Eluents borate-based

It is sometimes possible to improve detection by changing the pH of the eluent, or by the use of photochemical reactions. The common barbiturates used in therapy are weak acids that are easily separated in their acid (unionised) forms. Because the conjugate bases are much stronger chromophores than the acids, barbiturates have been detected by post-column mixing with a pH 10 borate buffer followed by uv absorption at 254 nm. An example of the second approach is the detection of cannabis derivatives in body fluids involving the conversion of cannabis alcohols to fluorescent derivatives on subjecting the column effluent to intense uv radiation. 

The conditions of IC analysis (Table I) chosen were based on the need for separation of formate ion from common atmospheric contaminants, such as chloride ion, and other organic anions, such as acetate. The conditions were also optimized to obtain a suitable detection limit. Thus, a weak borate eluent (0.005 combined with a 500 mm anion separator column (and a 150 mm precolumn) was chosen. Conversion of the pre-column and separator column to their borate forms (from the normal carbonate form) was necessary. The process of continually passing the borate eluent through the columns until a stable baseline was obtained required several hours. 

The eluents suitable for the separation of amino acids on latex cation exchangers do not comprise the classical citrate/borate buffers but mixtures of nitric acid and potassium oxalate. In comparison to buffers composed of sodium citrate and borate, these components may be obtained at much higher purity. The retention of the amino acids to be analyzed, however, is possibly affected by the sample pH due to the limited buffer capacity of the eluents that are based on nitric acid and potassium oxalate. Fig. 4-21 shows the separation of a calibration standard for collagen hydrolysates on an Amino Pac PA-1 latex cation exchanger at ambient temperature. The advantage is the short... 

The detection of hydroperoxides in this method is based on chemiluminescence. The system was optimised using r-buthylhydroperoxide, f-amylhydro-peroxide and cumenehydro-peroxide. Cytochrome C was used as a catalyst, the eluent was 0.25 M borate buffer. Detection limits were 5 nmol of active oxygen, which was only sufficient for laboratory experiments. 

Electrical conductivity is the most common detection methods for ions in solution. Small et al [34] were the first to separate ions chromatographically and detected them by suppressed conductivity. The suppressor (see Sections 3.6 and 4.3) plays an important role in detection by converting the eluent into a less conductive form while at the same time maximizing analyte response by converting them into the corresponding acids or bases. Strongly dissociated ions are easily detected, because they are fully ionized after suppression. For weakly dissociated species such as orthosilicate, borate, orthophosphate, organic acids. 

The latest development for this type of application combines the key benefits of electrolytic eluent generation and matrix elimination to fecilitate the determination of trace anionic impurities in borated water [192]. Figure 10.109 shows a schematic diagram of such a system configuration, which is also based on two... 

Figure 10.109 Schematic diagram of the system setup for trace anion anaiysis in borated water based on eluent generation and matrix eiimination.

---