Volatile organic compounds (VOCs), including semi-VOCs, are one of the most important classes of environmental pollutants because of their significant health effects. On-site or in-field, real-time measurement of VOCs is critical to timely assess environmental contamination, to develop effective risk management strategies, and to protect environmental and human health. Although many portable and handheld gaseous VOC detectors are commercially available, they are unsuitable for on-site or in-field, sensitive VOC analysis due to the lack of an automated miniature sampling/preconcentration platform that can directly handle samples. Zebra Analytix is developing a microsystem that can be coupled to these portable/handheld instruments for addressing this critical unmet need. Moreover, it can be adjusted to extract and concentrate VOCs from other liquid samples for food quality/safety testing, biomonitoring, clinical diagnosis, etc. The microsystem can also be modified for concentration of VOCs from gaseous samples or for extraction and concentration of VOCs from solid samples.
But, how can a handheld, miniature gas chromatography (GC) system accomplish the concentrations of VOCs needed to produce results? The system being developed consists of two chips in a tandem configuration. The first chip is designed to extract VOCs directly from samples. The extracted VOCs are concentrated in the second chip, in which the concentrated VOCs can be released on demand for subsequent analysis. In conventional preconcentrators, the packed structures can provide high adsorption capacity but they have disadvantages.
Micro preconcentrators (µPCs ) can be divided into three broader categories. The first consists of micro-cavities or micro-channels filled with granular forms of adsorbent material. The second type utilizes adsorbent materials in thin film form deposited on a membrane or inside microfabricated channels/cavities. In the first category, drawbacks include high-pressure drops and power consumption, and higher costs. The µPCs in the second category, on the other hand, have low power consumption and are typically manufactured with a MEMS-compatible process; however, they have limited capacity due to small surface areas.
Zebra’s µPC belongs to the third category, which is characterized by forming closely-spaced high-aspect-ratio embedded microposts and coating them with a thin film adsorbent layer. This category is an innovative approach for increasing adsorbent sites (concentration factor and sample capacity) while avoiding high-pressure drops and power consumption. Dr. Masoud Agah, Zebra’s Chief Technology Officer, along with his group, is one of the pioneers in the development of this approach.
The article appeared, in part, in Pittcon Today, February 28, 2018