UDC 613.632.4-074

A Method for Determining Dinil in Workplace Air

Yu. V. Marich and V. D. Borskii

Chernigov Regional Sanitary and Epidemiological Station

Dinil is currently determined by the method of Z. M. Pimenova and A. P. Martynova (M. S. Bykhovskaya et al.; E. A. Peregud and E. V. Gernet). We have developed a method with a number of advantages: the sensitivity of the determination is increased; the use of highly volatile ethyl ether as an extractant is eliminated, reducing laboratory air contamination and preventing possible distortion of the analytical results caused by the appearance of an uncharacteristic yellow color in the solution being measured colorimetrically; the use of concentrated alkali solutions is eliminated, preventing the possibility of burns; the laborious shaking of the contents of test tubes is replaced by mixing mutually soluble components; the time required for the final color to develop is reduced from 20–30 to 2 min, and the stability of the color is increased; and a stable matching color scale has been developed, with its formulation supplied as ready-made tables or composition curves.

The method is based on the colorimetric determination of a pinkish-violet product formed by the reaction of nitro derivatives of dinil with alkali in a toluene–acetone medium, followed by acidification of the solution. The sensitivity of the method is 1 μg of dinil in 2 ml of nitrating mixture. Aromatic hydrocarbons and their nitro and halogen derivatives interfere with the determination.

The following reagents are required for the determination: nitrating mixture: 10 g of chemically pure ammonium nitrate, dried at approximately 80° and then dissolved in 100 ml of chemically pure concentrated sulfuric acid; toluene; acetone; normal sodium hydroxide solution; 2% sodium carbonate solution colored straw-yellow with methyl orange; cobalt chloride: 2 g of the hexahydrate dissolved in 100 ml of water; salicylic acid: dissolve 1 g in 1 l of hot water and cool; ferric salicylate is prepared by mixing solutions of ferric ammonium alum and salicylic acid; ferric ammonium alum solution: dissolve 2 g of uneffloresced salt in 100 ml of water, adding 0.5 ml of concentrated sulfuric acid; dilute 1 ml of this solution to 100 ml with salicylic acid solution; the resulting ferric salicylate solution remains stable for a long time; acetic acid diluted with water (1:1).

For sampling, 2 L of air is passed over 10–15 min through an absorber fitted with a porous plate and containing 2 mL of nitrating mixture.

Fifteen minutes after sampling (or later), the contents of the absorber are transferred to a small flask or test tube; the absorber is rinsed twice with 5 mL portions of water, which are combined with the nitrating mixture. The liquid is cooled to 30°C or below and transferred to a separatory funnel. The flask is rinsed with 2–3 mL of water, which is poured into the separatory funnel. Two milliliters of toluene is measured into the funnel, and the mixture is shaken vigorously for 2 min. After the layers separate, the aqueous layer is removed, and the extract of the dinyl nitro derivatives is washed with 5 mL of a 2% soda solution. If the wash liquid becomes colored, another 1–2 mL of soda solution is added to the funnel. After separation of the aqueous layer, the extract is poured into a small bottle or test tube with a ground-glass or polyethylene stopper. A 1 mL portion of the extract is transferred to a colorimetric tube, and 8 mL of acetone and 1 mL of 0.1 N sodium hydroxide are added. The liquid is mixed, and after approximately 2 min, 2 drops of acetic acid are added and the color is measured.

A calibration scale is prepared from aliquots of a standard solution of dinyl in nitrating mixture, each made up to 2 mL with nitrating mixture. If the reagents used are sufficiently pure and give a colorless blank, a simulated scale or a single extract of nitrodinyl may be used.

All glassware used should be thoroughly cleaned of acids and toluene. On contact with the diluted sample at temperatures above 30°C, toluene can form dinitrotoluene, which interferes with the analysis.

A simulated scale for the approximate determination of dinyl is prepared by mixing solutions of cobalt chloride, ferric salicylate, and salicylic acid according to the proportions given in Table 1.

