Inorganic cations detection limits

Ion chromatography. Ion chromatography is a powerful technique for analysis of both anions and cations. Detection limits usually range from low parts-per-billion to low parts-per-million. For application in plastic materials analysis, the method provides two type of information (a) free ionic content and (2) total content of some of the inorganic elements (for example, chloride, sulfur, etc.) after suitable sample mineralization. 

Applications Applications of IC extend beyond the measurement of anions and cations that initially contributed to the success of the technique. Polar organic and inorganic species can also be measured. Ion chromatography can profitably be used for the analysis of ionic degradation products. For example, IC permits determination of the elemental composition of additives in polymers from the products of pyrolysis or oxidative thermal degradation. The lower detection limit for additives in polymers are 0.1% by PyGC... 

Since the early 1990s an increasing number of papers has been devoted to the application of CE for the analysis of both inorganic cations [906-915] and low-molecular-mass anions [915-922]. Standard CE methods have been developed and validated for determining inorganic anions (e.g. chloride, sulfate and nitrate), small carboxylic acids and metal ions that all have limited or no UV absorbance. In those situations, short UV wavelengths (190 nm) or indirect UV detection should be used. Such methods might be extended to metallic... 

CE has been used for the analysis of anionic surfactants [946,947] and can be considered as complementary to HPLC for the analysis of cationic surfactants with advantages of minimal solvent consumption, higher efficiency, easy cleaning and inexpensive replacement of columns and the ability of fast method development by changing the electrolyte composition. Also the separation of polystyrene sulfonates with polymeric additives by CE has been reported [948]. Moreover, CE has also been used for the analysis of polymeric water treatment additives, such as acrylic acid copolymer flocculants, phosphonates, low-MW acids and inorganic anions. The technique provides for analyst time-savings and has lower detection limits and improved quantification for determination of anionic polymers, compared to HPLC. 

As pointed out above, IC is a well-established method for the analysis of inorganic anions and has become the method of choice in many application areas. Many techniques are available using singlecolumn [46] or dual-column systems with various detection modes. IC can be used both for analytical and preparative purposes. Large sample volumes, up to 1300 pul, can be injected to determine trace anions and cations and to attain detection limits of 10-400 ng/1. For determinations at a pig/1 to mg/1 level, a sample size of 10-50 xl is sufficient. Preconcentration is necessary for lower concentrations (an additional column, a sample pump, an extra valve and an extra time are the disadvantages of this approach [47]). With an IEC column and isocratic... 

EPMEs based on carbon paste modified with antibiotics vancomycin, teicoplanin and teicoplanin modified with acetonitrile are proposed for the determination of d-2-HGA [47]. The proposed electrodes can be used reliably for enantiopurity tests of d-2-HGA using direct potentiometric method of analysis. The linear concentration ranges recorded for EPMEs are 10 7-10 3, 10 7-10 2 and 10 6-10 2 mol/L with detection limits of 1.00 x 10 8, 1.00 x 10 8 and 1.00 x 10 7 mol/L for the vancomycin, teicoplanin and teicoplanin modified with acetonitrile-based EPME, respectively. The selectivity was determined over l-2-HGA, creatine, creatinine and some inorganic cations. The proposed EPMEs were applied for the assay of d-2-HGA in urine samples. The duration of one analysis is 10 min, including the calibration of the instrument and the determination of the amount of d-2-HGA in the urine sample. 

Adsorptive stripping voitammetry has also been applied to the determination of a variety of inorganic cations at very low concentrations. In these applications, the cations are generally complexed with surface active complexing agents, such as dimethylglyoxime, catechol, and bipyridine. Detection limits in the 10 to 10 " M range have been reported. 

Many inorganic cations and anions catalyze indicator reactions—that is, reactions whose rates are readily measured by instmmental methods, such as absorption spectrophotometry, fluorescence spectrometry, or electrochemistry. Conditions are then employed such that the rate is proportional to the concentration of catalyst, and, from the rate data, the concentration of catalyst is determined. Such catalytic methods often allow extremely sensitive detection of the catalyst concentration. Kinetic methods based on catalysis by inorganic analytes are widely applicable. For example, the literature in this area lists more than 40 cations and 15 anions that have been determined by a variety of indicator reactions. Table 29-3 gives catalytic methods for several inorganic species along with the indicator reactions used, the method of detection, and the detection limit. 

The introduction of microprocessor technology, in connection with modem stationary phases of high chromatographic efficiencies, makes it a routine task to detect ions in the medium and lower ppb concentration range without pre-concentration. The detection limit for simple inorganic anions and cations is about 10 ppb based on an injection volume of 50 pL. The total amount of injected sample lies in the lower ng range. Even ultrapure water, required for the operation of power plants or for the production of semiconductors, may be analyzed for its anion and cation content after preconcentration with respective concentrator columns. With these pre-concentration techniques, the detection limit could be lowered to the ppt range. However, it should be emphasized that... 

In Inorganic Chemistry, typical spray reagents for cations include potassium iodine (0.2%, aqueous), hydrogen sulphide (saturated aqueous solution), ammonium sulphide (0.2 N, aqueous), quercetin (0.1%, alcoholic), l-(2-pyridylazo)-2-naphthol (PAN) (0.2%, methanolic), oxine (8-hydroxyquinoline) (1% methanolic, view under visible and UV light), and sodium rhodizonate (0.5%, aqueous). Reaction with dithizone to produce coloured dithizonate chelates of many metals is particularly suitable if quantitative spectrometric analysis (in situ or after elution) is to be carried out. Anions are detected with bromocresol purple (0.1%, alcoholic), 1% ammoniacal silver nitrate + 0.1% alcoholic fluorescein/UV light, zirconium alizarin lake (0.1% in HC1 solution), and ammonium molybdate (1%, aqueous) followed by SnCl2 (1%) and HC1 (10%). Typical detection limits range from 10 ng (10 9g) to several pg (10 6g). 

In potentiometry, all ions present in the solution principally contribute to the potential of the working electrode. As the ratio between the analyte concentration and that of other species in the solution generally is rather low, the analyte contribution to the detector signal is often low, which results in relatively poor detection limits. To circumvent this problem, ion-selective membranes (ISM), which permit only some ions to pass through the membranes, are commonly employed. In this way, detection limits down to 10 mol/L can be achieved. The ISM also reduces the influence from matrix components, which allows measurements in complex matrices such as blood or seram without interferences. The long-term stability of these electrode may, however, be a problem, as the electrodes might have to be replaced after a few hours or days. Common analytes are inorganic anions and cations, especially alkali and alkaline earth metals ions. A further application is the indirect detection of amino acids, where the... 

Generally speaking, most inorganic anions and cations have weak absorption in UV-Visible spectral region. Thus, only selected ions can be determined by UV detection. Therefore other detection techniques such as amperometry, spectrometry, and refractive index are used for food analysis. The best detection limit is offered by mass spectrometry because of the reduction of chemical noise especially in complex matrices. 

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