Detection of cations

Detections of cationic surfactants in commercial products and environmental samples... 

The widespread use of cationic surfactants as detergents and disinfectants in many different home- and industrial-cleaning products suggests its likely presence in the aquatic environment, such as in surface water from WWTP. Environmental detections of cationic surfactants have been reported at the submicrogram-per-htre level in water and sediment matrices. The presence of surfactants in surface water also suggests potential toxicity for organisms, such as fish... 

Fig. 10.41. Detection of cationic surfactants by a //-cyclodextrin with seven appended naphthoate fluorophores (Choppinet P. et al. (1996) J. Chem. Soc. Perkin Trans. 2, 249).

Z. M. Shakhsher and W. R. Seitz, Optical detection of cationic surfactants based on ion pairing with an environment-sensitive fluorophore, Anal. Chem. 62, 1758-1762(1990). 

Protonated and cationized species are the most commonly detected ions using the ES process if a positive ionization mode is selected. Protonation is a result of the addition of proton(s) to a neutral molecule for every proton added, a net charge of +1 will result. Similarly, canonization is due to the addition of cation(s) to a neutral molecule. Detection of cationized ions can be useful in the determination of molecular mass of unknown analytes.If ESI is operated under negative ion mode, deprotonated ions will usually be the most dominant ions. Eor either operation mode, solvent adducts of the protonated/deprotonated ions are frequently detected in ESI/MS mass spectra. 

Alginate is another biopolymer extensively studied for its gel formation property with applications in the food packaging and pharmaceutical industries as well as for membranes and as biosensors. Such LDH hybrid assemblies were recently used for the detection of cations such as Ca [HO]. 

L. Authier, B. Schollhorn and B. Limoges, Detection of cationic phenolic derivatives at a surfactant-doped screen-printed electrode for the sensitive indirect determination of alkaline phosphatase, Electroanalysis, 10... 

V.18 PRELIMINARY TESTS FOR AND SEPARATION OF CERTAIN ANIONS After the systematic separation and detection of cations, the search for anions should be started. At this stage already considerable information is available about the presence or absence of certain anions. Not only the preliminary wet and dry tests supplied this information, but during the separation of cations a number of facts became available thus the presence of phosphate, borate, fluoride, citrate, tartrate, and oxalate has been detected, before the precipitation of Group III cations. Similarly, the presence of chromate (or dichromate), permanganate and arsenate has been established at various stages of these separations. When the systematic examination for anions is carried out, such findings should be kept in mind. 

BGE gives a peak in the direction of reduced absorbance when a sample ion passes through the detector. The absorbing reagent, which is sometimes called a visualization reagent, should have a mobility that matches those of the sample ions as closely as possible. Chromate is often used for the indirect detection of anions and a proton-ated amine cation, such as benzylamine, for detection of cations. 

More recently, studies using small PAMAM dendrimers functionalized with naphthyl units at the periphery have demonstrated their ability toward detection of cationic species such as Cd(II) [91] or Al(III), Zn(II), and Cu(II) [92]. Analytical studies demonstrated a decrease in the exciplex emission during the titration process. 

INSTRUMENTAL TECHNIQUES FOR SILICATE IMPURITY ANALYSIS Detection of Cations... 

The metal or alloy dissolves completely the sample does not contain noble metals such as gold or platinum. The solution can be used for the separation and detection of cations, as described under Section 5.7. 

F. Inokuchi, K. Araki, S. Shinkai, Facile detection of cation- r interactions in calix[n]arenes by mass spectrometry, Chem. Lett., 1994, 1383-1386. 

An ion chromatograph using a suppressed IC mode of operation can be viewed as a moderate-pressure-performance liquid chromatograph. A schematic of the essential components of an IC is shown in Fig. 4.59. Because the trace concentration levels of various inorganic anions is of most interest to TEQA, we will focus our discussions on how anions are measured. Alkali and alkaline-earth metal ions and the ammonium ion are common applications of IC. In fact, NH4 can only be measured chromatographically by cation IC The transition metal ions can also be separated and detected, however, atomic spectroscopy, to be discussed after we complete IC, is the predominant TEQA determinative technique. We will not discuss the separation and detection of cations here. 

Recently, a novel two electrode differential potentiometric cell for enzyme electrode systems has been described that provides enhanced substrate sensitivities compared to conventional cells composed of a single enzyme electrode and reference (Cha, G.S. Meyerhoff, M.E. Electroanalysis, in press). The cell employs two working enzyme electrodes, one which responds to the analyte in the positive potential direction via detection of cations, and one which responds to the same analyte but in a negative direction owing to anion detection. A similar approach can be applied in the design of new two electrode gas-selective sensors with enhanced gas sensitivity. 

While detection of cations via porphyrin-ba.sed materials has been explored less than anion sensing, the ability of a porphyrin to coordinate different metals and the unique spectral signatures that result form the basis for metal ion detection. Use of free-base porphyrins in polymer matrices has allowed for the detection of heavy metal ions by Ache et Immobilization of 5,10,15,20-tetrakis(4-N-methylpyridyOporphyrin on Nafion membranes pennitted detection of cadmium and mercury in solution with detection limits of 5 X 10 M and 2 x 10 M, respectively over a 20-minute measuring period. The method is subject to interferences from other metal ions, but the researchers were able to detect several ions simultaneously using pattern-recognition techniques such as principal component analysis. Sol-gel films doped with 5,l0,l5,20-tetra(p-sulfonatophenyDporphyrin have also been used by Ache and coworkers for the fluorimetric determination of mercury in solution, with a detection limit of approximately 7 X 10... 

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