Interference with phosphate determination nitrate

Ion chromatography can be used to determine chloride concentrations of 2—1000 ppb with a carbonate—bicarbonate eluent (23). Eluoride, nitrite, phosphate, bromide, nitrate, and sulfate do not interfere and can be measured simultaneously with a total analysis time of <30 min. 

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. 

Modifiers are, however, used in a rather indiscriminate way in many laboratories. If used carelessly they can contaminate the sample solution with the element that is being determined and they can actually add to the background interference which one intends to reduce. By carefully optimizing the ashing and atomization temperatures for specific food matrices, as described above, the use of matrix modifiers can be reduced to the cases when they are really necessary. An additional benefit of matrix modification is that the sample and standard matrix are made very similar, this often making the standard addition method unnecessary. How this is carried out is described in detail in most instrument manuals and in specific textbooks. Commonly used modifiers are ammonium nitrate, ammonium phosphate, Mg nitrate, Pd nitrate, and ascorbic acid. 

Kopito and Shwachman (K7) have described a method for the analysis of lead in either freshly voided or partially decomposed urine. The lead in 25 or 50 ml of urine is coprecipitated on bismuth hydroxide by adding bismuth nitrate and ammonia. After centrifuging, the precipitate is dissolved in acid to a final volume of 5 ml, and this solution is aspirated. With a 25-ml sample, 0.05-0.2 ppm of lead can be determined. The bismuth does not interfere with the lead absorption, and it suppresses interferences from sodium, potassium, calcium, magnesium, and phosphates. This procedure appears to offer sufficient sensitivity and the advantages of freedom from interference and simplicity in operation. Control of pH is not critical. Kopito and Shwachman claim that in... 

A. Analysis of Wastewater and Natural Waters. The presence of certain anions in wastewater effluents can cause deterioration of natural water systems. Phosphorous and nitrogen can be present in several chemical forms in wastewaters. Phosphorous is usually present as phosphate, polyphosphate and organically-bound phosphorus. The nitrogen compounds of interest in wastewater characterization are ammonia, nitrite, nitrate and organic nitrogen. Analyses are often based on titrimetric, and colorimetric methods (3). These methods are time consuming and subject to a number of interferences. Ion Chromatography can be used to determine low ppm concentrations of these ions in less than thirty minutes with no sample preparation. 

Procedure (determination of inorganic phosphate (a) in the acetic acid extract). The 8-hydroxyquinoline forms a precipitate in acidic ammonium molybdate solution, which will interfere unless the aliquot is <5 ml. It should therefore be removed by ignition as follows. Transfer 10 ml acetic acid extract to a 45-ml silica basin, add 0.5 ml 1 M magnesium acetate and evaporate to dryness on a water-bath. (Note do not use magnesium nitrate, which reacts adversely on heating with 8-hydroxyquinoline.)... 

Often, greater accuracy may be obtained, as in Volhard type titration, by performing a back titration of the excess silver ions. In such a case, a measured amount of standard silver nitrate solution is added in excess to a measured amount of sample. The excess Ag+ that remains after it reacts with the analyte is then measured by back titration with standard potassium thiocyanate (KSCN). If the silver salt of the analyte ion is more soluble than silver thiocyanate (AgSCN), the former should be filtered off from the solution. Otherwise, a low value error can occur due to overconsumption of thiocyanate ion. Thus, for the determination of ions (such as cyanide, carbonate, chromate, chloride, oxalate, phosphate, and sulfide, the silver salts of which are all more soluble than AgSCN), remove the silver salts before the back titration of excess Ag.+ On the other hand, such removal of silver salt is not necesary in the Volhard titration for ions such as bromide, iodide, cyanate, thiocyanate, and arsenate, because the silver salts of these ions are less soluble than AgSCN, and will not cause ary error. In the determination of chloride by Volhard titration, the solution should be made strongly acidic to prevent interference from carbonate, oxalate, and arsenate, while for bromide and iodide analysis titration is carried out in neutral media. 

Cvetkovic and coworkers [74] evaluated a mixed Ni and Sr nitrates matrix modifier for the determination of Se in wines by Zeeman ET-AAS. Samples were heated on a boiling water bath with small amounts of HNO3 and H2O2. To eliminate interferences, especially sulfates and phosphates, Se was complexed with APDTC and extracted into methylisobutyl ketone (MIBK) and the graphite furnace temperature program was optimized for both aqueous and organic solutions. Selenium concentrations up to 0.93 pg l-1 were detected in wines from the Republic of Macedonia. 

The chloride was added as an interference in the nitrate determination and the pH was adjusted to 1.5 with sulfuric acid to preserve the samples. In the determination of silica, the participants were to analyze the samples by either the colorimetric molybdosilicate method or the heteropoly blue method. Phosphates were to have been determined by... 

The nitrite and nitrate reduction currents are enhanced in the presence of certain heavy elements such as La(III), Yb(ni), U(IV), and Ce(III). Simultaneous determination of nitrate and nitrite is achievable with careful choice of supporting electrolyte. Typical detection limits of 1 pmol 1 are encountered. Interference may arise from sulfate, phosphate, and oxalate. 

The advantage of discrete analyzers is that sample crossover in the system itself is the lowest possible. Volumes of 75 pi of reagent and sample volumes as large as 100 pi are sufficient. In an automated system with a throughput of 200 determinations per hour in the same sample 6 to 10 components (such as ammonium, alkalinity, aluminum, boron, bromide, calcium, chloride, chromium(VI), cyanide, fluoride, iron, magnesium, nitrate, nitrite, phosphate, etc.) can be determined. In discrete analyzers normally conventional spectrophotometric methods are used. These methods are prone to interference of the matrix of the sample. As a good concept for interference studies still is not available, interferences are as yet not sufficiently studied systematically even for routine analyses. 

Sulfate is still determined in CE systems with barium and a metallochromic indicator such as dimethylsulfonazo(III) (DMSA(III)) or methylthymol blue. As DMSA(in) is a metallochromic indicator, interfering cations should be removed prior to the determination step. Such pretreatment can be done in the flow-through system. The method suffers interference only from high concentrations of potassium, phosphate, hydrogen ion, chloride, and nitrate. As a consequence the method performs favorably when applied to groundwater, wastewater, or percolation water from tipped refuse. 

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