Phosphate interference from

Hardness can also be calculated by summation of the individually deterrnined alkaline earths by means of atomic absorption analysis. Basic samples must be acidified, and lanthanum chloride must be added to minimise interferences from phosphate, sulfate, and aluminum. An ion-selective electrode that utilizes ahquid ion exchanger is also available for hardness measurement however, this electrode is susceptible to interferences from other dissolved metal ions. 

Kellum [115] has described a class-selective oxidation chemistry procedure for the quantitative determination of secondary antioxidants in extracts of PE and PP with great precision (better than 1 %). Diorgano sulfides and tertiary phosphites can be quantitatively oxidised with /-chloropcroxybenzoic acid to the corresponding sulfones and phosphates with no interference from other stabilisers or additives. Hindered phenols, benzophenones, triazoles, fatty acid amides, and stearate... 

A similar study has also been conducted to determine the suitability of ascorbic acid 2-phosphate (AAP) as an alternative substrate to 4-AP for AP under identical conditions [48], Although 4-APP and AAP were suitable substrates for amperometric immunosensors, 4-APP was superior owing to its sixfold faster enzymatic reaction and lower detection potential (approximately 200-400mV). Notably, the lower detection potential for the hydrolysis product of 4-APP minimizes interferences from other species and hence improves the sensitivity of the immunosensor. 

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. 

The method is either not affected by or can allow for interference from phosphate, sulfate, carbonate, bicarbonate, nitrate, coloured metal complexes, ammonia dyes, detergents, phenols, and other ultraviolet-absorbing substances. The method incorporates three features designed to reduce interferences ... 

This analytical procedure is based on an optimum analysis condition for segmented continuous flow analysis. The sample is combined with a molybdate solution at a pH between 1.4 and 1.8 to form the //-molybdosilicic acid. After an appropriate time for reaction, a solution of oxalic acid is added, which transforms the excess molybdate to a non-reducible form. The oxalic acid also suppresses the interference from phosphate by decomposing phosphomolyb-dic acid. Finally, a reductant is added to form molybdenum blue. Both ascorbic acid and stannous chloride were tested as reductants. 

Pruszkowska et al. [135] described a simple and direct method for the determination of cadmium in coastal water utilizing a platform graphite furnace and Zeeman background correction. The furnace conditions are summarised in Table 5.1. These workers obtained a detection limit of 0.013 pg/1 in 12 pi samples, or about 0.16 pg cadmium in the coastal seawater sample. The characteristic integrated amount was 0.35 pg cadmium per 0.0044 A s. A matrix modifier containing di-ammonium hydrogen phosphate and nitric acid was used. Concentrations of cadmium in coastal seawater were calculated directly from a calibration curve. Standards contained sodium chloride and the same matrix modifier as the samples. No interference from the matrix was observed. 

Table 4.7.3 Concentrations of polyols in urines of patients with metabolic disorders, as determined by method 1. Concentrations are in mmol/mol creatinine (age-controlled reference range). Bold values are above the reference range. Dist. Disturbed peak, not quantifiable due to interference from a coeluting fragment of C6-polyols, GALT galactose-1-phosphate uridyltransferase, n.d. not detectable, RPI ribose-5-phosphate isomerase, TALDO transaldolase...

Su and Puls (2001b) investigated possible interferences from different oxyanions on the sorption of As(V) and As(III) on Peerless zerovalent iron. Using chloride as a relatively nonreactive standard, Su and Puls (2001b) found that phosphate had the greatest effect in decreasing arsenic sorption on zerovalent iron. This observation is consistent with other batch (Kanel et al., 2005) and column (Su and Puls, 2003) studies. Like As(V), phosphate can form inner sphere complexes (Chapter 2) or produce distinct precipitate layers on zerovalent iron surfaces (Su and Puls, 2001b, 4564). 

Ratnaraj and Patsalos [37] described an HPLC method for simultaneous determination of vigabatrin and gabapentin in human serum after precolumn derivatization with o-phthaldialdehyde in the presence of mercaptoethanol and fluorimetric detection at 440 nm with excitation at 340 nm. Separation was achieved on a Hypersil BDS C18 (3 /tm) column (12.5 cm x 3 mm) with a mixture of 250 mM phosphate buffer, acetonitrile, water, and methanol as a gradient mobile phase (flow rate 0.45 ml/min). The method was linear over the concentration range of 25-400 yg/ml for vigabatrin. The lower limit of detection was 1 /(M for both analytes. Within- and between-batch RSD were 2-i% and 3-4%, respectively. No interference from other commonly prescribed antiepileptic drugs was observed. 

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. 

Oxalic acid is added to minimize interference from phosphate... 

In atomic absorption spectroscopy (AAS) both ionization and chemical interferences may occur. These interferences are caused by other ions in the sample and result in a reduction of the number of neutral atoms in the flame. Ionization interference is avoided by adding a relatively high amount of an easily ionized element to the samples and calibration solutions. For the determination of sodium and potassium, cesium is added. To eliminate chemical interferences from, for example, aluminum and phosphate, lanthanum can be added to the samples and calibration solutions. 

Rat liver mitochondria were isolated as described (4). The initial rate of ATP synthesis associated with the oxidation of succinate was followed by monitoring fluorometrically the ATP-linked NADPH production in the presence of hexokinase and glucose-6-phosphate dehydrogenase (10). Control experiments showed no interference from unexpected reduction of NADP+ or from electron backflow. Possible ATP formation via mitochondrial adenylate... 

Derivatisation-electron capture gas chromatography has been used to determine pg L 1 quantities of nitrite in water without interference from halides, nitrate, phosphate, sulphate, bicarbonate, ammonium and alkali metals and alkaline earth metals [792],... 

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... 

Reactions 8 and 9 are combined for the removal of the phosphate ion from solutions in which it interferes with the normal course of analysis (cf. Section V.13). 

In our experiments, hair (20 mg) is soaked in 2 mL of phosphate buffer (pH 5.5) containing cocaine hydrochloride (1,000-10,000 ng/mL) for 1 h at 37°C. To avoid interference from a variety of factors (see below) including possible adsorption of drugs on the walls of the polystyrene test tubes, the contaminated hair is subjected to the following treatments before commencing with the wash kinetic experiments in a new test tube. 

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