Having a Field Day
Over the last two decades a variety of portable or transportable gas chromatographs (GC) have been specifically designed for field use. Each instrument has introduced innovations that have simplified the task of onsite air monitoring. Portable instrument users are well aware of the advantages of field sampling. These advantages include more representative results, because there is no sample degradation during transport, and rapid answers, because results are available almost immediately. Results at the field site allow the user to revise their sampling strategy in real time to possibly complete the sampling more efficiently and at a lower cost. In the case of a hazmat incident, rapid results can be crucial in determining the extent of a potential health hazard.
Naturally the lighter, faster and more sensitive a field portable instrument is, the more beneficial this is for the end user. A portable instrument must be ergonomically designed for comfortable transport by a wide variety of users. High-speed analysis is important because it increases the number of samples that can be taken over the course of a day, which can help better define the boundaries of contamination. Low detection limits can also help accurately delineate the edges of a contamination plume.
There is significant discussion regarding the very definition of field portable. There are many different definitions of portable, which often depend on the user, their specific application and both environmental and sampling conditions. Access to AC power in the field, the need to move the instrument around a site, sources of support equipment, intrinsic safety, etc. are important considerations at certain field monitoring sites. The general consensus regarding the definition of field portable instrument is as follows:
The advantages of field sampling include more representative results, because there is no sample degradation during transport, and rapid answers, because results are available almost immediately.
- Combined weight below 15 pounds for the instrument and any required support equipment;
- Size less than 1,000 cubic inches;
- On-board consumables (e.g. carrier gas and batteries) for eight hours of field operation;
- Built-in display and controls so a laptop is not required in the field to retrieve data or view results; and
- Instruments should be rugged and weatherproof with controls that are easy to manipulate while wearing thick gloves.
Anecdotally this definition seems to be reasonably well-accepted and puts some boundaries around which characteristics make an instrument portable.
Another important consideration is ease of use. An often-heard comment is that an instrument is not very useful if no one can remember how to operate it. With staff reductions, inter-company transfers and increased workloads, the expertise to effectively use an instrument is a valuable and limited resource. A portable instrument should be easy-to-learn and hard-to-forget. An intuitive user interface, large well labeled keys and a brief easy-to-read and understand user manual are all important attributes that can make an operator quickly understand how to properly use all the features of an instrument. An easy-to-use instrument is a valuable addition to any air-monitoring program.
One example of this new kind of technology is a new high-speed portable GC developed by Photovac Inc. specifically designed for accurate, rapid screening of common volatile organic compounds (VOCs) on site. The self contained, battery operated gas chromatograph incorporates proprietary detector and valve technology to increase the resolution of GC peaks and speed of analysis. The gas chromatograph is designed for high-speed analysis of benzene, toluene, ethylbenzene, and m-xylene (BTEX); however it can be modified for analysis of a wide range of volatile organics.
High-speed analysis is important because it increases the number of samples that can be taken over the course of a day, which can help better define the boundaries of contamination.
The PetroPROTM field portable GC is designed to take ambient air samples. Since a portable instrument must be robust enough for field use, a 1.0 micron hydrophobic particle filter is used to keep debris out of the sample inlet. A positive displacement diaphragm pump is used to draw samples into the sample loop. Typical run time for the pump is 10 to 20 seconds. Before and during the sample time, heavier VOCs are backflushed from the precolumn. The sample inlet path is made from inert materials, such as stainless steel, and PEEK to maintain sample integrity: low loss at low concentrations and low memory at high concentrations. This ensures minimal carryover between samples under field conditions where the characteristics of the sample are often unknown. Once the sample loop is filled, carrier gas sweeps the sample from the loop onto the precolumn and then the compounds of interest are gated onto the analytical column.
Once through the column, the sample flows through a photoionization detector with a 10.6 eV lamp. Photoionization is a field proven technology that provides for very low detection limits for many volatile organic compounds. A proven technology such as photoionization is readily understood and acceptable to users and regulatory agencies that may be overseeing a project.
The high speed chromatograph in the portable package analyzes BTEX in less than two minutes down to single parts per billion (PPB) levels for benzene and toluene.
Access to AC power in the field, the need to move the instrument around a site, sources of support equipment, intrinsic safety, etc. are important considerations at certain field monitoring sites.
Since a truly portable instrument does not require a laptop in the field, the GC has a built-in graphic display that displays the name of the compound detected as well as the concentration of the compound in the sample. This eliminates the need to interpret results in the field. The results are also stored in the GC's memory for later download to a personal computer if required. The other functions are programmed into an interface with an intuitive menu that makes searching for certain functions easy. All complex tasks are preprogrammed at the factory and need not be changed by the user.
A portable gas chromatograph can be an important tool for air monitoring of VOCs. With a portable GC that is both easy-to-use and fast, emergency workers can get real-time results they need. These real-time results can help protect the safety of employees at a field site and health of people in the surrounding community. An example of real-time monitoring using a portable GC occurred during a tire landfill fire. A portable GC was used to monitor for benzene levels in the smoke plume downwind of the fire as well as to monitor levels of benzene inside homes approximately one mile from the landfill. Getting rapid results allowed the monitoring group to determine that benzene levels in the plume were below the action limits both in the smoke plume and inside nearby homes.
American Industrial Hygiene Association -- www.aiha.org
Federal Remediation Technologies Roundtable -- Technology Cost and Performance Review -- costperformance.org
Centers for Disease Control -- Analysis of Portable Gas Chromatography -- www.cdc.gov/niosh/nmam/pdfs/chapter-i.pdf
U.S. Environmental Protection Agency -- National Exposure Research Laboratory for Environmental Sciences -- www.epa.gov/nerlesd1/verification/site/tech-rpts.htm
This article originally appeared in the April 2003 issue of Environmental Protection, Vol. 14, No. 3, p. 45.
This article originally appeared in the 04/01/2003 issue of Environmental Protection.