In 2018, an update on regulations for respiratory medical devices meant that volatile organic compounds (VOCs) emitted from the devices must be addressed. ISO 10993-1 highlights the need for medical device engineers and manufacturers to characterize these chemicals, particularly plastics, because these often emit chemicals such as phthalates and polychlorinated biphenyls, which are thought to be a health concern.1,2

Fig. 1 - The sampling and analysis process for TD–GC–MS.

Within ISO 10993-1, a new standard method — ISO 18562 — setting out how to measure VOCs emitted from respiratory medical devices, was introduced. Now, all manufacturers of breathing gas pathway devices and component suppliers need to perform tests according to this standard method.

Three major hazards associated with medical devices are listed in ISO 18562: particulate matter, leachables, and VOCs. ISO 18562-3 — which focuses on the tests for VOC emissions — requires that samples are collected in sampling tubes and a subsequent analysis carried out using thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS) (see Figure 1). Resulting chromatographs should show which chemicals are emitted from a sample and the amounts emitted.

Micro-Chamber/Thermal Extractor

To develop compliant products and routinely monitor product quality, manufacturers can implement in-house screening for convenience. Markes’ Micro-Chamber/Thermal Extractor™ (μ-CTE™) can be used to prepare samples for TD–GC–MS to enable the rapid screening of VOCs. The μ-CTE requires minimal sample preparation and is simple to operate. Samples are placed inside one of either four or six microchamber sample pots (depending on the model), and the lids are then sealed shut. A sorbent tube is attached to the outlet of each chamber, and a flow of gas (air or nitrogen) sweeps the VOCs from the samples into the sorbent tube.

The temperature can be set from ambient up to 120° or 250 °C (again, depending on the model). The sorbent tube is packed with adsorbent material, which traps the VOCs ready for transferring to the TD. The device is compact, robust, and, together with TD, enables the GC–MS instrument to provide emissions data that correlate with longer-term reference tests. It can also be used to develop new products as well as to determine the quality of raw materials.3

The μ-CTE has three modes of operation — bulk emissions testing, surface emissions testing, and permeation testing — which means it can be used for a variety of investigations.

Fig. 2 - Bulk emissions testing: samples are placed in microchamber sample pots, and VOCs are swept from the sample into a sorbent tube by a gas flow.

Bulk Emissions Testing. Samples for bulk emissions testing are placed directly into the microchamber sample pots where gas is passed over and around the entire sample before sweeping the VOCs into sorbent tubes (see Figure 2). Examples of bulk materials include polymer beads, foams, liquids, powders, and complete small modules (e.g., printed circuit boards, plastic toys, and other small molded components).4,5

Fig. 3 - Surface emissions testing: samples are cut out of a material and sealed in place in a microchamber sample pot to collect VOCs from only the exposed area.

Surface Emissions Testing. In real-world use, some materials will only have one surface exposed to the patient (e.g., breathing bags) and, in this case, this is the only surface that needs to be tested (see Figure 3). Samples may be cut or punched out of the test material and sealed in place at the top of the microchamber sample pot using sprung spacers so that only VOCs from the surface of interest are collected. Samples of different thicknesses can be accommodated using appropriately sized spacers.

Fig. 4 - Microchamber permeation accessories enable permeation tests on nitrile gloves, for example.

Permeation Testing. Permeation testing is used to measure VOCs permeating through a thin layer of material. The material (for example, nitrile gloves or membranes used in filtering systems) is held at the top of a permeation accessory within a microchamber sample pot and sealed in place, with a gap at the top to collect VOCs (see Figure 4). A liquid sample is introduced, via a septum, into a well at the bottom of the permeation accessory.

The microchamber sample pot is then placed in the μ-CTE and gas is passed over the sample. VOCs permeating the material through to the top of the sample pot can be collected periodically in sorbent tubes to determine the length of time it takes for the VOCs to pass through the material.

Fig. 5 - Chromatogram to show the emission profile of a medical device.

Once a sample has been taken using the μ-CTE, the sorbent tube is placed in an automated TD unit. The VOCs emitted from the sample are introduced to a GC–MS for separation and analysis. Chromatographic data is generated to identify the chemicals emitted (see Figure 5).

Instruments such as the Micro-Chamber/Thermal Extractor™ (μ-CTE™) can be used for the rapid screening of VOCs released from a material.

Using μ-CTE technology in conjunction with TD–GC–MS analysis enables the testing of VOC emissions from raw materials through to the final devices. The generation of a comprehensive chemical profile can result in the detection of a wide range of volatile and semi-volatile organic compounds emitted by a sample. This methodology can be used to obtain useful emissions data on medical devices to comply with regulations and to develop new low-VOC-emitting materials, thus protecting the patient and future-proofing the product.

References

  1. P. Schossler, et al., “Beyond phthalates: Gas phase concentrations and modeled gas/particle distribution of modern plasticizers,” Science of The Total Environment, 2011, 409: 4031–4038.
  2. B. Mull, W. Horn and O. Jann, “Investigations on the emissions of biocides and PCBs under low volume conditions,” Chemosphere, 2015, 118: 65–71.
  3. T. Schripp, B. Nachtwey, J. Toelke, T. Salthammer, E. Uhde, et al., “A micro- scale device for testing emissions from materials for indoor use,” Analytical and Bioanalytical Chemistry, 2007, 387(5): 1907–1919, 2007.
  4. G. Mitchell, et al., “Emissions from polymeric materials: characterized by thermal desorption-gas chromatography,” Polymer Degradation and Stability, 2014, 107: 328–240.
  5. I. T. Pecault, “Volatile organic compound and semi-volatile organic compound outgassing rates for ethylene propylene diene monomer and fluoropolymer seals ,” Optical Engineering, 2017, 56(11): 115108.

This article was written by Nikhil Sahotra, PhD, Materials Emission Specialist, Markes International, Gwaun Elai Medi-Science Campus, Llantrisant, UK. For more information, click here .