Interference with phosphate determination

El-Kommos and Emara [47] determined primaquine and other secondary aromatic amines pharmaceuticals by a spectrophotometric method using 4-dimethyl amino cinnamaldehyde. The reaction of the reagent with primaquine and with the other amines was investigated. Powdered tablets were extracted with methanolic 0.1 M perchloric acid. The extract was mixed 1 1 with methanolic 0.2% of 4-dimethyl amino cinnamaldehyde and the mixture was diluted with methanol before measurement of the absorbance at 670 nm for primaquine phosphate. Beer s law was obeyed for 2-20 pg/mL of primaquine. The pink and green color formed with primaquine was stable for at least 24 h. Recoveries were good. Amodiaquine did not interfere with the determination of primaquine. 

The interference from 02 was also investigated with the SOD-based biosensors, in which 02 was generated from K02 rather than from the xanthine-XOD system since the enzymatic system requires 02 for the 02, generation. The removal of 02 from the phosphate buffer by bubbling N2 into the solution was found to produce no observable change in the current response of the SOD-based biosensors toward K02, suggesting that 02 does not interfere with 02, determination under the present experimental conditions. 

A number of metals [including Be, Ga, In, Sc, Fe(III), U, V, and Zr] interfere with the determination of Al. Anions that form complexes with A1 (e.g., fluoride, phosphate, citrate) prevent the formation of the ternary aluminium complex. Before the determination, Al should be separated from interfering elements, or they should be masked. 

In water and beverages strontium can be measured directly, but food and biological materials require a pretreatment with hydrochloric acid (3 M) and lanthanum chloride [91]. In urine strontium can be determined after dry-ashing and addition of lanthanum [91] or directly after 1 2 dilution with an acidic lanthanum chloride solution [92], The determination of strontium in bone requires special attention because the bone matrix contains high amounts of calcium and phosphate, which can easily interfere with the determination of strontium. Razmilic described a method to isolate strontium from the calcium phosphate matrix by ion exchange chromatography. The pretreated samples then can be analysed by both emission and absorption spectrophotometry measurements without chemical, ionization, or bulk interferences [93,94]. 

Seasalt also may cause errors in the spectrophotometric signal. These salt effects are either a suppression of the analyte absorbance (e.g., in the determination of silicate and phosphate) by the ions of seawater or an effect of the buffer capacity of seawater (e.g., shifts in the reaction pH interfere with the determination of ammonia). 

Interferences may affect the linearity of the calibration and are chiefly due to the emission lines produced by other species close to those of the analyte. They may be minimized by selecting a different spectral line for the analysis, or by altering the spectral resolution or filter. The presence of anions that form very stable compoimds with the metal ions, such as sulfate and phosphate may interfere with some determinations. 

Vishwavidyalaya et al. [22] used a difference-spectrophotometric method for the estimation of primaquine phosphate in tablets. One portion of powdered tablets, equivalent to 7.5 mg of primaquine phosphate, was extracted with hydrochloric acid-potassium chloride buffer (pH 2) and a second portion was extracted with phosphate buffer (pH 10). Primaquine phosphate was determined from the difference in absorbance of the acid and alkaline extracts at 254.2 nm. The calibration graph was rectilinear from 2 to 14 pg/mL of primaquine phosphate. Recovery was 98.6% and no interference was observed from excipients. Results compared with those by the British Pharmacopoeial method. 

Detergent must not be very expensive Detergent should be readily removable after treating membrane fraction Detergent must not interfere with assays such as lipids, protein colorimetric determinations and enzymatic activity many of the nonionic detergents contain high phosphate levels that interfere with certain lipid analyses and certain of the polyoxyethylene derivatives affect protein colorimetric and enzyme assays... 

Although this hydrolysis is usually fairly rapid it is desirable to obtain conditions of a general nature that would be likely (a) to effect the complete hydrolysis of the more resistant phosphorofluoridates, (6) to ensure homogeneity of the reaction mixture so as to avoid possible mechanical losses of oily material, and (c) to ensure that the hydrolysis does not proceed so far as to cause an accumulation of phosphate ions, which might interfere with the subsequent determination. 

Examples (/ ) Chemical Interferences due to Anion (P04 ) Phosphate ions have been found to interfere with determination of Mg and Ca by AAS. The absorption due to Mg and Ca are appreciably weaker in the presence of P043 ions than in their absence. This is evidently on account of the formation of fairly stable phosphates of Mg and Ca which do not readily split-up into the respective atoms in the mantle of a flame. 

