Correct and precise gas chromatography column installation is critical to system performance. Columns that are installed at an improper or inconsistent depth will adversely affect analyte response and harm column-to-column response reproducibility. The installation technique itself can minimize or eliminate many problems.
There are two traditional ways to install capillary GC columns. The first is the “hot swap” technique, where a column is installed while the injection and detector zones remain at operating temperatures. The alternative method is to allow the temperature zones of the instrument to cool before GC column installation. Each technique has advantages and disadvantages.
Figure 1 - The patent-pending design of the Cool-Lock Nut helps to simplify the column installation process. The installation wheel (main body) allows chromatographers to change the nut without waiting for the oven to cool. The lower securing nut maintains the capillary column at a specified depth and helps to ensure consistent and proper installation depth throughout the installation process.
The hot swap technique does not cool the temperature zones and allows for a fast change of columns to minimize the instrument’s downtime. However, the hot inlet and detector parts need to be handled with gloves and proper care to prevent burns. Conversely, permitting the heated zones to cool removes the possibility of burns but requires time for the instrument to cool, reheat, and then condition. This longer process results in significant downtime, adversely affecting laboratory production. Because uptime and throughput are so important in most laboratories, the hot swap technique is often the more attractive alternative, but worn-out gloves and burned fingers lead to installation errors.
The Cool-Lock Nut GC installation tool (Phenomenex, Inc., Torrance, CA) (Figure 1) addresses the negative aspects of traditional methods, allowing fast column switching with high accuracy. The example below demonstrates how installing a GC column at the proper depth with the Cool-Lock Nut can help to ensure accurate and reproducible chromatography results.
Figure 2 - Temperature measurements of the Cool-Lock Nut and a standard nut over time on an Agilent 5980 GC system. For the experiments, the initial oven temperature was set to 360 °C and then lowered to 45 °C. The oven door was then opened, exposing the nut to room temperature (25 °C). Temperature was immediately measured using a noncontact thermometer. Note: Oven temperature was set to zero, allowing the oven fan to stay on during all temperature readings. The first experiment (a) was done with the injector temperature set at 250 °C, and the second (b) at 300 °C.
Temperature measurements of the Cool-Lock Nut and a standard nut were measured on an Agilent 5980 GC system (Agilent Technologies, Wilmington, DE) using a noncontact thermometer. The initial oven temperature was set to 360 °C and was then lowered to 45 °C. The oven temperature was then set to zero and the door was opened to expose the nut to room temperature (25 °C). The oven fan stayed on during all temperature readings. Temperature readings were taken immediately with the injector temperature set either at 250 °C (Figure 2a) or 300 °C (Figure 2b).
A comparison of GC analysis using proper and improper GC column installation depths was done using an Agilent 5980 GC system (Figure 3). For the run using the proper installation depth, the end of the column was installed 5 mm above the tip of the ferrule. In the run with the improper column depth, the end of the column was positioned just above the tip of the ferrule.
Figure 3 - Comparison of a GC analysis using (a) proper and (b) improper installation depths. In analysis with the proper installation, all peaks had high responses (a). In contrast, when the column was installed improperly, the responses were greatly reduced (b). Samples: 1) 4-chlorophenol, 2) chlorobenzene, and 3) pentachlorophenol.
Results and discussion
The Cool-Lock Nut’s patent-pending design helps to simplify the column installation process. The nut’s upper portion is similar to the traditional nut, allowing a precise fit onto an Agilent GC system. The addition of the knurled installation wheel and a second securing nut provides an additional benefit for the chromatographer (Figure 1). The installation wheel (main body) enables chromatographers to change the nut without waiting for the oven to cool. While the upper portion of the nut remains hot from the heat emitting from the inlet or detector, the installation wheel tracks the temperature of the surrounding air. This allows it to cool down faster than the standard nut.
Figure 2 shows the temperature differences of a traditional-style nut versus the Cool-Lock Nut when the GC oven door is opened and permitted to cool down at room temperature (25 °C). When the inlet is set at 250 °C, the traditional-nut temperature remains near 55 °C while the Cool-Lock Nut is around 30 °C (Figure 2a). If the inlet temperature is increased to 300 °C, the traditional nut remains at 70 °C while the Cool-Lock Nut quickly cools down to 35 °C (Figure 2b). This lower temperature makes it more comfortable for chromatographers to manually install or remove the nut without waiting for the inlet/detector to cool. The Cool-Lock Nut’s ability to cool down quickly is an advantage over the hot swap technique.
The Cool-Lock Nut’s lower securing nut maintains a capillary column at a specified depth before it is installed into the inlet or detector. This helps to ensure consistent and proper installation depth throughout the installation process and helps to improve analysis sensitivity and reproducibility. An example of how proper and improper installation depths may affect chromatography results is shown in Figure 3. Greater response for all analytes is seen when the proper installation depth is achieved. When the column is installed improperly, pentachlorophenol has a 60% decrease in response. Having a second bottom securing nut that locks the GC column in place is key to ensuring that the proper installation depth is achieved and helps to improve analysis sensitivity and reproducibility.
The design of the Cool-Lock Nuts helps to eliminate column installation problems. It combines the advantages of the two traditional installation techniques—speed and cool surface temperatures—without the disadvantages. In addition, the second bottom securing nut locks the GC column in place at a specified depth to ensure that the proper installation depth is achieved. This helps to improve analysis sensitivity and reproducibility.
Mr. Kelly is Senior GC Application Chemist, Phenomenex, Inc., 411 Madrid Ave., Torrance, CA 90501-1430, U.S.A.; tel.: 310-212-0555; fax: 310-328-7768; e-mail: firstname.lastname@example.org.