Frequently Asked Questions (FAQs): Air Sampling

1. What is the maximum temperature for Restek TO-Can and SilcoCan canisters?
2. What is the maximum pressure for Restek TO-Can and SilcoCan canisters?
3. What is the difference between a TO-Can and a SilcoCan canister?
4. Are Restek air sampling canisters shipped under pressure or vacuum?
5. Can Restek repair canisters and controllers?
6. What critical orifice should I select based on my canister size and sampling time requirements?
7. How can I optimize my TO-14 or TO-15 analysis?
8. Does Restek provide gas calibration standards?
9. What do I do with my empty reusable gas cylinders?
10. Can my gas standard be recertified?
11. What regulator should I use with my gas standard?
12. How can I troubleshoot pressure problems in my gas standard?
13. What is the maximum pressure for gas sampling bags?
14. Which bag should I use for my sample?
15. How long can I keep my samples in gas sampling bags?
16. When should I use solvent desorption (thermal desorption) vs. other air sampling techniques?
17. What is the advantage of using Siltek-treated gas sample loops or valves?
18. What kind of fittings are on Restek’s gas sample loops?
19. What is a “PI” marked or TPED gas sample cylinder?
20. What is the difference between treated and untreated cylinders?
21. How do I order a dip tube for my sample cylinder?
22. How can I clean a treated gas sampling cylinder?
23. How do you convert a gas standard concentration from percent to ppmv?
24. Why would I choose a RAVEqc quick-connect air valve over a traditional diaphragm valve like a RAVE or RAVEn valve?
25. Are RAVEqc quick-connect air valves compatible with Entech Micro QT valves?
26. Is the sealing mechanism the same for RAVE, RAVEn, and the RAVEqc air sampling valves?
27. Will the O-ring in a RAVEqc quick-connect air valve eventually wear out?
28. Do I need to use a RAVEqc valve bracket?
29. Which RAVEqc quick-connect air valves do I need?

If your question doesn’t appear on the list, you can contact Restek’s expert chemists.

1. What is the maximum temperature for Restek TO-Can and SilcoCan canisters?

The maximum recommended temperatures are as follows:

• 80 °C for a SilcoCan canister (with or without a gauge) cleaned in the presence of oxygen.
• 120 °C for a TO-Can or SilcoCan canister with a gauge cleaned in the presence of an inert gas.
• 140 °C for a TO-Can or SilcoCan canister without a gauge cleaned in the presence of an inert gas.

Do not exceed the maximum recommended temperatures.

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2. What is the maximum pressure for Restek TO-Can and SilcoCan canisters?

The maximum recommended pressure for all Restek air sampling canisters is 40 psi (~ 2.75 bar) as described in these instructions. Do not exceed the maximum recommended pressure.

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3. What is the difference between a TO-Can and a SilcoCan canister?

Restek’s TO-Can canisters (toxic organics) are general-purpose canisters that are intended to be used for methods such as TO-14A, TO-15, IP-1A, ASTM D5466, OSHA PV 2120, and NJ DEP Low Level TO-15. These canisters feature a proprietary electropolished surface that is designed to maintain compound stability. TO-Can canisters are functional equivalents to “SUMMA” canisters.

SilcoCan canisters are Siltek treated and are more inert than TO-Can canisters. They are ideal for low-level reactive sulfurs (5–20 ppb) as well as some of the more challenging TO-14A and TO-15 compounds. These Siltek-treated canisters are typically recommended for the collection and storage of sulfur-containing or brominated compounds. Siltek-treated accessories should be used with these canisters to provide the most inert sampling pathway.

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4. Are Restek air sampling canisters shipped under pressure or vacuum?

Each canister is slightly pressurized with contaminant-free nitrogen to approximately 15 psig (1.0 bar) prior to shipment.

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5. Can Restek repair canisters and controllers?

Repair services are available for most of our current canister and controller products (excluding RAVEqc quick-connect air valves). Custom catalog (cat.#) numbers and details for these repairs are presented in the table below.

Reconditioning services are also available for our current generation canisters. We will replace the valve and clean and leak test the canister at a cost that is less than replacing the entire canister. To request reconditioning services, please follow these steps:

1. Contact Restek’s customer service team or your local international representative to place an order for custom cat.# 569419 (RAVE diaphragm valve) using a purchase order.

2. Obtain a service authorization number (SRV#) to place on the shipping container.

3. Clean the canister before shipment to Restek.

4. Include a completed "Health and Safety Declaration."

5. Return the canister intact. Do not remove valves, gauges, or parts from the canister.

To request any of these repair services, simply contact our Customer Service Team or your local Restek International Representative.

