Bio-monitoring of VOCs Using Breath Samples

Volatile organic compounds have been used extensively at the workplace, used in many consumer products, and are also emitted from various processes, materials and human activities. Exposure to these chemicals by inhalation, ingestion or through the skin can contribute to total body burden. Most exposure data are based on air sampling; however, exposure through skin absorption and ingestion can be significant in many situations. Biological sampling is the better approach to assess total human exposure in relationship to health risks. However, the currently accepted biological approach frequently entails the use of an invasive procedure to collect the biological material (e.g. blood), and the low concentrations of VOCs present in such matrices can pose many analytical problems resulting in frequent non‐detection of the chemicals. Some of these problems are presented below:

• Due to the volatility of this class of compounds and the use of common collection device (i.e. Vacutainer® tubes) for blood samples, the VOCs present in the blood will be drawn into the partial vacuum existed in the headspace inside the tube. Combining with the frequent agitation/shaking during handling and transportation, significant losses into headspace will occur.
• VOCs are known to have very short half‐lives in humans. As such, the time of sampling and analysis are critical in their analysis.
• The commercial available Vacutainer® tubes can generate background interference as a result of the plastic content of the tube and the rubber cap, which can also provide an adsorptive surface for other organics from the surrounding environment to seep into the

Why Using Breath Sample for Biological Monitoring

• Non‐invasive and simple, samples can be collected at any time
• No need for medical professionals to take the samples
• Allow easy detection of VOCs at the parts per trillion (ppt) levels
• Repeat samples can be collected easily.

The Principle of Biological Monitoring Using Breath Samples

For volatile organic compounds, sampling and analysis of breath is a better measurement than blood and urine for biomonitoring. The concentration of the VOCs in the blood is in equilibrium with the concentration in the air in the alveolar portion of the lungs. This is because both capillary blood wall and alveoli walls are thin enough to allow the free exchange of chemicals through the tissue membrane. Therefore, VOC concentrations in alveolar (end‐tidal) air are proportional to that of blood. Breath sampling offers many advantages in the monitoring of VOCs for human exposure. The main advantage is the non‐invasive nature of specimen collection. In addition, specificity can be assumed as the unchanged VOCs are measured. An adult, exhaling deeply, typically breathes out over 4L of air. Only the last 100 ml of this, all from the alveolar portion of the lungs, is retained by the Bio‐VOC sampler. It is important that only the alveolar air is sampled, not that from the mouth or bronchial passages. As the Bio‐VOC holds 129 ml of air therefore, typically 1 L. of alveolar air is required to pass through the device to ensure an undiluted sample. Once the breath has been collected, a screw‐in plunger is used to steadily discharge the sample into a concentrating (sorbent) tube. After collection in a sealed sorbent tube, the breath sample is stable for transportation and analysis – a distinct advantage over blood and urine samples. The sample is then transported back to the laboratory and analyzed by thermal desorption GC/MS system. Since the entire breath sample will be used for analysis, the sensitivity especially when coupled with “Selective Ion Monitoring” mode of the mass spectrometer will be ultra low at the parts per trillion range. This approach makes possible detection of ultra‐low concentrations of VOCs in blood with positive confirmation and sample integrity.