Simultaneous determination of oxalic and citric acids in urine by high-performance liquid chromatography

Evaluation of a high-performance liquid chromatography method for urinary oxalate determination and investigation regarding the pediatric reference interval of spot urinary oxalate to creatinine ratio for screening of primary hyperoxaluria

BACKGROUND

Urinary oxalate can provide important clues for the screening and monitoring of children with primary hyperoxaluria (PH), which is a potentially life-threatening condition. However, little effort has been devoted to improve the oxalate assay in recent years. We have proposed a reliable and cost-effective high-performance liquid chromatography (HPLC) method for urinary oxalate determination.

METHODS

Urine specimens were centrifuged after one-step derivatization, and the supernatants were subjected to HPLC analysis.

RESULTS

The method was validated with consistent linearity from 0.0625 to 2.0 mmol/L with coefficients of variation ≤7.73%, good recovery, low carryover, satisfactory sample stability, and analytical specificity. The lower limit of quantification and the limit of detection were 0.03130 and 0.0156 mmol/L, respectively. Imprecision values were ≤2.92% and ≤16.6% for externally and internally produced controls, respectively. The pediatric reference interval of spot urinary oxalate to creatinine ratios was established together with its application in screening of PH in patients with renal diseases, revealing its successful deployment in our laboratory.

CONCLUSIONS

This reliable HPLC method could serve as a significant tool to determine urinary oxalate levels for screening and monitoring of children with PH in routine clinical laboratories.

A tri-serine tri-lactone scaffold for the quantification of citrate in urine

Tri-serine tri-lactone based fluorescent sensors can discriminate structurally similar anions, including mono-, di- and tri-carboxylates with 100% correct classification.

Oxalic acid and sclerotial differentiation of Polyporus umbellatus

The present investigation aimed to uncover the effects of exogenous oxalic acid during the sclerotial formation of Polyporus umbellatus, with an emphasis on determining the content of the endogenic oxalic acid in the fungus. To this end, the oxalic acid content of the vegetative mycelia, sclerotia, culture mediums and sclerotial exudate were measured using High Performance Liquid Chromatography (HPLC). Furthermore, the lipid peroxidation was estimated by detecting thiobarbituric bituric acid reactive substances (TBARS). The results showed that the exogenous oxalic acid caused a delay in sclerotial differentiation (of up to 9 or more days), suppressed the sclerotial biomass and decreased the lipid peroxidation significantly in a concentration-dependent manner. Oxalic acid was found at very low levels in the mycelia and the maltose medium, whereas it was found at high levels in the mycelia and sucrose medium. After sclerotial differentiation, oxalic acid accumulated at high levels in both the sclerotia and the sclerotial exudate. Oxalic acid was therefore found to inhibit P. umbellatus sclerotial formation.

High-throughput and rapid fluorescent visualization sensor of urinary citrate by CdTe quantum dots

In this paper, we have presented a novel CdTe quantum dots (QDs) based fluorescent sensor for visual and turn-on sensing of citrate in human urine samples. The europium ion (Eu(3+)) can lead to the fluorescence quenching of thioglycollic acid (TGA) modified CdTe QDs due to photoinduced electron transfer accompanied by the change of emission color from yellow to orange. Next, addition of citrate breaks the preformed assembly because citrate can replace the CdTe QDs, based on the fact that the Eu(3+) ion displays higher affinity with citrate than the CdTe QDs. Thus the photoinduced electron transfer is switched off, and the fluorescence emission of CdTe QDs is rapidly (within 5min) recovered, simultaneously, the orange emission color restores to yellow. Such proposed strategy may conveniently discriminate the patient of renal stone from normal person by naked eyes. In addition to visualization detection, the fluorescence responses can be used for well quantifying citrate in the range of 0.67-133μM. So, the present, simple, low-cost and visualized citrate fluorescence sensor has great potential in the applications for earlier screening in clinical detection.

Simultaneous chemiluminescence determination of citric acid and oxalic acid using multi-way partial least squares regression

A novel kinetic chemiluminescent method proposed for the simultaneous determination of oxalic acid and citric acid in their mixtures.

Screening of different probiotic strains for their in vitro ability to metabolise oxalates: any prospective use in humans?

