QUANTITATIVE DETERMINATION OF BENZENE, TOLUENE AND XYLENE IN SOLVENT AND IN AIR BY GAS-CHROMATOGRAPHY

In the air of workshops, there very frequently exist benzene, toluene and xylene vapors in mixture, but it is difficult to quantitatively determine each of them from the mixed vapor, while it is important because benzene is more toxic than the other. The determination was done by means of gas-chromatography. 1) First, the method of quantitative determination of benzene, toluene and xylene in solvent was studied. The most suitable condition in the gas-chromatography was as follows: Stationary phase D.O.P 200cm Column temperature 125°C Sample inlet temperasure 145°C Carrier gas Hydrogen Gas flow rate 40ml/min Detector 64-128mV Sensitivity 100mA Sample quantity 0.02-0.05ml The minimum determinable concentration of solvents by this method was 0.1% and the error was within 0.5% of the value determined. 2) As to the quantitative determination of benzene, toluene and xylene in air, the method to analyse colorimetrically after their separation by gas-chromatography is accompanied with gross error and of no practical use, because the vapors are condenced near the outlet. 3) When the air was supplied into the gas chromatograph without any procedure, the minimum determinable value was about 75 p.p.m. for 100 ml. of air, which is the muximum amount that can be supplied. 75 p.p.m. is too high to be the desirable minimum value. Hence a concentration process is required for the quantitative determination of benzene, toluene and xylene in the air. 4) In order to concentrate benzene, toluene and xylene in the air, one liter of air was passed at the rate of 100 milliliter a minute through a small column filled up with 1 gm .of solid support (DOP) and cooled by dry ice. By such a procedure, the column showed a good retentive capacity, and the result was satisfactory even when two liters of air was passed at the same rate. 5) In order to keep from the disturbance by steam, it is necessary to set phcphorus pentoxide column before the concentriation column during air-sampling. Silicagel and molecularsieve are inadequate as desiccating agents, because these also absorb benzene, toluene and xylene as well as steam. 6) When the concentration column including benzene, toluene and xylene are attached to the inlet of the gas-chromatograph and heated at 130°C, their vapors are sent quickly into the gas-chromatograph with carrier gas. Thus a satisfactory gas-chromatogramm is obtained. 7) In the quantitative determination of benzene, toluene and xylene vapors in air, the adequate column temperature is 100°C instead of 125°C as applied to the analysis of solvents, because at 125°Cthe vapors are not separated sufficiently from steam. The desirable flow rate of the carrier gas is 60 ml/min in consideration of the extention of the retention time that follows the fall of the column temperature. The other conditions are the same as the analysis of solvents, except for changing of sensitivity to 2 mV. 8) Quantitative determinations by the method mentioned above were made in air samples including benzene, toluene and xylene vapors in the known concentration. The results indicated that the method was fairly accurate. 9) The minimum determinable concentration by this method applying one liter of air is apploximately 2 p.p.m. for benzene, 4 p.p.m. for toluene and 10 p.p.m. for xylene, and these are equivalent to about 0.003 mV (4mm) in the peak height of gas-chromatogramm. 10) In application of this method to the field measurment, the air samples are taken into the concentration columns with phoshorus pentowide columns. They are maintainable for a long time if the columns are corked tightly. It is also desirable to know previously what kinds of substances with low boiling point exist together, because they may disturb determination of benzene, toluene and xylene.