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6. What critical orifice should I select based on my canister size and sampling time requirements?

The following table lists the recommended orifice diameters, associated flow rate ranges, and canister volumes and sampling times:

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7. How can I optimize my TO-14 or TO-15 analysis?

In addition to our comprehensive Guide to Whole Air Canister Sampling, we have an in-depth series of blog posts detailing air analysis. These valuable resources will help you optimize your analyses.

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8. Does Restek provide gas calibration standards?

Restek provides gas calibration standards manufactured by Spectra/Linde, Airgas (formerly Scott/Air Liquide), and other gas calibration suppliers. These air standards include TO-14A, TO-15, environmental blends, Scott transportable pure gases & mixtures, natural gas, and refinery gas, as well as related accessories. We can also source custom, made-to-order gas calibration standards. To request a quote, simply complete this form.

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9. What do I do with my empty reusable gas cylinders?

Local regulations can vary greatly. If you wish to dispose of or recycle empty cylinders, be sure to do so according to local regulations.

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10. Can my gas standard be recertified?

Recertification is available for gas standards. Gas standards can be expensive and tend to be stored in the lab for months, if not years, so it is wise to have the composition recertified by a qualified vendor. For gas standards purchased from Restek, request recertification directly from Spectra/Linde Gases, Inc. (1-800-932-0624) or Airgas (formerly Scott/Air Liquide gas) (1-800-331-4953). For gas standards purchased from vendors other than Restek, it is necessary to contact the vendor who manufactured the mixture.

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11. What regulator should I use with my gas standard?

We offer six regulators for our gas standards. Specifications are summarized below:

	DCG Partnership Cylinders: Size: 7.6 x 24 cm CGA-170/110 connection U.S. DOT Specs: DOT-4B-240ET Please note: This cylinder is not approved for use in Canada. Recommended regulator: cat.# 22032		Airgas 110 L (Pi-marked Cylinders for EU Regulations): Aluminum construction Size: 8.3 x 29.5 cm Volume/Pressure:   110 liters of gas @ 1,800 psi CGA-180 outlet fitting Weight: 2.2 lb/1 kg DOT Specifications: 3AL2216 Recommended regulator: cat.# 26371, 26372, 21572, or 21572-R100
	Spectra (Linde) 104 L: Aluminum construction Size: 8 x 24 cm Volume/Pressure:   104 liters of gas @ 1,800 psi CGA-180 outlet fitting Weight: 1.5 lb/0.7 kg Recommended regulator: cat.# 21572,  21572-R100, 26371, or 26372		Airgas 124 L: Aluminum construction Size: 8.3 x 30 cm Volume/Pressure:   124 liters of gas @ 1,800 psi CGA-180 outlet fitting Weight: 2.3 lb/1 kg Recommended regulator: cat.# 26371, 26372, 21572, or 21572-R100
	Airgas 14 L: Contents: 14 liters Pressure: 240 psig (17 bar) Outlet Fitting: CGA 160 Weight: 1.5 lb/0.7 kg Dimensions:   3" diameter x 11" height   (7.6 x 28 cm) DOT Specifications: 4B240 Please note: This cylinder is not approved for use in Canada. Recommended regulator: cat.# 22690		Airgas 48 L: Contents: 48 liters Pressure: 300 psig (21 bar) Outlet Fitting: CGA 165 Weight: 1.75 lb/0.8 kg Dimensions:    4" diameter x 16 ¼" height    (10.2 x 41 cm) DOT Specifications: 39 NRC Please note: This cylinder is not approved for use in Canada. Recommended regulator: cat.# 22691

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12. How can I troubleshoot pressure problems in my gas standard?

The most common problem encountered with gas standards is the absence of a pressure reading at the regulator. To check your regulator, remove it from the cylinder, and connect it to a cylinder that you are sure has pressure. If the regulator registers a reading on the “good” cylinder, the problem is likely that the cylinder in question is empty. If the regulator does not register a reading on the “good” cylinder, then the problem is the regulator and it must be repaired or replaced.

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13. What is the maximum pressure for gas sampling bags?

The maximum recommended pressure for all Restek gas sampling bags (including Tedlar, ALTEF, and multi-layer foil bags) is approximately 2 psi (~ 0.14 bar) or ≤80% filled. Exceeding the pressure or fill volume may result in a leak and/or sample loss.

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14. Which bag should I use for my sample?

ALTEF bags are an alternative to Tedlar bags for the collection of volatile organic compounds (VOCs); however, these bags are not recommended for ketones, acetates, hydrogen sulfide, and permanent gases.

