Stainless steel and glass are the most commonly used materials in GC Inlet and sample handling systems. However, surface imperfections and inherent chemical dependent adsorption exist with even the highest quality 316L stainless steel, causing substantial losses of vapor phase chemicals. At elevated temperatures, surface metal oxides can be catalytic, especially exposed iron on the surface or in pores below the surface. The fact that 316SS is about 67%-70% iron makes catalytic losses a certainty unless the surface is treated with Silonite™. Glass, although more inert than stainless steel, also contains additives which have a negative effect on surface inertness. These include Iron, Sodium, and Boron.
Placing a thin layer of Silonite™ over these surfaces eliminates exposure of the sample to these reactive additives and impurities.
Stainless steel canisters offer a tremendous advantage over other air sampling media, namely Tedlar bags and adsorbent traps. Since their introduction in the late ‘70s, canisters have continued to grow in popularity due to their ease of sampling, long storage times, low blank levels, and the ability to perform multiple analyses in the laboratory. Like Tedlar bags, the concentration of the sample is not altered in the field. The sample is simply placed in a container that preserves the concentration until the analysis is performed from days to weeks later in a laboratory. Whether the concentration is PPM level or Sub-PPB, the sampling is performed the same way, eliminating much of the responsibility on the part of the individual performing the sampling.
It was about 30 years ago that the first release of EPA Method TO-14 appeared for monitoring of VOCs in ambient air that specified the use of 6L stainless steel canisters having a special internal “SUMMA” passivation to improve chemical inertness. Although “SUMMA” really refers to the process used to apply a Nickel/Chromium oxide layer to the inside of the canister, the canisters themselves became known as SUMMA canisters. The whole purpose of applying the Ni/Cr Ox layer was to prevent exposure to iron, as iron is known to catalyze the reaction and subsequent loss of several of the VOCs in the TO-14 method list, thereby reducing the effectiveness of the canister as a sampling and storage device. With canister whole air sampling, it’s all about how long the sample can remain in the canister without any of the concentrations changing. The Ni/Cr Ox layer greatly improved the stability of TO-14 compounds in 304 stainless steel canisters relative to uncoated canisters. Considering that 304 stainless is 70% iron, applying something to the internal surface to cover up the iron is really not an option.
The SUMMA passivation process has some drawbacks. First, although the Ni/Cr Ox layer prevents exposure to iron, it leaves an ionically bound surface that will adsorb polar VOCs and aromatic compounds unless there is enough water vapor in the canister to out-compete these compounds for this somewhat active surface. This works for the compounds on the TO-14 list, but more reactive compounds including reduced sulfurs and amines still exhibit poor stability. Also, it is important to realize that extra water must be added to SUMMA canisters to keep VOCs in the gas phase when performing sampling when relative humidities dip below about 20%. Remember that “percent relative humidity” is temperature dependent. When sampling on a Winter day where the ambient temperature is below 0 deg C, collected canisters will almost certainly be below 20% RH when brought back into a laboratory that is at a more comfortable 25 deg C. In these cases, water should be added to SUMMA canisters “prior” to sampling, by injecting about 50ul into the evacuated 6L canister before deployment to the field. Also, during canister cleaning, it is recommended to fill and evacuate SUMMA canisters a few times at room temperature before heating the canisters, as raising the temperature to 80 deg C will drop the Relative Humidity to just 1-2%, and polar compounds will stick quite effectively to the SUMMA passivated surface, preventing their removal from the canister.
SUMMA Canister manufacturing is also expensive, as it creates extremely toxic chromium waste that requires disposal into specialized landfills. For the past 15 years, deactivation layers consisting of vapor deposited silica have been replacing the SUMMA passivation process, as the silica layer is more inert, requires no water vapor to complete the canister passivation, and produces no toxic waste. The gas phase deposition process also makes for a smoother deposition, relative to the diffusion limited liquid phase SUMMA deposition process. Silonite Canisters have this internal silica layer and have been demonstrated by independent laboratories to be the most inert canister available, based specifically on the recovery of hydrogen sulfide. The silica layer is similar to the inside of a GC column, and Silonite canisters are helping to increase the range of compounds recoverable to approach nearly that of “all GC compatible compounds”. For SVOC range compounds (Semi-Volatiles), Silonite canisters must be heated during analysis to ensure that these heavier compounds are driven quantitatively into the gas phase, just like a GC column needs to be heated to elute heavier injected compounds. Entech has developed laboratory analyzers that automate the heating process, making it possible to extend the range of recoverable compounds from C1-C12, to C1 to over C25.
You can tell them that almost all canisters made today are not SUMMA Canisters, but are either Silonite Canisters or some other brand. Please see our complete discussion of canisters in our “Understanding Canisters Technology” document in our Technical Library. Beware of other canisters on the market with “no internal coating at all”. These manufacturers have simply electropolished and nitric acid passivated the 304 stainless, which only removes the iron that is right on the surface. When brand new, these canisters are shown to be inert because initially there is little iron on the very surface after nitric acid stripping during manufacturing. However, as these canisters age, oxidation and corrosion will expose the iron just under the surface, drastically reducing the stability and recovery of extremely carcinogenic compounds such as carbon tetrachloride. Many of these canisters are marketed as “SUMMA-Like”, but they don’t have the actual SUMMA applied NiCrOx surface that is hundreds of atoms thick, preventing the iron well below the surface to ever be exposed, even after 20 years. Finally, “all ceramic” deactivated glass canisters, called Bottle-Vacs, do not have reactive iron to worry about, and have shown recoveries equivalent or superior to those of SUMMA canisters for TO-14A and TO-15 compounds, and these are slowly gaining popularity as a low cost solutions for canister sampling. Bottle-Vacs are also becoming popular for diluting very high concentration canister samples in the laboratory prior to analysis.
