Analysing VOCs

Volatile organic compounds are harmful to human health and the environment, but testing for these gases is improving

Volatile organic compounds (VOCs) are released into the atmosphere in the form of gases from certain man-made and natural solids and liquids and can be harmful to both human health and the environment. They are most commonly emitted naturally from plants but are also released from man-made products and processes such as building materials, fossil fuels during industrial use and paint and coatings. VOCs can be harmful to the environment and human health, resulting in short-term and long-term adverse health effects such as headaches, nausea, and damage to liver, kidneys and the central nervous system, and – in some cases – cancer.

As a result, they are subject to stringent regulations from the European Environment Agency (EEA) and the United States Environmental Protection Agency (EPA), including the EPA Method 524.3 for the measurement of purgeable organic compounds in water. These are complemented by legislation set out by more specific regulatory authorities concerning particular products.  

The Clean Air Act enforced by the US government defines VOCs as any organic compounds that participate in atmospheric photochemical reactions and sets out a requirement for products to contain limited VOC content. In addition, the European legislation REACH (Registration, Evaluation and Authorisation of Chemicals), requires companies to register chemical substances they produce or use in their products with the European Chemical Agency (ECHA) to demonstrate that the use of their substances poses no risk to humans and the environment. Product specific regulations include the European Decopaint Directive (2004/42/EC), which places a limit on the total content of VOCs in certain paints and varnishes and in vehicle refinishing products to reduce VOC emissions and protect the environment. A revision to this directive is expected in 2011 which is likely to include more product groups. In North America, the Consumer Product Safety Improvement Act (CPSIA) aims to improve safety of consumers with a focus on children’s products. This includes keeping VOC emissions in toy coatings and paints to a minimum.

The negative impact VOCs can have on human health and the environment make the analysis and detection of VOCs important, particularly in the indoor environment where concentrations are up to ten times higher than outdoors. However, as concentrations of VOCs are usually low and therefore difficult to detect, the analysis of these compounds and their effects on human health and the environment has proven a challenge in previous years.

Current methods of analysing VOCs do not detect the low levels of VOCs often present in the atmosphere and therefore do not meet US and European regulatory requirements in terms of method detection limit (MDL) levels. New and more sensitive methods are being developed to detect low levels of VOCs in line with changing regulations.

While the overall process of analysing VOCs is a mature technique, there are continuous innovations that allow laboratories to meet lower detection limits and analyse new compounds with higher throughput and improved quality. GC-single quadrupole MS can decrease analyst review time by 50%, dramatically increasing sample throughput while still detecting lower method detection limits (MDLs) of VOCs than traditional methods.

Analysis of VOCs by GC-single quadrupole MS according to well-established US EPA methodologies and in line with EU regulations requires integration of a range of instrumentation; from the sample introduction system to the gas chromatograph and mass spectrometer, to the software for data interpretation, analysis and reporting1.

A standard GC-MS method for VOC analyses has been developed using the Thermo Scientific ISQ gas chromatograph/single quadrupole mass spectrometer (GC-MS). After establishing a baseline of performance, improvements to the method were tested by combining changes to the GC-MS and applying a software package developed around routine environmental GC-MS workflows.

The GC-MS was evaluated at a scanning speed of 2,650 amu/sec (0.1 sec) over a mass range of m/z 35 to 300. An OI Eclipse 4660 Purge and Trap Sample Concentrator equipped with a sample heater and 4551A autosampler were used to deliver 5mL of sample for the analysis and was operated at a sample purge temperature of 40°C. The internal standard and surrogates were added by the Standard Addition Module (SAM) unit. The gas chromatograph was operated in the split mode. The water management temperature was set at 110°C (purge), 0°C (desorb) and 240°C (bake). Purge took place at 40mL/minute for 11 minutes, the desorb temperature was 190°C for 0.5 minutes and bake rinse cycles took place twice at 210°C for 10 minutes.   

In addition, the GC-MS was coupled to a TR 524 20 meter x 0.18mm, 1.0µm column and split ratio inlet conditions were 40/1 at constant pressure of 25 psi at 175°C. GC temperature was set at 40°C for four minutes, 18°C per minute to 100°C and 40°C per minute to 230°C for five minutes. The solvent delay was 0.5 minutes before activating filament and the MS source temperature was 250°C.

The EPA Method 524.3 recommended range of values for the purge and trap parameters reduced the cycle time of the purge and trap and minimised the amount of water injected. The shorter desorb time and a rapid oven temperature program on a narrow-bore 0.18mm id capillary column gave a shorter analysis time of 15 minutes (Figure 1). Improvement in the carrier gas control reduced band broadening of the first six gases, resulting in more Gaussian peak shapes (Figure 1). Better precision with high scan speeds of 2,650 u/sec resulted in achievement of excellent detection limits and was compatible with faster chromatography. A combination of shortened analytical time and reduction in data review time lead to an overall improvement in productivity (Figure 2).

Thermo Scientific EnviroLab Forms 3.0 software ensured streamlined and rapid creation of reports with flags for data points that fail specific quality control criteria specified by the user. Data review is also simplified by the software by showing where peaks were manually integrated and whether the quality control (QC) criteria passed or failed. Available flags include manually integrated, ion ratio failure, below detection limit and carryover flags.

Experimental results show that by using a GC-single quadrupole MS to detect VOCs, laboratories can reduce analyst review time by 50%, resulting in an increased number of samples that can be analysed during a 12 hour shift. This method also allows laboratories to achieve regulatory compliance by attaining lower MDLs as set out by EEA and EPA regulations. All of these improvements resulted in doubling the throughput of samples analysed in a 12 hour shift – from 24 to 48. In addition to this, the gas chromatograph/single quadrupole mass spectrometer was found to provide good sensitivity, spectral purity and linear dynamic range for the analysis of VOCs.