BACKGROUND

Oxalate is the salt-forming ion of oxalic acid and can generate oxalate salts combining with various cations, such as sodium, potassium, magnesium, and calcium. Approximately 75% of all kidney stones are composed primarily of calcium oxalate (CaOx) and hyperoxaluria, a condition involving high urinary oxalate concentration, is considered a primary risk factor for kidney stone formation, known as nephrolithiasis. Current therapeutic strategies often fail in their compliance or effectiveness, and CaOx stone recurrence is still common. After an initial stone, there is a 50% chance of forming a second stone within 7 years if the condition is left untreated. The potential therapeutic application of some probiotics, mainly lactobacilli and bifidobacteria, in reducing hyperoxaluria in vivo through intestinal oxalate degrading activity is compelling and initial reports are promising. This study was undertaken to screen different Lactobacillus and Bifidobacterium strains for their capacity to degrade oxalate in vitro using reverse-phase high-performance liquid chromatography (HPLC).

METHODS

The oxalate-degrading activity of 13 lactobacilli and 5 bifidobacteria was tested using a novel HPLC method after growth in a broth culture added with 10 mM ammonium oxalate. Experiments were repeated 3 times. Oxalobacter formigenes (DSM 4420) was used as positive reference to validate HPLC oxalate-degrading capability assays.

RESULTS

Lactobacillus strains were more efficient than bifidobacteria in degrading oxalates. L. paracasei LPC09 (DSM 24243) gave the best result, as 68.5% of ammonium oxalate was converted at the end of incubation, whereas the following best converters belong to the L. gasseri and L. acidophilus species. The relatively low conversion rate observed for most bifidobacteria can probably be attributed to intrinsic oxalate toxicity toward this genus.

CONCLUSIONS

Humans lack the enzymes needed to directly metabolise oxalate, and this potentially toxic compound is, therefore, managed using alternative pathways. As oxalate-degrading bacteria are present in the endogenous microbiota of the human intestine, although with significant individual differences, it is possible to hypothesise that the administration of selected oxalate-degrading probiotics could be an alternative and innovative approach to reducing the intestinal absorption of oxalate and the resulting urinary excretion.

In vitro anti-inflammatory activity of selected oxalate-degrading probiotic bacteria: potential applications in the prevention and treatment of hyperoxaluria

Oxalate (Ox) is a very common component of the human diet, capable to collect in the renal tissue and bind calcium to form calcium oxalate (CaOx) crystals. A supersaturation of CaOx crystal may cause nephrocalcinosis and nephrolithiasis. The inflammation derived from the CaOx crystal accumulation, together with innate or secondary renal alterations, could strongly affect the renal function. In this case a consumption of probiotics with either oxalate-degrading activity at intestinal level and systemic anti-inflammatory activity could be an alternative approach to treat the subjects with excess of urinary oxalate excretion. 11 strains of lactic acid bacteria (Lactobacilli and Bifidobacteria), already included in the list of bacteria safe for the human use, were investigated for their capability to degrade oxalate by mean of RP-HPLC-UV method and modulate inflammation in an in vitro model system based on peripheral blood mononuclear cells. Four promising bacterial strains (Lactobacillus plantarum PBS067, Lactobacillus acidophilus LA-14, Bifidobacterium breve PBS077, Bifidobacterium longum PBS078) were identified as innovative biological tools for the prevention and the therapeutic treatment of hyperoxaluria and the inflammatory events associated to the Ox accumulation.

PRACTICAL APPLICATION

The oxalate-degrading activity of some probiotics and their capability to modulate the release of inflammation mediators could be exploited as a new nutraceutical and therapeutic approach for the treatment of oxalate accumulation and the related inflammatory state.

Washing of banked blood by three different blood salvage devices

BACKGROUND

Storage lesions in red blood cells (RBCs) lead to an accumulation of soluble contaminants that can compromise the patient. Organ failures, coagulopathies, and cardiovascular events including lethal cardiac arrest have been reported, especially with massive transfusion or in pediatric patients. Washing improves the quality of stored RBCs, and autotransfusion devices have been proposed for intraoperative processing, but these devices were designed for diluted wound blood, and limited data on their performance with RBCs are available.

STUDY DESIGN AND METHODS

Three autotransfusion devices (Electa, Sorin; CATS, Fresenius; OrthoPAT, Haemonetics) differing in function of their centrifugation chambers were evaluated with RBCs at the end of their shelf life and with dilutions thereof. Elimination rates of potassium, plasma free hemoglobin, total protein, citrate, acid equivalents, and iomeprol added as a marker substance were analyzed, in addition to RBC recoveries.

RESULTS

Product hematocrit (Hct) levels ranged between 54.8 and 72.6%. RBC recovery rates were between 62.7 and 95.0%, the lowest being with the OrthoPAT processing of undiluted RBCs. Plasma elimination rates increased with predilution and ranged from 46.6% to 99.5%, the lowest being with the CATS and undiluted RBCs. Washing did not change pH and buffering capacity of RBCs.

