Packed columns programming

One question of chief interest concerns the number of runs that can be run with one individual SEC column. The lifetime of the sorbent itself must be tested as well as the maximum run number for the packed column. Because column packing procedures for SEC columns are rather time-consuming and all SEC columns have to be checked very carefully with respect to performance, very frequent repacking of the column is unreasonable. Therefore, CIP protocols are generally necessary. The CIP protocol should be developed as part of the process validation program. 

Early work relied on the use of packed columns, but all modern GC analyses are accomplished using capillary columns with their higher theoretical plate counts and resolution and improved sensitivity. Although a variety of analytical columns have been employed for the GC of triazine compounds, the columns most often used are fused-silica capillary columns coated with 5% phenyl-95% methylpolysiloxane. These nonpolar columns in conjunction with the appropriate temperature and pressure programming and pressure pulse spiking techniques provide excellent separation and sensitivity for the triazine compounds. Typically, columns of 30 m x 0.25-mm i.d. and 0.25-qm film thickness are used of which numerous versions are commercially available (e.g., DB-5, HP-5, SP-5, CP-Sil 8 CB, etc.). Of course, the column selected must be considered in conjunction with the overall design and goals of the particular study. 

Figure 6.3 Conparlson of the separation of the octylphenol poly(ethylene glycol) ether, Triton X-16S on a packed column, left, and an open tubular column, right, using UV detection. For the packed column separation al0cmx2mmI.D. column packed with Nucleosil C g, d. 3 micrometers, temperature > 170 C, and mobile phase carbon dioxide (2 ml/min] and methanol (0.15 nl/rnin). pressure programmed from 130 to 375 bar in 12 min were used. For the open tubular column separation a 10 m x 50 micrometers I.O., SB-Biphenyl-30, temperature = 175°C, mobile phase carbon dioxide (0.175 ml/min) and 2-propanol (0.0265 ml/min) pressure programmed, 125 bar for 5 min, then ramped from 125 to 380 bar over 19.5 min, and held at 380 bar for 15 min. were used. (Reproduced with permission from ref. 57. Copyright Preston Publications, Inc.) ...

A limitation in the use of API sources results from the frequent application of mobile-phase composition programming in pSFC. Pinkston el al. [411] have compared electrospray and electron impact for open-tubular and packed-column SFC-MS. Direct on-line coupling of SFC to FAB/MS (as well as SFC-ELSD) is also very promising to detect components which give no response in a UV detector [412]. 

For capillary GC, the split/splitless inlet is by far the most common and provides an excellent injection device for most routine applications. For specialized applications, there are several additional inlets available. These include programmed temperature vaporization (PTV) cool on-column and, for packed columns, direct injection. PTV is essentially a split/splitless inlet that has low thermal mass and a heater allowing rapid heating and cooling. Cool injection, which can be performed in both split and splitless mode with the PTV inlet, reduces the possibility of sample degradation in the inlet. Capabilities of the commonly available inlets are summarized in Table 14.3. 

The accuracy of temperature controllers and sensors is typically about 0.1°. Because of their high-thermal mass, packed columns are more often operated isothermally, while due to their low-thermal mass, capillary columns are most often temperature programed. Important parameters related to basic column dimensions are shown in Table 14.4. 

Fig. 21.1. Gas-liquid chromatogram of BSTFA-derivatized EO sample (column 6-ft X 1/8-in o.d. stainless steel packed with 3% SP-2100 on 100/120 mesh Supelcoport column programmed from 150° C to 350° C at 4° C/min sample size 2 pL). (Reprinted/redrawn with permission from Analyt. Chem., 56, 603A (1984). Copyright 1984 American Chemical Society.)...

The optimum conditions for capillary chromatography of material heart cut from a packed column demand a highly sophisticated programming system. The software provided with the model 8700 provides this, allowing methods to be linked so that pre-column and analytical column separations are performed under optimum conditions. 

Column pressure usually has little effect on enantioselectivity in SFC. However, pressure affects the density of the mobile phase and thus retention factor [44]. Therefore, similar to a modifier gradient, pressure or density programming can be used in fast separation of complex samples [106]. Later et al. [51] used density/temperature programming in capillary SFC. Berger and Deye [107] demonstrated that, in packed column SFC, the effect of modifier on retention was more significant than that of pressure. They also showed that the enhanced solvent strength of polar solvent-modified fluid was nof due fo an increase in densify, caused by fhe addition of fhe liquid phase modifier, buf mainly due fo fhe change in composition. 

In a similar manner to the program for optimization of a packed column, the program written in table (2) is in a very simple form that can be translated easily to the basic language used by other computers. The output will be sent directly to the monitor screen in the output window. However, by replacing the PRINT statements by LPRINT statements the output will be sent to a printer. If the clipboard is defined a file, and the result print, statements are replaced by write statements, then the results can be sent to the clipboard and pasted into word processing text. An example of an output from the program Is shown in Table (3),... 

The halogenated method employs a packed column of 1% SP-1000 on Carbopak-B (60-80 mesh) as its primary analytical column. The column is 8-ft X 0.1-in. i.d. It is operated at a helium flow rate of 40 mL/min under programmed temperature conditions of 45 °C isothermal for 3 min, then 8 °C/min to 220 °C, and then held at 220 °C for 15 min or until all compounds have eluted. An electrolytic conductivity detector operated in the halide-specific mode is used for measurement. 

The aromatic method uses as its primary analytical column a packed column of 5% SP-1200 + 1.75% Bentone 34 on Supelcoport (100-120 mesh). The carrier gas is helium at a flow rate of 30 mL/min. The temperature is programmed as follows (for lower boiling compounds) 50 °C isothermal for 2 min, then 6 °C/min, then 6 °C/min to 90 °C, and then held until all compounds have eluted (for a higher boiling range of compounds) 50 °C isothermal for 2 min, then 3 °C/min to 110 °C, and then held until all compounds have eluted. A photoionization detector with a 10.2-eV lamp is used for measurement. 

Figure 24-10 Comparison of (a) isothermal (constant temperature) and ( >) programmed temperature chromatography. Each sample contains linear alkanes run on a 1.6-mm-diameter x 6-m-long packed column containing 3% Apiezon L (liquid phase) on 100/120 mesh WarAport 30 solid support with He flow rate of 10 mL/min. Detector sensitivity is 16 times greater in panel a than in panel b. [From H. M McNair and E. J. Bonelli, Basic Gas Chromatography (Palo Alto. CA Varian Instrument Division. 1968).]...

This equation may be used to characterize capillary columns or when employing programmed pressure or temperature conditions for packed columns. 

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