Semivolatile Organic Compounds (SVOC) Analysis

The “semivolatile” contaminant grouping is composed of compounds with broad chemical properties and structural features. Examples of semivolatiles compounds include hydrocarbons, aldehydes, ethers, esters,  phenols, organic acids, ketones, amines, amides, nitroaromatics, PCBs (also known as Aroclors), PAHs, phthalate esters, nitrosamines, haloethers and trihalomethanes.

The term "semi-volatile compounds" refers to organic compounds that possess Henry’s law constants (H) in the range of 10^-5 - 3 x 10^-7 atm*m³/mol* and demonstrate higher boiling points, usually greater than that of water with correspondingly low vapor pressure from 10^-14 - 10^-4atm. *H range defined as volatility from liquid to air.

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The sample type or matrix dictates the technique needed to successfully extract target contaminants or contaminant groups. Sample preparation technology is constantly evolving with improvements in technology extraction efficiency and cost. Several extraction techniques can be used to remove semivolatile contaminants from aqueous or solid/semisolid matrices.

Generally an aqueous sample of a known volume is extracted with solvent or diluted with solvent. Techniques for extracting water-based samples include separatory funnel liquid-liquid extraction (LLE), continuous liquid-liquid extraction (CLE), solid phase extraction (SPE), automated SPE (ASPE) and solid phase micro extraction (SPME).

Extraction techniques for solid samples like soil or sediment are designed to remove the native substances from these complex multi component mixtures and transfer the semivolatiles present into an organic solvent. As with aqueous samples there are various solid sample extraction techniques including soxhlet (SLE), automated soxhlet (ASLE), microwave assisted (MAE), super critical fluid (SFE), accelerated solvent extraction (ASE), and ultrasonic extraction. In nonaqueous matrices acid- base partitioning is typically not required. However, due to the complex component nature of solid samples additional sample cleanup steps such as gel permeation chromatography (GPC) may be necessary.

For semivolatile analysis specifically, most environmental laboratories rely on gas chromatography for detection and quantitation. It is important to note that gas chromatography has been at the center of U.S. EPA’s strategy for monitoring organic contaminants since the early to mid 1970s. The ability to quickly separate large compound groups with high resolution and the availability of detectors with various affinities provide a definite advantage when analyzing complex samples. 

In environmental analysis, HPLC is often used to analyze compounds that are not amenable to GC. The high temperatures that compounds are exposed to for the required vaporization step of GC sample introduction can cause difficulty when analyzing thermally labile or chemically active compounds. Strategies for managing this influence of temperature induced instability such as derivatization or analyte protectants are often not required when using HPLC. Examples of semivolatiles typically analyzed using HPLC include PAHs, nitro-aromatics, explosives and many other compounds.