Oxalate distribution in soils under rhubarb (Rheum rhaponticum)

Oxalate in soils may enhance phosphate availability, promote mineral dissolution, and increase the mobility of aluminium and heavy metal cations by complexation. Rhubarb (Rheum rhaponticum L.) has very high content of oxalate in leaves and petioles, and therefore the topsoil under rhubarb might have elevated contents of oxalate. Soil samples were collected at depths of 0–2.5 and 2.5–5?cm from 10?cm sections along 100?cm transects from rhubarb plants at four locations in Denmark, and from seven layers in a soil profile to 80?cm depth at one location. Oxalate was extracted from the soil with 0.2?M phosphate at pH 2 by reciprocal shaking for 24?h and then determined by a new fast capillary zone electrophoresis method with 300?mM KH₂PO₄ and 0.30?mM TTAB electrolyte adjusted to pH 7, developed and tested to analyse high-ionic-strength soil extracts. Rhubarb increases the oxalate content in soil under the leaves slightly. The average content of oxalate in the upper 0–5?cm soil was 444?µmol/kg at the Kaldred site, and 111–333?µmol/kg at the three other locations. In the soil profile, the content of oxalate decreased from 500?µmol/kg in 0–5?cm depth to 110?µmol/kg at 75–80?cm depth. No significant seasonal changes in oxalate contents were observed, while an annual variation of 100?µmol/kg could be observed at 0–2.5?cm depth. During plant decay in autumn, a slight increase in oxalate content was observed at 30?cm soil depth. In conclusion, the role of oxalate in weathering and metal transport appears to be limited in soils under rhubarb. Oxalate might stimulate microbiological growth and phosphate mobilisation in the rhizosphere, but concentrations observed are too low to impose any toxic effects to organisms.     

Immune Complex of Banana Oxalate Oxidase: Use in Quantitation of Urinary Oxalate

Abstract

Oxalate oxidase (oxalate:oxygen oxidoreauctase, FC 1.2.3.4), isolated from ripe banana peel was precipitated by rat antiserum. Compared with native enzyme, this immune complex possessed higher specific activity, greater stability, broader pH range for optimal activity and higher resistance to thermal and heavy metal inactivation. These improved characteristics of the immune complex make it ideally suited for its use in the determination of urinary oxalate. A simple method of determining oxalate in urine samples, using this preparation is described.     

Evaluation of Oxalate Decarboxylase and Oxalate Oxidase for Industrial Applications

Increased recirculation of process water has given rise to problems with formation of calcium oxalate incrusts (scaling) in the pulp and paper industry and in forest biorefineries. The potential in using oxalate decarboxylase from Aspergillus niger for oxalic acid removal in industrial bleaching plant filtrates containing oxalic acid was examined and compared with barley oxalate oxidase. Ten different filtrates from chemical pulping were selected for the evaluation. Oxalate decarboxylase degraded oxalic acid faster than oxalate oxidase in eight of the filtrates, while oxalate oxidase performed better in one filtrate. One of the filtrates inhibited both enzymes. The potential inhibitory effect of selected compounds on the enzymatic activity was tested. Oxalate decarboxylase was more sensitive than oxalate oxidase to hydrogen peroxide. Oxalate decarboxylase was not as sensitive to chlorate and chlorite as oxalate oxidase. Up to 4 mM chlorate ions, the highest concentration tested, had no inhibitory effect on oxalate decarboxylase. Analysis of the filtrates suggests that high concentrations of chlorate present in some of the filtrates were responsible for the higher sensitivity of oxalate oxidase in these filtrates. Oxalate decarboxylase was thus a better choice than oxalate oxidase for treatment of filtrates from chlorine dioxide bleaching.     

Determination of Urinary Oxalate With Disposable Oxalate Oxidase Hembrane Strips

Abstract

We describe in this paper a simple and easy method of entrapping oxalate oxidase and peroxidase in acrylamide membrane and demonstrate the use of such enzyme membrane strips in the rapid determination of urinary oxalate. A crude preparation of 45-60% acetone cut obtained from banana fruit peel (Musa paradisiaca; French plantain) homogenate serves as a source of oxalate oxidase, which decomposes oxalate into CO₂ and H₂O₂. the oxalate content of a given urine sample is determined by introducing a small enzyme membrane strip (1 × 1 cm) into an aliquot of buffered urine containing a suitable chromogen for peroxidase and then measuring the colour developed due to the interaction of peroxidase with the newly formed H₂O₂ and the chromogen. Urine samples are pretreated with sodium nitrite to eliminate the interference of ascorbic acid in the assay. the enzyme membrane assay compares well with that of wet enzyme assay of oxalate in sensitivity and reliability.     

