Ion-pair absorption

ION PAIR ABSORPTION OF IONIZED DRUGS—FACT OR FICTION 53... 

Jonkman, J. H. G. Hunt, C. A., Ion pair absorption of ionized drugs—fact or fiction ... 

Dicarbocyanine and trie arbo cyanine laser dyes such as stmcture (1) (n = 2 and n = 3, X = oxygen) and stmcture (34) (n = 3) are photoexcited in ethanol solution to produce relatively long-Hved photoisomers (lO " -10 s), and the absorption spectra are shifted to longer wavelength by several tens of nanometers (41,42). In polar media like ethanol, the excited state relaxation times for trie arbo cyanine (34) (n = 3) are independent of the anion, but in less polar solvent (dichloroethane) significant dependence on the anion occurs (43). The carbocyanine from stmcture (34) (n = 1) exists as a tight ion pair with borate anions, represented RB(CgH5 )g, in benzene solution photoexcitation of this dye—anion pair yields a new, transient species, presumably due to intra-ion pair electron transfer from the borate to yield the neutral dye radical (ie, the reduced state of the dye) (44). 

Three important detectors make use of the ionization, called here the initial ionization, that follows the absorption of x-rays by a gas and the ejection ol photoelectrons from the molecules involved. These photoelectrons subsequently ionize other molecules. The relatively large energy of the x-ray quantum thus leads to the production of a number of ion pairs, each consisting of an electron and a relatively immobile positive ion. if these ion pairs do not recombine, the extent of this initial ionization is determined by (and measures) the energy of the x-ray quantum. 

The ionic or polar substances can be seperated without any reaction on specially treated chromatographic columns and detected refractometrically. This is necessary because alkyl sulfosuccinates show only small absorption in the UV-visible region no sensitive photometric detection can be obtained. Separation problems can arise when common steel columns filled with reverse phase material (or sometimes silica gel) are used. This problem can be solved by adding a suitable counterion (e.g., tetrabutylammonium) to the mobile phase ( ion pair chromatography ). This way it is possible to get good separation performance. For an explanation of separation mechanism see Ref. 65-67. A broad review of the whole method and its possibilities in use is given in an excellent monograph [68]. 

All these methods give similar results but their sensitivities and resolutions are different. For example, UV-Vis spectrophotometry gives good results if a single colorant or mixture of colorants (with different absorption spectra) were previously separated by SPE, ion pair formation, and a good previous extraction. Due to their added-value capability, HPLC and CE became the ideal techniques for the analysis of multicomponent mixtures of natural and synthetic colorants found in drinks. To make correct evaluations in complex dye mixtures, a chemometric multicomponent analysis (PLS, nonlinear regression) is necessary to discriminate colorant contributions from other food constituents (sugars, phenolics, etc.). 

Wilson, C. G. Tomlinson, E. Davis, S. S. Olejnik, O., Altered ocular absorption and disposition of sodium cromoglycate upon ion-pair and complex coacervate formation with dodecylbenzyldimethyl-ammonium chloride, J. Pharm. Pharmacol. 31, 749-753 (1981). 

The bleaching of carotenoids was simultaneous with the formation of near-infrared absorbing intermediates in the microsecond timescale. The formation of an adduct ion-pair is instantaneous during the laser pulse (<10ns) with maximum absorption in the region 830-950 nm, depending on... 

El-Ashry et al. [36] studied the complex formation between the bromophenol blue, primaquine, and other important aminoquinoline antimalarials. The colorimetric method used was described as simple and rapid and is based on the interaction of the drug base with bromophenol blue to give a stable ion-pair complex. The spectra of the complex show maxima at 415 420 nm with high apparent molar absorptivities. Beer s law was obeyed in the concentration range 1-8,2-10, and 2-12 pg/mL for amodiaquine hydrochloride, primaquine phosphate, and chloroquine phosphate, respectively. The method was applied to the determination of these drugs in certain formulations and the results were favorably comparable to the official methods. 

About 1910, M. Curie suggested that ions were responsible for the chemical effects of radioactive radiations. Soon thereafter, mainly due to the pioneering work of Lind on gases, the notation M/N was introduced for a quantitative measure of the radiation effect, where N is the number of ion pairs formed and M is the number of molecules transformed—either created or destroyed. This notation, referred to as the ion pair yield, was most conveniently employed in gases where N is a measurable quantity. However, for some time the same usage was extended to condensed systems assuming that ionization did not depend on the phase. This, however, is not necessarily correct. The notation G was introduced by Burton (1947) and others to denote the number of species produced or destroyed per 100 eV absorption of ionizing radiation. In this sense, it is defined... 

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