GLYCOLS: METHOD 5523, Issue 1, dated 15 May 1996 - Page 3 of 5
c. d. e. 10.
through the sampler at 1 L/min for 60 min. Cap the ends of the tubes and allow to stand overnight. Desorb (steps 5 through 7) and analyze together with standards and blanks (steps 11 and 12). Prepare a graph of DE vs. µg analyte recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graphs are in control.
MEASUREMENT: 11.
Set gas chromatograph according to manufacturer’s recommendations and to conditions given on page 5523-1. Inject 1-µL sample aliquot manually using solvent flush technique or with autosampler. NOTE: If peak area is above the linear range of the working standards, dilute with methanol, reanalyze and apply the appropriate dilution factor in the calculations. 12. Measure peak areas.
CALCULATIONS: 13.
14.
Determine the mass, µg (corrected for DE), of each glycol found in the sample front (W f) and back (Wb) sorbent sections, and in the average media blank front (B f) and back (Bb) sorbent sections. NOTE: If Wb > Wf /10, report breakthrough and possible sample loss. Calculate concentration, C, of each analyte in the air volume sampled, V (L):
C
(Wf Wb Bf Bb) V
,mg/m 3
EVALUATION OF METHOD: The method was evaluated for six glycols (ethylene, propylene, 1,3-butylene, diethylene, triethylene, and tetraethylene). Desorption efficiency (DE) was determined by spiking known amounts of each glycol in methanol solution onto the glass fiber filter plug of the XAD-7 OVS tubes, drawing air through the spiked tubes at 1 L/min for 60 min, and analyzing. Recovery data along with LODs and LOQs for each analyte are listed in Table 2. When stored at 5 C, ethylene glycol samples on XAD-7 OVS tubes were stable for 14 days, and the other glycols were stable up to 28 days. Glycol aerosols were generated at three concentration levels (6 samples per concentration) from a ROSCO™ Model 1500 Fog Machine. Precision [as calculated from the pooled relative standard deviation ( r)] and mean bias for the glycols are as follows: Analyte Ethylene glycol Propylene glycol 1,3-butylene glycol Diethylene glycol Triethylene glycol Tetraethylene glycol (2 levels)
Range Studied (µg/sample) 33 to 218 26 to 187 34 to 178 68 to 219 33 to 201 32 to 197
Precision ( r) 0.043 0.062 0.054 0.047 0.075 0.035
Bias -15% -3.2% -0.5% -0.2% -4.0% +20%
The low recovery for ethylene glycol possibly may be attributed to increased volitility when sampled at 1 L/min [1]. Although hexylene glycol is separated by the chromatographic conditions given in the method, no evaluation of sampling or analytical parameters was done for this compound. REFERENCES: [1]
Pendergrass, S.M. [1994].
Development of a sampling and analytical methodology for the
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
