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Comparing Packed Traps vs Capillary Traps for TO15 Analysis

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Comparing Packed Traps vs Capillary Traps for TO15 Analysis

Until recently, virtually every trapping system designed for analyzing air in stainless steel canisters via TO15 have used packed traps to concentrate the sample while removing unwanted air, CO2, and water vapor.  Packed traps have a high trapping capacity, and the use of multiple beds of adsorbents of increasing strength has allowed a wider boiling point range of compounds to be recovered.  However, it has long been known that preconcentration onto packed traps has never been able to approach the reproducibility of loop injection, which can show precision of +-1-2% RSDs.  Precision generally ranges from 4-10% using packed traps when the sample or standard remains unchanged, but can increase to a much wider error range when moisture levels or preconcentration volumes vary in the sample, which they often do when analyzing air samples or while generating calibration curves.

Entech has identified the reasons for these inconsistencies when using packed traps.  Since adsorbents, like all other solids, expand and contract upon heating and cooling, the adsorbent is expected to shrink during cooling in preparation for the next sample to be analyzed.  As an adsorbent cools, frictional forces between the adsorbent particles tend to create “channels” through the adsorbent.  These channels are low impedance flow paths where resistance to flow decreases by the 4th power of the distance between particles.  That is, if even a very small gap were to form that is only twice the distance normally found between particles, the flow increase through this small gap would be 16 times greater than the flow passing through the more densely packed adsorbent.

This in turn allows a much greater extent of chemical penetration into the trap.  It is also expected that there will be slight differences with each cooling in the way that a trap will create these channels, resulting in inconsistencies in the recovery efficiency of the trap.  Upon thermal desorption, these channels will close back up as the traps are heated, further reducing the potential for recovery of compounds that have traveled further into the trap.

Open Tubular Capillary Columns, whether WCOT or PLOT columns, have a coating on the internal surface that is just a fraction of the total inner diameter of the column.  A WCOT column may have 0.1-7um on the walls, which is not much compared to their 100um to 530um inner diameters.  Even PLOT columns have normally just 10-20um layer of particles, which still leaves most of the inside of the column empty.  When these columns heat and cool, there is almost no difference in percentage of open internal diameter, so channeling becomes an impossibility.  This means that used as traps, capillary columns are much more likely to provide a totally reproducible solution that will provide far better precision than packed columns.

A second problem with pack traps comes from the size of the adsorbent particles that are used.   Packed columns and packed traps usually have particles sizes that are at least 10 times larger than those found on the inner surface of a capillary column.  The use of smaller particles smaller than about 100 mesh in packed traps makes the pressure drop too great, making their use impractical.  if these particles were thought of as spheres to a first approximation, a 10x difference in diameter means a 1000x difference in volume, as volume varies by the cube of the radius of a sphere.  This huge difference in particle volume is extremely important when evaluating release rates of chemicals trapped within these particles, which directly relates to faster injection rates and better chromatography when back-desorbing into a capillary GC system. Adsorbent particles with 1000x less volume will also clean up much faster when exposed to very high concentration samples.  This has a big advantage with soil gas analysis, as the accidental analysis of high concentration samples can cause packed traps to become so contaminated that they can take days to clean up, whereas capillary traps show cleanup rates that are 10-100x faster, often allowing acceptable blanks directly following a sample that is 100x over the high point on the curve.

Water management is substantially improved used capillary columns with smaller particles, as the ability to dry purge out water is dependent on how fast water molecules can find their way out of the inside of the adsorbent particles.  An air sample that is at 50% Relative Humidity at 25 deg C contains 1.5% water vapor, which stated in terms relative to VOC analyte levels is 15 million PPBv water vapor.  Packed traps with their larger particles have a problem releasing more than 97% of the water during dry purging, which still leaves 500,000 PPB of water (0.5 million PPB), which creates a substantial challenge for the GCMS.  Due to the far faster equilibration of water molecules when using particles that have 1000x less volume, water can be released to >99.999%, literally leaving a water peak in the run that is 10-20PPB, which will never cause interferences in the MS, or cause excess column damage to the capillary column in the GC.  Even with injections every 20 minutes, a GCMS response will not drop down during the course of the day, as water has been completely removed by the capillary traps prior to sample injection.

Capillary columns do not have the capacity of packed columns, but when doing a splitless injection onto a capillary based GC which most TO15 systems do, capacity isn’t the issue, because a packed trap fully loaded would overload a capillary column by 50-100 times.  The issue is whether capillary columns can retain all compounds of interest, while trapping a volume large enough to reach required detection limits.  Using a series of capillary columns of increasing strength, all of the advantages listed above are realized (faster and more complete release, faster cleanup, far better water management) while retaining all compounds of interest.  If further reduction of volume is needed before injection, the primary capillary column trap can be backflushed with a smaller volume into a second capillary column focusing trap, so that a very fast injection can be performed into the GC or GCMS for optimum peak shape without the use of any liquid nitrogen.