A Novel Enzyme Membrane Electrode for Oxalate Determination in Foodstuffs

Abstract

An enzyme membrane electrode usable for the assay of oxalate in foodstuffs is described. A commercially available preactivated polyamide membrane was used for the immobilization of oxalate oxidase. The bioactive disk thus obtained was associated with an amperometric transducer. The resulting self-contained enzyme electrode wich allows oxalate determination in various materials with minimal pretreatment exhibits a linear calibration ranging from 10–7 M and 10–4 M in the cell. The response-time was comprised between 20 seconds and 1 minute, depending on the oxalate content in the sample. The electrode-response was very stable for at least 4 months, a period during which more than 150 assays were performed.

The results obtained with several food materials were in good agreement with those obtained with the conventional spectrophotometric method. Assays were also performed with a microprocessor-based analyzer normally used for glucose measurements with a glucose oxidase electrode When the analyzer is equipped with an oxalate oxidase membrane, without further setting, oxalate can be determined in the range 5 10^?3 M-10^?1 M in the sample.     

Electrochemical Determination of Oxalate at Pyrolytic Graphite Electrodes

The electrocatalytic oxidation of oxalate at several carbon based electrodes including basal plane (BPPG) and edge plane (EPPG) pyrolytic graphite and glassy carbon (GC) electrode, was studied. The electrodes were examined for the sensing of oxalate ions in aqueous solutions and all three electrodes showed a response to oxalate additions. The peak of oxalate oxidation at BPPG electrode appeared at lower potential, +1.13 V vs. SCE, than at EPPG (+1.20 V vs. SCE) and GC electrode (+1.44 V vs. SCE). Oxalate oxidation at BPPG electrode was studied in more details for response characteristics (potential and current), effects of pH, temporal characteristics of response potential and current. The results indicated that oxalate oxidation proceeds as two‐electron process at the BPPG electrode with a transfer coefficient β and a diffusion coefficient D evaluated to be 0.45 and 1.03 (±0.04)×10^?5 cm² s^?1 respectively. The BPPG electrode was found to be suitable for oxalate determination in aqueous media showing linear response to oxalate concentration with a sensitivity of 0.039 AM^?1 and a limit of detection of 0.7 μM.     

Flow-injection amperometric determination of oxalate with immobilized oxalate oxidase

Oxalate is immobilized on controlled-pore glass and is used on-line in a glass minicolumn (2.5×25 mm). The hydrogen peroxide formed is detected amperometrically. Oxalate (6×10^?6?9×10^?4 M) is determined in a flowing stream of pH 3.5 citrate (or succinate) buffer. As little as 20 ng (in 40 μl; 5.7×10^?6 M) of oxalate can be detected. Copper inhibition can be removed either by adding EDTA to the carrier stream or incorporating a chelating-resin minicolumn into the flow system prior to the enzyme column.     

Comparison of Oxalate Oxidase Enzyme Electrodes for Urinary Oxalate Determinations

Abstract

Enzyme electrodes for oxalate were constructed by immobilizing oxalate oxidase enzyme (E, C, 1,2,3,4) on both potentiometric carbon dioxide and amperometric hydrogen peroxide sensors. These systems were optimized, and the response characteristics of the two biosensors examined in a comparison study. Areas investigated include linear range, calibration curve slope, response time, limit of detection, and lifetime. Selectivity studies were carried out with the system and showed no measurable response to millimolar levels of various L-amino acids, metal ions or ascorbic acid.

This comparison was extended into the choice of an optimal sensor for urinary oxalate determinations with minimal sample pretreatment. The peroxide sensor performed best in urine samples, allowing for the 1:40 dilution necessary to minimize the effect of any interferents present. At this or greater dilution, the recovery of standard additions of oxalate averaged 95.5%, with an average relative standard deviation of 4.9%. The system retained its activity throughout two weeks of continued use.     

Potentionetric Titrations Of Oxalate With A Fluoride-Selective Electrode

Abstract

Two methods for oxalate determination with a fluorideselective electrode are proposed. For oxalate amounts higher than 0.2 mmol, the joint precipitation of oxalate and standard fluoride with lanthanum(III) can be used. For smaller oxalate amounts, the precipitation of oxalate with excess of lanthanum(III) followed by back-titration with fluoride, is suitable. The end-points are located using the second derivative procedure and by means of the Gran method, respectively.     

Determination of Serum Urea with an Enzyme Thermistor Using Immobilized Urease

Abstract

The application of an enzyme thermistor device in a simple and accurate procedure for the determination of serum urea is described. The enzyme thermistor measures the heat produced when urea is passed through a small column containing immobilized urease. The stability and sensitivity as well as the performance with clinical serum samples of the system is evaluated. Advantages are the simplicity, the low enzyme cost and the insensitivity to the optical properties of the sample and interfering substances, which may affect the commonly used assay procedures.     

