Spectrophotometric determination of trace amounts of acetylacetone in aqueous solutions

MICROCHEMICAL

JOURNAL

36, 297-300 (1987)

Spectrophotometric Determination of Trace Amounts Acetylacetone in Aqueous Solutions S. A. Department

B. B.

RAHIM,~

of Chemistry, Received

IBRAHEEM,

AND

W. A.

BASHIR

of Science, University of Mod, April 10, 1987; accepted June 1, 1987 College

of

Mod,

Iraq

A sensitive spectrophotometric method for the determination of trace amounts of acetylacetone in aqueous solution is carried out. In the presence of bicarbonate solution, diazotized anthranilic acid reagent reacts rapidly with acetylacetone to form a yellow-colored compound with maximum absorption at 330 nm, which is water-soluble and reasonably stable. Adherence to Beer’s law is observed in the range 20-200 kg of acetylacetone/25 ml, with a molar absorptivity of 19.5 x lo3 liters mol-t cm-t, a sensitivity index of 0.005 1 )*g cm-*, relative to + 0.3 to - 0.9%, and a relative standard deviation of OS- 1.4%, depending on the concentration level. 0 1987 Academic Press. Inc.

INTRODUCTION

Acetylacetone (pentane-2,4-dione) is an important organic compound in both industrial fields and the laboratory. Spectrophotometric methods, in addition to their analytical characteristics, allow the determination of trace amounts of various compounds. It is, therefore, not unexpected that most of the used and applied methods call for spectrophotometry. The spectrophotometric methods available for the determination of acetylacetone are very few (Z-3) and are not completely satisfactory from the analytical point of view. One method (I), based on the coloration of the hydrazone derivative of the compound in alkaline medium, seems to be slow unless heated for 30 min. The two other methods (2, 3) either resort to extraction and are not sensitive (2) or are lengthy and suspected to suffer from interference (3). Therefore, the development of an analytical photometric method for the intended compound seems desirable. In the course of our studies on the analysis of organic compounds, we have found that diazotized anthranilic acid reacts rapidly and sensitively with acetylacetone in aqueous solution to give, in the presence of alkaline solution, a yellow water-soluble and relatively stable colored compound. The intended reagent has been used for the determination of acetone in acetic acid (4), of ethanol in methanol (5), and of acetone in aqueous solution (6). MATERIALS

AND METHODS

Apparatus

The spectrophotometric measurements were carried out on a pye Unicam 30 uv double-beam spectrophotometer using l-cm silica glass cells. t To whom correspondence

SP

should be addressed. 297 0026-265X/87 $1 SO Copyright 0 1987 by Academic Press, inc. All rights of reproduction in any form reserved.

298

RAHIM,

IBRAHEEM,

AND

BASHiR

Reagents All chemicals used were of reagent grade. Acetylacetone solution. A standard 1000 ppm solution of acetylacetone in aqueous solution was prepared. Less concentrated solutions were made by dilution with distilled water. Diazotized anthranilic acid solution. A 0.7-g sample of anthranilic acid was dissolved in about 70 ml of distilled water (heating may be required), 0.35 g of sodium nitrate was added, and the solution was stirred vigorously and cooled to 0°C in ice. Then 2 ml of concentrated hydrochloric acid solution was added with stirring. After 15 mitt, the volume was adjusted to 100 ml with additional cooled (YC) distilled water. This reagent solution is stable for about 1 day (6). Sodium bicarbonate solution. A 10% (w/v) solution was prepared. Foreign compound solution. A 1000 ppm solution of each compound tested was prepared. Procedure and calibration graph. To a series of 25ml volumetric flasks were transferred from about 20 to 200 kg of acetylacetone, 0.5 ml of diazotized reagent solution, 1 ml of bicarbonate solution, and distilled water to the mark. The flasks were settled for 1 min, and the absorbances were read, against a reagent blank prepared in the same manner but without acetylacetone, at 330 nm using l-cm cells. The color was stable for about 15 min. A rectilinear calibration graph passing through the origin was obtained, indicating that Beer’s law was followed over the concentration range of 20-200 kg of acetylacetone in a final volume of 25 ml, i.e., 0.8-8 ppm. The molar absorptivity, calculated in the region of least photometric error and at the wavelength of maximum absorption, was found to be 19.5 x lo3 liters mol-t cm-l, with a Sandell sensitivity index (7) of 0.0051 ug cme2. For the subsequent experiments, 100 pg of acetylacetone was taken and final volumes were brought to 25 ml. RESULTS

