Split Column Method

Split column method (BS 1902-5.8 1992) (4)— This method is used to measure values for the high thermal conductivity materials up to 80 W/mk such as those containing carbon, and the test can therefore be performed under... 

While single-column methods work quite well, these methods have two main drawbacks. First, when coupling turbulent-flow directly to a mass spectrometer, the mobile-phase effluent (4 or 5 mL/min) has to be split to make the effluent flow compatible for mass spectrometers (< 1 mL/min). Although narrow-bore TFLC columns (0.5 mm i.d.) can be operated at 1-1.5 mL/min, only some mass spectrometers are capable of operating at these flow rates. The splitting will result in lower detection limits. The lower sensitivity is not due to the detection limit of the mass spectrometer, which acts as a concentration detector, but to the fact that the analyte is more diluted when contained in the higher TFLC flows. There is also more mobile-phase waste to dispose. Of course, this may not be a major drawback, if one were to collect fractions... 

Injection of the protein sample (antigen or antibody). In frontal analysis the sample is applied continuously to the column by switching to the eluent containing the protein at the desired concentration. With the split-peak method, small pulses are repeatedly injected into the column. 

While capillary columns have improved the resolution of pyrolyzate compounds, the type of stationary phase is still important in the discriminatory power of PGC. A dual-column method has been reported in an effort to further improve the discrimination of PGC of paint samples (248). This method uses a polar and a nonpolar capillary column connected to the same injection port of a gas chromatograph. The pyrolyzate vapors are split between the two columns, and a separate, different pyrogram is generated simultaneously for the same sample. 

Gas phase chromatography is a separation method in which the molecules are split between a stationary phase, a heavy solvent, and a mobile gas phase called the carrier gas. The separation takes place in a column containing the heavy solvent which can have the following forms ... 

Figure 12.22 SFC-GC analysis of aromatic fraction of a gasoline fuel, (a) SFC trace (b) GC ttace of the aromatic cut. SFC conditions four columns (4.6 mm i.d.) in series (silica, silver-loaded silica, cation-exchange silica, amino-silica) 50 °C 2850 psi CO2 mobile phase at 2.5 niL/min FID detection. GC conditions methyl silicone column (50 m X 0.2 mm i.d.) injector split ratio, 80 1 injector temperature, 250 °C earner gas helium temperature programmed, — 50 °C (8 min) to 320 °C at a rate of 5 °C/min FID detection. Reprinted from Journal of Liquid Chromatography, 5, P. A. Peaden and M. L. Lee, Supercritical fluid chromatography methods and principles , pp. 179-221, 1987, by courtesy of Marcel Dekker Inc.

It is crucial in quantitative GC to obtain a good separation of the components of interest. Although this is not critical when a mass spectrometer is used as the detector (because ions for identification can be mass selected), it is nevertheless good practice. If the GC effluent is split between the mass spectrometer and FID detector, either detector can be used for quantitation. Because the response for any individual compound will differ, it is necessary to obtain relative response factors for those compounds for which quantitation is needed. Care should be taken to prevent contamination of the sample with the reference standards. This is a major source of error in trace quantitative analysis. To prevent such contamination, a method blank should be run, following all steps in the method of preparation of a sample except the addition of the sample. To ensure that there is no contamination or carryover in the GC column or the ion source, the method blank should be run prior to each sample. 

Averaging Method. A drill rig and auger were used to collect columns of soil from depths of 0 to 6, 0 to 12, 0 to 24, 0 to 36, and 0 to 48 inches. The holes were drilled about one foot apart and the augers decontaminated between holes. Each of the five samples were transferred to a clean, stainless-steel pan and thoroughly blended prior to splitting into the sample containers. 

Thus, the column diameters chosen for the two dimensions are determined by the amount of sample available and will dictate the flow rate ranges available to use. In split-flow systems, where only a portion of the first-dimension effluent is injected into the second dimension, the choice of column size is unlimited and the two methods can be developed independently. In comprehensive systems where the entire sample from the first dimension is injected into the second dimension, the flow rates are generally lower in the first dimension to accommodate the lower injection volumes into the second dimension. For example, for a 1-mm ID column in the first dimension with a flow rate of 50 (tL/min and a sampling rate of 1 min, 50 pL could be injected onto the second dimension. A 50-(lL injection onto a4.6-mm ID column flowing at 1 mL/min should be accommodated fairly well based upon its composition. In Chapter 6, the first dimension column diameters are estimated based upon the injection volume and sampling rate into the second dimension. 

We use the second-dimension separation from Fig. 6.6 with a 25 pL injection volume and 2.5 min sampling time the separation is an RPLC method that uses a monolithic column. Thus, 10 pL/min is the maximum flow rate in the first-dimension. Fig. 6.7 shows the development of the first-dimension column that utilizes a hydrophilic interaction (or HILIC) column for the separation of proteins at decreasing flow rates. The same proteins were separated in Fig. 6.6 (RPLC) and 6.7 (HILIC) and have a reversed elution order, which is known from the basics of HILIC (Alpert, 1990). It is believed that HILIC and RPLC separations are a good pair for 2DLC analysis of proteins as they appear to have dissimilar retention mechanisms, much like those of NPLC and RPLC it has been suggested that HILIC is similar in retention to NPLC (Alpert, 1990). Because the HILIC column used in Fig. 6.7 gave good resolution at 0.1 mL/min and no smaller diameter column was available, the flow was split 10-fold to match the second-dimension requirement... 

The generation of an initial population of random separation sequences is done first. The sequences describe both in which order the components are separated and which separation method is used. For example the sequence on left in Figure 13 is described by the string 23 12 14 11. The first integer is for the separation method and the second for the heavy key component of the split in the column. The first separation is made by method 2 and the components heavier than no.3 (i.e. 4 and 5) go to bottom. In the next separation method 1 is used and component heavier than 2 (i.e. 3) goes to bottom, etc. 

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