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.
Sources of these compounds include pesticides and herbicides (containing phosphorus, sulfur, chlorine or nitrogen), flame retardants, ingredients in cleaning agents and personal care products, solvents and chemicals used in textile/electronic manufacturing and material manufacturing process additives.
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Environmental analysts sample air, water, soil and biota to monitor for the presence and concentrations of contaminants present. Due to the tendency of contaminants to accumulate, concentrate and persist in these natural matrices analysts can gain valuable information to help limit the spread and impact of contamination on environmental health by analyzing these matrices. Generally environmental analysis for SVOCs focuses on the extraction, identification and quantitation of contaminants.
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.
Environmental analysts rely on traditional chromatographic techniques for separation and detection of many semivolatile compounds. Gas chromatography (GC), high performance liquid chromatography (HPLC) and ion chromatography (IC) dominate the techniques used to identify organic contaminants.
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.
GC and HPLC provide the initial separation of sample components prior to introduction into mass spectrometry instrumentation. The complexity of environmental samples like soil extracts requires separation mechanisms that can isolate target compounds and remove unwanted interferences. Furthermore the presence of many chemical groups, the influence of conflicting chemical properties, matrix interferences and chromatographic resolution limitations on columns create challenges for accurate identification and quantitation. LC/MS and GC/MS techniques provide mass spectrums for compounds that can be used to overcome many of the challenges in identification and quantitation of environmental contaminants.
Through mass spectrometry a mass spectrum is created with mass assignments corresponding to the atomic weight of a target compound and/or its ionized fragments. This data can assist in the identification and confirmation of semivolatile compounds. In addition, mass spectrometry provides the ability to analyze broader compound classes, remove additional matrix interferences as well as gain sensitivity/selectivity.
Among the challenges in pesticide analysis are location, crop and seasonal-specific use of pesticides. Making the challenges even more complex are novel pesticides, some unidentified, which are being developed and implemented every day across the globe. Because of this, and the unknown effects of long term exposure the list of pesticides that require monitoring is ever-growing.
Polycyclic aromatic hydrocarbons (PAHs) are some of the most widespread organic pollutants. In addition to occurring naturally in oil, coal, and tar deposits, PAHs are produced by incomplete combustion of fossil fuels and other organic matter. The compounds are of concern because many have been identified as carcinogenic, mutagenic, or teratogenic. Due to these health risks, regulatory agencies, such as the Environmental Protection Agency (EPA), have defined maximum allowable levels of PAHs in the environment. Sensitive analytical methods are essential in the determination of the presence and levels of PAHs.
Polychlorinated biphenyls were traditionally used as coolants and insulating fluids (transformer oil) for transformers and capacitors. Production was banned in 1979 due to their toxic and persistent characteristics that are potential threats to the environmental health. Due to their significant presence as an additive in a vast array of other manufactured goods from 1930-1970 continuous monitoring efforts are necessary.
Nitrosamines are a type of disinfection byproduct that stems from drinking water disinfection treatment through the chloramination process. Due to the carcinogenic nature of nitrosamines at very low levels, new regulations setting detection limits at PPT (ng/L) levels have been set for nitrosamines in drinking water and food products. EPA Method 521 recommends carbon SPE cartridges and this method can be easily adapted for the analysis of nitrosamines.
Regulatory agencies publish guidance for monitoring semivolatile contaminants in the environment. Despite the common goal of limiting environmental exposure to these compounds due to their potentially detrimental impact, regulations can vary based on location. Regulations often group SVOC based on several criteria including detection methods, end use, common compound structural attributes and other justifications. Frequently used SVOC methods are listed below.