Setting New Standards in Semivolatile Water Testing

It’s often said that what goes around comes around, and that is certainly true for volatile organic compounds (VOCs). Historical monitoring shows that VOCs released as a result of industrial processes, and often in large volumes, can persist in the environment and eventually migrate into water sources. Many of these compounds remain in the water supply even after attempts at treatment and can accumulate in the human body if consumed.1

VOCs include all organic compounds that can volatize under normal atmospheric conditions of temperature and pressure. However, as the boiling point of these chemicals increases, the demarcation line between volatile organic compound and semivolatile organic compound (SVOC) is somewhat arbitrary. An accepted classification starts considering as semivolatiles all the organic compounds having a boiling point higher than 240-260°C.2

SVOCs are of particular concern due to their well-documented toxicity and environmental prevalence. Generated by a wide range of industrial processes, the most frequently detected SVOCs include those used as or derived from pesticides, herbicides, flame retardants, cleaning agents and chemicals used in textile and electronics manufacturing. These compounds have been linked to a variety of health issues, including anemia and cancer, and are regularly detected in groundwater, waterways, and drinking water.

Due to the health threat posed by SVOCs, the US EPA has established strict MCLs for these compounds in groundwater and drinking water.

Bringing SVOC Water Testing Regulations up to Date

Due to the health threat posed by these compounds, the United States Environmental Protection Agency (EPA) has established strict maximum contaminant levels (MCL) for SVOCs in groundwater and drinking water. These legally enforced standards are set for each compound at a level at which no predicted adverse effects would occur. MCLs for most known compounds range from 0.0002 mg/L to 1 mg/L, depending on the substance, its potential effects and persistence in the environment.3

To support the collection of consistent data, the EPA has released a number of recommendations around water testing. The first guidelines for the testing of SVOCs by gas chromatography-mass spectrometry (GC-MS), known as Method 8270, were released in 1980. The recently revised Method 8270E is followed by most environmental laboratories that analyze SVOCs in extracts prepared from water and various types of solid waste matrices, soils and air sampling media, following different extraction methodologies like liquid-liquid extraction (LLE), solid-phase extraction (SPE), Soxhlet extraction, ultrasonic extraction and accelerated solvent extraction (ASE), according to the type of sample. In particular, ASE uses a pressurized fluid extraction device according to Method EPA 3545, recently included in the latest 8270E revision as a suitable sample preparation technique.4

Since the EPA guidelines were first established, advances in GC-MS technology have revolutionized the environmental analysis landscape. Single quadrupole and triple quadrupole mass spectrometers have become much more sensitive and source fragmentation methods have improved considerably. The latest generation of instruments now provides a greater response for high-mass analytes and much has been learned about the origin and nature of different ion species.5

These technological improvements and a more in-depth understanding of SVOCs mean that even safer water standards can be enforced. This necessitates adjustments in outdated tuning criteria and testing method protocols. To bring Method 8270 testing protocols in line with the capabilities of modern GC-MS instruments, the EPA has therefore updated the ion abundance criteria for the measurement of the decafluorotriphenylphosphine (DFTPP) ion ratios, an important standard that’s used to demonstrate the validity of analytical measurements in environmental monitoring. Moreover, the use of the GC-MS/MS technology and selected ion monitoring/chemical-ionization (SIM/CI) acquisition mode have been added, permitting higher selectivity and even more sensitivity for multi-components analysis.

GC-MS Technologies Drive Robust
Testing Guidelines

GC-MS has long been a powerful technique for the identification and quantitation of semivolatiles in complex matrices. However, recent advances in GC-MS technology are enabling the detection of SVOCs across a much broader range of concentrations. The wide dynamic range achieved by today’s generation of single quadrupole systems allows trace levels of SVOCs to be detected within multi-analyte samples. These improvements in sensitivity and specificity allow data to be collected for a much greater set of analytes.

Moreover, by using a split-splitless injector module, a much greater detection range can be achieved using a single instrument. By applying both split and splitless methods (with a concentration range of 2–200 ppm and 0.2–50 ppm respectively) using an extended dynamic range detection system, a single quadrupole GC-MS instrument can meet the latest Method 8270E requirements within the working range of 0.2–200 ppm using the same column.

It isn’t just improvements in instrument sensitivity and dynamic range that are helping SVOC testing laboratories meet the revised guidelines. Modern chromatography data systems, which are used to control testing runs and manage data, can include built-in tune check reports that can establish whether runs pass Method 8270E criteria (see Table 1). These solutions are helping laboratories achieve the highest levels of quality assurance automatically.

Table 1. An example of a DFTPP spectrum check for ion abundance criteria, generated using Thermo Fisher Scientific Chromeleon Chromatography Data System Software.

Minimizing Downtime and Accelerating Analysis

The EPA Method 8270E is used in almost all environmental laboratories on a routine basis for the analysis of SVOCs in extracts prepared from many types of environmental matrices like solid waste, soils, air sampling media, river water and sludge.

