Chromatographic-grade gases, purity

Carbon Dioxide (CO2)—Supercritical fluid chromatographic grade, 99.99 % minimum purity, sun>lied pressurized in a cylinder equipped with a dip tube for removal of liquid CO2. (Warning—Liquid at high pressure. Release of pressure resiflts in production of extremely cold solid CO2 and gas which can dilute available atmospheric oxygen.)... 

The highest purity (>99.99%) oxygen is obtained through further refinement. At 99.99% the impurities total only 100 ppm. This grade of oxygen is used in the manufacture of electronic components, fiber optics (qv), etc, or for gas chromatograph calibration or research appHcations. 

Materials. Olefins were Phillips pure grade, appearing to be better than the reported 99% purity by gas chromatographic analysis on an AgN03 column. Methylene blue was U.S.P. basic blue No. 9, and methanol was Baker spectrophotometric reagent. All other solvents were either chromatographic or spectroscopic grade. 

Pyridine is commercially available in several grades for specific applications. Specifications vary according to country but are usually greater than 99.8% purity by gas chromatographic analysis (Scriven etal., 1996 Burdick Jackson, 1997). 

Materials. The gases used had a purity >99% the carbon monoxide contained <1% hydrogen by GLC silica gel, 4 m X 1/8 inch, 70 °C, Perkin-Elmer F 11 hot wire gas chromatograph and argon as carrier gas. All hydroformylation experiments were performed with a 1 1 mixture of carbon monoxide and hydrogen. The olefinic substrates were Fluka AG pure or very pure grade. a-Ethylstyrene, prepared according to Ref. 21, was > 98% pure by GLC. 

Photoisomerizations were carried out using a 450 watt Hanovia medium pressure mercury source, and each reaction was followed to the photo-stationary state by gas chromatographic determination of the cis/trans ratios. Twice recrystallized trans-stilbene (Aldrich), spectrophotometric grade cyclohexane, and dry, high purity carbon dioxide were used in these experiments. 

Gas chromatographic analysis today throws an increasingly clear light upon questions regarding the purity of natural perfumery materials. As a result perfumers can now, if they are willing to pay the price, work with reliably pure materials if they choose to use a commercial grade they know, more precisely than in the past, the material s degree of purity. 

Sample Treatment. Research grade isobutylene (99.5 mole % purity) was used after degassing by the freeze-pump-thaw method for most experiments. The only impurity detected by gas chromatographic analysis was 0.02% isobutane. C8 and Ci2 compounds which were used as gas chromatographic standards were obtained from the Chemical Samples Co. (Cleveland). Research grade rare gases were used. 

Samples. The n-decane used in this study was of research grade, obtained from Phillip 66 Petroleum Chemical Company. The purity was 99.95% as determined by the manufacturer from a chromatographic analysis. No treatment (6) other than degassing was performed on it. 0, 0 dichloroethyl ether was obtained from K K Chemical Laboratory and was purified by gas chromatography (GC) following the procedures described by Chu (ll). 

The carrier gas is chosen for its inertness. Its only purpose is to transport the analyte vapors through the chromatographic system without interaction with the sample components. The gas is obtained from a high-pressure gas cylinder and should be free from oxygen and moisture. High-purity grades of carrier gas are usually less expensive in the long run. Helium is the most popular GC carrier gas in the United States. 

Quality assurance of mixed gases begins with analysis of the raw materials. The purity of the raw materials must be known for the grade of mixture desired. Some of the instrumentation used for routine quality assurance of gases and vaporized liquids in the modem gas laboratory includes gas chromatographs equipped with detectors of the following types ... 

The price of a column ( 200- 800) may be viewed as relatively small compared to the initial, the routine, and preventive-maintenance costs of the instrument. In fact, a laboratory may find that the cost of a set of air and hydrogen gas cylinders of research grade purity for FID operation is far greater than the price of a single conventional capillary column Consequently, the column should be carefully selected for an application, handled with care following the suggestions of its manufacturer, and installed as recommended in the user s instrument manual to derive maximum performance from a gas chromatographic system. 

Air Generator An air generator is, in fact, a sophisticated air purifier. Typically, the source is house air from a compressor or low-grade compressed-air cylinders. When properly installed (Figure 10.4), a zero-air generator will provide air at a purity exceeding the quality demands of your gas chromatograph. 

Inert Gas—Argon or Helium only, high-purity grade (that is, chromatographic or zero grade), 99.998 % minimum purity, 5 ppm maximum moisture. 

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