Sometimes called a direct or flash injector. The following figure is a schematic of a packed column injector, Sample gases can't interact and possibly stick to the septum. Gas that bathes the underside of the injector's septum so that hot vaporized
One modification of this is a small ancillary flow of carrier This is howĪll packed column injectors work everything that is injected goes onto Injector, ALL the vaporized sample enters onto the column. Sample, solvent, analyte and all, onto the column. Regulator through the injector and into the GC column-sweeps the gaseous Pressurized, inert, carrier gas-which is continually flowing from a gas The sample is immediately vaporized and a Injector is kept hot by a relatively large, metal heater block that is Rubber septum (using a special microliter syringe) into the hot (usuallyĢ00+ degrees C) GC injector that is lined with an inert glass tube. Too: A small amount of liquid (~ 1 microliter) is injected through a silicon Solvent although much of this process also holds for gas GC injections We willĪssume in this explanation that some analytes are dissolved in a (liquid) The normal sequence of events in a GC injection is as follows. With peaks that elute nearby (the 11 and 12 minute peaks, for instance). Not overloaded while the group between 10 and 14 minutes still shows overloadingĬharacteristics: long drawn-out tailing and much less than baseline separation The second eluting peak (about 6 minutes) is clearly The following figure shows a little better chromatography with fewer In the resolvable (not overloaded) range, having large masses of componentsĬan also distort the peak shape of some of the lower mass components. And while some of the other components are An example of this appears in the first figure below. Would be overloaded by those high concentratedĬomponents. The sample had to be diluted before it was analyzed. This sample size requirement initially meant that if samples containedĬomponents that were too concentrated for a capillary chromatographic analysis, Particular component or less, sometimes much less.
In the microgram range (10 -6 grams) per injection, capillaryĬolumns routinely only handle 50 nanograms (10 -9 grams) of a While the average sample mass ofĮach component in a mixture that is separable by packed column GC can be 2 to 4 mm), require relatively specialized injectors and ancillaryįlow and pressure controllers and 2) capillary columns require a smallerĪmount of sample than packed columns. Meters long) has approximately 100,000 theoretical plates while theīut with this separation power comes some limitations: 1) CapillaryĬolumns, because they have smaller diameters (0.05 to 0.53 mm) than packedĬolumns (i.d. This means that the average capillary column (30 Resolving power or efficiency) per meter as compared to packed columnsĪnd 2) since they have less resistance to flow they can be longer than The great analytical strength of capillary gas chromatography lies in itsĬapillary columns have 1) more theoretical plates (a measure of column Split/Splitless and On-Column Gas Chromatographic Injectors
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