September 27, 2018

How quartz filters address challenges in air monitoring

By Lynn Tian, Product Manager

Tackle challenging air monitoring applications with high-purity quartz filters that have high temperature resistance and low contaminant content.

Whether it’s in the office, the factory, on the road or in the place where you live—air quality matters.

A better understanding of the impact of air quality on human health has led to a demand for precise data on contaminants in the air around us and a push to meet air quality standards set by organizations such as the US Environmental Protection Agency and European Commission.

The workflow for analyzing the elemental composition of airborne particulates differs depending on the elements of interest. Choosing the right filter for your investigational target is critical to success. In this blog, we review some of the key parameters in air quality monitoring, and how quartz filters enable us to accurately measure these parameters in challenging applications.

Key particulate parameters: size, composition and concentration

  • Size: Contaminant particle size affects the time particulate matter spends in the atmosphere before settling down, making it crucial for understanding air quality. For example, PM10 and PM2.5, particulate matter less than 10 micrometers and 2.5 micrometers in diameter respectively, are of key size parameters that are commonly measured in roadside air monitoring. They are in the range to affect human health.
  • Composition: Identifying particle composition and the presence of elements such as carbon or heavy metals can help determine both the source of particulates and their likely effects on human health.
  • Concentration: Measuring levels of particulate contaminants in the air is critical to understanding air quality. By passing a known volume of air through a filter with a known particle retention, scientists can not only collect a particulate sample for further analysis, but also calculate concentrations of compounds trapped by the filter.

Applications for quartz filters

Accurate, reliable air quality monitoring begins with selecting the right filter for sample collection, and then following the relevant workflows for that specific filter. High-purity quartz filters which provide both high temperature resistance and low contaminant levels are the best choice for:

  • Organic carbon/elemental carbon (OC/EC) monitoring
  • Heavy metal testing.

Organic carbon/elemental carbon (OC/EC) monitoring

A typical OC/EC testing method involves initially heating up a filter stepwise in an oxygen-free atmosphere to around 700°C. This process decomposes most organic carbon and all carbonates, leaving behind some elemental carbon. The vaporized organic carbon is converted to CO2, which may then may be measured by reducing to methane and using a flame ionization detector (FID).

An FID cannot be used to measure inorganic carbon. So, to measure the remaining elemental carbon, the temperature is lowered and a small amount of oxygen added to the chamber. A second 850°C heating step burns off the remaining elemental carbon, oxidizing it into CO2 for FID analysis.

Combining both FID values provides a measure of both organic and elemental carbon on the filter, and therefore in the original air sample.

These steps necessitate the use of a filter that is both carbon-free and has high temperature resistance. As a material, quartz is well-suited to the task. High purity quartz filters contain no carbon and can remain stable at temperatures up to 900°C.

Heavy metal testing

Detecting heavy metals in air requires high-volume air filtration, with sampling often for a minimum of 8 hours. This extended sampling time helps maximize reliability and the detection of low-level pollutants.

The workflow for heavy metal testing involves weighing the filter before and after sampling to determine the total mass of particles captured. There are then several possible analytical methods to identify and measure heavy metal pollution including:

  • Energy dispersive X-ray fluorescence (EDXRF)
  • Acid digestion followed by inductively coupled plasma mass spectrometry (ICP-MS).

It’s essential for the accuracy of these methods to select filters with very low heavy metal content. Filters that contain measurable amounts of key elements, such as lead (Pb) and copper (Cu), will lead to inaccurate results.

Quartz consists of pure SiO2, and high quality quartz filters contain negligible amounts of heavy metal contaminants, particularly when compared with glass fiber. As a result, they will have little effect on the measurement and are well-suited for heavy metal testing.

At GE Healthcare Life Sciences, we provide a broad range of filtration solutions, including high-purity quartz filters.

Our QM-A, QM-H, and QM-B quartz fiber filters are resistant to very high temperatures—up to 800°C for QM-A and QM-B and 900°C for QM-H—and are low in heavy metals and other contaminants. They are particularly suitable for high-temperature and high sensitivity applications, such as OC/EC analysis.

Our team of experts is familiar with a wide range of filtration applications and can advise on which materials are most suitable for a given application. Contact your local GE Healthcare Life Sciences representative to discuss your needs.