It is well recognized that interrelations exist. How much sodium one needs depends upon his potassium intake his calcium needs are determined in part by his phosphate intake his need for a specific amino acid may be determined in part by the amount of the other amino acids that he gets (they can interfere with each other s utilization). Only by further experimentation can we determine how important antagonisms and other interrelations are in human nutrition. If highly important, they will seriously complicate the picture but will not change its basic outlines. 

Chloride ion-selective electrodes The most important region of application is the determination of chlorides in waters, including sea water (for a review, see [167]), in serum [110,112,371] (review in [167]) and in soil [151,219,341], The determination of chloride ions in sweat made screening for cystic fibrosis possible in new-born babies (review, [45,55a, 262]). Br , I and S " interfere in the determination of chlorides in phosphate rocks [81]. Sulphite can be determined directly using an electrode with an Hgj CI2 - HgS membrane [398] on the basis of the reaction... 

The fluoride ion selective electrode is the most popular means of fluoride ion determination after sample destruction by any method but it does have limitations. It can be used either directly to measure the fluoride potential6 or as an end-point detector in a potentiometric titration with a lanthanum(l II) reagent as titrant.4,7 Problems can be experienced with potential drift in direct potentiometry, especially at low fluoride ion concentrations. Titration methods often yield sluggish end points unless water miscible solvents are used to decrease solubilities and increase potentia 1 breaks and sulfate and phosphate can interfere. End-point determination can be facilitated by using a computerized Gran plotting procedure.4... 

The extremely low solubility of lead phosphate in water (about 6 x 10 15m) again suggests potentiometric analysis. Selig57,59 determined micro amounts of phosphate by precipitation with lead perchlorate in aqueous medium. The sample was buffered at pH 8.25-8.75 and a lead-selective electrode was used to establish the end-point. The detection limit is about 10 pg of phosphorus. Anions which form insoluble lead salts, such as molybdate, tungstate or chromate, interfere with the procedure. Similar direct potentiometric titrations of phosphate by precipitation as insoluble salts of lanthanum(III), copper(II) or cadmium(II) are suggested, the corresponding ion-selective electrodes being used to detect the end-point. 

The presence of low concentrations of phosphate has long been known to interfere with other fluorimetric analytical procedures this ability of trace amounts of phosphate to quench the fluorescence of chelates has been applied to the determination of the phosphates themselves. Several chelates were investigated measurement of the decrease of fluorescence of the aluminium-morin complex after phosphate addition proved to give the most satisfactory results65 (see Section II.B.2.a). 

However, the relative rates with His 12 and 119 vary widely depending on the structure of the reagent. The d antipodes generally favor reaction at His 12, the l compounds at His 119. No convincing correlation of all these facts with the X-ray structure has yet been made. In view of the fact that sulfate or phosphate ions seriously interfere with the alkylation reaction 160), the X-ray structures determined in the presence of these ions may be misleading. However, Bello and Nowoswiat have shown (69) that with RNase-A in crystalline form the alkylation with bromo-acetic acid is comparable, but not identical, to that found in dilute solution. 

Kaiser [3U used on-line sample preparation to determine trace anions in solvents, including isopropanol, acetone and Af-methylpyrrolidone. A large solvent injection can interfere with both the ion exchange separation and the conductivity detection by causing large disturbances in the baseline. In this application the anions were concentrated on a AG9-HC guard column and then the solvent was sent to waste before it could enter the analytical column. After the solvent was cleared from the AG9-HC concentrator column, the AG9-HC concentrator was switched in line with the AS9-HC analytical column for the separation. The method detection limits for chloride, sulfate, phosphate and nitrate are reported in the sub pg/1 range. 

In a more recent work Ito [101] has described a simple and highly sensitive ion chromatographic method with ultraviolet detection for determining iodide in seawater. A high-capacity anion exchange resin with polystyrene-divinylbenzene matrix was used for both preconcentration and separation of iodide. Iodide in artificial seawater (salinity, 35 % ) was trapped quantitatively (98.8 0.6%) without peak broadening on a preconcentrator column and was separated with 0.35M sodium perchlorate+ 0.10M phosphate buffer (pH 6.1). On the other hand, the major anions in seawater, chloride and sulphate ions, were partially trapped (5-20%) and did not interfere in the determination of iodide. The detection limit for iodide was 0.2pg L 1 for 6mL of artificial seawater. This method was apphed to determination of iodide (ND-18.3pg L ) and total inorganic iodine (I +I03 -I, 50.0-52.7pg L 1) in seawater samples taken near Japan. 

Chemical interference arises when the determinant element forms a thermally stable compound with one or more concomitant ions or molecules present in the sample solutions.9 The best known examples are the interference of phosphate,... 

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