Interferences cation-anion

The anion interference with cationic response (or vice versa) ... 

Hydrogen peroxide Removal of interferences by anion and cation resin, luminol CL, rainwater 35 nM 46... 

An analytical procedure that quantifies the total AE concentration resolved by alkyl chain length for various environmental matrices (influent, effluent, and river water) was developed by Di Corcia et al. [41]. The method utilises a reverse-phase column to extract and concentrate AE from surface waters and wastewaters and utilises strong anionic and cationic exchange columns to remove potential interferences. Samples are passed through the RP extraction column (Ci). AE and potential anionic and cationic interferences are eluted from the Ci column and passed directly through the SAX and SCX. The SAX and SCX columns retain anionic and cationic materials while non-ionic AE are not retained. Recovery of AE from influent, treatment plant effluent, and river water is quantitative (65—102%) over a range of concentrations for all matrices. 

The major anions and cations in seawater have a significant influence on most analytical protocols used to determine trace metals at low concentrations, so production of reference materials in seawater is absolutely essential. The major ions interfere strongly with metal analysis using graphite furnace atomic absorption spectroscopy (GFAAS) and inductively coupled plasma mass spectroscopy (ICP-MS) and must be eliminated. Consequently, preconcentration techniques used to lower detection limits must also exclude these elements. Techniques based on solvent extraction of hydrophobic chelates and column preconcentration using Chelex 100 achieve these objectives and have been widely used with GFAAS. 

The sample-preparation technique may depend on a number of variables, for example the molecular weight of sample and interferences, the sample volume and analyte concentration, buffer salt (anion and cation) content and metal concentration and type. Other than filtration for particulate removal, most of the approaches are based on the use of chromatographic media for cleaning up samples before analysis. 

Several factors affect the selection of the buffer solution, such as the optimum pH the buffer anionic or cationic species (which can interfere in the subsequent purification steps) the pH variation with ionic strength or temperature the buffer reactivity with the proteins in solution the biological activity (e.g. phosphates can inhibit or activate a protein in biological reactions) the interaction of the buffer with other components the buffer permeation in biological membranes the toxicity the light absorption at 280 nm the cost (especially if used in large-scale processes) and the protein solubility. 

First-pass extraction of PAH is highly variable both between species and between individuals within a species, which adds to the inherent inaccuracy of the estimate of RBF by this method. Furthermore, the test compound may interfere with the extraction of either PAH or TEA by competing for transport by the organic anion or cation transporters (Newman and Price 1999 Ragan and Weller 1999). 

Various authors have shown that non-ionic surfactants have a beneficial effect on the hydrolysis of cellulosic and lignocellulosic substrates, whereas anionic and cationic surfactants alone interfere negatively (Castanon and Wilke, 1981 Helle et al, 1993 Park et al, 1992 Ooshima et al., 1986 Traore and Buschle-Diller, 1999 Ueda el al., 1994 Eriksson el al., 2002). Increases in the amount of reducing soluble sugars and substrate conversion were reported. The effect depends on the substrate and is not observed for soluble substrates, such as carboxymethylcellulose or cellobiose. Nonionic surfactants increased the initial rate of hydrolysis of Sigmacell 100, and when they were added later in the process they were less effective (Helle et al, 1993). They same authors found also that the addition of cellulose increases the critical micelle concentration of the surfactant, which indicates that the surfactant adsorbs to the substrate. Surfactants are more effective at lower enzyme loads and reduce the amount of adsorbed protein (Castanon and Wilke, 1981 Ooshima et al, 1986 Helle et al, 1993 Eriksson et al., 2002) which can be used to increase desorption of cellulase from the cellulosic substrate (Otter et al., 1989). Anyhow, the use of surfactants to enhance desorption of cellulases from textile substrates in order to recover and recycle cellulases was not successful (Azevedo et al., 2002b). 

For standardised methods the calibration curve is always produced with a pure-element solution. Hence, interferences have to be considered and eliminated, leading to time consuming checks of variable parameters such as matrix effects, anion or cation influences or interferences caused by acids. 

Although the method is rapid and straightforward, the use of free terbiiun as a sensing tool has several weaknesses, such as the potential for false positives or false negatives through com-plexation of anionic interferents to the exposed tripositive cation. 

We have seen similar improvements in the dipicolinate system in terms of increased resistance to common cationic and anionic interferents. The inclusion of D02A improved Tb-DPA binding in the presence of a wide array of interfering ions, most up to concentrations five orders of magnitude greater than that of DPA (92). This indicates that [Tb(D02A)] is able to bind... 

The advantage of using HPLC-ICP-OES for metal analysis is when direct nebulisation of solutions of samples can cause matrix interference on ICP-OES. An important use of this technique would be the detection of variable oxidation states of elements and it can also preconcentrate trace elements on a column which can be eluted from the column and nebulised using ICP-OES friendly solvents. See schematic diagram 7.16 showing an anion and cation HPLC coupled with ICP-OES. 

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