Multi-layer foil gas sampling bags are recommended for light, low molecular weight analytes including methane, carbon dioxide, carbon monoxide, and permanent gases. These bags are not recommended for low (ppm) level VOCs due to background levels.

Tedlar bag compatibility is similar to ALTEF bag compatibility, except that Tedlar bags contain trace amounts (≤1%) of dimethylacetamide (DMAC) and phenol, due to their manufacturing process, while ALTEF bags do not. Therefore, some labs prefer ALTEF bags to prevent exposure of their samples to DMAC and phenol.

For reactive compounds like ammonia and chlorine gas, Restek does not recommend the use of sampling bags. Instead, we recommend SilcoCan air sampling canisters.

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15. How long can I keep my samples in gas sampling bags?

Single-use sample bags are typically intended for short-term storage (approximately 24–48 hours). Storage for >48 hours is usually not recommended, unless validation studies verify longer stability of target analytes. We recommend the following guidelines when using gas sampling bags:

Before Sampling

• Store unused bags in a clean environment, sealed in an outer bag to prevent adsorption of contaminants.
• Preclean bags before use by flushing with high-purity nitrogen.
• Leak rate should not exceed 0.1" Hg/min.

During Sampling

• Do not fill bags more than 80%.
• Be sure the PTFE tubing used for bag connection is clean.
• Use a vacuum box sampler for direct bag filling, in order to avoid contamination from a sampling pump.
• 3 L/min is a typical flow rate.

After Sampling

• Bags are intended for a single use due to potential sample adsorption onto the bag film.
• Hold times are typically 48 hours, unless validation study demonstrates longer stability.
• Protect samples from direct sunlight and store above 0 °C to prevent condensation.
• Transport in rigid, opaque container to prevent bag puncture; do not ship by air unless samples will be kept in a pressurized area.

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16. When should I use solvent desorption (thermal desorption) vs. other air sampling techniques?

Please refer to the following table for a comparison of the advantages and disadvantages of canisters, gas sampling bags, and solvent desorption tubes (thermal desorption tubes).

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17. What is the advantage of using Siltek-treated gas sample loops or valves?

Siltek treatment is a passivation process that applies an inert, integral layer to components used for chromatographic analysis. Unlike traditional deactivations, it is not susceptible to cleavage or formation of active silanols and, therefore, greatly reduces both bleed and the breakdown or adsorption of active components, compared to conventional surface coatings. This unique surface provides an inertness range that surpasses other surface deactivations used in gas chromatography. In sensitive analyses, Siltek-deactivated system components provide outstanding analytical results. For more information on Siltek treatment and treated products, refer to our surface treatment FAQs.

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18. What kind of fittings are on Restek’s gas sample loops?

Our gas sample loops have 1/16" fittings, a 1 mm inner diameter (ID), and are for use with “W type” valves.

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19. What is a "-PI" marked or TPED gas sample cylinder?

To comply with the European Union Transportation of Pressurized Equipment Directive (TPED), Restek offers “-PI” marked cylinders for use in European Union (EU) countries. The mathematical Pi mark is required to be stamped into the cylinder (metal) if the cylinder is sold into an EU country.

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20. What is the difference between treated and untreated cylinders?

Siltek-treated sample cylinders are recommended for the collection, storage, and analysis of ppb levels of sulfur, mercury, or other sensitive compounds. Because these compounds quickly react with stainless steel surfaces, accurate determination of these compounds is not possible when samples are collected and stored in untreated sample cylinders. Siltek passivation techniques bond an inert layer into the surface of stainless steel, preventing active compounds from reacting with or adsorbing to the steel. Please refer to this stability study for additional information.

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21. How do I order a dip tube for my sample cylinder?

A dip tube (also known as an outage tube) provides vapor space above liquefied gases in a sampling cylinder so that if expansion occurs with an increase in temperature, the pressure is not significantly increased. Basically, the length of the dip tube is used to determine the filling capacity of the cylinder.

This blog post contains detailed instructions on how to select and order an appropriate dip tube. Restek sample cylinder valves can be ordered with or without a dip tube from this page or by contacting our U.S. customer service team or your local Restek representative.

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22. How can I clean a treated gas sampling cylinder?

To clean a treated part, rinse with a solvent that will dissolve probable surface contaminants (i.e., use a nonpolar solvent to remove hydrocarbon contaminants, or a more polar solvent to remove more active contaminants). Avoid using cleaners containing abrasives as they can scratch the surface layer. Mild sonication might assist in removing contaminants, but do not oversonicate—this could damage the surface layer. Do not use basic solutions with pH>8.

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23. How do you convert a gas standard concentration from percent to ppmv?