AND DISCUSSION

Absorption spectrum. When acetylacetone in aqueous solution was treated with diazotized anthranilic acid reagent solution according to the recommended procedure, an absorption peak was obtained. The intense absorption at 330 nm, characteristic of the yellow compound, was used in all subsequent studies; The reagent blank shows a slight absorbance at the wavelength of maximum absorption. Effect ofanthranilic acid amount. The effect of the amount of anthranilic acid in the diazo reagent solution was first examined. The color reaction was performed using O.l- to l-g amounts of acid. The experimental data revealed that increasing acid amounts led to absorbance increases and reached a maximum value at 0.7 g. Higher amounts decreased the absorbance slightly. Therefore, the above amount was recommended in the procedure when a loo-ml volume of diazo reagent solution was prepared. Replacing anthranilic acid with orthanilic acid could not give rise to a more useful result. Effect of nitrite amount. Keeping the optimum amount of anthranilic acid con-

SPECTROPHOTOMETRIC

DETERMINATION

OF ACETYLACETONE

299

stant, the amount of sodium nitrite for maximal absorbance was sought. The color reached maximum formation when 0.35 g of sodium nitrite was used for diazotizing anthranilic acid. Effect of mineral acid concentation. A diazotization reaction is well known to take place in acidic medium. In this respect, hydrochloric, nitric, sulfuric, and phosphoric acids were tried. The experimental results showed that maximum color formation could be obtained on using 1.8-2.3, 2, OS- 1.0, and OS- 1.5 ml of the concentrated acids, respectively. The color became more stable when hydrochloric or phosphoric acid was tried. A 2-ml volume of concentrated hydrochloric acid solution was recommended for the diazotization process. Volume of diazo reagent solution. The volume of the diazo reagent for maximum intensity was next examined. A 0.4- to 0.6-ml sample of the reagent gave maximum absorbance practically. A OS-ml sample of reagent was selected for the procedure. Effect of sodium bicarbonate solution. Neither acidic nor neutral solutions could develop the color, while alkaline solutions developed the color rapidly. Potassium and sodium hydroxides and sodium carbonate, bicarbonate, and acetate solutions were used. The experimental investigations revealed that the resultant color became more stable, although less intense, with decreasing base strength down to sodium bicarbonate; sodium acetate could not develop the color. A 0.8to 1.2-ml sample of 10% sodium bicarbonate solution gave the useful results, and 1 ml of the prescribed bicarbonate solution was incorporated into the procedure. Order of addition of reagents. For maximum and stable absorbance readings, the order cited in the procedure was followed. Effect of time on color development. A study of the time effect on color development showed that the color formed practically completely in about 1 min and remained so for about 1.5 min, after which a gradual slow decrease was observed. Trials attempted to further increase color stability were without effect. Accuracy and precision, and sensitivity. Under the optimized conditions, the accuracy and precision of the method were checked. The results, from five determinations of standard solutions, are compiled in Table 1, and indicate a reliable method. The sensitivity of the method was 0.0051 kg C m-2. The interfering effect of some diverse organic compounds was examined by using an aliquot of sample solution containing 100 p.g of acetylacetone and the

TABLE 1 Accuracy and Precision of the Method Acetylacetone taken (cLd 20 150 200 a Relative error. b Relative standard deviation.

Accuracy (error %o)’

Precision (RSD)b

-0.8 +0.3 -0.9

1.4 0.6 0.5

300

RAHIM,

IBRAHEEM,

AND BASHIR

TABLE 2 Interfering Effect Foreign compound Acetone Acetonitrile I-Butanol Cyclohexanone Cyclopentanone NJ-Dimethylforamide Dimethylsulfoxide Dioxane Ethanol Ethylacetate Methanol Oxalic acid I-Propanol 2-Propanol

foreign compound, and applying tained are shown in Table 2.

Amount added (pg)

Error (%)

1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000

+0.3 -1.2 -1.7 +o.g +0.6 +0.8 +0.9 -0.9 +0.5 +I.6 +1.2 +1.2 -1.9 - 1.7

the recommended

procedure.

The results ob-

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