Rapid Headspace Analysis of Total VOC's by PID

The headspace method is based on Henry’s law which states that at equilibrium, the concentration in the gas phase is proportional to the concentration in the liquid phase times Henry’s law constant (KH):
C(liq) = C(gas) x KH
This means that “at equilibrium”, the liquid phase concentration can be determined by measurement of the concentration in the gas phase.

The PID Analyzers, Model 102 (Fig 1) is an easy to use photoionization based analyzer that has embedded software for headspace measurements of total VOC’s in soil, water, food, plastics, etc. The PID is very sensitive and has a 90% response time of 1 second. It is also an ideal tool for prescreening samples (to prevent sample overload) for the mass spectrometer or other analytical tool for determining the sample composition.
Fig. 1 Model 102 with multiple Heads

The headspace method is easy to perform, requires a minimum of equipment, and requires only that the sample and standards be at equilibrium and at the same temperature to obtain accurate results. A typical procedure involves weighing (or measuring) 1 g of soil into a 40 mL VOA sample vial, DI water is used to fill the vial. Then 15 cc of liquid is removed through the septum and the capped vial is placed in an oven at 60 C for 15 minutes, shaken and cooled to room temperature. Standards bracketing the samples should be run at the same time and under exactly the same conditions. The PID analyzers Model 102 should be in the headspace mode. Then take ten cc of gas is from the vessel via a gas syringe, connect it to the 102 via a tight piece of tubing and press ENT. The peak concentration will be displayed. The concentration can then be determined by comparison to a calibration curve generated from standards. Liquid samples can be handled in a similar manner. The total analysis time is < 15 seconds per sample. Fig. 2 Headspace for Water Sample

Fig.3 Headspace for Soil Sample

Analysis of ppb Levels of Low MW Organics Compounds Using an 11.7 PID-GC

The ionization potential (IP) of low molecular weight saturated organic compounds are > 10.6 eV but < 11.7 eV. This group of compounds (ethane-butane), chloroalkanes (CH3CL. CHCl3, CCl4, CH2CL2, C2H4Cl2 etc.), oxygenates (methanol & formaldehyde) are difficult to do with any single detector except the PID with an 11.7 lamp. The dynamic range of the PID with an 11.7 eV lamp is about 106 with detection limits in the 50-100 ppb range. These detection limits could be improved using thick film capillary columns. A comparison of the range of the 11.7 eV lamp with other GC detectors is shown below.

The response of low MW alkanes C2-C6 for the PID 11.7 is shown in the chromatograph below:
C2-C6 HC with the PID 11.7

Note that the PID 10.6 eV will only respond to C5 & C6 alkanes.
The chromatogram below via PID 117 detects some chlorinated HC including ethylene dichloride (C2H4Cl4). (IP= 11 eV). Of course, the PID 11.7 also detects low ppm levels of MeOH and chloroform as shown below. Note the high sensitivity of the low MW chlorinated hydrocarbon.

The PID 11.7 also has a high sensitivity to formaldehyde, one of the few detectors that respond to formaldehyde at ppb levels without the need for derivitization. A chromatogram of methanol and formaldehyde is given below.

Remote Monitoring of Methane for Landfills and Septic Systems

Remote CH4 Measurement Final_Presentation[1]

#NASA doesn’t get enough credit for spinoffs created from their technology projects

I am concerned with NASA’s future now that I observed the takeoff of the last space shuttle last week.

Photo from NASA Facebook page

I just came across a link on AOL about 10 NASA technologies from the Space shuttle and it prompted me to write this info in my blog.

Article that prompted this blog post

A case in point-Our company HNU/PID was started in the early 1970’s as a result of a NASA photoionization mass spectrometry (PIMS) project in the late 1960’s

I was recognized recently with an “Outstanding Achievement Award” from the Northeastern Section of the American Chemical Society for the development of the first handheld photoionization (PID). This product , that has saved thousands of lives of workers involved in cleaning up hazardous waste sites, in the 80’s was created as a result of NASA’s investment in PIMS technology in the 1960’s. The hand held PID was the star of EPA’s superfund program in the 80’s and 90’s and saved many lives during the largest industrial hygiene project in the world. The PID was also selected by the EPA in the late 1970’s as a method for developing lower cost and more sensitive method for analyzing volatile organics in drinking water. Since HNU was started we have sold more than 50,000 PID’s and saved many lives.

Cape Cod Times Article


With the cancellation of the space shuttle program, many of my colleagues and I wonder where NASA is going. Technology is the engine that helped make this country great and it is technology that will keep this country competitive in the future.

If you have a similar story, or feel strongly about NASA’s future please publicize it and write a letter to your congressmen & senators.

Dr. Jack Driscoll
Sandwich, MA

New Features of the Model 301MP Area & Stack Monitor

We used a photoionization detector (PID) to analyze ppb levels of ethylene oxide (ETO). The range of the Model 301MP Area Monitor was extended so that the same analyzer can be used to measure both workplace exposure levels of ETO and stack levels. This 25 point sequencer has separate banks for the permissible exposure (PEL) and stack levels. The software was modified and a programmable sample ahead feature was implemented. This sample ahead feature provides a faster analysis time since the sampling is done during the analysis of the sample. As soon as the sample is injected, sample ahead can be started and the next sample will begin purging the sample line and the sample loop. With a 15 second inject time, the sample can be purged for 75 seconds before the new sample is injected which is adequate to clean the line from 2,000 ppm to < 1 ppm. When the high level bank points are sampled, the range is automatically switched from 0-20 to 0-2000 ppm. For the PEL sample bank, the range is switched to 0-20 ppm. The capillary column used for the analysis was an 0.53 mm thick film (7.5 micron). The detection limit for ETO was 5 ppb extending the range from 5 ppb to 2,000,000 ppb or 400,000:1. A photo of the 301C is shown below. For more info, visit our website at http://www.hnu.com.