Page:NIOSH Manual of Analytical Methods - 3701.pdf/2

 TRICHLOROETHYLENE by portable GC: METHOD 3701, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS: 1.

2.

EQUIPMENT:

Trichloroethylene (TCE)* in air, working standards prepared in the field by filling Tedlar bags with commercially prepared and certified standards (preferred) or prepared in the field by injecting known amounts of pure trichloroethylene into Tedlar bags containing a metered volume of pure air or nitrogen. Cylinder of air, nitrogen or helium for use as carrier gas and field blanks.



See SPECIAL PRECAUTIONS.

1. Portable gas chromatograph (GC), with photoionization detector, preferably with gas sampling loop and (if appropriate) strip chart recorder. 2. Personal sampling pump, 0.02 to 0.05 L/min or other rate suitable for filling sample bag, with flexible connecting tubing. 3. Bags, Tedlar, 2- to 20-L or other appropriate sizes. 4. Syringes, gas-tight, of various sizes appropriate to the GC, and for preparation of bag standards. NOTE: To reduce the possibility of contamination, use separate, previously unused syringes for working standards and samples. Test syringes for contamination occasionally by filling them with clean air and analyzing the contents. 5. Label tape and marking pen for labelling bags.

SPECIAL PRECAUTIONS: TCE is a suspect carcinogen [2]. Shipment of compressed gases must comply with 49 CFR 171-177 regulations regarding shipment of hazardous materials.

SAMPLING AND MEASUREMENT: 1.

2.

Start GC instrument and recorder and allow to warm up according to manufacturer's instructions. NOTE: A straight line baseline should be attained at the highest sensitivity likely to be used. Select one of the following sampling modes: a. Spot sample. Draw air sample into the gas sampling loop of the GC with the on-board sampling pump, if supplied. Alternatively, inject an aliquot of air to be sampled into the GC with a gas-tight syringe. NOTE: A large contributor to random error in the method is imprecision of replicate injections. To improve precision: (1) use a gas sampling loop for injections, if available; (2) make at least three replicate determinations per sample; (3) use an injection volume large enough to be precisely readable, and consistent with that used in calibration; and (4) set conditions such that peaks are at least 50% of full scale. b. Integrated air sample for TWA determination. (1) Evacuate a clean sample bag using the inlet port of a personal sampling pump. NOTE: To reduce memory effects and contamination, use only previously unused sample bags. (2) Attach the sample bag to a personal sampling pump suitable for bag filling with a minimum length of flexible tubing. (3) Pump the air to be sampled into the sample bag at a rate calculated to fill ≤ 80% of the sample bag capacity over the sampling period. NOTE: The flow rate must remain within ± 5% of the initial setting throughout the sampling period. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94