BTEX analysis

Increase in temperature during the extraction process enhances the diffusion during the extraction process towards the fiber, decreasing the time to reach equilibrium. However, the distribution constants of the analytes decrease with increasing temperature because it also favors evaporation of BTEX towards the headspace, reducing the concentration in the liquid phase. Therefore, as seen in Table 14.3, room temperature is often the most suitable temperature for BTEX analysis. 

Gas Chromatographic and Detection Conditions for BTEX Analysis in Water... 

In active sampling, the most employed samphng method for BTEX analysis, air is forced with a pump to pass for a certain time through adsorbent tubes. The mass flow has to be exactly known and calibrated in order to know the total volume of air from which analytes have been desorbed. Sample volumes ranging from 2 to 101 are taken in 15 to 60 min. A small amount of sorbent in a small bed (typically less than 2 g of sorbent in tubes of less than 5 mm internal diameter and 15 cm in length) is enough to retain all target analytes due to the fast kinetics of adsorption. 

For BTEX analysis in air with either active or passive " sampling, carbon disulfide is the most used extracting agent due to its high adsorption capacity that displaces other molecules... 

Automatic instruments are used to measure analyte concentrations in situ. Sampling, sample preparation, separation, and detection steps are performed onfield. Online gas chromatograph instmments are often used to measure BTEX in ambient air." " Table 14.10 shows some commercially available online instruments for BTEX analysis ... 

Seller HR (2002) Analysis of benzylsuccinates in groundwater by liquid chromatography/tandem mass spectrometry and its use for monitoring in situ BTEX biodegradation. Environ Sci Technol 36 2724-2728. 

Several soil-vapor monitoring techniques are currendy being used to define areas of volatile organic chemical contamination. These procedures usually involve the collection of representative samples of the soil gas for analysis of indicator compounds. Maps marked with concentration contours of these indicator compounds can be used to identify potential sources to delineate the contaminated area. Indicator compounds (usually the more volatile compounds) are selected for each specific situation. For gasoline contamination, the compounds are usually benzene, toluene, ethylbenzene, and total xylene (BTEX). In the case of a fuel oil spill, the most commonly used indicator is naphthalene. Some laboratories have adapted the laboratory procedures used for quality analysis of wellhead condensate (i.e., normal paraffins) to include light-end (<8 carbons) molecular analysis. 

Chemical analysis of water samples collected from monitoring wells and adjacent ditches was performed for BTEX, total organic carbon (TOC), chromium, and lead. Results of analysis presented a complicated chemical distribution in a dynamic... 

MTBE can be analyzed for with U.S. EPA SW-846 Method 8015 or 8021 however, 8021 has lower detection limits, is subject to less interference in highly contaminated samples and tends to be more economical by providing BTEX data in the same analysis. Concerns about coelution with some alkanes requires at least one confirmatory analysis with SW-846 Method 8260 per site. 

It is not surprising that the data produced as total petroleum hydrocarbons (EPA 418.1) suffer from several shortcomings as an index of potential ground-water contamination or health risk. In fact, it does not actually measure the total petroleum hydrocarbons in the sample but rather, measures a specific range of hydrocarbon compounds. This is caused by limitations of the extraction process (solvents used and the concentration steps) and the reference standards used for instrumental analysis. The method specifically states that it does not accurately measure the lighter fractions of gasoline [benzene-toluene-ethylbenzene-xylenes fraction (BTEX)], which should include the benzene-toluene-ethylbenzene-xylenes fraction. Further, the method was originally a method for water samples that has been modified for solids, and it is subject to bias. 

In New York and Massachusetts where PCB contamination is always a possibility, the laboratory tests required by the state environmental protection agencies for analysis of a petroleum-contaminated soil are as follows (a) flash point (b) total petroleum hydrocarbon (TPH) (c) PCB screening (d) total organic halides (TOH) (e) reactivity of cyanide and sulfide (f) BTEX or equivalent (g) eight metals under TCLP (Toxicity Characteristics Leaching Procedure) for USTs and (h) full range of tests under TCLP for ASTs and spills. 

You are the boss of a commercial analytical laboratory and your job is to check all results before they are sent to the customers. One day you look at the numbers from the analysis of benzene in BTEX (see Chapter 2) contaminated groundwater samples. For a given sample, your laboratory reports a benzene concentration in water of 100 /UgL 1. 

