Effect of interferents on the performance of direct-reading organic vapor monitors

Figures & data

Table 1. Test matrix indicating sample numbers and independent variables

	Cyclohexane:interferent ratio
Concentration (ppm)	0%:100%	33%:67%	50%:50%	67%:33%	100%:0%
30	5	5	5	5	1
150	5	5	5	5	1
300	5	5	5	5	1
475	5	5	5	5	1	Total	× 5 Replicates
Total	20	20	20	20	4	84	420

Table 2. Frequency (in percentage) of trials where monitor measurement was below the detection limit (false negatives) in the presence of a known concentration

Monitor	Concentration (ppm)
	Combined^a		30		150		300		475
	Number of trials^b	Percent	Number of trials	Percent	Number of trials	Percent	Number of trials	Percent	Number of trials	Percent
PID1	114	27.1%	79	75.2%	18	17.1%	13	12.4%	4	3.8%
PID2	76	18.1%	62	59.0%	9	8.6%	5	4.8%	0	0.0%
PID3	76	18.1%	61	58.1%	8	7.6%	6	5.7%	1	1.0%
PID Group	266	21.1%	202	64.1%	104	33.0%	24	7.6%	5	1.6%
FID1	15	3.6%	4	3.8%	4	3.8%	2	1.9%	5	4.8%
FID2	27	6.4%	9	8.6%	6	5.7%	5	4.8%	7	6.7%
FID3	19	4.5%	2	1.9%	7	6.7%	5	4.8%	5	4.8%
FID Group	61	4.8%	15	4.8%	17	5.4%	12	3.8%	17	5.4%
SAP1	3	0.7%	3	2.9%	0	0.0%	0	0.0%	0	0.0%
SAP2	0	0.0%	0	0.0%	0	0.0%	0	0.0%	0	0.0%
SAP3	0	0.0%	0	0.0%	0	0.0%	0	0.0%	0	0.0%
SAP Group	3	0.2%	3	1.0%	0	0.0%	0	0.0%	0	0.0%

Notes: n = 420 trials for individual monitors and n = 1260 trials for monitor groups. ^aCombined data from all four concentrations (30, 150, 300, and 475 ppm). ^bNumber of trials where the monitor measurement was below the detection limit.

Table 3. Frequency (in percentage) of trials where monitor measurement (mixed response factor applied) was over twice the tube value

	Concentration (ppm)
	Combined^a		30		150		300		475
Monitor	Number of trials^b	Percent	Number of trials	Percent	Number of trials	Percent	Number of trials	Percent	Number of trials	Percent
PID1	83	19.8%	6	5.7%	15	14.3%	36	34.3%	26	24.8%
PID2	122	29.1%	13	12.4%	33	31.4%	31	29.5%	45	42.9%
PID3	123	29.3%	14	13.3%	28	26.7%	42	40.0%	39	37.1%
PID Group	328	26.0%	33	10.5%	76	24.1%	109	34.6%	110	34.9%
FID1	4	0.95%	2	1.9%	0	0.0%	2	1.9%	0	0.0%
FID2	67	16.0%	21	19.1%	18	17.1%	16	15.2%	12	11.4%
FID3	29	6.9%	8	5.7%	10	9.5%	4	3.8%	7	6.7%
FID Group	100	7.9%	31	9.8%	28	8.9%	22	7.0%	19	6.0%
SAP1	123	29.3%	40	38.1%	41	39.1%	37	35.2%	5	4.8%
SAP2	73	17.4%	21	20.0%	19	18.1%	18	17.1%	15	14.3%
SAP3	54	12.9%	34	32.3%	10	9.5%	10	9.5%	0	0.0%
SAP Group	250	19.8%	95	30.2%	70	22.2%	65	20.6%	20	6.4%

Notes: n = 420 trials for individual monitors and n = 1260 trials for monitor groups. ^aCombined data from all four concentrations (30, 150, 300, and 475 ppm). ^bNumber of trials where the monitor measurement was more than twice the tube value.

Figure 1. Mean monitor concentration in ppm with 95% confidence intervals. Tube = charcoal tube; mPID = PID with mixed response factor applied; mFID = FID with mixed response factor applied; cPID = PID with cyclohexane response factor applied; cFID = FID with cyclohexane response factor applied; PID = PID with no response factor applied; FID = FID with no response factor applied.

Figure 2. Mean percentage charcoal tube values (%CT) with 95% confidence intervals. CYC = cyclohexane; HEX = hexane; TOL = toluene; MEK = methyl ethyl ketone; TCE = trichloroethylene; and MIX = mixture of all interferents.