CONCLUSION

Autotransfusion devices offer a practical and obviously economical option to wash banked RBCs intraoperatively to prevent hyperkalemia and other disturbances in massive transfusion or pediatric patients. Predilution improves elimination rates, especially in devices that produce high product Hct levels. With a Y-tubing the RBCs should bypass reservoir and vacuum, and the procedure should be guarded by a policy and procedure manual and a quality management system.

Microfluidic chip-capillary electrophoresis with dynamic multi-segment standard addition for rapidly identifying nephrolithiasis markers in urine

A microchip-CE device was fabricated for bed-side monitoring of nephrolithiasis biomarkers in urine by incorporating on-chip continuous passive mixing and standard addition to reduce sample matrix interference, increase sample throughput and eliminate accessories for active mixing. Under optimized conditions with buffer containing 20 mM borate and 0.5 mM CTAB at pH 10.3, sample and standards injected electrokinetically at -350 V for 10 s for online mixing in a Y-merging flow microchannel prior to CE separation and UV detection at 210 nm, both inhibitors (citrate, CA) and promoters (oxalate, OA and uric acid, UA) for nephrolithiasis can be separated and determined in human urine in a single run completed within 10 min after a simple 50-fold sample dilution and filtering. Satisfactory working ranges from 0.13-40, 0.25-40 and 0.025-40 mM, LOD 2.6, 6.1 and 0.7 μM, repeatability (%RSD, n=5) for migration time 1.40, 1.43, 0.47 and peak area 4.46, 6.10, 1.98, respectively, for CA, OA and UA are obtained for urine samples. The use of on-chip standard addition is shown to improve repeatability of the migration time, assist the identification of nephrolithiasis markers from difficult samples with noisy baseline and enlarge the working range for nephrolithiasis marker determination. The device developed can be used for both routine and emergency monitoring to deliver results on demand for bedside monitoring and public health protection. It provides an early detection of nephrolithiasis to enable timely treatments, ease anxiety of parents for neonates consuming suspected contaminated food, and quick results for patients in a critical condition.

Determination of trace amounts of oxalate in vegetable and water samples using a new kinetic-catalytic reaction system

This paper describes a new, simple, sensitive, and selective catalytic-kinetic-spectrophotometric method for the determination of trace amounts of oxalate in vegetable and water samples. The method is based upon the catalytic effect of oxalate on the oxidation of crystal violet (CV) by dichromate in sulfuric acid media. The reaction was followed by measuring the decrease in absorbance of CV at 630 nm (lambdamax of CV). The dependence of sensitivity on the reaction variables was studied and discussed. Under the optimum conditions, a fixed time procedure was used to obtain a linear calibration curve in the oxalate concentration ranges of 0.20-5.5 microg mL(-1) of oxalate. The calculated detection limit was 0.050 microg mL(-1). The relative standard deviations for ten replicate determinations of 0.40, 1.8, and 2.5 microg mL(-1) of oxalate were 6.0%, 2.5%, and 1.8%, respectively. The effect of the presence of various species commonly associated with real samples was also investigated. The proposed method was successfully applied for the determination of oxalate in vegetable and spiked water samples.

Metabolic activity of probiotics-oxalate degradation

Urinary tract stones are an important clinical problem in human and veterinary medicine. Hyperoxaluria is the single strongest promoter of kidney stone formation. The aims of the present study were to (a) evaluate oxalate degradation by a range of Bifidobacteria species and Lactobacillus species isolated from the canine and feline gastrointestinal tract in vitro and (b) to determine the impact of oxalate degradation by selected strains in vivo. The bacteria were grown in oxalate-containing media and their ability to degrade oxalate in vitro was determined using reverse-phased HPLC. Bifidobacteria species and Lactobacillus species that degraded oxalate in vitro and survived gastric transit were selected for further examination. The selected probiotics were fed to rats for 4 weeks. Urine was collected at week's 0, 2 and 4 and oxalate levels determined by HPLC. In vitro degradation was detected for 11/18 of the Lactobacillus species. In contrast, the capacity to degrade oxalate was not detected for any of the 13 Bifidobacterium species tested. Lactobacillus animalis 223C, Lactobacillus murinus 1222, L. animalis 5323 and L. murinus 3133 were selected for further investigation in a rat model. Urinary oxalate levels were significantly reduced (p<0.05) in animals fed L. animalis 5323 and L. animalis 223C but were unaltered when fed L. murinus 1222, L. murinus 3133 or placebo. Probiotic organisms vary widely in their capacity to degrade oxalate. In vitro degradation does not uniformly translate to an impact in vivo. The results have therapeutic implications and may influence the choice of probiotic, particularly in the setting of enteric hyperoxaluria.