Due to the highly complex nature of sample matrices, MS systems require routine maintenance procedures, commonly involving frequent venting and re-establishment of the vacuum. This process can take time away from analysis, lead to instrument downtime between experiments, and result in equipment wear and tear. However, thanks to improvements in the component technologies, the latest systems are not only capable of detecting trace levels of SVOCs but can also reduce the time and resources typically spent on instrument maintenance and performance optimization. A focus on maximizing instrument uptime — a factor that is particularly important for high-throughput routine laboratories — has resulted in innovative solutions designed to accelerate routine maintenance operations.

Systems that allow the ion source to be cleaned or the column to be replaced without breaking the MS vacuum can simplify routine maintenance procedures and maximize instrument uptime. Some modern GC-MS systems permit full removal of the ion source, lenses and repeller through the front vacuum interlock without the need to vent the system. As a result, this simplified approach enables rapid cleaning or changing of the ion source.

Additionally, by isolating the mass spectrometer (which is under vacuum) from the GC system, regular maintenance operations, such as septum or liner replacement and trimming or replacement of the analytical column, can be performed very quickly with almost no downtime.

Ongoing advances in GC-MS technology are enabling the adoption of more robust methods that are capable of generating more precise and accurate data in shorter time frames.

Implementing More Cost-Effective Analysis

Conventional GC-MS methodologies involve the use of helium as a carrier gas to assist analytes in moving forward through the analytical column. As molecules are released from the stationary phase into the gas phase, they mix with the carrier gas that allows the analyte to travel through the column. Throughout this partitioning process, favored by the increasing temperature of the column, the carrier gas can influence a molecule’s diffusion rate and linear velocity. Traditionally, helium has been the carrier gas of choice; however, with global helium supplies dwindling and costs rising, labs are looking to cheaper alternatives such as hydrogen and nitrogen. While hydrogen is a reactive gas and has the propensity to impact on the ionization of certain compounds, nitrogen, though inert, shows a much lower optimum linear velocity with a consequently longer analysis time. Fortunately, a new injector design is now available for using nitrogen during the injection process (which involves higher gas consumption) with no effect on the separation process into the analytical column.6

The latest GC-MS systems include inlets that can supply both gases: nitrogen for the septum purge and split flows, and helium only to feed the analytical column at the optimum flow rate. The inclusion of injectors that can accommodate both helium and nitrogen can offer significant cost savings over the lifetime of helium cylinders by dramatically reducing the helium consumption without compromising on performance. Depending on the experimental conditions, a helium-saving injector enables a single cylinder of helium to supply a GC-MS system for 14 years.7

The Future of SVOC Testing

Ongoing advances in GC-MS technology are enabling the adoption of more robust methods that are capable of generating more precise and accurate data in shorter time frames. As we learn more about SVOCs and their impact, not only on human health but on the environment as a whole, their detection and identification will become increasingly important to support the safer use and disposal of these compounds.

About the Author: Dr. Daniela Cavagnino received a master’s degree in chemistry from the University of Milan, Italy. She started her career in gas chromatography at Thermo Fisher Scientific, spending several years in the R&D laboratories working on GC technology innovation. She conveyed her technical background into product management and marketing management roles and now has more than 10 years of experience promoting GC/GC–MS technology and applications in several different market segments.

References

1. Moran, MJ; Hamilton, PA; Zogorski, JS. “USGS Fact Sheet 2006-3048: Volatile Organic Compounds in the Nations Ground Water and Drinking-Water Supply Wells—A Summary,” 2006.

2. World Health Organization. Report on a WHO Meeting, Berlin, 23-27 August 1987. EURO Reports and Studies 111. Copenhagen, World Health Organization Regional Office for Europe, 1989.

3. U.S. EPA. National Primary Drinking Water Regulations. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Organic

4. U.S. EPA. 2017. SW-846 Test Method 8270E: Semivolatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS). https://www.epa.gov/sites/production/files/2017-04/documents/method_8260d_update_vi_final_03-13-2017_0.pdf

5. Eichelberger, JW; Harris, LE; Budde, WL. Reference Compound to Calibrate Ion Abundance Measurements in Gas Chromatography-Mass Spectrometry Systems. Analytical Chemistry, 47(7):995–1000, 1975.

6. Law, R; Cojocariu, C; Cavagnino, D. Optimized GC-MS solution for semivolatiles (SVOC) analysis in environmental samples in compliance with the U.S. EPA Method 8270D. https://assets.thermofisher.com/TFS-Assets/CMD/Application-Notes/AN-10522-GC-MS-SVOC-EPA-Method-8270D-AN10522-EN.pdf

7. McCauley, E; Magni, P; Santoro, M; Pelagatti, S. Helium Carrier Gas Conserving Inlet for Gas Chromatography, Thermo Scientific PN10410 https://assets.thermofisher.com/TFS-Assets/CMD/posters/PN-10410-ISC2014-­Helium-Carrier-Gas-PN10410-EN.pdf

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