample, the equilibrium state is achieved quickly and extraction percent is independent of time. This is the most important advantage of this method.

2) The centrifugation of cloudy solution. After cen-trifugation, the determination of analytes in the sedi-mented phase can be performed by instrumental analysis. Rapidity, high enrichment factor, simplicity of operation and low cost are some of the advantages of this method.

This work is mainly focused on the suitability of DLLME combined with UV-Vis spectrophotometry for determination of azide ion. The influence of the different experimental parameters on the yield of the sample preparation step is described and discussed. To evaluate the applicability of the proposed method, it was then applied for determination of azide ion in water and biological samples.

EXPERIMENTAL

Apparatus. A Hitachi model 3310 UV-Vis spectro-photometer with 1 cm quartz micro cells was used for recording absorbance spectra. All spectral measurements were performed by using of the blank solution as a reference. A Hettich centrifuge (EBA 20) with 10 mL calibrated centrifuge tubes was used to accelerate the phase separation process.

Reagents. All chemicals used were of analytical reagent grade. Doubly distilled water was used throughout the work. A stock solution of 1000 mg/L of azide ion was prepared by dissolving 0.1548 g sodium azide (Merck) in water and diluting to 100 mL in a volumet-

ric flask. A 100 pM malachite green solution (Merck) was prepared by dissolving appropriate amount of this reagent in water and diluting to 100 mL in a volumetric flask. The acetate buffer solution (pH 5.2) was used to adjust the pH.

Recommended procedure. For the DLLME under optimum conditions, an aliquot of the solution containing of azide ion (so that its final concentration would be in the range of 0.5-50 pg/L), 1.0 mL of100 pM malachite green solution and 1.0 mL of acetate buffer solution were placed in a 10 mL screw cap glass test tube with conical bottom and the contents were diluted with water. 400 ^L of acetone (as a disperser solvent) and 100 ^L of1,2-dichlorobenzene (as extraction solvent) were mixed and injected rapidly into the aqueous sample by syringe. A cloudy solution was formed in the test tube. At this step, the analyte in water sample was extracted into the fine droplets of 1,2-dichlorobenzene. The mixture was centrifuged for 2.0 min at 4000 rpm. Afterward the dispersed fine droplets of 1,2-dichloroben-zene were sedimented on the bottom of test tube. The supernatant aqueous phase was readily decanted with a Pasteur pipette. The remained organic phase was diluted to 400 pL with ethanol and the absorbance measured at 620 nm against blank in a 1 cm quartz micro cell. The entire scheme of the procedure is shown in Fig. 1.

Pretreatment of biological samples. Separation of azide ion from biological samples (serum and urine) was carried out according to reference [21]. 1.0 mL of sample, 2 mL of1.0 M sodium hydroxide and 0.5 mL of 30% hydrogen peroxide were transferred to distillation flask. After 3 min, it was added 3 mL of freshly prepared alkaline 2.0% (w/v) SnCl2 solution. Then, 5 mL of saturated potassium hydrogen sulphate was added and the

X, nm

Fig. 2. Absorption spectra of the ion pairing product of azide ion with malachite green after DLLME. Conditions of azide ion, ^g/L: 1 - 0.50, 2 - 1.0, 3 - 2.0, 4 - 3.0, 5 -5.0, 6 - 10, 7 - 20, 8 - 30, 9 - 40, 10 - 50; 10 ^M malachite green; pH 5.2.

0.4 г

0 5 10 15 20

Concentration of malachite green,

Fig. 3. Effect of malachite green concentration on the ab-sorbance of the system. Conditions: 10 ^g/L azide ion, pH 5.2.

0.3 г

23456789 pH

Fig. 4. Effect of pH on the analytical signals. Conditions: 10 ^g/L azide ion, 10 ^M malachite green.

distillation apparatus connected up. The distillation was carried by passing nitrogen gas and azide ion was collected in 25 mL of 0.05 M sodium hydroxide as absorber. After distillation, the distilled portion was diluted to 50 mL in a volumetric flask. Then an appropriate aliquot was treated under the recommended procedure for DLLME and subsequent determination of azide ion.

RESULTS AND DISCUSSION

In acetate buffer, azide ion reacts with malachite green to form an ion pair complex that can be extracted into 1,2-dichlorobenzene. Therefore, it can be a suitable method for separation and preconcentration of azide ion by DLLME. Figure 2 shows the visible absorption spectra of the ion pair complex of azide ion with malachite green after DLLME, which exhibits a maximum absorbance at 620 nm. Therefore, all absor-bance measurements were performed at this wavelength. For achieving the highest efficiency and sensitivity in DLLME of azide ion, the influence of effective variables was investigated and optimum conditions were obtained.

Effect of the malachite green concentration. The effect of malachite green concentration on the absor-bance of the system was investigated within the range 2.5—15 ^M. The results revealed that the absorbance increased by increasing reagent concentration up to 10 ^M, and remained nearly constant at higher concentrations (Fig. 3). Therefore, a concentration of 10 ^M malachite green was applied in the proposed method.

E

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