Table 1. Simulated scale for the approximate determination of dinyl

The ethyl ether used in the existing method for determining dinyl is extremely volatile and flammable, appreciably soluble in water, and lost during extraction. Even the highest-purity ether can develop peroxide compounds during storage; these convert dinyl nitro derivatives into nitrophenol-type compounds, causing the final color of the solutions to acquire an uncharacteristic yellow tinge.

We investigated the possible use of several other extractants, of which benzene, toluene, and chloroform proved suitable for this purpose. The method was subsequently developed using toluene, a less volatile and less toxic substance. Unlike ether, toluene is practically insoluble in water and in aqueous acid and alkali solutions. Its initial volume remains unchanged during extraction, eliminating the need for additional measurements and replenishment; possible losses of the final extract do not cause analytical error. On this basis, toluene may be considered a much more suitable extractant than diethyl ether for the determination of dinyl.

In selecting the optimum quantities of extractant and acetone for a single analysis, we sought to achieve complete extraction of the nitro derivatives of dinil from 15 ml of the aqueous phase. It was necessary to prevent the toluene–acetone solution from separating into layers upon addition of aqueous alkali, to ensure the optimum ratio of toluene to acetone in the final solution for color development, and to obtain a final solution volume of 10–11 ml for convenient visual and photoelectric colorimetry. Accordingly, we examined the completeness of extraction of 200 µg of dinil as nitro derivatives from solutions containing 2 ml of nitrating mixture and 8, 18, or 28 ml of water. Extraction was carried out with 2 and 5 ml of toluene. After phase separation and removal of the extract, the aqueous layers were extracted again and found to contain no more than 0.5 µg of dinil, indicating that extraction into 2 ml of toluene was practically complete.

Similar studies were conducted with 10 ml of ethyl ether and an aqueous-phase volume of 10 ml. In this case, the amount of unextracted dinil was determined to be 0.7 µg.

The optimum ratio of toluene to acetone volumes for color development was determined. When more than 2 ml of toluene is present in 10 ml of the mixture, the final color of dinil after addition of aqueous alkali becomes less intense and acquires a yellow tint. A ratio of 1 ml of toluene per 10 ml of mixture was adopted to ensure satisfactory results.

For full development of the color of the final product, it is sufficient to add 0.1 ml of 0.1 N alkali, but with this quantity of alkali the reaction proceeds slowly, and the alkali may be insufficient if acidic impurities are present in the mixture. We considered it expedient to add 1 ml of 0.1 N sodium hydroxide to the solution. The color then reaches its maximum intensity after approximately one minute, but after 5–8 minutes it begins to fade under the action of excess alkali. Addition of 1–2 drops of a 50% acetic acid solution changes the pink color to a more stable pink-violet. The samples remain suitable for colorimetry for up to half an hour.

Unlike concentrated aqueous alkali solutions, dilute solutions of up to 0.15 N are soluble in the toluene–acetone system and react more rapidly. Mixing and a 30-minute exposure period are no longer required, and the final solution remains homogeneous, improving the conditions for colorimetry.

Using the proposed method and a sufficiently pure nitrating mixture, quantities of dinil as small as 0.25 and 0.5 µg can be reliably distinguished from each other and from the control sample. With the ether–acetone method, this is practically impossible.

Table 2

Results of dinil determination

Comparative analyses were performed on air containing different concentrations of dinil. Two liters of air were passed through an absorption device with a porous plate, filled with 4 ml of nitrating mixture. The mixtures were diluted with water to 30 ml; 15 ml of each was analyzed by the proposed method and the remaining 15 ml by the ether–acetone method. Some of the data obtained are presented in Table 2.

In examining the rate of nitration of dinil, we found that, after its addition to the nitrating mixture and mixing, the final stage of nitration is reached after 2 minutes at room temperature.

References

Bykhovskaya, M. S., Ginzburg, S. L., and Khalizova, O. D. Methods for the Determination of Harmful Substances in Air. Moscow, 1966, p. 298. — Peregud, E. A., and Gernet, E. V. Chemical Analysis of Air in Industrial Plants. Moscow–Leningrad, 1965, p. 36.

Received March 4, 1970.