Friday, January 30, 2015

Real-Time Detection of ppb Levels of Benzene in Industrial Atmospheres

Accepted for presentation at the 2015 American Industrial Hygiene Conference and Exposition on Wednesday June 3, 2015 at SPCC: 355 C


Real-Time Detection of ppb Levels of Benzene in Industrial Atmospheres 
By: J.N. Driscoll and Jennifer Maclachlan

Objective
The OSHA method for benzene involves the collection on a charcoal tube and return to the lab, for desorption with carbon disulfide and analysis by gas chromatography with a flame ionization detector (GC-FID). While the PID is an ideal tool for detecting low or sub ppm levels of benzene, it responds to all VOC’s, so the measurement of benzene at or below 1 ppm is not very accurate.  We propose to develop a hand held GC with a PID to detect to detect low ppb of benzene in real time and “on site”.
Method
The hand held GC weighs less than 3 pounds, is able to operate for >6 hours on a battery,is easy to operate and has a small external tank for carrier gas (nitrogen) that can be clipped onto a belt. The hand held GC stores the peak height and concentration data. If a chromatogram is needed, up to 20 are stored in memory and if more are needed, the 0-1 VDC analog output can be connected directly to a PC with PeakWorks.


Results

A permeation tube was used to generate ppb levels of benzene in air. A chromatogram of 500 ppb of benzene in air is shown in the figure below. The detection limit for benzene is approximately 5 ppb. The analysis time is 2 minutes presently but with some optimization, it can be reduced to about 1 minute which would be ideal.  






Conclusions
The GC/PID method provides a very rapid and sensitive technique for the analysis of benzene  at ppb levels. The precision of benzene for 5 samples at 1/10th of the PEL was excellent at 5.8%. A special precolumn with back flushing removes interferences.


Section: Real Time Detection Systems #RTDSC #RealTimeDetection

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