EPA Methods List with Links



US EPA Method 25A - Determination Of Total Gaseous Organic Concentration Using A Flame Ionization Analyzer



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1.0 Scope and Application.



1.1 Analytes.



1.2 Applicability. This method is applicable for the determination of total gaseous organic concentration of vapors consisting primarily of alkanes, alkenes, and/or arenes (aromatic hydrocarbons). The concentration is expressed in terms of propane (or other appropriate organic calibration gas) or in terms of carbon.



1.3 Data Quality Objectives. Adherence to the requirements of this method will enhance the quality of the data obtained from air pollutant sampling methods.



2.0 Summary of Method.



2.1 A gas sample is extracted from the source through a heated sample line and glass fiber filter to a flame ionization analyzer (FIA). Results are reported as volume concentration equivalents of the calibration gas or as carbon equivalents.



3.0 Definitions.



3.1 calibration drift

Means the difference in the measurement system response to a mid-level calibration gas before and after a stated period of operation during which no unscheduled maintenance, repair, or adjustment took place.



3.2 calibration error

Means the difference between the gas concentration indicated by the measurement system and the know concentration of the calibration gas.



3.3 calibration gas

Means a known concentration of a gas in an appropriate diluent gas.



3.4 Measurement system

Means the total equipment required for the determination of the gas concentration. The system consists of the following major subsystems:



3.4.1 Sample interface

Means that portion of a system used for one or more of the following: sample acquisition, sample transportation, sample conditioning, or protection of the analyzer(s) from the effects of the stack effluent.



3.4.2 Organic analyzer

Means that portion of the measurement system that senses the gas to be measured and generates an output proportional to its concentration.



3.5 Response time

Means the time interval from a step change in pollutant concentration at the inlet to the emission measurement system to the time at which 95 percent of the corresponding final value is reached as displayed on the recorder.



3.6 Span Value

Means the upper limit of a gas concentration measurement range that is specified for affected source categories in the applicable part of the regulations. The span value is established in the applicable regulation and is usually 1.5 to 2.5 times the applicable emission limit. If no span value is provided, use a span value equivalent to 1.5 to 2.5 times the expected concentration. For convenience, the span value should correspond to 100 percent of the recorder scale.



3.7 Zero drift

Means the difference in the measurement system response to a zero level calibration gas before or after a stated period of operation during which no unscheduled maintenance, repair, or adjustment took place.



4.0 Interferences. [Reserved]




5.0 Safety.



5.1 Disclaimer. This method may involve hazardous materials, operations, and equipment. This test method may not address all of the safety problems associated with its use. It is the responsibility of the user of this test method to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to performing this test method. The analyzer users manual should be consulted for specific precautions to be taken with regard to the analytical procedure.



5.2 Explosive Atmosphere. This method is often applied in highly explosive areas. Caution and care should be exercised in choice of equipment and installation.



6.0 Equipment and Supplies.



6.1 Measurement System.

Any measurement system for total organic concentration that meets the specifications of this method. A schematic of an acceptable measurement system is shown in Figure 25A-1. All sampling components leading to the analyzer shall be heated > 110C (220F) throughout the sampling period, unless safety reasons are cited (Section 5.2). The essential components of the measurement system are described below:



6.1.1 Organic Concentration Analyzer.

A flame ionization analyzer (FIA) capable of meeting or exceeding the specifications of this method. The flame ionization detector block shall be heated >120EC (250F).



6.1.2 Sample Probe.

Stainless steel, or equivalent, three-hole rake type. Sample holes shall be 4 mm (0.16-in.) in diameter or smaller and located at 16.7, 50, and 83.3 percent of the equivalent stack diameter. Alternatively, a single opening Probe may be used so that a gas sample is collected from the centrally located 10 percent area of the stack cross-section.



6.1.3 Heated Sample Line.

Stainless steel or Teflon tubing to transport the sample gas to the analyzer. The sample line should be heated (>110 C) to prevent any condensation.



6.1.4 calibration Valve Assembly.

A three-way valve assembly to direct the zero and calibration gases to the analyzers is recommended. Other methods, such as quick-connect lines, to route calibration gas to the analyzers are applicable.



6.1.5 Particulate filter.

An in-stack or an out-of-stack glass fiber filter is recommended if exhaust gas particulate loading is significant. An out-of-stack filter should be heated to prevent any condensation.



6.1.6 Recorder.

A strip-chart recorder, analog computer, or digital recorder for recording measurement data. The minimum data-recording requirement is one measurement value per minute.



7.0 Reagents and Standards.



7.1 calibration Gases.

The calibration gases for the gas analyzer shall be propane in air or propane in nitrogen. Alternatively, organic compounds other than propane can be used; the appropriate corrections for response factor must be made. calibration gases shall be prepared in accordance with the procedure listed in Citation 2 of Section 16. Additionally, the manufacturer of the cylinder should provide a recommended shelf life for each calibration gas cylinder over which the concentration does not change more than ± 2 percent from the certified value. For calibration gas values not generally available (i.e., organics between 1 and 10 percent by volume), alternative methods for preparing calibration gas mixtures, such as dilution systems (Test Method 205, 40 CFR Part 51, Appendix M), may be used with prior approval of the Administrator.



7.1.1 Fuel.

A 40 percent H2/60 percent N2 or He gas mixture is recommended to avoid an oxygen synergism effect that reportedly occurs when oxygen concentration varies significantly from a mean value.