The figures below show 250cc of an 84 compound gas standard at 10 PPB that was trapped on a 3-stage primary trap with 3 capillary columns of increasing strength, then backflused onto a second multi-column trap with shorter column lengths, and then finally backflushed onto a capillary GCMS system.  Pre-heating of the second “focusing” trap prior to GC injection allows “near liquid nitrogen focusing trap” injection rates, while again providing much better water management than dry purged packed traps or “Cold Trap Dehydration” have been able to demonstrate.  Preconcentration systems using Multi-Capillary Column Traps have a tremendous advantage for the TO15 laboratory, as productivity and costs savings can be substantial, with significantly less downtime when accidently analyzing high concentration samples which is probably the number one cause of system downtime in todays TO15 laboratories.  Maximizing uptime and productivity can make the difference of being competitive or not in today’s and tomorrow’s TO15 market.


Introducing The Cryogen-Free 7200CTS.

Entech is proud to release the world’s first multi-capillary column trapping system (MCCTS) patent pending, for the precise concentration of vapor phased volatile chemicals in the range of C3 to C18 without the need for liquid nitrogen or complicated electronic cooling. With over 28 years of continuous improvements and industry feedback, the 7200CTS is as established and reliable as it is new and improved.

Improved Performance And Dynamic Range For EPA Method TO-15 using the Entech 7200 and Thermo Scientific ISQ QD GCMS

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Canister sampling and analysis for measurement of volatile chemicals are finding use in a growing number of diversified applications. This has required air laboratories to accommodate an even wider dynamic range of sample concentrations, and a growing list of compounds to include those once thought to be incompatible with canister sampling techniques. New materials for the internal lining of canisters and field sampling systems, as well as laboratory analyzers optimized using 3D Computer Assisted Design software, have provided the improved performance needed to meet these challenges. A new Air Toxics TO-15 Analyzer based on the Entech 7200 Preconcentrator and Thermo Scientific ISQ QD GCMS system is demonstrated here, creating performance levels well beyond what was previously possible. Every aspect of the sample preparation and analysis process has been optimized to improve linearity, recovery, sensitivity, and dynamic range. Linear calibrations that meet TO-15 criteria are now possible over a dynamic range of 100-2000 fold, reducing the number of dilutions necessary, while lowering detection limits to meet today’s Low Level TO-15 standards. The improved recovery and linearity also reduces the downtime previously caused by systems that were only marginally meeting the method linearity requirements. The following application note will describe the new advancements in the 7200/ISQ GCMS system that have resulted in a dramatic improvement over prior technology.

4700 Precision Static Diluter

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The Next Generation in Standards Preparation

The 6 Channel 4700 Precision Diluter represents the next generation in accurate canister standards preparation. Utilizing a combination of precise gas flow control, exact pressure measurements, and an ultra-inert flow path, the 4700 is capable of performing multistage dilutions for achieving standards ranging from part-per-billion to low part-per-trillion. The 4700 works with canisters and Bottle-Vacs™ to create dilutions up to 100x, and then allows a second dilution of up to another 100x to yield a total 2 step dilution of up to 10,000x.

With the 4700, small 100L cylinders at 1PPM will allow over 15,000 6L canisters to be filled to atmospheric pressure with a 1PPB mixture by first making a 20PPB working standard that can be further diluted into each canister to be tested. This results in just pennies worth of standard being consumed when performing inertness testing of canisters every 1-2 years. By contrast, typical dynamic diluters that must balance flows and pressures can typically only fill 50–100 6L canisters per high concentration cylinder, making field canister inertness testing prohibitively expensive.

Performing US EPA Method TO15


More Accurate Than Dynamic Dilution Performs 2-10,000 Fold Dilutions!

  • Precise pressure measurement of each standard for accurate mass delivery to the receiving canister
  • Unlike Dynamic Dilution, a single sensor meters in all gases, cancelling out gain and zero errors
  • Always comes with 6 channels fully installed, with a re-dilution channel to make lower level standards.
  • Water is added manually to canisters (70ul), which is more accurate than using an online humidifier (4600A/D)

1000x Calibration Range using 4700 Prepared 0.4 PPB and 20PPB Standards

4700 Prepares the 20PPB standard from 1PPM cylinders, then re-dilutes the 20PPB standard further down to 0.4 PPB. The 7200 can take different volumes from each canister to dramatically increase the dynamic range while performing GCMS calibrations and method validations


4700 Software – Dilution Report

Fully documents Standards Preparation with times and dates & Simplifies Calibration QA Strategies

4700 Precision Static Diluter Features

An optional digital scale can be used to validate dilution ratios gravimetrically, thus  eliminating any need for expensive annual sensor calibrations.