MiniCansTM are the next generation of air sampling canisters from Entech. Designed for tool-free operation and advanced robotic analyzers, Silonite™ (SUMMA vs Silonite™) treated MiniCans™ allow the recovery of a wider range of compounds than any other sampling canister. Like their larger 6L cousins, MiniCans™ excel at recovering compounds that are incompatible with tube sampling technology, including Siloxanes, H2S, mercaptans, formaldehyde, amines, ammonia, and many other thermally labile compounds. Despite the MiniCan’s small size, advances in GCMS sensitivity allow for detection limits that easily surpass EPA Method TO-14a and TO-15 requirements. The MiniCan’s superior analytical performance, low shipping weight, lower cost, and autosampler friendly design make it an ideal solution for advanced air monitoring applications.
* Discount applies to price after customer volume discounts are applied. Promotion ends 1/15/18 at 5pm PST. Purchase Orders must be submitted by that time.
Bottle-Vac™ samplers are the most economical gas-phase sample collection containers available. They use Micro-QT™ Valves which are small and non-contaminating by design. Our Bottle-Vac™ samplers are as gas-tight as stainless-steel canisters, making them a low-cost alternative for whole air sampling. A sample is only exposed to treated glass, 316 stainless or Silonite™ coated stainless steel, and a small O-ring which forms the seal at the cap. All of these materials are inert, allowing for a wide range of analytes to be recovered. Time-weighted sampling techniques are possible using MiniCan™ sampling inlets, or by using Helium Diffusion Sampling.
H2S and Methyl Mercaptan recovery has continued to be a analytical challenge when sampled into canisters at PPB to sub-PPB levels. The presence of more than 10–15% relative humidity within a sampling canister has been shown to dramatically reduce reliable storage time of H2S and to a lesser extent Methyl Mercaptan, relative to dry samples.
Fortunately, Entech offers an economical solution. Now, laboratories can choose to collect H2S and Methyl Mercaptan samples into new H2S Bottle-Vac™ canisters. These canisters are designed to accommodate a specific amount of Silica gel within the sampler in order to dehydrate the sample upon collection. This small amount of Silica gel effectively removes more than 90% of the water vapor without affecting quantitative recoveries of H2S and Methyl Mercaptan. Easily collect H2S, COS, and more into 500mL and 1L H2S Bottle-Vac™ canisters and reliably retain >80% recovery even after a 1–2 week storage time prior to analysis. For the collection of heavier sulfur compounds which are less affected by humidity levels, simply utilize standard Bottle-Vac™ or Silonite™ canisters.
Entech Sorbent Pens™ represent in advancement passive ’diffusive’ sampling, incorporating many subtle but critical engineering design elements that ensure quantitative recovery, reproducibility, and cost effective long term use. The result of decades of research into volatile chemical sampling and analysis has resulted in a sampler so accurate and reproducible that the data is almost unbelievable!
Passive or diffusive sampling is defined as the unassisted molecular diffusion of gaseous analytes through a diffusive region and onto an adsorbent. The DSP (Diffusive Sorbent Pen) does not require a pump and contains no moving parts. After sampling, the adsorbed analytes are desorbed directly into the GC or GCMS of choice.
Canisters offer a simple and highly effective means of measuring volatile chemicals in air ranging from PPM to sub-PPB levels. The “GC grade” internal surfaces of canisters allow for a much wider range of recovery relative to most adsorbent-based samplers, without the inaccuracies inherent with adsorbent- based methods such as volume measurement errors during sampling, inconsistent recoveries, breakthrough, and reverse adsorption, to name a few. Over the years, smaller canisters have become more popular due to their ease of use relative to the heavier 6L canisters, as well as to the reduced need for very large sample sizes as laboratory analyzers become more sensitive. Along with the reduction in size has come the development of different surface treatments and types of canisters, including fused silica lined stainless steel (eg.Silonite MiniCans) and deactivated glass (Bottle-Vac) canisters. These canisters actually extend the range of compounds that can be successfully collected, stored, and analyzed by GC and GCMS relative to the older SUMMA technology, as their internal surfaces are much more like that of a GC column. Looking at this another way, if a volatile or light semivolatile compound is GC compatible, it will likely be compatible with these newer sampling canisters. A complete overview of the different types of canisters in use today can be found in the Entech Document 501, “Understanding Sampling Canister
A new, simplified approach for filling air sampling canisters during monitoring of Environmental pollutants in air is described. The new approach uses helium diffusion to drive the sampling process in a way that has several advantages over vacuum sampling. Canisters are filled with helium after cleaning, using a valve and inlet fitting combination that allows the proper time integrated sample to be collected simply by removing the valve and allowing helium to leak out through a calibrated orifice. Orifice sizes are available for performing a range of integration times from 3 hours to 1 month, without the need for an external flow controller. Elimination of the flow controller from the flow path reduces sample loss, prevents contamination from previous sampling events, greatly increases simplicity and reliability of the sampling process, and increases the molecular weight range recoverable to include Semi-Volatile compounds. Utilizing HDS™ can also reduce the potential for contamination during field and lab leak checking. Data is presented detailing the advantages of HDS™, including comparisons with vacuum sampling canisters to show precision and sampling consistency.
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.