Silicate interference from

Subsequent work showed that a modification of the synthesis procedure produced a 10A hydrate which> if dried carefully, would maintain the interlayer water in the absence of excess water (27). This material is optimal for adsorbed water studies for a number of reasons the parent clay is a well-crystallized kaolinite with a negligible layer charge, there are few if any interlayer cations, there is no interference from pore water since the amount is minimal, and the interlayer water molecules lie between uniform layers of known structure. Thus, the hydrate provides a useful model for studying the effects of a silicate surface on interlayer water. 

Silicate, chromate, molybdenate, and humic acids also may create significant interferences with the sorption of As(V) and As(III) on zerovalent iron (Su and Puls, 2001b Giasuddin, Kanel and Choi, 2007). Interferences from borate and sulfate, however, were negligible with As(V) and only minor with As(III). Some interferences with As(III) and As(V) sorption occurred with carbonate and nitrate (Su and Puls, 2001b). Similarly, Farrell et al. (2001) concluded that carbonate and nitrate could hinder the efforts of zerovalent iron to lower As(V) concentrations in water to below 5 pgL-1. 

For very alkaline waters, it may be necessary to include other species such as carbonate or silicate ions. Acid water will contain H+ ions, but water with a pH of <4.5 may not provide a usable acidity due to interference from other species such as some iron hydroxides. 

The most sensitive flame spectrometric procedure for the determination of strontium is FES, the emission intensity at 460.7 nm being measured from a nitrous oxide-acetylene flame. A detection limit of 1 ng ml-1 or better is generally readily attainable, although the element has a low ionization potential and addition of potassium or caesium at a final concentration of 2-5 mg ml 1 is essential as an ionization buffer. Chemical interference from phosphate, silicate and aluminium is reduced dramatically in this flame. 

Metal salts may be used in the treatment of wool. Flame methods for the determination of aluminium [185], barium, chromium, copper, mercury, strontium, tin, zinc [186] and zirconium [187] in wool have been published. Standard additions to wool cleaned by soaking and washing it with disodium EDTA (800 ml of 0.5 M for 30g wool with soaking for 3 days and double washing) was used as the calibration technique. This compensated for interferences from hydrochloric acid and amino-acids. The samples were equilibrated to a constant humidity for 24 h and then 0.3 g sealed with 5 ml of constant boiling point hydrochloric acid in a glass tube. The tubes were placed in an oven at 110UC for 20 h. The nitrous oxide/acetylene flame was used for the determination of aluminium and zirconium. Sulphate, phosphate, citrate and silicate have been found to interfere in the determination of titanium and zirconium in fire-proofed wool [188], These flame... 

A number of techniques have been developed for the trace analysis of silicones in environmental samples. In these analyses, care must be taken to avoid contamination of the samples because of the ubiquitous presence of silicones, particularly in a laboratory environment. Depending on the method of detection, interference from inorganic silicate can also be problematic, hence nonsilica-based vessels are often used in these determinations. Silicones have been extracted from environmental samples with solvents such as hexane, diethyl ether, methyl isobutylketone, ethyl acetate, and tetrahydrofuran (THF)... 

David (D5) determined potassium in the air-acetylene flame in ammonium chloride extracts of soil and found no interference from a 40-foId excess of phosphate, aluminum, sulfate, and silicate,... 

A glass membrane electrode was used to measure the pH of the silicate solutions. Adsorption of the smaller alkali metal cations, K, Na, and Li, caused an underestimation of the pH. The pH error reached several pH units for the most alkaline Li silicate samples. On the other hand, the errors for Na silicates were around 0.5 pH unit and the errors for larger cations were relatively small. Corrections to the measured pH were made by comparison of the electrode response for the silicate solutions with that for alkali metal hydroxide solutions of known concentration. Since the hydroxide content of the base solutions is known, the interference from cation adsorption was calculated and added to the pH measured for the silicate solutions (16). 

Cleanup is performed by column chromatography. Silica/allumina or Florisil (synthetic magnesium silicate salt), deactivated or suitably activated (for instance 130 °C for 12 h ) are the most frequently used stationary phases. Their performances are checked by standard solution in order to find out the best solvent or mixture of solvents and the optimum volume to be used for selectively eluting PCBs and leaving interferents in the column. V-Hexane and dichloromethane are the most widely used solvents. Better precision on cleanup results has been observed when Florisil cartridges are used instead of silica gel ones. In some cases, in order to minimize interference from other non-PCB organic compounds, additional fractionations are performed. 

Isolation of the hydrocarbons from other lipids The total lipid extract may be subjected to removal of elemental sulphur by passage through an activated copper column (Blumer, 1957) and then to chromatographic separation on adsorbent columns or thin layer plates. For column chromatography, silic el is used with a short alumina bed on the top of the silic el. Both adsorbents should be partially deactivated by the addition of water (2—5%) to prevent the formation of artifacts (Blumer, 1970). Elution with a non-polar solvent such as hexane or pentane and subsequently with mixtures of non-polar and polar solvents, e.g. benzene and methanol, permits the isolation of several fractions containing saturated, unsaturated, aromatic hydrocarbons and more polar compounds (methyl esters, alcohols, acids, phenols and heterocyclic compounds). The interference from esters encountered in the isolation of aromatic hydrocarbons can be avoided prior to separation by saponification of the esters of fatty acids, which are easily removed. 