The 4700 comes standard with six channels.  This allows for dedicated ISTDs, CalSTDs, and  sample dilution channels.

The 4700 Precision Diluter  can easily perform 1–100x dilutions (100 PPB to 1 PPB), or dilutions up to 10,000x by using CH6…

The 4700 conserves cylinder standards relative to dynamic blending.

The 4700 can create 1 PPB challenge standards for 6L canister inertness validation tests. (One 102L cylinder fills 1800 6L canisters).

High concentration samples such as soil gas can be effortlessly diluted with the 4700.

How are you going to Show Compliance to the new US EPA Guidance Documents on Canister Analysis?

The current EPA NATTS Technical Assistance Document, and soon the updates to EPA Method TO15 require recovery testing of VOCs being reported through each sample train and canister on a periodic basis. Each sample train and canister must show >80% recovery of target compounds. Entech has an easy solution that provides a full 24-hour continuous challenge stream at low to sub-PPB levels through up to 5 samplers and canisters at a time. Read More

That would be 25 sampling systems per week, or over 1000 complete systems a year using a single 4700. Just another example of how Entech is providing complete solutions to support air analysis laboratories, ensuring that canisters remain the Gold Standard of air analysis. Rely on Entech products to keep your air and soil gas monitoring solutions running smoothly.

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The 4700 uses precise pressure control, rather than mass flow controllers to meter in the standard. This approach has several advantages. First, very little of the standard mix is used in making a standard. This allows the original cylinder to last longer, keeping cylinder pressures higher where contents are more stable. Secondly, the mixing region used in a dynamic diluter is eliminated, substantially reducing surface area and carryover.

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Micro-QT Valves – The future of air sampling and analysis.

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Tool Free, Leak Free - Micro-QT™

The Micro-QT is a next generation gas valve offering uncompromising leak-tight performance in an ergonomic design. The Micro-QT is also versatile, providing numerous connection options to cover a wide range of applications. Once the valve is connected to tubing using compression fittings, mating male and female valve ends is literally just a quick “snap”.

Originally designed for environmental air sampling and analysis, the Micro-QT has found a place in numerous other applications. Micro-QT’s feature a distinctive bright and colorful Silonite coating that prevents gas phase compounds from interacting with the metal surface. The rugged, solid design stands up to thousands of connections, while maintaining leak tight operation. For scientists and professionals working with VOC and SVOCs, the Micro-QT’s compact internal volume reduces exposure to potentially contaminated surfaces and allows for easy cleaning.

Designed specifically for tool-free air sampling and hassle-free analysis.

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The Most Durable and Accurate Sample Collection Valves for EPA Methods TO-14A and TO-15.
There are several ways to fill a MicroValve™ canister or Bottle-Vac™ depending on sampling requirements. Here’s a brief overview:
Grab Sampling
MiniCan™ or Bottle-Vac™ samplers are filled within 0.1–0.3 minutes using an unrestricted sampler with a Micro-QT™ valve.
Restricted Critical Orifice Sampling
Sample collected using a filtered orifice restricted sampler. Fill rates are constant until the canister reaches ½ atmosphere.
Time Integrated Sampling
Time-integrated sampling is used for slow filling of canisters to determine average target compound concentrations. Fill times are 10–50 times longer than with critical orifice restricted samplers. Use CS1200E and the PN: 30-22800 adapter for Micro-QT™ Valve Samplers.
Instructions for Field Sampling
Micro-QT Valve Brochure

The Micro-QT™ Valve is optimized for volatile and light semi-volatile compounds. The Micro-QT™ Valve is compatible with all existing Entech sampling devices by simply adding a female Micro-QT™ to ¼” adapter (PN 30-22800).

Micro-QT™ Valve Kit
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SiloniteTM MicroValves

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The Micro-QTTM is a next generation pneumatic valve offering uncompromised leak-tight performance in an ergonomic design. The Micro -QTTM is also versatile, providing numerous connection options to cover a wide range of applications. Once connecting the valve to tubing using compression fittings, mating male and female valve ends is literally just a quick “Snap!”

Originally designed for environmental air sampling and analysis, the Micro-QTTM has found a place in numerous other applications. Micro-QT’s feature a distinctive bright and colorful SiloniteTM coating that prevents gas phase compounds from interacting with the metal surface. The rugged, solid design stands up to thousands of connections, while maintaining leak tight operation. For air, gas, and headspace sampling professionals, the Micro QT’sTM compact internal volume reduces exposure to potentially contaminated surfaces and allows for easy cleaning.

Entech 2018 Catalog

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This is the complete Entech 2018 Catalog. You can download the PDF or use our Flipbook viewer (below) for a smoother experience. Please note that not all sampling products are included. The Entech store is the best place to find photos and descriptions of every product we carry.



