An ion chromatographic method for the simultaneous determination of inorganic phosphate, bromide, nitrate and sulphate in human serum

Analytical methods for quantitating sulfate in plasma and serum

Circulating sulfate needs to be maintained at sufficiently high levels for healthy growth and development. Animal studies have shown the adverse physiological consequences of low circulating sulfate level on the skeletal, neurological and reproductive systems. However, sulfate is not routinely measured in clinical investigations, despite the importance of sulfate being documented over the past several decades. Several methods have been developed for measuring serum and plasma sulfate level in animals and humans, including a range of barium sulfate precipitation techniques that have been a major focus of sulfate analytics since the 1960s. Evaluation of an ion chromatography method demonstrated its utility for investigation of sulfate levels in human health. More recently, liquid chromatography-tandem mass spectrometry has been used to show hyposulfatemia in a human case of mild skeletal dysplasia. This article provides an overview of analytical methods for measuring sulfate in serum and plasma, highlighting the strengths and limitations of each method.

Enzymatic Behavior Regulation-Based Colorimetric and Electrochemiluminescence Sensing of Phosphate Using the Cobalt Oxyhydroxide Nanosheet

In this work, a convenient and flexible assay for colorimetric and electrochemiluminescence (ECL) sensing of phosphate was proposed based on the enzymatic behavior regulation of the cobalt oxyhydroxide (CoOOH) nanosheet. CoOOH as a novel nanoenzyme exhibited a peroxidase-like activity, which could catalyze different substrates such as 2, 2'-azinobis-3-ethylbenzthiazoline-6-sulfonate (ABTS) and 4-chloro-1-naphthol (4-CN) with hydrogen peroxide (H₂O₂) as the electron acceptor. Phosphate could specifically regulate the enzymatic behavior of the CoOOH nanosheet via the deactivating effect. A high level of phosphate enabled a weak color change of ABTS, which offered a "turn-off" model of the colorimetric assay with a limit of detection of 0.673 μM. Based on the similar enzymatic behavior, this strategy could then be applied in the ECL assay utilizing l-arginine-6-aza-2-thiothymine-protected gold nanoclusters (Arg-ATT-AuNCs) as ECL signal indicators. Specifically, 4-CN was catalyzed to generate the precipitate and lead to the quenching on ECL emission. Different from colorimetric behavior, phosphate with a high concentration could induce strong ECL performance, which enabled the "turn-on" model of the ECL assay with a more sensitive determination down to 0.434 nM. This flexible enzymatic behavior regulation could then allow the phosphate measurement in environmental samples including tap water and river water with satisfactory accuracy, which holds the potential in the field of environmental protection.

Optical Nanosensors for in vivo Physiological Chloride Detection for Monitoring Cystic Fibrosis Treatment

Personalized approaches for continuous monitoring of chloride levels are potentially valuable for evaluating the efficacy of new treatments of genetic disorders such as cystic fibrosis. In this report, we validated optode-based nanosensors for real-time chloride monitoring in the interstitial fluid of living animals. These nanosensors take advantage of a ratiometric sensing scheme which demonstrates reversible and selective chloride detection in the physiological range. We further investigate how skin pigmentation affects the sensor performance during in vivo fluorescence imaging. We successfully monitored endogenous chloride changes using nanosensors during pharmacological treatment in a cystic fibrosis mouse model. We believe this platform is a valuable tool for chloride detection which could assess the efficacy of new treatments for cystic fibrosis.

Environmental exposure of humans to bromide in the Dead Sea area: Measurement of genotoxicy and apoptosis biomarkers

Bromide (Br^-) is a bromine atom with a negative charge which is released mainly in the production of pesticides and flame retardants. It is also found naturally in seawater. Br¯ has been associated with many detrimental effects such as respiratory problems, gastric hemorrhages, and dermal burns. The aim of the study was to monitor serum bromide in humans and to correlate its level with genotoxicity and apoptosis in human. The study utilized comet assay, to measure DNA damage in peripheral leukocytes (i.e. T%DNA), enzyme-linked immunosorbent assay were used to determine fortilin level as an apoptosis marker, and spectrophotometry to measure serum Br¯ in two populations at the Dead Sea area, which are located close to and far from a local bromine factory: Ghor As-safi and Deir Alla, respectively. The biomarkers were compared with the correlating serum Br¯. A total of 397 individuals were involved in the study. The serum Br^- and the genotoxicity biomarker were significantly higher (p <  0.001) in Ghor As-safi than in Deir Alla. In contrast, serum fortilin did not differ significantly between the two regions (p >  0.05). T%DNA was significantly correlated (r = 0.867, p <  0.01) to serum Br¯. In conclusion, residing near a bromide source site is increasing the bromide body burden, and enhancing genotoxicity with no detectible apoptosis. Furthermore, the selected biomarkers could serve as tools to assess the toxicity of bromide as a consequence of environmental exposure.

