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FLEXO Magazine : February 2009
TECHNOLOGIES & TECHNIQUES The GC column separates the individual solvents in a mix- ture through a physical process based on the different boiling points of those solvents. Solvents with lower boiling points move through the column more quickly and are detected first, while higher-boiling solvents move through the column more slowly and are detected later. The length of time that it takes for an individual solvent to travel from the front of the column to the end is called the reten- tion time of that solvent component. This value is used by the data system to identity the solvent by name. The GC Oven. The purpose of the GC oven is to maintain ac- curate temperature control of the column. The oven temperature is usually programmed from a low to a high temperature to shorten the sample analysis time. The GC Detector. Each separated sol- vent is detected as it comes out the end of the GC column. This information is used to determine the amount of each solvent in the printed sample. The most commonly used GC detector is the flame ionization detector (FID). This detector can measure the level of solvents in parts per million (ppm), so it is well suited for residual solvent testing. The FID is a very stable and robust GC detector and requires only minimal routine maintenance. It uses hydrogen and air to produce a very small, colorless flame through which the solvent mol- ecules must pass. As the solvent molecules pass through the flame they are ionized. These elec- trically charged ions are captured or collected by the FID collector assembly. This extremely small electrical signal is then amplified. The amplified signal is digitized and sent to the computer and stored as a data file on the hard drive. It is important to note that the FID detector cannot detect water, but this is not necessary for residual solvent testing. There is an additional use for the GC in the quality control laboratory: for the testing of ink solvent mixtures and bulk solvent quality. Testing for the amount of water in those samples is important. A second type of GC detector called the Thermal Conductivity Detector, or TCD for short, is necessary when testing for the amount of water in an ink or solvent mixture. The GC Data System. The purpose of the GC data system is three-fold. It stores the parameters that control the operation of the GC hardware. It also contains the data generated by the detector and ana- FIGURE 2. Between A&.V, you'll find the world's finest selection of flexo materials. Anderson & Vreeland offers the finest and most complete selection of materials and equipment for conventional and digital flexography. We support these materials with almost 50 years of flexo experience that results in smoother and easier integration of technical advancements affecting flexo prepress, including digital workflow. We invite you to "Experience the differenceD with Anderson & Vreeland. . A" I %F 1) . ANDERSON& M VREELAND INC. Toll-free Phone: 866.282.7697 · Toll-free Fax: 800.223.6869 www.AndersonVreeland.com · E-mail: info@AndVre.com @ Registered trademarks of Flint Group Printing Plates, Chemence, Toyobo Co. and Fulflex
Sustainable Winter 2009