Interfering ions, removal

Remove an interfering ion (remove an ion that co-elutes with the sample ion). 

Although cold plasmas have benefits in removing interfering ions such as ArO+, they are not necessary for other applications where interferences are not a problem. Thus, in laboratories where a range of isotopes needs to be examined, the plasma has to be changed between hot and cold conditions, whereas it is much simpler if the plasma can be run under a single set of conditions. For this reason, some workers use warm plasmas, which operate between the hot and cold conditions. 

Recovery from Brines. Natural lithium brines are predominately chloride brines varying widely in composition. The economical recovery of lithium from such sources depends not only on the lithium content but on the concentration of interfering ions, especially calcium and magnesium. If the magnesium content is low, its removal by lime precipitation is feasible. Location and avadabiHty of solar evaporation (qv) are also important factors. 

In the presence of certain cations [sodium, potassium, lithium, calcium, aluminium, chromium, and iron(III)], co-precipitation of the sulphates of these metals occurs, and the results will accordingly be low. This error cannot be entirely avoided except by the removal of the interfering ions. Aluminium, chromium, and iron may be removed by precipitation, and the influence of the other ions, if present, is reduced by considerably diluting the solution and by digesting the precipitate (Section 11.5). It must be pointed out that the general method of re-precipitation, in order to obtain a purer precipitate, cannot be employed, because no simple solvent (other than concentrated sulphuric acid) is available in which the precipitate may be easily dissolved. 

Treat the fluoride sample solution in the same manner as described for the calibration curve after removing interfering ions and adjusting the pH to about 5 with dilute nitric acid or sodium hydroxide solution. Read off the fluoride concentration from the calibration curve and the observed value of the absorbance. 

Remove the interfering ion prior to electroanalytical measurement, e.g. by precipitation, dialysis, etc. 

A few DBFs, such as bromate, chlorate, iodate, and chlorite, are present as anions in drinking water. As a result, they are not volatile and cannot be analyzed by GC/MS. They are also difficult to separate by LC, but will separate nicely using ion chromatography (IC). At neutral pH, HAAs are also anions and can be separated using 1C. A number of methods have been created for these DBFs using both IC/ inductively coupled plasma (ICF)-MS and IC/ESl-MS. Fretreatment to remove interfering ions (e.g., sulfate and chloride), along with the use of a suppressor column prior to introduction into the MS interface, is beneficial for trace-level measurement. 

Lithium may be recovered from natural chloride brines. Such recovery processes may require additional steps depending on the magnesium and calcium content of the brine. The process involves evaporation of brine, followed by removal of sodium chloride and interferring ions such as calcium and magnesium. Calcium is removed by precipitation as sulfate while magnesium is removed by treating the solution with lime upon which insoluble magnesium hydroxide separates out. Addition of sodium carbonate to the filtrate solution precipitates hthium carbonate. 

Considerable inter-element interference effects have been reported on the actual hydride-forming step. Elements easily reduced by sodium borohydride (e.g. silver, gold, copper, nickel) give rise to the greatest suppressions. These interfering ions may be removed by the addition of masking agents that complex with them. 

Sulphur, as sulphide ion, may be detected by predpitation as black lead sulphide with lead acetate solution and acetic add or by the purple colour produced on addition of disodium pentacyanonitrosoferrate(m). Halogens are detected as the characteristic silver halides by the addition of dilute nitric acid and silver nitrate solution. Cyanide and sulphide ions both interfere with this test for halide by forming silver cyanide and silver sulphide precipitates. If nitrogen or sulphur has been detected, therefore, the interfering ions must be removed by boiling the acidified fusion solution as detailed later, before the silver nitrate solution is added to detect the halogen. 

The full-scan BPC obtained from LTQ-FTICR LC-MS data does not display diclofenac or its monohydroxyl metabolite (Ml) that were spiked into rat bile sample due to the significant interference from ions of endogenous components in the bile (Fig. 6.9a). In contrast, MDF analysis of the LC-MS data file completely removed these interfering ions, resulting in a BPC that clearly exhibits only the drug and Ml (Fig. 6.9b). The same bile sample was analyzed with NLS and PIS using a triple-quadmpole instrument. Diclofenac lost a neutral fragment (46 Da) to form a major ion at m/z 250 under CID conditions (Fig. 6.8a). 

J.J. Schoeman, H. Macleod, The effect of particle size and interfering ions on fluoride removal by activated alumina, Water SA 13 (4) (1987) 229-234. 

Removal of interfering ions prior to analysis One application of ion exchange is in the conversion of alkali metal sulfates or phosphates to the chlorides. Thus cation exchange can be used for separating potassium from sulfate or alkali metals from phosphate. The procedure involves washing out the sulfuric or phosphoric acid... 

Boron was removed from distilled water by using a column of Dowex-1 (OH -form). For the photometric determination as a boron-curcumin complex, interfering ions were removed on small columns of Dowex-1 (formiate) and Dowex-50 (Na ) For the evaporation and ashing step, calcium hydroxide was used (recovery of one ng ca. 80%). By complexation of bivalent ions with 1,2-diamino-cyclohexane-NJ, N, N -tetra-acetic acid, water samples at pH 5.5 passed through a colunm of Dowex 50 W-X 8 (NH4) for the determination of barium Elution followed with 4 M nitric acid. Particular references for the separation of barium from sodium, calcium and sulfate are given. 

Quadrivalent cerium was precipitated with Fe(OH)3 after dissolving in hydro-cloric acid interfering ions were removed by extraction with After eva-... 

Prior removal of interfering ions with an additional set of biased collection electrodes 55) or chromatography are possibilities. The latter approach has been successful... 

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