Anionic detection, impurities

The sodium hydroxide is titrated with HCl. In a thermometric titration (92), the sibcate solution is treated first with hydrochloric acid to measure Na20 and then with hydrofluoric acid to determine precipitated Si02. Lower sibca concentrations are measured with the sibcomolybdate colorimetric method or instmmental techniques. X-ray fluorescence, atomic absorption and plasma emission spectroscopies, ion-selective electrodes, and ion chromatography are utilized to detect principal components as weU as trace cationic and anionic impurities. Eourier transform infrared, ft-nmr, laser Raman, and x-ray... 

In this context it is important to note that the detection of this land of alkali cation impurity in ionic liquids is not easy with traditional methods for reaction monitoring in ionic liquid synthesis (such as conventional NMR spectroscopy). More specialized procedures are required to quantify the amount of alkali ions in the ionic liquid or the quantitative ratio of organic cation to anion. Quantitative ion chromatography is probably the most powerful tool for this kind of quality analysis. 

FBAs can also be estimated quantitatively by fluorescence spectroscopy, which is much more sensitive than the ultraviolet method but tends to be prone to error and is less convenient to use. Small quantities of impurities may lead to serious distortions of both emission and excitation spectra. Indeed, a comparison of ultraviolet absorption and fluorescence excitation spectra can yield useful information on the purity of an FBA. Different samples of an analytically pure FBA will show identical absorption and excitation spectra. Nevertheless, an on-line fluorescence spectroscopic method of analysis has been developed for the quantitative estimation of FBAs and other fluorescent additives present on a textile substrate. The procedure was demonstrated by measuring the fluorescence intensity at various excitation wavelengths of moving nylon woven fabrics treated with various concentrations of an FBA and an anionic sizing agent. It is possible to detect remarkably small differences in concentrations of the absorbed materials present [67]. 

Ion-exchange chromatography (both cation and anion) can also be undertaken in HPLC format. Though not as extensively employed as reverse-phase or size-exclusion systems, ion-exchange-based systems are of use in analysing for impurities unrelated to the product, as well as detecting and quantifying deamidated forms. 

Smith et al (76,773 analyzed hydralazine in a drug mixture containing hydralazine hydrochloride, hydrochlorothiazide, and an impurity derived from the latter. The column was 1 m x 2.1 mm (ID) stainless steel, packed with a strong anion exchanger on 30 Jm Zipax . The mobile phase was pH 9 2 borate buffer containing 0.005M sodium sulfate (5 methanol), at 1.7 ml per minute. Detection was by ultraviolet absorption at 25 nm. 

The applicability of cITP-NMR for the analysis of trace impurities was demonstrated by the selective detection of 1.9 nmol of atenolol injected in a sample containing a 1000-fold excess of sucrose [100]. cITP-NMR has also been used for the analysis of a cationic neurotoxin present in a homogenate of the hypo-branchial gland of the marine snail Calliostoma canaliculatum [109]. Korir et al. [110] used an anionic cITP separation with online NMR detection to separate and identify nanomole quantities of heparin oligosaccharides. Although only a few cITP-NMR applications have appeared, the ability to selectively separate, concentrate, and detect charged analytes makes cITP-NMR a potentially powerful method for trace analysis. 

The separation mechanism is quite different from other chromatographic techniques and a broader spectrum of possible impurities can be detected at the same system (e.g., inorganic small cations, anions by indirect detection, chiral separations by adding a chiral selector, proteins and peptides by adding a polymer to the separation buffer, etc.)... 

From 1993 to the present, several publications have described anion and cation analysis for determination of pharmaceutical counterions (Pigure 16). and impurity profiling. For these applications, several buffers were used on different CE instruments. In most cases, detection was indirect or direct UV detection for analytes such as bromide that do absorb at 200 nm. Two papers describe use of a conductivity detector. 

The detection limits and the analyte-to-matrix ratios for inorganic and organic anion impurities in boric acid, obtained using hydrostatic or electro-kinetic injection and with sample stacking (the capillary is filled with the sample up to the detector, a voltage is applied to preconcentrate the sample anions at the sample-buffer interface, a reversed EOF is used to remove the matrix components and... 

Comparison of limits of detections (LOD) and analyte-to-matrix ratios (ATMR) for inorganic and organic anion impurities in boric acid obtained using hydrostatic and electrokinetic injection and sample stacking [40]... 

Traditionally, potentiometric sensors are distinguished by the membrane material. Glass electrodes are very well established especially in the detection of H+. However, fine-tuning of the potentiometric response of this type of membrane is chemically difficult. Solid-state membranes such as silver halides or metal sulphides are also well established for a number of cations and anions [25,26]. Their LOD is ideally a direct function of the solubility product of the materials [27], but it is often limited by dissolution of impurities [28-30]. Polymeric membrane-based ISEs are a group of the most versatile and widespread potentiometric sensors. Their versatility is based on the possibility of chemical tuning because the selectivity is based on the extraction of an ion into a polymer and its complexation with a receptor that can be chemically designed. Most research has been done on polymer-based ISEs and the remainder of this work will focus on this sensor type. 

The centers of Fa type have deeply been studied in alkali-earth oxides and have recently been detected in ZnS. Unlike F, this center contains an impurity ion in the immediate neighborhood with the anionic vacancy (for... 

Hanko, V.P., Rohrer, J.S.J. Determination of neomycin sulfate and impurities using high-performance anion-exchange chromatography with integrated pulsed amperometric detection. J. Pharm. Biomed. Anal. 43, 131-141 (2007)... 

It seems that radical anions centered on a pentacoordinated antimony atom have never been detected, and previous observations of SbFj have been assigned later to an impurity species SbFjO ... 

Like all carbohydrates, palatinitol may be separated in alkaline environment on a strongly basic anion exchanger in the hydroxide form and may be detected via pulsed amperometry. Fig. 8-81 shows a corresponding chromatogram with the separation of both isomers. Sorbitol, mannitol, and isomaltose can be detected as impurities in the same run. 

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