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

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.

Free Bluetooth Wireless Capability for all PID Analyzers Portable Instruments

We recently added bluetooth capability to our Model 102 portable photoionization analyzer . This wireless capability links the datalogging in the 102 with the free logging software in the external PC to produce 1 to 5 graphs (PID ppm/ppb and three other channels selecte from one [IR(CO2, CG or TCD)/TCD/or CG and two other electrochemical sensors (select from > 30 EC Sensors). A typlical plot of PID VOC's ppb and ppb is shown below:

The data is logged into an EXCEL compatable file that is saves in CSV format for opening directly into EXCEL. The format is shown below:

The portable analyzers include the following:

Model 102 PID (only)
Model 102+ PID with multisensor capability and ppb option
Model 113 O2 and other electrochemical sensors (choose from 30)
Model 107 stack gas analyzer
Model 113 with TCD or CG + EC sensors
Model 114 IR + with CO2 or CH4 sensor plus 2 EC sensors

We are offering free bluetooth capability for all new portable analyzers. Contact us at http://www.hnu.com and check out our blogs: http://analyzersource.blogspot.com & http://gasanalysis.blogspot.com

Can I still get my old HNU PI101 fixed?

That was a common question at the AICHE (#AIHA) show in Portland, OR (May 14-20, 2010). We, PID Analyzers, LLC, brought one of the first PI101's (1st portable photoionization analyzer) ever built to the show. I had many people who stopped, looked at the PI101 and said "I used one many years ago but I didn't realize  that you still made them". I said that we stopped making them about ten years ago but we can still fix them,  Several people asked about an 11.7 probe for their 101 and I said "we can still supply one". I even had one industrial hygienist who stopped by who said " I bought my PI101 25 years ago and it still works. I said "you should send it in for a clean and cal, it will probably need one after 25 years".

Some of our competitors build their PID's like cell phones. That is, their lifetime is just over 2 years and spare parts are available only for several years beyond that. We can fix PI101's that were built 35 years ago. The PI101 was the first portable analyzer that was used extensively in reducing exposure to vinyl chloride, solving exposure problems at Love Canal (1st Superfund Site) and written in to the Superfind legislation. Note that Superfund was "the world's largest industrial hygiene program". That is all history now but the PI101 is still around and can still be fixed 35 years later. For more information click here. 

A photo of the PI101 with its successor, the Model DL102, is shown in the photo below:   

                                                                    Model PI101

Multisensor 102+

PID Analyzer's Portables Now Can Have Wireless Capability

PID Analyzer's portable analyzers now have wireless capability through Bluetooth. A sending unit is embedded into the analyzer and the receiving unit is plugged into a PC via the RS232 port. The free logging software that comes with our portables has  multichannel (up to 5) logging and is used to collect the data.  The data is graphed and can be saved in comma delimited ASCII format and imported directly into EXCEL. A typical graph of ppb VOC (blue) and ppm CO2 (red) is shown in the graph below:

The graph displays the effect of rain on VOC's (upper) and CO2 (lower) in the outside air for the Model 102+. The Model 102+ was upstairs and the PC was downstairs about 150' away. Another option for wireless on the portables is also available now. This uses a Mica 2 mote from Crossbow and is available an as option. The advantage of the Crossbow includes a longer range (different frequencies) and additional sensor capability such as geographic position sensor (GPS) through an eight channel ADC. Contact PID Analyzers for additional information. A Paper on a Model 102 with wireless and GPS is available here.

Measure VOC’s with an Inexpensive Multipoint PID or FID

PID Analyzers has designed an inexpensive  2, 3 or 4 point  sequencer (MP) that can used with the Model 201B to monitor both  the  inlet and outlet of VOC removal devices such as thermal oxidizers, scrubbers or carbon beds. The 201 MP can also be used to monitor 2-4 points in a process or different  areas in a room or plant. PID or FID Analyzers (Model 201B) equipped via a 2-4 point sequencer to provide rapid measurement of the removal efficiency of the pollution control device thereby  eliminating the  need for  two separate analyzers. The Analyzers & MP are housed in a NEMA 4 enclosure that can be Z purged (optional) to meet Class1 Div 2 requirements.