7.1.2 Zero Gas.

High purity air with less than 0.1 part per million by volume (ppmv) of organic material (propane or carbon equivalent) or less than 0.1 percent of the span value, whichever is greater.



7.1.3 Low-level calibration Gas.

An organic calibration gas with a concentration equivalent to 25 to 35 percent of the applicable span value.



7.1.4 Mid-level calibration Gas.

An organic calibration gas with a concentration equivalent to 45 to 55 percent of the applicable span value.



7.1.5 High-level calibration Gas.

An organic calibration gas with a concentration equivalent to 80 to 90 percent of the applicable span value.



8.0 Sample Collection, Preservation, Storage, and Transport.



8.1 Selection of Sampling Site.

The location of the sampling site is generally specified by the applicable regulation or purpose of the test (i.e., exhaust stack, inlet line, etc.). The sample port shall be located to meet the testing requirements of Method 1.



8.2 Location of Sample Probe.

Install the sample Probe so that the Probe is centrally located in the stack, pipe, or duct and is sealed tightly at the stack port connection.



8.3 Measurement System Preparation.

Prior to the emission test, assemble the measurement system by following the manufacturer's written instructions for preparing sample interface and the organic analyzer. Make the system operable (Section 10.1).



8.4 calibration Error Test.

Immediately prior to the test series (within 2 hours of the start of the test), introduce zero gas and high-level calibration gas at the calibration valve assembly. Adjust the analyzer output to the appropriate levels, if necessary. Calculate the predicted response for the low-level and mid-level gases based on a linear response line between the zero and high-level response. Then introduce low-level and mid-level calibration gases successively to the measurement system. Record the analyzer responses for low-level and mid-level calibration gases and determine the differences between the measurement system responses and the predicted responses. These differences must be less than 5 percent of the respective calibration gas value. If not, the measurement system is not acceptable and must be replaced or repaired prior to testing. No adjustments to the measurement system shall be conducted after the calibration and before the drift check (Section 8.6.2). If adjustments are necessary before the completion of the test series, perform the drift checks prior to the required adjustments and repeat the calibration following the adjustments. If multiple electronic ranges are to be used, each additional range must be checked with a mid-level calibration gas to verify the multiplication factor.



8.5 Response Time Test.

Introduce zero gas into the measurement system at the calibration valve assembly. When the system output has stabilized, switch quickly to the high-level calibration gas. Record the time from the concentration change to the measurement system response equivalent to 95 percent of the step change. Repeat the test three times and average the results.



8.6 Emission Measurement Test Procedure.



8.6.1 Organic Measurement.

Begin sampling at the start of the test period, recording time and any required process information as appropriate. In particulate, note on the recording chart, periods of process interruption or cyclic operation.



8.6.2 Drift Determination.

Immediately following the completion of the test period and hourly during the test period, reintroduce the zero and mid-level calibration gases, one at a time, to the measurement system at the calibration valve assembly. (Make no adjustments to the measurement system until both the zero and calibration drift checks are made.) Record the analyzer response. If the drift values exceed the specified limits, invalidate the test results preceding the check and repeat the test following corrections to the measurement system. Alternatively, recalibrate the test measurement system as in Section 8.4 and report the results using both sets of calibration data (i.e., data determined prior to the test period and data determined following the test period).

NOTE: Note on the recording chart periods of process interruption or cyclic operation.



9.0 Quality Control



10.0 Calibration and Standardization.



10.1 FIA equipment can be calibrated for almost any range of total organic concentrations. For high concentrations of organics (> 1.0 percent by volume as propane), modifications to most commonly available analyzers are necessary. One accepted method of equipment modification is to decrease the size of the sample to the analyzer through the use of a smaller diameter sample capillary. Direct and continuous measurement of organic concentration is a necessary consideration when determining any modification design.



11.0 Analytical Procedure.

The sample collection and analysis are concurrent for this method (see Section 8.0).



12.0 Calculations and Data Analysis.



12.1 Determine the average organic concentration in terms of ppmv as propane or other calibration gas. The average shall be determined by integration of the output recording over the period specified in the applicable regulation. If results are required in terms of ppmv as carbon, adjust measured concentrations using Equation 25A-1.



13.0 Method Performance.



13.1 Measurement System Performance Specifications.



13.1.1 Zero Drift. Less than ±3 percent of the span value.



13.1.2 calibration Drift. Less than ±3 percent of span value.



13.1.3 calibration Error. Less than ±5 percent of the calibration gas value.



14.0 Pollution Prevention. [Reserved]




15.0 Waste Management. [Reserved]




16.0 References.



1. Measurement of Volatile Organic Compounds-Guideline Series. U.S. Environmental Protection Agency. Research Triangle Park, NC. Publication No. EPA-450/2-78-041. June 1978. p. 46-54.



2. EPA Traceability Protocol for Assay and Certification of Gaseous calibration Standards. U.S. Environmental Protection Agency, Quality Assurance and Technical Support Division. Research Triangle Park, N.C. September 1993.



3. Gasoline Vapor Emission Laboratory Evaluation-Part 2. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards. Research Triangle Park, NC. EMB Report No. 75-GAS-6. August 1975.



17.0 Tables, Diagrams, flowcharts, and Validation Data.

Figure 25A-1. Organic Concentration Measurement System.