APPENDIX E-REFERENCE METHOD FOR DETERMINATION OF HYDROCARBONS CORRECTED FOR METHANE

1. Principle and Applicability.

1.1 Measured volumes of air are delivered semicontinuously (4 to 12 times per hour) to a hydrogen flame ionization detector to measure its total hydrocarbon (THC) content. An aliquot of the same air sample is introduced into a stripper column which removes water, carbon dioxide, and hydrocarbons other than methane. Methane and carbon monoxide are passed quantitatively to a gas chromatographic column where they are separated. The methane is eluted first, and is passed unchanged through a catalytic reduction tube into the flame ionization detector. The carbon monoxide is eluted into the catalytic reduction tube where it is reduced to methane before passing through the flame ionization detector. Between analyses the stripper column is backflushed to prepare it for subsequent analysis. Hydrocarbon concentrations corrected for methane are determined by subtracting the methane value from the total hydrocarbon value.

Two modes of operation are possible: (1) A complete chromatographic analysis showing the continuous output from the detector for each sample injection; (2) The system is programed for automatic zero and span to display selected band widths of the chromatogram. The peak height is then usea as the measure of the concentration. The former operation is referred to as the chromatographic or spectro mode and the latter as the barographic or "normal" mode depending on the make of analyzer.

1.2 The method is applicable to the semicontinuous measurement of hydrocarbons corrected for methane in ambient air. The carbon monoxide measurement, which is simultaneously obtained in this method, is not required in making measurements of hydrocarbons corrected for methane and will not be dealt with here.

2. Range and Sensitivity.

2.1 Instruments are available with various range combinations. For atmospheric analysis the THC range is 0-13.1 mg./m.3 (0-20 p.p.m.) carbon (as CH1) and the methane range is 0-6.55 mg/m.3 (0-10 p.p.m.). For special applications, lower ranges are available and in these applications the range for THC is 0-1.31 mg./m.3 (0-2 p.p.m.) carbon (as CH1) and for methane the range is 0-1.31 mg./m.3 (0-2 p.p.m.).

2.2 For the higher, atmospheric analysis ranges the sensitivity for THC is 0.065 mg./m.3 (0.1 p.p.m.) carbon (as CH) and for methane the sensitivity is 0.033 mg./m.3 (0.05 p.p.m.). For the lower, special analysis ranges the sensitivity is 0.016 mg./m.3 (0.025 p.p.m.) for each gas.

3. Interferences.

3.1 No interference in the methane measurement has been observed. The THC measurement typically includes all or a portion of what is generally classified as the air peak interference. This effect is minimized by proper plumbing arrangements or is negated electronically.

4. Precision, Accuracy, and Stability.

4.1 Precision determined with calibration gases is ±0.5 percent of full scale in the higher, atmospheric analysis ranges.

4.2 Accuracy is dependent on instrument linearity and absolute concentration of the calibration gases. An accuracy of 1 percent of full scale in the higher, atmospheric analysis ranges and 2 percent of full scale in the lower, special analysis ranges can be obtained.

4.3 Variations in ambient room temperature can cause changes in performance characteristics. This is due to shifts in oven temperature, flow rates, and pressure with ambient temperature change. The instrument should meet performance specifications with room temperature changes of ±3° C. Baseline drift is automatically corrected in the barographic mode.

5. Apparatus.

5.1 Commercially Available THC, CH, and CO Analyzer. Instruments should be installed on location and demonstrated, preferably by the manufacturer, or his representative, to meet or exceed manufacturer's specifications and those described in this method.

5.2 Sample Introduction System. Pump, flow control valves, automatic switching valves, and flowmeter.

5.3 Filter (In-line). A binder-free, glassfiber filter with a porosity of 3 to 5 microns should be immediately downstream from the sample pump.

5.4 Stripper or Precolumn. Located outside of the oven at ambient temperature. The column should be repacked or replaced after the equivalent of 2 months of continuous operation.

5.5 Oven. For containing the analytical column and catalytic converter. The oven should be capable of maintaining an elevated temperature constant within ±0.5° C. The specific temperature varies with instrument manufacturer.

6.4 Zero Gas. Air containing less than 0.065 mg./m.3 (0.1 p.p.m.) total hydrocarbons as methane.

6.5 Calibration Gases. Gases needed for linearity checks (peak heights) are determined by the ranges used. Calibration gases corresponding to 10, 20, 40, and 80 percent of full scale are needed. Gases must be provided with certification or guaranteed analysis. Methane is used for both the total hydrocarbon measurement and methane measurement.

6.6 Span Gas. The calibration gas corresponding to 80 percent of full scale is used to span the instrument.

7. Procedure.

7.1

Calibrate the instrument as described in 8.1. Introduce sample into the system under the same conditions of pressure and flow rates as are used in calibration. (The pump is bypassed only when pressurized cylinder gases are used.) Figure El shows a typical flow diagram; for specific operating instructions refer to manufacturer's manual. 8. Calibration.

8.1 Calibration Curve. Determine the linearity of the system for THC and methane in the barographic mode by introducing zero gas and adjusting the respective zeroing controls to indicate a recorder reading of zero. Introduce the span gas and adjust the span control to indicate the proper value on the recorder scale. Recheck zero and span until adjustments are no longer necessary. Introduce intermediate calibration gases and plot the values obtained. If a smooth curve is not obtained, calibration gases may need replacement.

