Introducing Entech’s breakthrough technology for whole air sample collection
Helium Diffusion Sampling (HDS™)
Introducing Entech’s breakthrough technology for whole air sample collection – Helium Diffusion Sampling (HDS™). We now offer HDS™ active sampling solutions for indoor air monitoring that simplify the collection of airborne chemicals for GC and GC/MS analysis. Rather than performing a traditional vacuum sampling event, MiniCans and Bottle-Vacs™ are initially filled with helium, or helium with a recovery surrogate, and active sampling occurs in response to the controlled exchange of helium with air through a diffusion region. Read More
How Does Helium Diffusion Sampling Work?
Helium diffuses much faster than air and other chemicals to be sampled. The vacuum created by escaping helium actively draws surrounding air into the sampler. This active air sampling causes the collection rates for all compounds to be the same, so individual sampling factors do not have to be determined as with other diffusion sampling devices. The net result is a technique that is more of a helium-driven TO-15 sampling canister than a diffusive sampling device, as only the helium is operating under the control of diffusion.
Two indoor air HDS™ sampling versions are available from Entech
Silonite™ MiniCans for Helium Diffusion Sampling Features
Diffusion zones are factory set and remain constant
Weighing the sampler after collection and again after evacuation determines collected sample volume.
Verified leak free with gauge prior to sampling
Perfect for whole air sampling
Ultra-inert and compact sampling surfaces.
HDS™ Indoor Air Samplers
Indoor Air Monitoring
Using Helium Diffusion Sampling into Silonite® Canisters and Bottle-Vacs™ for indoor air monitoring has never been so easy and cost effective!
Introducing Entech’s low-cost external HDS™ Samplers that allow any Silonite® Canister or Bottle-Vac™ to be used to perform time-integrated sampling both simply and cost-effectively. HDS™ utilizes a simple diffusion zone to control the exchange rate of helium and air, with diameters that are 20–50 times larger than typical critical orifice samplers, making particulate plugging virtually impossible.
HDS™ eliminates the need for sampler calibration, as the relative diffusion rate of Helium to air is virtually constant. Unlike passive sampling with tubes – where compounds lighter than Benzene are not properly recovered – HDS™ monitors retain all compounds heavier than Helium. This allows even Ethane, Ethylene, and Acetylene to be collected quantitatively.
HDS™ Samplers also increase their weight as more air exchanges with Helium, so collected amounts can be determined in the laboratory gravimetrically for extremely accurate and defensible measurements. Just select the color coded sampler below and the required container size is shown in the table to achieve the sampling duration desired. All of these new samplers can also be used to perform quick grab sampling (2–30 seconds) into containers that are shipped to the field under vacuum rather than being filled with helium. For more dusty locations, samplers are available with a built-in filter.
HDS™ MicroValve™ Samplers-Fill Durations
HDS™ Indoor Air Samplers – Simple, Reliable, and Cost-effective.
Ceiling measurements have historically been a challenge because there is no way to quickly and reproducibly collect a sample using tube and badge samplers. MiniCans™ and Bottle-Vac™ samplers make this easy. Simply opening and closing the evacuated container accomplishes the task in just a few seconds with extremely high precision. These whole air samplers can easily be checked prior to filling to show that they are still under vacuum; assuring a defensible sample collection process. Detection limits are equal whether performing STEL or TWA sampling procedures because the sampling container is always filled with the same amount of sample. Even a small 50cc MiniCan™ or Personal Monitor using a vacuum to collect the sample will achieve the same detection limits as the larger sampling MiniCans™ and Bottle-Vacs™ because just 0.25cc is typically used during each analysis to achieve a 0.05 PPM detection limit for most compounds by GC/FID or GCMS.process. Detection limits are equal whether performing STEL or TWA sampling procedures because the sampling container is always filled with the same amount of sample. Even a small 50cc MiniCan™ or Personal Monitor using the vacuum to collect the sample will achieve the same detection limits as the larger sampling MiniCans™ and Bottle-Vacs™ because just 0.25cc is typically used during each analysis to achieve a 0.05 PPM detection limit for most compounds by GC/FID or GCMS.
HDS™ Personal Monitor shown using vacuum rather than helium diffusion sampling to collect an instantaneous ceiling measurement sample
Vacuum sampling for 15 minutes into a Bottle-Vac™ or MiniCan™ is easily accomplished using a simple restrictor and transfer line leading to the evacuated sampler worn on a convenient waist-mounted pouch. The chart below shows the fill times based on the size of the sampler used. Note that filling with a critical orifice sampler maintains a constant flow rate only until the canister or Bottle-Vac™ is half full, then the flow rate will begin to decrease. Fortunately, the sampling can be stopped at 50% of atmospheric pressure while still providing several times the amount of sample needed by a laboratory to perform the analysis. Typically laboratories will measure the pressure, dilute the sample 2–3x to create a positive pressure in the container, and then adjust for the dilution when determining concentrations. Using this approach, the dilution amount is very reliably determined via pressure measurement, allowing a high degree of accuracy.
STEL monitoring shown with Silonite™ filtered inlet line sampling directly into a Bottle-Vac™ in pouch attached to belt.
Canisters and Bottle-Vac™ samplers provide an exciting new way to collect whole air samples in the workplace to determine exposure levels. Whole air sampling does not attempt to “extract” chemicals at the time of sampling and is therefore inherently more reproducible and defensible than the badge, cartridge, and tube sampling. Whether performing Ceiling, STEL, or Time Weighted Average sampling, detection limits are always the same because the total amount of sample collected in each case is the same. Interaction of the target compounds with the matrix is substantially reduced by leaving the sample analytes in the gas phase, virtually eliminating any matrix effects on target compound measurements.