In the selection of a microbial system and bioremediation method, some examination of the degradation pathway is necessary. At a minimum, the final degradation products must be tested for toxicity and other regulatory demands for closure. Recent advances in the study of microbial metabolism of xenobiotics have identified potentially toxic intermediate products (Singleton, 1994). A regulatory agency sets treatment objectives for site remediation, and process analysis must determine whether bioremediation can meet these site objectives. Specific treatment objectives for some individual compounds have been established. In other cases total petroleum hydrocarbons total benzene, toluene, ethyl benzene, and xylene (BTEX) or total polynuclear aromatics objectives are set, while in yet others, a toxicology risk assessment must be performed. 

Distribution of contaminant subgroups at 214 sites. PAH = polynuclear aromatic hydrocarbons BTEX = benzene, toluene, ethylbenzene, and xylene. (From USEPA, Analysis of Facility of Corrective Action Data, U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, Technology Innovation Office, Washington, D.C., January, 1994.)... 

If BTEX components and MTBE are not sufficiently resolved in a complex gasoline mixture, their identification and quantitation with a PID becomes questionable. False positive results and high bias are common in gasoline component analysis with EPA Method 8021. 

Gasoline and its components are usually analyzed with the PID/FID combination (EPA Methods 8021 and 8015). In these methods, the PID and the FID may be connected in series to one column or in parallel to two columns. The PID is used for the analysis of individual compounds (BTEX and oxygenated additives, such as MTBE), and the FID is used for TPH analysis. 

The non-selective FID does not provide the second detector confirmation for BTEX, whereas the PID has only a marginal selectivity to aromatic compounds. In a typical analysis of gasoline in water by EPA Method 8021, benzene and MTBE results tend to be biased high due to coelution with other constituents false positive results are also common. 

Confirmation with a second column of a dissimilar polarity and a second, selective detector is necessary for the correct identification and quantitation of BTEX and oxygenated additives. And yet, even when a dissimilar column and a second PID are used in confirmation analysis, false positive detection of MTBE often takes place. 

The photo ionization detector (PID) contains an ultraviolet lamp that emits photons that are absorbed by compounds (aromatic rings, alkynes, and alkenes) in the ionization chamber. The ions created are then collected at electrodes, thus giving a signal. The most common use for this detector is for the analysis of BTEX. 

The LT system was mobilized to the site after preparation of a detailed site specific Work Plan and Health and Safety Plan. An Air Permit was received from the Stanislaus County Air Resources Board. The soil was excavated from a 50 ft. by 50 ft. area. During treatment the treated soil was composited daily and analyzed using a Hanby Environmental Test Kit for petrolevim hydrocarbons. This simple test kit, which provides rapid soil analysis, was used as a means of process control. The processed soil operating temperature and retention time was optimized at 422°F and 22 minutes, respectively. The treated soil samples were collected and analyzed for TPH and BTEX s by an independent third party. The average of the 18 samples collected and analyzed using approved analytical techniques are provided on Table I. The treated soil exceeded the treatment criteria of 100 ppm total petrolevim hydrocarbons and 700 ppb toluene. 

Figure 8.13 Analysis of o-xylene and BTEX (in water) using solid-phase microextraction (a) direct SPME fibre mode (b) headspace SPME fibre mode (c) results obtained for o-xylene using mode (a) (d) results obtained for BTEX using mode (b) , no stirring IH, with stirring , with stirring, plus salt , benzene , toluene a, ethylbenzene , m-, p-xylene(s) x, o-xylene [4] (cf. DQ 8.11).

Volatile compounds in the atmosphere, workplace and on industrial sites need to be monitored with regard to safety considerations, e.g. emissions to the atmosphere, or occupational standards. These volatile compounds, e.g. BTEX, can be trapped either on a solid support material (e.g. for thermal desorption), or liberated from a water sample and then trapped (e.g. via purge-and-trap), prior to analysis. 

Leconte, A., Comparison of purge-and-trap-GC with headspace solid-phase microextraction-GC for the analysis of BTEX in water , MSc Dissertation, Northumbria University, Newcastle, UK, 1997. 

Infrared (IR) spectroscopy is regularly used for the identification of compounds, often in conjunction with nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). However, it can also be used for the quantitative analysis of environmental compounds, e.g. BTEX, in a sample extract. 

---