Determination of Urinary Oxalate by Ion Chromatography

Abstract

The factors which are important for calcium oxalate renal stone formation may be studie, in vitro, using the constant composition mineralization method (Gaur and Nancollas, Kidney Int., 26, 767 (1984). Since the molar calcium/oxalate rations in vivo are relatively high (normal range, 5–50) the rates of these seeded crystallization reactions at constant supersaturations are markedly dependent upon the concentrations of oxalate ion. Kinetic studies therefore require a rapid and reliable method for the analysis of this ion. A Dionex QIC analyzer incorporating an anion fiber suppressor unit and conductometric detector has been used to develop a method for the determination of urinary oxalate. The eluent, consisting of a mixture of 3.23 × 10^?3 mol L^?1 NaHCO₃ and 2.41 × 10^?3 mol L¹ Na₂CO₃, was used isocratically at a flow rate of 2.2 cm³ min^?1. The 14 min analysis time was considerably shorter than that reported for previous ionchromatographic methods. The minimum detectactable oxalate in urine was 0.11 × 10^?3 mol L^?1 with a RSD of about 10%. The method is especially suitable for monitoring oxalate in urine mineralization experiments.     

Construction and Characterization of a Beet Stem Based Biosensor for Oxalate

Abstract

This report describes the construction and characterization of an oxalate-sensing electrode. The electrode is based on the incorporation of ground beet stem into the graphite paste of a graphite paste electrode. The hydrogen peroxide generated by enzymatic degradation of oxalate is monitored at a working voltage of 0.900 V vs SCE. All measurements were conducted in a succinic acid/EDTA buffer at pH 4.00. Under these conditions, the electrodes exhibit reproducible responses to oxalate. The lower limit of oxalate detection was less than 1.03 × 10^?4 M. The time to achieve a steady state response after exposure to a step change in oxalate concentration in solution is less than one minute. The magnitude of response to oxalate over the oxalate concentrations studied varies among several electrode tested as does the degree of linearity of response. An electrode studied still exhibited analytically useful responses to oxalate on the 15th day of its use. The beet stem-based electrodes display little response to glycolic acid, glucose, DL-valine, or pyruvate.     

Studies with the Selectrode: Determination of Oxalate Ion Activity

Abstract

A solid state oxalate sensor is reported utilizing a commercial ion-selective electrode, the Selectrode^TM. Comparative measurements in aqueous solution of similar carboxylate ions and common inorganic anions, indicates appreciabl'e selectivity for oxalate. The Selectrode^TM was activated with a mixture of silver sulphide, lead sulphide, and lead oxalate.     

Comparative study of potentiometric and amperometric tissue-based electrodes for oxalate

Acetone-precipitated pulp from banana skins is physicall entrapped at the tip of a carbon dioxide gas-sensor and on a hydrogen peroxide sensor probe to determine oxalate potentiometrically and amperometrically in aqueous solution and inurine. The enzyme present in the tissue is oxalate oxidase. The potentiometric response has a slope of 47–50 mV/decade for 1 × 10^?4 M–2 × 10^?3 M oxalate with a detection limit of 2 × 10^?5 M. The amperometric response is linear for 2 × 10^t-5–3 × 10^?4 M oxalate with a dectection limit of 2 × 10^?6 M. Average recoveries of oxalate added to aqueous samples were 96.2% and 98.0%, and average relative standrd deviations were 3.8% and 3.6% for the potentiometric and amperometric systems, respectively. Oxalate was determined in six control urine samples, with relative errors of about 2.5%, by both electrode systems after a simple clean-up.     

Enzymatic Assay of Oxalate in Urine by Flow Injection Analysis Using Immobilized Oxalate Oxidase and Chemiluminescence Detection

Abstract

A flow injection analysis (FIA) method for the assay of oxalate in urine samples is described, which utilizes an incorporated column reactor of immobilized oxalate oxidase. The hydrogen peroxide generated is detected by chemiluminescence via reaction with luminol and hexacyanoferrate(III). Special empasis is placed on the role of L-ascorbic acid, which has been claimed to constitute the most serious interference in these types of assays. The possible elimination af this constituent by addition of sodium nitrite, as previously used in batch procedures, did not improve the selectivity of the approach. The FIA approach described, which has a detection limit (3[sgrave]) of 34 μM in undiluted urine samples and allows a sampling frequency of ca. 55 s/h, is shown to offer itself as convenient and rapid means for screening purposes.     

