Removal of interfering

Spectrophotometric deterrnination at 550 nm is relatively insensitive and is useful for the deterrnination of vitamin B 2 in high potency products such as premixes. Thin-layer chromatography and open-column chromatography have been appHed to both the direct assay of cobalamins and to the fractionation and removal of interfering substances from sample extracts prior to microbiological or radioassay. Atomic absorption spectrophotometry of cobalt has been proposed for the deterrnination of vitamin B 2 in dry feeds. Chemical methods based on the estimation of cyanide or the presence of 5,6-dimethylben2irnida2ole in the vitamin B 2 molecule have not been widely used. 

Trace enrichment and sample clean-up are probably the most important applications of LC-LC separation methods. The interest in these LC-LC techniques has increased rapidly in recent years, particularly in environmental analysis and clean-up and/or trace analysis in biological matrices which demands accurate determinations of compounds at very low concentration levels present in complex matrices (12-24). Both sample clean-up and trace enrichment are frequently employed in the same LC-LC scheme of course, if the concentration of the analytes of interest are Sufficient for detection then only the removal of interfering substances by sample clean-up is necessary for analysis. 

The reduction of K2TaF7 can also be performed using sodium vapors [584]. This process is conducted at an Na pressure as low as 0.1 torr, which enables the removal of interferring gases such as N, O and H20. The interaction begins at 350°C. The temperature further increases up to 800°C to prevent the condensation of sodium and the formation of colloidal tantalum powder. The product of the interaction is removed from the reactor after cooling and treated with boiled HC1 and HF solutions. The method enables the production of coarse grain tantalum powder with 99.5% purity. 

Procedure (tin in canned foods). The procedure provides for the removal of interfering copper by the addition of diethylammonium diethyldithiocarbamate in chloroform reagent. ... 

Exudate collection in trap solutions usually requires subsequent concentration steps (vacuum evaporation, lyophilization) due to the low concentration of exudate compounds. Depending on the composition of the trap solution, the reduction of sample volume can lead to high salt concentrations, which may interfere with subsequent analysis or may even cause irreversible precipitation of certain exudate compounds (e.g., Ca-citrate, Ca-oxalate, proteins). Therefore, if possible, removal of interfering salts by use of ion exchange resins prior to sample concentration is recommended. Alternatively, solid-phase extraction techniques may be employed for enrichment of exudate compounds from the diluted trap solution (11,22). High-molecular-weight compounds may be concentrated by precipitation with organic solvents [methanol, ethanol, acetone 80% (v/v) for polysaccharides and proteins] or acidification [trichloroacetic acid 10% (w/v), per-... 

For the IR spectroscopic identification of additives in polymeric products, in many cases it is necessary to first isolate the additive either by solvent extraction, chromatographic separation or removal of interfering constituents by ashing, etc. 

Beck and Brink [28] have described a sensitive method for the routine assay of cobalamins in activated sewage sludge. The method involves extraction with benzyl alcohol, removal of interfering substances using a combination of gel filtration and chromatography on alumina, concentration of the extract by lyophilization, and direct determination of total cobalamin by high-speed liquid chromatography, in comparison with cobalamin standards. 

Although the removal of interfering substances is an important application of separation methods, this chapter is more concerned with the use of these procedures to isolate, identify or quantify a particular substance or group of substances in the presence of other very similar substances. The quantitation of one amino acid in the presence of other amino acids is only one example of such an analytical problem. 

Saltzman, B. E., and A. F. Wartburg, Jr. Absorption tube fm removal of interfering sulfur dioxide in analysis of atmospheric oxidant. Anal. Chem. 37 779-782, 1965. 

Improve selectivity, by removal of interfering species from the sample matrix... 

