Supelco OMI™ Indicating Purifiers: An Essential Part of Gas Delivery

By: Robert F. Wallace, Reporter EU Vol 23

Robert F. Wallace


Most chromatographers realize the importance of using gas purifi ers as part of a gas delivery system for the supply of high purity carrier gas for gas chromatography (GC) instruments. Unfortunately, the replacement of these purifi ers as they become spent may be overlooked, potentially leading to chromatographic problems. The dilemma facing chromatographers is determining the proper time to change-out purifi ers. Changing too early does not allow for the maximum return of the purifi er cost. Changing too late runs the risk of contaminants entering the GC. The solution is to install an indicating purifi er downstream from all other purifi ers.

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Why Use an Indicating Purifier?

Capillary columns can degrade rapidly when exposed to oxygen or water vapor in the carrier gas. Even the highest purity carrier gas may contain trace amounts of these contaminants. Installing an indicating purifi er as a fi nal safeguard before the carrier gas enters the GC is recommended as part of any carrier gas delivery system. An indicating purifi er is designed to give a visual indication of carrier gas contamination by color change. Contaminants may originate from the gas source (cylinder or generator) or from leaks in the system. By placing an indicating purifi er downstream of all other gas purifi ers, the user can determine if the purifi ers installed upstream have expired and need replaced. Note that it is important to mount the indicating purifi er in a prominent location so that it can be routinely inspected visually.

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The Supelco OMI Purifier

The Supelco oxygen moisture indicating (OMI) purifi er simultaneously and irreversibly reduces oxygen and water to less than 10 ppb in a carrier gas stream. Oxygen and water breakthrough are minimized because the OMI purifi er is capable of handling oxygen surges of several hundred parts per million, or carrier gas delivery rates up to 1000 cc/minute (~150 psig). The OMI purifi er can also remove carbon dioxide, carbon monoxide, most sulfur compounds, most halogen compounds, alcohols, phenols, and other trace impurities. Because of its capacity to remove a number of impurities, it provides point-ofuse gas polishing in addition to a fi nal visual assurance of the gas quality before it enters the GC. The main reason for the OMI purifi er’s effectiveness is the Nanochem® resin, a material developed for the demanding gas purity needs of the semiconductor manufacturing industry. Contaminants, even at concentrations below 1 ppm, progressively change the resin’s color from black to light brown. Because Nanochem’s color change can be seen at a glance through the OMI purifi er’s clear glass body and plastic safety guard, remaining purifi cation capacity can easily be monitored. When the color change reaches the replacement mark, simply change the tube.

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Manufacture/Installation of the OMI Purifier

The Supelco OMI purifier is packaged in an atmospherically controlled environment. Foil seals on each end of the purifi er prevent contamination of the resin from oxygen and water. Installation into the beveled thorns inside the holder will produce a closed system for the carrier gas fl ow to assure the resin is not exposed to ambient contaminants. These thorns also allow the OMI purifier to maintain a leak free connection. The inert glass body prevents the diffusion of oxygen and water into the carrier gas stream, which helps eliminate unacceptable background noise that can affect highly sensitive detectors.

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OMI Purifier Versus Other Purifiers

The OMI-2 purifier removes up to 0.16 grams of oxygen or 0.2 grams of moisture. Figure 1 shows that these capacities equal or exceed those of many non-indicating ambient temperature purifi ers. Unlike many other purifiers, OMI purifi ers are effective at the removal of contaminants other than just oxygen and moisture. In fact, an OMI purifier will remove all critical carrier gas contaminants, providing a carrier gas purity that is better than most certified gases.

Figure 1.Comparison of Purifier Capacities of Ambient Temperature Purifiers

The OMI purifier should not be confused with the green oxygen indicating tubes that contain manganese oxide. These tubes will only indicate oxygen. Additionally, concentrated oxygen surges above 10 ppm will swamp the manganese oxide, allowing oxygen to breakthrough to the chromatographic system. Figure 2 shows comparisons of oxygen capacity. Given the low capacities of the green tube, they only signal an already existing problem. These green tubes offer no other carrier gas protection than for oxygen and will not ward off impending problems you may encounter.

Figure 2.An OMI Purifier Traps More Oxygen Compared to Green Indicating Purifiers

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The use of an indicating purifier mounted in a visible location close to the GC allows the user to easily determine when purifier change-out should occur. This will help insure a constant supply of clean carrier gas. The Supelco OMI purifier not only outperforms other indicating purifiers, it also outperforms many non-indicating purifiers. Connecting the OMI purifier downstream from other Supelco gas purifiers will give a purification system designed to economically give maximum gas purity, providing quality gas for excellent detector response.

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