The benzidine reaction forms the basis of a very sensitive spot test. A spot of acidified phosphate solution is placed on a filter paper followed by a drop of ammonium molybdate solution and then the benzidine solution. The filter paper is held over ammonia to neutralise the free acid and a blue stain appears. Under these conditions there is no interference from silicate or arsenate if they happen to be present. The method is sensitive to about 1 part in 50,000. 

While the SnCb reduction method gives very sensitive results, it is susceptible to salt interference, and has only a short-lived colored product. For this reason, the ascorbic acid method is preferred to the Sn(II) method however, longer color development time is necessary when ascorbic acid alone is used. The Murphy and Riley [83] method introduced the use of antimonyl tartrate, which catalyzes the reduction step, suppresses the interference from silicate, and avoids problems of chloride interference. Consequently, this method is used as the basis for many batch and automated techniques in current use (see. Table 8.2 and Table 8.4). 

Blomqvist, S., Hjellstrom, and Sjosten, A., Interference from arsenate, fluoride and silicate when determining phosphate in water by the phosphoantimonylmolybdenum blue method. International Journal of Environmental Analytical Chemistry 54, 31,1993. 

Principle Silicate reacts with molybdate under acidic conditions to form yellow p-molybdosilicic acid. This add is subsequently reduced with stannous chloride to form a heteropoly blue complex, which has an absorbance maximmn at 820 nm. Oxalic acid is added to reduce the interference from phosphate. 

Flame photometric determination cannot be recommended except for solutions containing upwards of 10 p.p.m. of magnesium because the resonance line occurs at 2852 A in the middle of an intense OH molecular band system and correction for this background is difficult even when a recording spectrophotometer is used. A hot flame is required and it has been reported by Knutson that some increase in sensitivity is obtained if an oxy-acetylene flame containing 55 per cent by volume of acetylene is used instead of the stoichiometric level of 29 per cent by volume. The resonance line suffers no serious spectral interference from other elements present in the sample solution but aluminium, chromium and molybdenum cause varying degrees of depression. Silicate, phosphate and sulphur ions depress the emission seriously and other anions less seriously and so standards should be made up to contain the same acids in the same concentrations as the samples. 

Most anionic surfactants are salts of moderately strong acids. As such, they can be titrated directly with base, provided that a suitable solvent system and visual or instrumental end point can be found. However, since anionic surfactants are generally found in the company of other ionic materials, some of them also acidic, direct acid-base titration is not used for most applications. For example, acid-base titration for assay of alkylarylsulfonate would risk high results because of titration of byproduct sulfate or other ions. Acid-base titration of LAS in a detergent formulation suffers from interference from such buffering compounds as sodium silicate and sodium tripolyphosphate. Titration with alkali is therefore limited to cases where the anionic surfactant can be isolated in pure form. 

The second method is the flow-coulometry and can be applied to orthophosphates with concentrations of 5x10 1x10 M contained in the interstitial water in sediments. The advantage of this method is that only small amounts of sample ( 100 p.1) are needed and the analytical results are entirely free from interference due to silicate ions. 

An alternative to the bridge technique was recently reported for thorium analysis in silicate rocks for which both Th and Th are measured on a single lon-counting detector (Rubin 2001). With careful chemistry and mass spectrometry, °Th/ Th ratios of igneous rocks can be measured with this technique with a precision that is similar to the bridge method. The disadvantage of this technique is that °Th ion-count rates are extremely low (around 10 cps) with normal silicate thorium ratios and are therefore subject to perturbations from background variation and low-level isobaric interferences in normal samples. 

KaoUn powder and other hydrated aluminum silicate clays, often combined with pectin (a complex carbohydrate), are the most widely used adsorbent powders (e.g., Kaopectate). Kaolin is a naturally occurring hydrated aluminum silicate that is prepared for medicinal use as a very finely divided powder. The rationale behind its use in acute nonspecific diarrhea stems from its ability to adsorb some of the bacterial toxins that often cause the condition. It is almost harmless and is effective in many cases of diarrhea if taken in large enough doses (2-10 g initially, followed by the same amount after every bowel movement). The adsorbents are generally safe, but they may interfere with the absorption of some drugs from the GI tract. 

The primary source of aluminum is the mineral bauxite, which is found in large deposits in Australia, Jamaica, and Sumatra. Transportation costs are high, and many steps are required to process the ore. Because bauxite ore is usually contaminated with the oxides of iron, titanium, and silicon, pretreatment is required before extraction of the metal can begin. The crude bauxite must be crushed, washed, and dried in a kiln to free it from silicate clays, which interfere with later purification steps. 

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