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Method 25A Sampling System

Method 25A Sampling System

The Apex Instruments Model SA-250P MiniFID is applicable to US EPA Method 25A for the determination of total gaseous organic concentration of vapors consisting primarily of alkanes, alkenes, and/or aromatic hydrocarbons (commonly referred to as total hydrocarbon concentrations). Concentrations are reported in terms of the gas used to calibrate the analyzer, normally in ppm propane. A gas sample is extracted from the source through a heated sample line and glass fiber filter to a flame ionization detectionanalyzer (FID).

SKU: Method 17 Sampling System-1 Category:


The MiniFID SA-250P flame ionization detector is a highly sensitive, but non-selective, detector for measuring hydrocarbons. It uses a simple principle where a flame strips hydrogen atoms from the hydrocarbon molecule, forming carbon radicals and electrons. This is ordinarily a short-lived condition with the charged components quickly recombining; however, in an electrostatic field the oppositely charged components can be driven towards electrodes. This creates an effective current within the flame proportional to the number of molecules of hydrocarbon present.

The molecular arrangement has an effect on the ionization mechanism within the flame and, therefore, the response of the analyzer. A response factor is used to correct this measurement response or the variation can also be accounted for by calibration using the target gas.

Heated to 191ºC

The MiniFID is heated to prevent any loss of sample through condensation and to remove any interference from water vapor around the detector. This means that the analyzer can be used to measure species that would be liquid at room temperature and hot, wet samples, such as those derived from combustion or other solvent processes.

Zero Air/Burner Air

The MiniFID has its own heated pump and clean up system in order to use ambient air for both supplying the flame and calibrating the zero point. The standard MiniFID uses a carbon scrubber cartridge which cleans the air efficiently and is suitable for normal conditions in ambient air and concentrations down to tens of ppm. The upgraded MiniFID Pure contains a heated catalytic air purifier suitable for areas where the ambient air contains high levels of hydrocarbons or where the measurement is in the 0-10ppm range. There is also the capability to connect synthetic air to the analyzer for the most accurate readings.

Oxygen Synergism

There is an effect within all FID analyzers where large variations in the oxygen concentration of the sample can lead to bias in measured concentration due to changing flame temperature. This can be mitigated by using a mixture of hydrogen and helium for fuel gas. We recommend this option for samples, such as those from variable combustion processes, where the oxygen level can fluctuate to a large extent. For processes within ambient levels (of oxygen, air and methane/propane, etc.) a proportional level of air should be used. For low oxygen sample gas in nitrogen, an increased level of air could be more appropriate.

Span Ranges Option

The standard ranges supplied with the MiniFID are 0-10ppm, 0-100ppm, 0-1,000ppm and 0-10,000ppm (1%). A high range version is also available with lowest range 0-100ppm. This is suitable for measuring concentration up to 10% propane equivalent.

Optional On-Board Data-Logging

The MiniFID is supplied with 0-10v and 4-20mA outputs for logging concentration, plus 4 contact closure outputs to indicate range selection. It is also available with on-board data logging with 64,000 bits of information. This is sufficient for 36 hours of logging at 2 second intervals. There is a straightforward USB connection to your laptop or computer for download using supplied software.

Integrated Heated Sample Line

Where other analyzers require you to use a separate heated line with a controller, meaning carrying around a second box, the MiniFID has integrated controls consisting of a thermocouple to display temperature and a safety interlock to prevent the analyzer from being used before the heated line is at operational set point. With the heated line removed, the interlock is bypassed so the analyzer can be used with or without the heated line as desired.

Compliant with EU and US EPA Regulations

The MiniFID is MCERTS certified as conforming to EN12619 and EN13266 specifications for measuring VOCs. It also complies with US EPA Method 25 for measuring hydrocarbons.

Sample Pressure Regulator

A bypass system, including a pressure regulator, provides a controlled back pressure at the sample capillary, which then allows a constant sample flow rate to the detector. This reduces the flow sensitivity of the analyzer for more accurate readings without the maintenance problems associated with the back pressure regulator being situated in the sample stream in most other FID analyzers. This arrangement allows for the highest possible sample flow rate, giving enhanced sensitivity with the lowest possible maintenance requirement.

Removable PTFE Sample Filter

The MiniFID is supplied with a heated filter body on the sample inlet, fitted with a proprietary hydrocarbon-free PTFE filter. This helps protect the analyzer from particulate matter in the sample, extending the lifetime of the analyzer and reducing maintenance costs.

Application Overview

The SA-250P is suitable for a wide range of applications from incinerators to high concentration solvent users. With good carbon correlation for aliphatics, alcohols, esters, ketones, and aromatics, it provides a reliable determination of total hydrocarbon levels. Heated flame ionization detector is the reference method technique for measuring total hydrocarbons (THC, VOC, TOC). The advantage of this method is that it can be used for hot, wet samples. Maintaining an elevated temperature prevents the dropout of heavy hydrocarbons along the sample line. This detection method is continuous with a fast response time making it very effective for alarm-status monitoring applications and other real-time reporting.


The MiniFID represents an intuitive, easy-to-use analyzer suitable for even the most inexperienced operators. Hydrogen/helium fuel mixture is recommended for applications where oxygen levels are unpredictable to minimize the effects of oxygen synergism. The SA-250P is also available with hydrogen fuel option for ambient applications where oxygen levels are stable. The fuel is shut off automatically if the flame fails. The sample pump is inoperable until the oven and heated line are up to temperature.


On-board data logger with 64,000 bit data memory and USB or serial connection. For logging of concentration only. Signal SIGEMS software is available for remote logging and reporting. The MiniFID can be upgraded to contain a catalytic air purifier, which in contrast to standard carbon-based air filters, provides an efficiency of 99% cleanup based on a test of 500ppm CH4 in air. Please contact us for further details on these options.