An Overview of Gas Chromatography Mass Spectrometry

When technical documentation isn’t sufficient to confirm compliance with regulations like EU REACH or RoHS, analytical testing is another way to ensure that your products are up to code. The gas chromatography mass spectrometry (GC-MS) system combines the capabilities of gas chromatography and mass spectrometry, two different analytical techniques, to create an exceedingly effective process. Keep reading to learn about how GC-MS can help you with your environmental compliance process.

Contact Enviropass to request GC-MS testing. Verify what regulated substances may be present in your products!

Overview of Gas Chromatography Mass Spectrometry

During the GC-MS process, the sample is first analyzed using gas chromatography, then transferred to a mass spectrometer.

Gas Chromatography

The first step of a gas chromatography (GC) analysis is to convert the sample into the gas phase. Since electronics are solid products, they are first dissolved using an organic solvent like dichloromethane. Any volatile solvent can be used as long as it’s compatible with the analyte – some examples of incompatibility would be if the analyte were not soluble in the solvent, or if the solvent reacted with the analyte to form a new compound. The dissolved sample is then injected into the gas chromatograph and vaporized.

Afterward, an inert gas – called the mobile phase –transports the samples through the instrument. These samples traverse a column known as the stationary phase. The stationary phase is often filled with a silicon-based compound, and as the sample passes through, it will interact with the various substances present in the sample. As a result, the substance separates – the compounds that interact strongly with the stationary phase will move through the instrument more slowly than compounds that experience little interaction. Consequently, the time it takes for the sample to move through the column – called the elution time – will help determine which substances are present.

However, multiple compounds can have very similar elution times, making it difficult to analyze complex samples using gas chromatography alone. As a result, many laboratories decide to perform an additional analysis using mass spectrometry (MS), leading to the GC-MS technique.

Mass Spectrometry

Once the sample has gone through the GC process, the gas is transferred through a tube to the mass spectrometer. There, the samples are blasted with a beam of electrons to ionize them. The ions then travel to a mass analyzer, which accelerates the ions into a magnetic field. Based on the weight of the ions, they will experience more or less deflection due to the magnetic field and land on the detector in different positions. The position of the ions will therefore denote the weight of the ion, allowing for the mass-to-charge ratio (m/z) to be calculated.

What is the m/z?

The m/z is simply the atomic mass of the compound divided by the formal charge of the compound. Since the formal charge is usually +1, the m/z is often just the mass of the compound. For example, toluene has an atomic mass of 92 and an m/z ratio of 92.

Below is a mass spectrum for toluene:

On the x-axis, you can see the m/z, which is used to characterize the substance (qualitative analysis). On the y-axis, you can see the relative abundance, which is used to calculate the concentration of each compound present in the sample (quantitative analysis). Learn more about interpreting mass spectra.

Applications of Gas Chromatography Mass Spectrometry for Electronic Product Testing

Despite the immense capabilities of GC-MS, it’s limited in the range of compounds it can test for. Compounds such as lead, mercury, and other heavy metals are typically not feasible analytes because they are non-volatile. An analytical method such as XRF would be more suitable in these cases.

However, GC-MS can still be beneficial for electronic product testing. For RoHS, GC-MS can test for restricted phthalates like DEHP. In addition, many substances listed under EU REACH are volatile organic compounds (VOCs), making them suitable analytes for GC-MS as well. This is also true for substances restricted under EU POP, TSCA-PBT, and halogen-free requirements.

Another use for GC-MS is root cause analysis. This can be helpful when electronic products fail to work because of the interference of unknown substances. Using GC-MS, technicians can detect and identify the substances causing the issue.

Other Considerations when Using Gas Chromatography Mass Spectrometry

Gas Chromatography Mass Spectrometry – Matrix interference

A potential challenge when using GC-MS is matrix interference. Matrix interference occurs when substances present in a sample interfere with the detection of the analyte. Since electronic components often consist of intricate layers and elements, they can be particularly susceptible. A big way this impacts GC-MS analysis is the generation of background noise – excessive background noise can introduce additional peaks to the mass spectrum, making the analyte peaks difficult to identify and potentially obscuring them.

Gas Chromatography Mass Spectrometry – Low Analyte Concentrations

When testing for regulations such as RoHS and REACH, your instrument must be able to detect very small concentrations of the analyte. Without sensitive techniques and proper sample preparation, detecting and quantifying such small amounts is challenging.

The gas chromatography tandem mass spectrometry (GC-MS/MS) technique is one approach to achieving lower detection limits. This technique follows a similar procedure to regular GC-MS, with the added benefit of the sample undergoing mass spectrometry analysis twice. Following the separation of ions based on their m/z, the ions are further separated into ion fragments and subsequently detected. This process enables the detection of different compounds that have the same m/z, allowing it to characterize the substance more precisely. At Enviropass, we rely on the GC-MS/MS technique to ensure maximum specificity in our testing procedures.

Learn more about the use of GC-MS/MS for applications like pesticide testing.

Portable Gas Chromatography Mass Spectroscopy Instruments

Many technicians use portable GC-MS instruments for field applications such as environmental testing and forensic analysis – this is especially useful when samples are prone to degradation. The trade-off is that their smaller size and limited battery power may not allow for procedures that are as complex. Portable GC/MS instruments also rely on manual sample injection, which is less convenient than the autosamplers that GC-MS devices typically use. Regardless, their size and portability make them very valuable for on-site analyses.

When obtaining technical documentation isn’t possible, it’s essential that you have the knowledge and resources to undergo product testing for your devices.

If you have any questions about GC-MS or want to inquire about our GC-MS/MS testing services, please get in touch with us for a free Enviropass consultation!