For gas standard concentrations, percentage is equivalent to 10,000 ppmv. For example, a concentration of 8.5% is equal to 85,000 ppmv.

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24. Why would I choose a RAVEqc quick-connect air valve over a traditional diaphragm valve like a RAVE or RAVEn valve?

High-quality diaphragm valves like RAVE and RAVEn valves are great choices for air sampling applications. However, like all diaphragm valves, they are installed using wrenches and users must be careful not to cause damage by cross threading or overtightening when making connections. In contrast, RAVEqc quick-connect air valves are tool-free valves that any user can connect and disconnect quickly, easily, and consistently. You can use a RAVEqc quick-connect air valve by itself or you can attach one to an existing bellows/diaphragm valve. Used in tandem, they can protect a more expensive valve from damage because the point of connection moves to the quick-connect valve, which is not vulnerable to damage from cross threading or overtightening. In addition, with two valves inline, you create extra security for your sample; should one valve fail, the second acts as a backup. Used alone or in tandem with another valve, RAVEqc valves are great options for labs interested in eliminating the use of wrenches for the many connections made between air sampling canisters and the associated devices used to collect and analyze air samples.

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25. Are RAVEqc quick-connect air valves compatible with Entech Micro QT valves?

Yes. Any male RAVEqc quick-connect air valve will connect to an Entech Micro-QT female valve, and any female RAVEqc quick-connect air valve will connect to an Entech Micro-QT male valve.

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26. Is the sealing mechanism the same for RAVE, RAVEn, and the RAVEqc air sampling valves?

No, RAVEqc quick-connect air valves use a different sealing mechanism as described below.

• RAVE and RAVEn air sampling valves are both diaphragm (or membrane) valves that seal by actuating a flexible metal diaphragm so that it either presses against a contoured seat within the valve—closing it—or it is released and flexes away from the seat, opening the valve to flow.
• Male and female RAVEqc quick-connect air valves create a seal by pressing special pistons against O-rings using internal springs to close the valve ends; this is the resting state when the valves are not connected. When the male and female valves are connected, the springs are compressed, which shifts the pistons and allows flow through a special channel that is also sealed by the O-rings.

Note that the O-rings contained within RAVEqc valves are made of Viton and do not off-gas under typical air sampling conditions, and, therefore, do not create background contamination. The O-ring is also chemically inert and will not negatively interact with any sample that is compatible with Viton material.

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27. Will the O-ring in a RAVEqc quick-connect air valve eventually wear out?

All O-rings have a finite life span, but RAVEqc quick-connect air valves are made with O-rings that have been proven to provide reliable actuations in the lab without problems. In addition, each valve is manufactured and tested to ensure it is ready for use when purchased. When O-rings do eventually wear out in RAVEqc quick-connect air valves, it is far more common for the failure to occur in the male valve because the mechanism that opens flow between the male and female valves requires a stem in the female valve to pass through the O-ring in the male valve. This is normal, but it does mean that male valves are likely to wear out before their female counterparts.

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28. Do I need to use a RAVEqc valve bracket?

A RAVEqc valve bracket is required for use with Restek 1, 3, 6, and 15 L air sampling canisters when using the compression fitting mounted directly on the ¼" canister tube stub. This bracket is not needed when using Restek miniature canisters or Entech canisters.

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29. Which RAVEqc quick-connect air valves do I need?

When selecting RAVEqc quick-connect air valves, first consider where you will be installing the valves. There are too many possible configurations to list individually, but you can identify the parts you need for your specific setup using these general considerations.

• Every RAVEqc quick-connect air valve has two halves (a valve side and a fitting side). Each side needs to be matched to the opposite gender valve or fitting (male to female and vice versa). On the fitting side, also be sure to match the dimension you are connecting to.
Examples:
• To connect directly to an air canister with a tube port ¼" female compression fitting, you can use any RAVEqc quick-connect air valve with a ¼" male compression fitting. You must also use a RAVEqc valve bracket if using a 1, 3, 6, or 15 L Restek air canister.

• To connect to the ¼" male compression fitting on a diaphragm valve that is installed on an air canister, use a RAVEqc quick-connect air valve with a tube end fitting.

• If you are using a RAVEqc quick-connect air valve with a tube end fitting, consider the dimensions/clearances you need for installation when selecting the valve length.
• If you are analyzing reactive compounds, we recommend using Siltek-treated RAVEqc quick-connect air valves for a highly inert sample path.
• Male valves are generally less expensive than female valves, so we recommend male valves for the devices you have the most of (probably air canisters, rather than cleaning ovens, etc.).

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