Eluents conductivity, minimization

The thermal stability of a conductivity detector is of great importance. Effective thermostating is highly required, as the temperature greatly affects the mobility of ions and, therefore, conductivity. A 0.5-3% increase of conductivity is usually expected per degree Celsius. Close temperature control is necessary to minimize background noise and maximize sensitivity this is an especially important issue if nonsuppressed eluents are used. 

The eluent leaving the suppressor column contains the sample ions as their respective highly conducting hydroxides in a weakly conducting background of water. The suppression reaction simultaneously serves two functions. First, it maximizes the detector sensitivity to the analyte cation by converting it to its hydroxide because the mobility of the hydroxide anion is 2.6 times that of the chloride ion. Second, the suppression reaction minimizes the detector sensitivity to the eluent. 

The general requirement for an anion chromatography eluent is that the eluting anion must have useful affinity for anion-exchange resins. Since it is important to minimize the conductivity of the eluent, the preferred anion is one which has a pKa... 

The katharometer detector [sometimes spelt catherometer and often referred to as the thermal conductivity detector (TCD) or the hot wire detector (HWD)] is the oldest GC detector still in use and commercially available. Although it is a relatively insensitive detector, it has survived largely as a result of its catholic response and use in preparative GC and gas analysis. It is simple in design and requires minimal electronic support and, as a consequence, is also relatively inexpensive. The precise manner in which it functions is not known as it responded to changes in both the thermal conductivity or the specific heat of the column eluent. It is possible that one or the other property may dominate in any particular system depending on the operating conditions employed, but the relationship is not simple. 

The detector works without direct contact of the electrode with the eluent or sample. The sensor is based on two metal tubes that are placed around a fused silica capillary with a detection gap of approximately 1.5 mm (Figure 4.2). The conductivity sensor is based on two metal tubes that act as cylindrical capacitors. The electrodes may be placed around any nonconducting tubing such as fused silica, PEEK, or Teflon. Dead volume of the connecting tubing is minimized and an extremely low dead volume cell can be manufactured. 

The syntheses of several monomers were conducted as shown in Schemes 3.2 and 3.3. Oligomers derived solely from 1 had minimal solubility. Oligomers derived from 9 were too difficult to purify since the butyl groups promoted excessively rapid migration on silica gel chromatography even with hexane as an eluent. Oligomers that were prepared from 10 or mixtures of 1 and 10 required protection of the hydroxyl moieties as t-butyldimethylsilyl ethers, and they suffered from silyl migration reactions. The use of monomer 8, however, proved to be optimal there were no protection/deprotection steps necessary and acceptable Rf values on silica gel could be maintained. 

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