In the field of environmental analysis, the analysis of volatile organic compounds (VOCs) usually refers to the analysis of compounds in environmental samples that have specific chemical properties, including low boiling points (below 200°C), low vapor pressures, low to medium water solubility, low molecular weights, and HLC(H)*10-3-10-5 atm*m3/mol. The main groups of compounds under this classification include halogenated hydrocarbons, aromatic hydrocarbons, ketones, nitriles, acrylates, acetates, ethers, sulfides, and so on. Since these compounds contaminate the environment, EPA and other regulatory agencies provide acceptable exposure limits and regulations for environmental releases of VOCs.
The VOC analysis involves ambient sampling of volatiles, sample concentration, and sample separation, followed by analysis of sample VOCs. In a sample vial, the unoccupied area above is often referred to as the headspace. The use of the headspace sampling method eliminates the need for lengthy and cumbersome sample pre-treatment, avoids interference from organic solvents, and reduces contamination of the column and injection port, which can lead to more accurate analytical results. Static headspace injection and dynamic headspace injection are the two most commonly used techniques for sample transfer and concentration.
Separation and detection systems are the core of VOC analyzers. Samples need to be separated from each component by a chromatographic column before detection, which affects the sensitivity of the subsequent detection and analysis. Common detection systems include hydrogen flame ionization detectors (FID), electron capture detectors (ECD), flame photometric detectors (FPD), and mass spectrometer detectors (MSD).
FID detects organic compounds by measuring the intensity of the ion stream formed by the action of the hydrogen flame. In a hydrogen flame, organic compounds burn to produce a large number of positive carbon ions. ECD utilizes the ability of electronegative substances to capture electrons for measurement and detection of electronic species. This method is highly sensitive and is currently an effective method for analyzing trace amounts of electronegative organic compounds. FPD has high sensitivity and selectivity for compounds containing sulfur and phosphorus. When phosphorus-containing substances are burned in a hydrogen-rich flame, each releases its own characteristic spectrum, and the FPD determines the intensity of the characteristic light through an interference filter using a photomultiplier tube. MSD, the most common detector, analyzes VOCs by collecting and recording cations ionized by high-speed electron impacts on gas molecules or atoms in order of magnitude of the mass ratio (m/z).
Amerigo Scientific offers a wide range of lab analyzers for volatile organic compounds and portable VOC monitoring instruments to help our customers ensure compliance with the composition and concentration of strictly regulated VOCs.
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