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Accurate Collection of Low Level TO-15 Compounds using Low Flow, 1 Week Time Integrated Sampling into Silonite Coated Canisters

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An improved technique is demonstrated for the accurate collection of TO-15 compounds over 1-7 days. Constant sampling rates and good recoveries of a l l TO15 compounds are demonstrated, using very low sampling rates that could potentially result in target compound losses and carryover if exposed filters and surfaces are not properly passivated. Consistent sampling rates and analyte recoveries are demonstrated using 3 Silonite coated and 2 uncoated CS1200E5 samplers as collected into 5 different Silonite coated canisters. Sampling rates were below 1cc/min to simulate the sampling rates used for collecting one week samples into 6L canisters. Five CS1200E5 samplers were also connected to 6L canisters and allowed to sample for 1 week to demonstrate consistent target compound recovery, and consistent final fill pressures using an updated flow control design which improves consistency for 1 week sampling.

Sample Canister Evaluation and Inertness Certification

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Stainless steel canisters offer a tremendous advantage over other air sampling media, namely Tedlar® bags and adsorbent traps. When canisters were first introduced, the “SUMMA” passivated canister was the only option available. Today, with the availability of electropolished, silica lined (Silonite™ and others), and glass (Bottle-Vac) canisters, as well as multiple valves and gauges to choose from, air monitoring personnel must be further educated on how to properly choose, clean, evaluate and certify a canister for TO14 and TO15 analysis. This document gives a background overview of different types of canisters as well as the procedure for properly certifying them for use.

For chemicals to remain in the gas phase, the internal canister surface must be inert to minimize adsorption.
Research efforts to create this level of inertness have led to SUMMA, electropolished, silica ceramic coated, and deactivated glass canisters. For more detail into the difference of each type of canister and properties, please refer to Entech Application Note Document 501, Understanding Sampling Canister Technology.
Due to the range of canister types and the wide variability of samples and conditions that each canister sees, it is a long established fact that not every canister will perform up to the original manufacturer’s specifications. For this reason, canisters must be evaluated individually to ensure that all target compounds can be recovered after a reasonable holding time. Entech recommends that canisters go through the evaluation and certification process described in this document once every two years or whenever a canister is suspected of having a problem.

Silonite Classical Canisters

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We have Canister sizes for all your needs

Entech’s SiloniteTM (SiloniteTM VS Summa) canisters feature a large volume capacity for detection of volatile chemicals down to the low part per trillion range. An inert and durable internal SiloniteTM coating provides a high-quality, long-term sample storage solution. Losses in the valve are avoided by using our new Toxic Organics ValveTM (TOV-2TM) which includes Entech’s new “sure-seal” technology and low carryover, replaceable nickel ferrules. An integrated valve guard is securely welded to the canister for superior light-weight valve protection without any stresses to the valve stem associated with heavy “strapped-type” valve guards. These canisters are certified to meet or exceed the technical specifications required for EPA methods TO-14a and TO-15. High-quality performance is verified for EVERY canister with our demanding chemical inertness tests.

Common Applications

Air Toxics


Soil Gas

Vapor Intrusion

Indoor Air Quality

Ambient Air

The Silonite™ Advantage

Learn more about Silonite™ Coated Canisters below!

Silonite™ Coated

100% inertness tested prior to shipment. Polished internal surface prior to Silonite™ coating for the most inert surface possible.
Silonite™ ensures there is no chance for corrosion and the subsequent loss of reactive compounds.
Silonite™ canisters are the only inertness-repairable canisters on the market. No need to fear canister inertness testing. Entech’s renewal process can return old Silonite™ cans to better than new conditions.
Externally electro-polished “after” Silonite™ coating to provide a more analytical and professional look.

Uncoated Canister

Rapidly lose their ability to recover important VOCs such as Carbon Tetrachloride. During the manufacturing of 6L half shells, organic contaminants in the form of grease and oils become trapped in the surface pores found in all stainless steel sheet metal.
Interior will easily corrode.
The metal oxides found in SUMMA canisters can actually be catalytic in promoting certain chemical reactions.
Because of the limited inertness of the SUMMA canister, a certain amount of water vapor is actually needed to allow Air Toxic compounds to remain stable. Even aromatic hydrocarbons can be lost to the surface of a SUMMA canister if enough water isn’t present.

Every Can is Tested

15L Canister

6L Canister

3.2L Canister

2.7L Canister

Want smaller cans? We have those too!

MiniCansTM are the next generation of air sampling canisters from Entech. Designed for tool-free operation and advanced robotic analyzers, Silonite® treated MiniCans™ allow the recovery of a wider range of compounds than any other sampling canister – including semi-volatiles up through the full diesel range and C25hydrocarbons.

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