Development of a photometric method for the quantitation of benzene in medical benzine

Status:

completed 12/2020

Aims:

Medical benzine (to DAB standards as used in Germany) is a mixture of saturated C6 and C7 hydrocarbons obtained from petroleum in a boiling range from 30 °C to 85 °C. As a consequence of this manufacturing process, the product may contain benzene. Medical benzine has traditionally been used in Germany to remove plasters and plaster residues and to degrease the skin. The permissible benzene content and its quantitation in medical benzine were – and still are – governed by the applicable editions of pharmacopoeias (such as the German DAB). Whereas benzene was still found in medical benzine in concentrations of up to 10% in the 1960s and 1970s, medical benzine currently used must be completely free of benzene. Other applications include use as a cleaning agent, for the removal of stains and as a solvent. Owing to its chemical composition, exposure to medical benzine may lead to disorders of the blood and the haematopoietic and lymphatic systems induced by benzene (formally recognized occupational disease (BK) 1318) and polyneuropathy and encephalopathy induced by organic solvents or their mixtures (BK 1317). Publications concerning these occupational diseases therefore also consider medical benzine as one of the possible sources of hazardous substances giving rise to them.

Up until publication of the first supplement to the DAB 10 in 2005, the benzene concentration was determined photometrically; until 1991, the maximum benzene content was stated not as a concentration in percentage by volume, but as the absorbance measured by the analytical system.

The purpose of this project was to enable the benzene concentrations to be determined by analysis of medical benzine mixtures with adjusted benzene concentrations under the conditions described up to DAB 9 in cases where only a measured value for a product used in the past is available.

Activities/Methods:

The first step involved determining the working range and thus also the absolute limit of quantitation of the photometer with respect to the benzene concentration under the measurement conditions described in DAB 9.

Based on the result, several mixtures with defined benzene concentrations were to be prepared from a standard commercial benzene-free medical benzine. The benzene content of these mixtures was ideally to cover the working range determined beforehand. Following analysis of the mixtures in the photometer, a function was to be defined representing the relationship between the measured value (absorbance) and the specified concentration of benzene in medical benzine. This in turn was to enable the benzene content to be determined from a given absorbance.

Results:

The working range of the spectrophotometer permits photometric quantitation of benzene up to a concentration of 4% in medical benzine to the specifications of DAB-DDR 75 and of 0.8 % in medical benzine to the specifications of DAB-DDR 87.

For each of the two analytical procedures, a linear working range was determined for the relationship between the measured absorbance and the benzene concentration in the test solution. At absorbances of between approximately 0.07 and approximately 0.7, this range corresponds to a benzene concentration of 0.1% to 1.0% according to DAB-DDR 75 and 0.02% to 0.2% according to DAB-DDR 87.

The linear working ranges cover the absorbances of 0.5 and 0.31 specified in the DAB-DDR 75 and DAB-DDR 87 regulations respectively as a measure of the permissible benzene concentration in medical benzine.

For given absorbances of a medical benzine, the benzene content can be calculated by means of the following formulae:

• To DAB-DDR 75: c(benzene) = (absorbance(sample) - 0.008)/0.7003 = X%
• To DAB-DDR 87: c(benzene) = (absorbance(sample) - 0.0008)/3.403 = X%

An absorbance of 0.5 corresponds to a benzene concentration of 0.7% according to DAB-DDR 75, and an absorbance of 0.31 to a benzene concentration of 0.091% according to DAB-DDR 87. Available absorbance values from studies conducted prior to 1991 can now be converted with ease to the corresponding benzene concentration and used in investigations into suspected cases of occupational disease.

A report has been submitted to the German Social Accident Insurance Institution for the health and welfare services (BGW). The results will be taken into account during revision of the IFA's ring binder concerning benzene.

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