9. Calculation.

9.1 Determine concentrations of total hydrocarbons (as CH1) and CH,, directly from the calibration curves. No calculations are

necessary.

9.2 Determine concentration of hydrocarbons corrected for methane by subtracting the methane concentration from the total hydrocarbon concentration.

9.3 Conversion between p.p.m. and mg./ m.3 values for total hydrocarbons (as CH1) methane and hydrocarbons corrected for methane are made as follows:

p.p.m. carbon (as CH4)= [mg. carbon (as CH)/m.3] X 1.53

10. Bibliography.

Fee, G., "Multi-Parameter Air Quality Analyzer", ISA Proceedings AID/CHEMPID Symposium, Houston, Texas, April 19-21,

1971.

Villalobos, R., and Chapman, R. L., “A Gas Chromatographic Method for Automatic

Monitoring of Pollutants in Ambient Air", ibid.

Stevens, R. K., "The Automated Gas Chromatograph as an Air Pollutant Monitor", 1970 Conference on Environmental Toxicology, U.S. Air Force, Wright-Patterson Air Force Base, Dayton, Ohio.

Stevens, R. K., and O'Keeffe, A. E., Anal. Chem. 42, 143A (1970).

Schuck, E. A., Altshuller, A. P., Barth, D. S. and Morgan, G. B., "Relationship of Hydrocarbons to Oxidants in Ambient Atmospheres", J. Air Poll. Cont. Assoc. 20, 297-302 (1970).

Stevens, R. K., O'Keeffe, A. E., and Ortman, G. C., "A Gas Chromatographic Approach to the Semi-Continuous Monitoring of Atmospheric Carbon Monoxide and Methane", Proceedings of 11th Conference on Methods in Air Pollution on Industrial Hygiene Studies, Berkeley, Calif., March 30-April 1, 1970.

Swinnerton, J. W., Linnenbom, V. J. and Check, C. H., Environ. Sci. Technol. 3, 836 (1969).

Williams, I. G., Advances in Chromatography, Giddings, J. C., and Keller, R. A., editors, Marcell Dekker, N.Y. (1968), pp. 178– 182.

Altshuller, A. P., Kopcznski, S. L., Lonneman, W. A., Becker, T. L. and Slater, R., Environ. Sci. Technol. 1, 899 (1967).

Altshuller, A. P., Cohen, I. R., and Purcell, T. C., Can. J. Chem., 44, 2973 (1966).

DuBois, L., Zdrojewski, A., and Monkman, J. L., J. Air Poll. Cont. Assoc. 16, 135 (1966). Ortman, G. C., Anal. Chem. 38, 644-646 (1966).

Porter, K., and Volman, D. H., Anal. Chem. 34, 748-749 (1962).

Crum, W. M., Proceedings, National Analysis Instrumentation Symposium ISA, 1962. Schwink, A., Hochenberg, H., and Forderreuther, M., Brennstoff-Chemie 72, No. 9, 295 (1961).

Instruction Manual for Air Quality Chromatograph Model 6800, Beckman Instrument Co., Fullerton, Calif.

Instruction Manual, Bendix Corp., Ronceverte, W. Va.

Instruction Manual, Byron Instrument Co., Raleigh, N.C.

MSA Instruction Manual for GC Process Analyzer for Total Hydrocarbon, Methane and Carbon Monoxide, Pittsburgh, Pa.

Monsanto Enviro-Chem System for Total Hydrocarbons, Methane and Carbon Monoxide Instruction Manual, Dayton, Ohio.

Union Carbide Instruction Manual for Model 3020 Gas Chromatograph for COCH-T/1, White Plains, N.Y.

Instruction Manual for 350 F Analyzer, Tracor Inc., Austin, Tex.

ADDENDA

B. Suggested Definitions of Performance Specifications:

Range-The minimum and maximum measurement limits.

Output-Electrical signal which is proportional to the measurement; intended for connection to readout or data processing devices. Usually expressed as millivolts or milliamps full scale at a given impedence. Full Scale-The maximum measuring limit for a given range.

Minimum Detectable Sensitivity-The smallest amount of input concentration that can be detected as the concentration approaches zero.

Accuracy-The degree of agreement between

a measured value and the true value; usually expressed at percent of full scale.

Lag Time-The time interval from a step change in input concentration at the instrument inlet to the first corresponding change in the instrument output.

Time to 90 Percent Response-The time interval from a step change in the input concentration at the instrument inlet to a reading of 90 percent of the ultimate recorded concentration.

Rise Time (90 percent)-The interval between initial response time and time to 90 percent response after a step decrease in the inlet concentration.

Zero Drift-The change in instrument output over a stated time period, usually 24 hours, of unadjusted continuous operation, when the input concentration is zero; usually expressed as percent full scale.

Span Drift-The change in instrument output over a stated time period, usually 24 hours, of unadjusted continuous operation, when the input concentration is a stated upscale value; usually expressed as percent full scale.

Precision-The degree of agreement between repeated measurements of the same concentration. It is expressed as the average deviation of the single results from the

mean.

Operational Period-The period of time over which the instrument can be expected to operate unattended within specifications. Noise-Spontaneous deviations from a mean output not caused by input concentration changes.

Interference-An undesired positive or negative output caused by a substance other than the one being measured. Interference Equivalent-The portion of indicated input concentration due to the presence of an interferent.

Operating Temperature Range-The range of ambient temperatures over which the instrument will meet all performance specifications.