Magnesium hydroxide is commonly produced from seawater, which is rich in Mg2+ ion. The average concentration of Mg2+ in seawater is about 1,300 mg/L. The first step of the process involves removal of interfering substances from seawater, the most notable being the water-soluble calcium bicarbonate. Bicarbonate removal is crucial, as it can form insoluble calcium carbonate, a side product that cannot be separated from magnesium hydroxide readily. Acidification of seawater converts bicarbonate into carbon dioxide, which is degassed by heating. Alternatively, seawater is treated with bme to convert calcium bicarbonate to carbonate ... 

Chromium [10,39], niobium [42], titanium [13], and 90% titanium/10% tungsten [58] have been used as adhesion layers for platinum deposition. Chemical etching procedures based on H202/ethylenediamine tetraacetic acid (EDTA)/ NH4OH have been described for removal of interfering titanium [13] or tita-nium/tungsten [58] adhesion components from the surface of platinum electrodes. The procedure was shown to be effective for more than 24 h after treatment,... 

Anthocyanin purification steps are important for anthocyanin characterization. Removal of interfering compounds allows for more reliable HPLC separation, spectral information, mass spectra, and NMR spectra during the identification of anthocyanins in plant extracts. 

A sample preparation is often necessary to isolate the components of interest from a sample matrix. Removal of interfering compounds prevents blocking of the HPLC column in spite of the... 

Distillation of sample is often necessary for the removal of interfering contaminants. The sample is buffered at pH 9.5 with borate buffer prior to distillation. This decreases hydrolysis of cyanates (CNO ) and organic nitrogen compounds. 

The solvent extract should be subjected to one or more cleanup steps for the removal of interfering substances. The presence of phthalate esters, sulfur, or other chlorinated compounds can mask pesticide peaks. The extract should, therefore, be cleaned up from the interfering substances using a florisil column or by gel permeation chromatography (see Chapter 1.5). The distribution patterns for the pesticides in the florisil column fractions are presented in Table 2.20.2. 

The total phenolic compounds in an aqueous sample can be determined by a colorimetric method using 4-aminoantipyrine. This reagent reacts with phenolic compounds at pH 8 in the presence of potassium ferricyanide to form a colored antipyrine dye, the absorbance of which is measured at 500 nm. The antipyrine dye may also be extracted from the aqueous solution by chloroform. The absorbance of the chloroform extract is measured at 460 nm. The sample may be distilled before analysis for the removal of interfering nonvolatile compounds. The above colorimetric method determines only ortho- and meta-substituted phenols and not all phenols. When the pH is properly adjusted, certain para-substituted phenols, which include methoxyl-, halogen-, carboxyl-, and sulfonic acid substituents, may be analyzed too. 

A simple sample dilution is sufficient for removal of interfering compounds. IPCR is still able to detect the antigen in sample dilutions [66], whereby the loss in sensitivity limits the usefulness of additional dilution in conventional ELISA. 

Removal of interfering matrix contaminants and/or improving the detection limits represent frequent problems in the analysis of natural, and particularly biological, samples. This potential has not yet been exploited fully in capillary electrochromatography. A typical example that demonstrates a combination of biorecognition-based separation with a subsequent capillary electrophoresis step is presented [180]. 

The process for converting the vegetation sample to a soluble form is selected for convenience, familiarity, safety, and optimal removal of interfering substances. A problem in dissolving salts of heavier Group IIA elements with mineral acids is that they may be insoluble sulfates. The most common method for bringing insoluble sulfates into solution is to subject the sample to hydroxide-carbonate fusion (fusion is discussed in Section 4.6.2 of your Radioanalytical Chemistry text). The fusion is performed in a metal crucible that is relatively insoluble under the fusion conditions. The temperature must be sufficiently high to melt the sulfates and convert them into carbonates. The carbonates are then dissolved to prepare the sample for analysis. 

H. G. Riepe, V. Loreti, R. Garcia-Sanchez, C. Camara, J. Bettmer, Removal of interfering elements in ICP-QMS for the determination of Pt, Rh, and Pd by chemically modi-bed sample introduction capillaries, Fresenius J. Anal. Chem., 370 (2001), 488 D491. 

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