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PetroPRO Fence Line Area BTEX Air-Monitoring Solution

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By. Jim Norgaard


June 2007

Over the last two decades a variety of portable or transportable gas chromatographs have been specifically designed for field use. Each instrument has introduced innovations that have simplified the task of on site 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 that can be attained as results are available almost immediately. Results at the field site allow the user to revise their sampling strategy in real-time to 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 in 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 a field portable instrument is as follows:
* Combined weight below 15 pounds for the instrument and any required support equipment
* Size less than l000 in³
* 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
* 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 what 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 work loads, 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.

Keeping all this in mind, Photovac Incorporated together with Quinn Technologies has developed a new high-speed portable gas chromatograph 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. This gas chromatograph is designed for high-speed analysis of benzene, toluene, ethyl benzene, and m-xylene; however, it can be modified for analysis of a wide range of volatile organics. Photovac will highlight the innovations incorporated into the design of the new gas chromatograph and how these features will improve the utility of this GC in the field, as well as provide more accurate and timely data under real world conditions.

The PetroPRO 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 10-20 seconds. Before and during the sample time heavier VOC’s are backflushed from the precolumn. The sample inlet path is made from inert materials, such as stainless steel and BTEX, 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 lop is filled, carrier gas sweeps the sample from the loop onto the pre-column, and then the compounds of interest are gated onto the analytical column.

One of the key features that enable the PetroPRO portable gas chromatograph to quickly analyze samples is the proven inert low-volume advanced alloy stainless steel diaphragm valves used in the sample path. These diaphragm valves direct the sample through the GC to provide efficient transfer with low dead volume for improved peak resolution. These valves have been used with great success in previous generation Photovac products.

In the PetroPRO, ultra-clean air containing less than 0.11PPM of total hydrocarbons is used as a carrier gas to push the sample though the GC. In order to increase the speed of analysis and eliminate sample condensation a low temperature, heated isothermal oven is used to heat the valves, sample loop, pre-column, analytical column, and detector. The oven is low temperature for three reasons. First, a higher oven temperature would require a larger battery with a higher weight. Second, BTEX analysis is well suited to a lower temperature oven. And third, the PetroPRO is intrinsically safe, which means the instrument can be safety taken into and used where explosive atmospheres may be present. In certain industries the presence or potential presence of an explosive atmosphere is quite common. This intrinsic safety design limits the temperature that can be generated in the instrument. 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 VOCs. A proven technology such as photoionization is readily understood and acceptable by users and regulatory agencies that may be overseeing a project.

Incorporating an inert sample path, low dead volume valves, rugged field column, an isothermal oven, and proven detector technology has allowed Photovac to develop a high-speed chromatograph in a truly portable package that analyses BTEX in less than three minutes down to single PPB levels for benzene and toluene. The total instrument weighs approximately 13 pounds in a package that is less than 700 in³ in size. The PetroPRO has a start key to begin sample introduction with a single key press. A dedicated calibration key reminds the user of the importance of regular calibration for maximum instrument accuracy and for quick access to starting a calibration. Since a truly portable instrument does not require a laptop in the field, the PetroPRO has a built-in graphic display that shows the name of the compound detected as well as the concentration of die compound in the sample. This eliminates the need to interpret results in the field. The results are also stored in the PetroPRO GC’s memory for later download to a PC, if required. The other functions are programmed into a very easy-to-use interface with an intuitive menu that makes searching for certain functions very easy. All complex tasks are pre-programmed at the factory and need not be changed by the user.

A portable gas chromatograph can be an important tool for air-monitoring of VOC’s. With a portable GC that is both easy-to-use and fast, emergency workers can get the 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 such real-time monitoring using a portable GC occurred during a tire landfill fire. The 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.

Jim Norgaard (BS & MS IIT, Chicago) is Photovac’s Vice President of product development, for more information email Jim at jnorgaard@photovac.com or visit www.photovac.com

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