Comparison of liquid medium and charcoal tube sampling methods for ethylene oxide

A modification of the NIOSH S-286 charcoal tube sampling method for ethylene oxide (ETO), by sue of a 600 mg versus a 150 mg charcoal tube, was compared to a wet collection method for ETO employing a liquid medium sampler (LMS) containing 10 mL of 0.1 N sulfuric acid and 10 mL of 3 mm diameter glass beads. Four concentrations of ETO were generated, 1, 5, 10 and 35 ppm ETO, and ten samples were collected by each method at each concentration. The physical conditions during sampling were held constant at 25°Cm 25% relative humidity (RH), and constant sampling flow rate. A manifold system was used to deliver the controlled ETO gas concentration. An infrared analyzer was used to detect changes in ETO gas concentration during sampling. The purpose of the comparison was to determine which method might be better for a four-hour sampling period for the concentrations and conditions given above. The results for the modified charcoal tube method were better than those of the LMS sampling method. A Wilcoxon matched-pairs signed-rank test was performed to test the equality of the methods' medians; the medians were not equal to a two-tailed P-value of 0.005. The overall mean collection efficiency for the charcoal tube method was 102% and that for the LMS sampling method was 32%, A paired T-test was used to compare the equality of the two methods' mean collection efficiencies. The mean were not equal at a two-tailed P-value of 0.001. The mean collection efficiencies at each concentration, plus the minus one standard deviation were plotted, to view the results graphically. The charcoal method obviously came much closer to the 100% collection efficiency that did the LMS sampling method.