Determination of Glucose in Diluted Blood with a Thermal Flow Injection Analysis Biosensor

Abstract

The glucose concentration in diluted whole blood has been measured, using a miniaturized thermal biosensor based on the enzyme thermistor principle. The biosensor is a small flow injection system. A sample volume of 20μl is injected into a flow of 50μl/min. The heat produced when the sample passes the enzyme column is measured with a thermistor connected to a Wheatstone bridge. The enzyme column contains glucose oxidase and catalase co-immobilized on a solid support material. Samples of whole blood usually cause problems in flow-systems. The blood cells tend to block the enzyme column and the back pressure increases. We have tested a superporous agarose material as enzyme support material using tenfold diluted samples of whole human blood. The blood was collected from the finger-tip and diluted with buffer containing an anticoagulant and sodium fluoride. The number of samples possible to inject and the accuracy compared to the Boehringer Mannheim Reflolux have been determined. At least 100 ten-fold diluted blood samples could be injected on a micro-column of superporous agarose. The obtained glucose concentration correlated well with the one obtained with the reference instrument.     

Evaluation of Ammonium Oxalate for Fractionating Metallic Trace Elements in Soils by Sequential Extraction

Abstract

Ammonium oxalate is largely used to extract the trace elements bound to Mn-oxides, amorphous compounds and crystalline Fe-oxides. The objective of this work was to evaluate the selectivity and the efficiency of ammonium oxalate for extracting Cd, Cu, Ni, Pb and Zn by sequential extraction of soils. For this purpose, three schemes were selected and applied to three different soil samples of the Swiss Jura. Each extraction scheme consisted of six steps, where different reagents were used to extract Cd, Cu, Ni, Pb and Zn bound to the Mn and Fe compounds. The results showed that metallic trace elements extraction with ammonium oxalate are very dependant on the metal studied. The reason could be the capability of oxalate to form stable complexes with the metals considered which sometimes are only slightly soluble.     

Flow-Injection Spectrophotometric Determination of Oxalate,Citrate and Tartrate Based on Photochemical Reactions

Abstract

A flow-injection configuration for the spectrophotometric determination of oxalate, citrate and tartrate is proposed. The procedure is based on the photochemical decomposition of the complexes formed between iron(III) and these anions. The iron(II) produced in the photochemical reactions was detected by measuring the absorbance after complexation with ferrozine (λ_max=562 nm). Linear calibration graphs were obtained over the concentration ranges 5.0 × 10^?6 - 1.0 × 10^?4 M, 8 × 10^?6 - 1.8 × 10^?4 M and 1.0 × 10^?6 - 2 × 10^?5 M for oxalate, citrate and tartrate, respectively. The relative standard deviations at the 1x10^?5 M concentration level were within the range 1.29 - 1.47 %. The sampling frequency was about 40 samples h^?1. The usefulness of the method was tested in the determination of oxalate in urine and spinach, of citrate in pharmaceuticals and soft drinks and of tartrate in pharmaceuticals. For the determination of oxalate in urine samples a prior separation of the analyte by precipitation with calcium chloride is recommended.     

Kinetics of Calcium Oxalate Reduction in Taro (Colocasia Esculenta) Corm Chips during Treatments Using Baking Soda Solution

The oxalates content has caused limited utilizations of taro (Colocasia esculenta) as a food material. The insoluble oxalates, especially needle like calcium oxalate crystal may cause irritation, and swelling of mouth and throat. Removal of oxalates in food can be done by physical processes, such as soaking, boiling, and cooking or chemical process by converting them into soluble phases. The purpose of this research were to investigate the effects of baking soda concentration (0-10% w/w) and temperatures (70-97 °C) on the reduction of calcium oxalate content in the taro corm chips and to develop a kinetic model of that process during boiling in baking soda solution. The kinetic model development was done by considering the dissolution of calcium oxalate, chemical reaction and thermal degradation that take place during boiling. The experimental results showed that increasing of baking soda concentration and temperatures were found to increase the reduction of calcium oxalate in the taro corm chips. Based on the product's functional properties, the best condition for calcium oxalate reduction was soaking in 10% w/w baking soda solution for 2 hours followed by boiling at 90 °C for 60 minutes. The kinetic modeling concluded that the calcium oxalate reduction was found to follow a pseudo first order reaction. The modeling results showed that the model is able to represent the phenomena quite well with the apparent reduction rate constant, k = 15.77 Exp (21.239)/RT minute^-1.     

Flow-injection determination of inorganic pyrophosphate with use of an enzyme thermistor containing immobilized inorganic pyrophosphate

Inorganic pyrophosphate immobilized on controlled-pore glass is used in a simple flow enzyme thermistor system. The heat produced in hydrolysis of pyrophosphate is enhanced. by using Tris-HCl buffer, pH 7.2, containing 1 mM magnesium chloride, as carrier stream. The calibration graph is linear for 0.1–20 mM pyrophosphate; 500 assays are possible without loss of enzyme activity. For 0.5-ml injections of 10 mM pyrophosphate, the relative standard deviation was 2.0% (n=30). A single determination takes 6 min. Calcuim and strontium interfere.