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Introducing Entech’s breakthrough technology for whole air sample collection

Helium Diffusion Sampling (HDSTM)

Introducing Entech’s breakthrough technology for whole air sample collection – Helium Diffusion Sampling (HDSTM). We now offer HDSTM 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-VacsTM 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

An HDSTM diffusion zone’s internal diameter is 20–50 times larger than typical critical orifice samplers, so particulate plugging is virtually impossible. HDSTM eliminates the need for sampler calibration, as relative diffusion rates of Helium and air are virtually constant. And unlike passive sampling with tubes – where compounds lighter than Benzene are not recovered quantitatively – HDS monitoring recovers all compounds heavier than Helium. Some important carcinogenic compounds quantitatively recovered using HDS that are not recoverable using passive tube sampling devices include Vinyl Chloride, 1,3-Butadiene, and Acrolein. HDSTM Samplers also increase their weight as more air exchanges with Helium, allowing sample collection amounts to be determined gravimetrically in the laboratory for extremely accurate and defensible measurements.
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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 HDSTM sampling versions are available from Entech

1) MiniCanTM and Bottle-Vac Samplers (refer to the image on the right). Special HDSTM MicroValves that are optimized for standard sampling event durations – the diffusion zone exists inside of the fitting.
2) Controlled helium / air exchange with an external HDSTM diffusion zone fitting that is designed to attach directly to Bottle-VacsTM and MiniCansTM with standard Micro-QTTM valves. Like the HDSTM MicroValves, these external HDSTM fittings feature a specific length or ID of the diffusion zone to provide an ideal sample fill duration and canister volume. It’s that easy. HDSTM collects an air sample much slower than vacuum driven controllers, allowing smaller canisters and Bottle-VacsTM to be used for long term sampling, at a substantially reduced cost. With HDSTM, collection of whole air samples has never been this easy, economical, and reliable!

SiloniteTM 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.

HDSTM Indoor Air Samplers

Indoor Air Monitoring

Using Helium Diffusion Sampling into Silonite® Canisters and Bottle-VacsTM for indoor air monitoring has never been so easy and cost effective!

Introducing Entech’s low-cost external HDSTM Samplers that allow any Silonite® Canister or Bottle-VacTM to be used to perform time-integrated sampling both simply and cost-effectively. HDSTM 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.
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HDSTM 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 – HDSTM monitors retain all compounds heavier than Helium. This allows even Ethane, Ethylene, and Acetylene to be collected quantitatively.

HDSTM 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.

HDSTM MicroValveTM Samplers-Fill Durations

HDSTM 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. MiniCansTM and Bottle-VacTM 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 MiniCanTM or Personal Monitor using a vacuum to collect the sample will achieve the same detection limits as the larger sampling MiniCansTM and Bottle-VacsTM 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 MiniCanTM or Personal Monitor using the vacuum to collect the sample will achieve the same detection limits as the larger sampling MiniCansTM and Bottle-VacsTM 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.

HDSTM 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-VacTM or MiniCanTM 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-VacTM 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 SiloniteTM filtered inlet line sampling directly into a Bottle-VacTM in pouch attached to belt.

Canisters and Bottle-VacTM 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.

Label: Ceiling - Vacuum Grab Sampling (5-10 sec)
STEL – Vacuum Sampling or Helium Diffusion Sampling™ (HDS) (15 min)
TWA CS1200P/ MiniCan™ Vacuum Sampling or Helium Diffusion Sampling™ (HDS) (1-8 hrs)

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