Dedicated columns

The influence of the low volatility of the higher molecular weight ethoxymers on GC analysis of APEO is demonstrated in Fig. 2.1.5(c) (bottom). Thus GC analysis without derivatisation is limited to oligomers with up to 4-5 EO units only. Higher ethoxymers can be detected only by GC after derivatisation (see also below) and often high temperatures, requiring dedicated columns and instrumentation, are necessary. 

Royal jelly SPE (Sep Pak) Alltech Furosine dedicated column DAD (280 nm) [51] ... 

Enantiomeric separation is a great challenge. Every separation requires a dedicated column. Some packings are more able to separate many racemates. When a chiral selector is used as the stationary phase, the primary retention mechanism is complexation with the surface-... 

True Highspeed separations with good resolution require dedicated columns allowing fast flow rates and easy access to the pores by the solute. In addition, they provide high separation volumes. In optimized system column dimensions, length and inner diameter have to be matched. 

Multielevation piperacks are usually needed to handle all the required services for piping, electrical, utilities, and instmmentation. The two-level rack is one of the most common but three-level ones are also used. The utility lines are usually mn in the upper level and the process lines in the lower levels. The larger-diameter lines are located to the outside of the rack to be closest to the column supports. Access platforms are required at the battery limit to provide operators access to the block valves and blinds. If long mns of hot pipe are required, a portion of the pipe rack needs to be dedicated to an expansion loop. A horizontal space in the piperack is provided for a set of lines to be flat-turned into a set of expansion loops with the large pipes located on the outside. AH of the pipe turns are in the same horizontal plane, which is an exception to normal piping practice. A flat turn takes up and blocks space for other pipes. Flat turns are generally only made from the outside of the rack to minimize this blockage. 

Sufficient engineering data for designing reactors for three-phase processes are available. A column reactor with gravitational liquid downflow was industrially proven. An MLR with forced liquid downflow with ejector was also well studied. Dedicated catalysts for particular processes must be, however, worked out. 

Column reactors are the second most popular reactors in the fine chemistry sector. They are mainly dedicated reactors adjusted for a particular process although in many cases column reactors can easily be adapted for another process. Cocurrently operated bubble (possibly packed) columns with upflow of both phases and trickle-bed reactors with downflow are widely used. The diameter of column reactors varies from tens of centimetres to metres, while their height ranges from two metres up to twenty metres. Larger column reactors also have been designed and operated in bulk chemicals plants. The typical catalyst particle size ranges from 1.5 mm (in trickle-bed reactors) to 10 mm (in countercurrent columns) depending on the particular application. The temperature and pressure are limited only by the material of construction and corrosivity of the reaction mixture. 

In 2001, Valko et al. reduced the column length to only 50 mm and increased the flow rate to 2mLmin [42]. The gradient time was diminished to 2.5 min with a gradient cycle time of 5 min. Measurement of CHI and evaluation of log P were excellent with a 3-fold improved productivity. In these conditions, the system dwell volume (Vd) becomes essential and only dedicated chromatographic devices with Vjy lower than 0.8 mL can be used [42]. Special attention should be paid to the injected volume, which must remain lower than 3 pL to avoid any overloading or extra-column volume contributions. 

Frames can be seen as structures where all relevant information about an object or a concept is collected. As an example the relevant information about a column in a chromatographic method can be represented by a dedicated general frame, COLUMN. Separate columns can be represented by so-called instantiations of this frame. Instantiations are copies of the general frame that contain the characteristics of a specific object, in this example the separate columns. 

Trisciani, A. and Andreolini, F, Evaluation of a micro-HPLC system dedicated to packed capillary column liquid chromatography, /. HRC CC, 13,270,1990. 

Principles and Characteristics As mentioned already (Section 3.5.2) solid-phase microextraction involves the use of a micro-fibre which is exposed to the analyte(s) for a prespecified time. GC-MS is an ideal detector after SPME extraction/injection for both qualitative and quantitative analysis. For SPME-GC analysis, the fibre is forced into the chromatography capillary injector, where the entire extraction is desorbed. A high linear flow-rate of the carrier gas along the fibre is essential to ensure complete desorption of the analytes. Because no solvent is injected, and the analytes are rapidly desorbed on to the column, minimum detection limits are improved and resolution is maintained. Online coupling of conventional fibre-based SPME coupled with GC is now becoming routine. Automated SPME takes the sample directly from bottle to gas chromatograph. Split/splitless, on-column and PTV injection are compatible with SPME. SPME can also be used very effectively for sample introduction to fast GC systems, provided that a dedicated injector is used for this purpose [69,70],... 

SFC-NMR is available from 200 to 800 MHz, and is suitable for all common NMR-detected nuclei. SFC/SFE-NMR requires dedicated probe-heads for high pressure (up to 350 bar) and elevated temperature (up to 100 °C). SFC-NMR is carried out with conventional packed columns, using modifier, pressure and temperature gradients. The resolution of 1H NMR spectra obtained in SFE-NMR and SFC-NMR coupling under continuous-flow conditions approaches that of conventionally recorded NMR spectra. However, due to the supercritical measuring conditions, the 111 spin-lattice relaxation times 7) are doubled. 

At Sirius, a dedicated instmment (Profiler LDA) has been developed for the rapid measurement of log D by liquid-liquid partition chromatography. In this instrument the column is coated with a layer of octanol, and the retention times are therefore tmly related to octanol/water partitioning. Although the method used was first described 25 years ago [29], it has been difficult to apply in an automated system because of the tendency of octanol to be flushed from the column by the eluent, thus requiring frequent renewals of the octanol coating. In our method, the octanol coating is kept in place by reversing the direction of the eluent after each... 

The waxes, the organic phase, and the aqueous products, on the contrary, were unloaded daily from the collection traps and analyzed with an off-line GC (Hewlett-Packard model 6890) equipped with two flame ionization detectors and two identical columns (Hewlett-Packard HP-5), one connected to an on-column injector and dedicated to the analysis of waxes (dissolved in CS2 before the injection), and the other connected to a split/splitless injector and used for the analysis of the liquid reaction products (aqueous and organic phases). CH3CN was added to the aqueous sample prior to the injection as internal standard. 

When a fast LC system is connected to a detector, care must be taken to ensure that the detector is well suited for the expected flow ranges and peak widths. Most manufacturers, especially those offering dedicated systems for sub-2-micron particle columns, offer efficient UV detectors. Flow rate is usually not an issue for UV and other flow-through cell-based detection systems. However, flow rate can become limiting for dead-end detectors that alter the column effluent, mainly by eliminating mobile phases such as ELSD, CAD, CLND, and mass spectrometers. 

The LC/MS throughput enhancement approach developed in our laboratory in 1997 and 1998 used multiple HPLC systems, each of which had dedicated HPLC pumps, autosamplers, and columns. 

The best-known and the most commonly used hyphenated method is GC-MS more specifically, and most commonly, capillary column GC combined with quadrupole MS. This type of instrumentation is controlled by computer and data collected and analyzed by dedicated computer programs. The mass spectra produced by the analytes can be compared to those in a library of mass spectra of known compounds using a computer search algorithm. The computer program finds known compounds that best match the spectra of the analytes of interest. 

The use of reverse-phase columns with pre-column derivatization of the amino acids offers an acceptable alternative to the dedicated instrumentation of an amino acid analyser or separation by HPLC followed by post-column derivatization. 

---