Spectrophotometric Determination of Oxalate Ion with N,N'-Diethyl-N,N'-[[4,4'-dihydroxy-1,1'-binaphthalene]-3,3'-diyl]bisbenzamide and Copper(II)

A simple and rapid spectrophotometric method for the determination of oxalate ion was established by the fading of a colored complex between N,N'-diethyl-N,N'-[[4,4'-dihydroxy-1,1'-binaphthalene]-3,3'-diyl]bisbenzamide and copper(II). Beer's law was obeyed in the concentration range of 0.1 - 2.0 microg cm(-3) for oxalate ion, with an effective molar absorptivity at 533 nm and the relative standard deviation being 8.0 x 10(3) dm(3) mol(-1) cm(-1) and 1.0% (n = 5), respectively. This proposed method has excellent reproducibility, and was applied to recovery tests of oxalate ion in tap water and human urine; the results were satisfactory. This is suggested that the method is based on the reaction of copper(II) to copper(I) with oxalate ion.

Kinetic Spectrophotometric Method for the Determination of Trace Amounts of Oxalate by an Activation Effect

A new, simple and inexpensive kinetic catalytic spectrophotometric method for the determination of oxalate is described. The method is based on an activation effect of oxalate on a catalytic effect of iron(II) on the oxidation of iodide by bromate. The reaction is monitored by measuring the absorbance of triiodide ion at lambda max = 352 nm. A calibration graph was obtained from 0.10 - 7.0 microg cm(-3) of oxalate with a detection limit of 0.080 microg cm(-3). The standard deviations for ten replicate determinations of 0.50, 1.0 and 5.0 microg cm(-3) of oxalate were 4.0, 2.6 and 1.8%, respectively. The applicability of the method was demonstrated by the determination of oxalate ion in real samples.

Development and validation of an assay for citric acid/citrate and phosphate in pharmaceutical dosage forms using ion chromatography with suppressed conductivity detection

The paper describes the development and validation of a simple, rapid, accurate, and sensitive ion chromatographic procedure to assay total citrate (citric acid/citrate) and phosphate in nine dosage forms. The dosage forms chosen represent all dosage forms in USP27-NF22 for which the respective monographs require an assay for either citric acid/citrate or citric acid/citrate and phosphate. Citrate and phosphate were separated in <10min by a hydroxide-selective column using anion-exchange chromatography with a 20mM potassium hydroxide eluent and detected by suppressed conductivity. The method showed linear responses over the concentration ranges 0.2-100microg ml(-1) (r(2) > 0.9990) for citrate and 0.2-60microg ml(-1) (r(2) = 0.9999) for phosphate, with limits of quantitation (signal-to-noise (S/N) = 10) of 0.2microg ml(-1) for both analytes. The accuracy of the procedure, determined by spiked recovery measurements, was within 95-105%. The intraday and the interday precision were demonstrated by the relative standard deviations (R.S.D.) of <1 and <2%, respectively, for both analytes. The ruggedness was determined by a full factorial design using analyst, equipment, column lot, and eluent preparation procedure as variables. The results show an overall R.S.D. of <3% and that an electrolytically generated 20mM KOH eluent produces assay results equivalent to a manually prepared 20mM NaOH eluent.

Simultaneous determination of polycarboxylic acids by capillary electrophoresis with a copper electrode

The simultaneous determination of polycarboxylic acids including oxalic acid, citric acid, malonic acid, malic acid, tartaric acid, aspartic acid and glutamic acid was achieved by capillary electrophoresis with a copper disk electrode (d = 200 microm). In the system. 0.2 mmol/l cetylpridinium bromide (CPB) was used as an electroosmotic flow (EOF) modifier to reverse the direction of EOF. The effects of the solution pH and CPB concentration on separation were evaluated to achieve the optimum separation conditions. At the working potential of +0.14 V (vs. saturated calomel electrode), the calibration curves for all polycarboxylic acids studied were linear with 2 approximately 3-orders of magnitude and all the detection limits (S/N = 3) were below 15 fmol except malonic acid. Furthermore, the oxalic and citric acids in urine were successfully separated and determined with high sensitivity.