Presentation of NO-metabolites (nitrate/nitrite) in blood serum and pleural effusions from cancer patients with pleurisy

To assess whether cancer-induced pleurisy is associated with an alteration of nitric oxide (NO)-synthase activity, the levels of nitrate/nitrite (NOx) were measured in blood serum (BS) and pleural effusion (PE) of 35 cancer patients (secondary pleural metastases and mesotheliomas), eight patients with benign lung diseases, and in BS of nine healthy donors. It was found that (1) BS of patients with secondary pleural metastases had an elevated level (P<0.015) of NOx (59.7+/-24.4 microM, n=28) in comparison with control level of BS for healthy donors (43.4+/-13.5 microM, n=9); (2) BS of mesotheliomas (32.1+/-12.2 microM, n=4) had significantly (P<0.05) lower level of NOx compared to BS of benign patients (61.2+/-28.8, n=6); (3) differences in mean levels of NOx in BS and same PE of examined patient groups did not reach statistical significance, excepting sub-group of patients with primary mammary carcinoma; (4) significant interindividual differences of NOx in all groups of patients were revealed; (5) fluids from about 11% of cancer patients contained extremely high levels of NOx over 100 microM; (6) a significant elevation of apparent NOx level in BS and PE of patients with secondary pleural metastases in comparison with those in BS of healthy donors was revealed when the native, i.e. protein-contained, samples were managed with Griess reagent. The results described here, point up the diverse role of NOx in cancer patients. Its role is far from being clear but it seems that NOx acts as a signaling mediator during the formation of pleural metastases and might be considered as a non-specific marker in the corresponding PE. Furthermore, NOx could be used to give rationale of proper application of anticancer drugs affecting diversely NO-synthase activity in cells. Besides, a casual effectiveness of NOx measurements in native samples from cancer patients using Griess reagent needs additional elaboration.

The clinical chemistry of inorganic sulfate

Although inorganic sulfate is an essential and ubiquitous anion in human biology, it is infrequently assayed in clinical chemistry today. Serum sulfate is difficult to measure accurately without resorting to physicochemical methods, such as ion chromatography, although many other techniques have been described. It is strongly influenced by a variety of physiological factors, including age, diet, pregnancy, and drug ingestion. Urinary excretion is the principal mechanism of disposal for the excess sulfate produced by sulfur amino acid oxidation, and the kidney is the primary site of regulation. In renal failure, sulfoesters accumulate and hypersulfatemia contributes directly to the unmeasured anion gap characteristic of the condition. In contrast, sulfate in urine is readily assayed by a number of means, particularly nephelometry after precipitation as a barium salt. Sulfate is most commonly assayed today as part of the clinical workup for nephrolithiasis, because sulfate is a major contributor to the ionic strength of urine and alters the equilibrium constants governing saturation and precipitation of calcium salts. Total sulfate deficiency has hitherto not been described, although genetic defects in sulfate transporters have been associated recently with congenital osteochondrodystrophies that may be lethal. New insights into sulfate transport and its hormonal regulation may lead to new clinical applications of sulfate analysis in the future.

Quantitation of sulfate and thiosulfate in clinical samples by ion chromatography

For assay of serum sulfate, quantitation by ion conductimetry after separation by anion-exchange chromatography is the method of choice. In comparison to classical barium precipitation methods, chromatographic methods demonstrate increased precision, specificity and sensitivity, and they may be superior to spectrophotometric methods that rely on organic cation precipitation of sulfate. The increased sensitivity and specificity, as well as the inherent capacity of chromatographic methods for simultaneous determination of other anions, has led to its increasing use in the determination of excreted sulfate in clinical profiles of urinary anion composition. Ion chromatography can also be used to quantitate free sulfate in other clinical samples, including cerebrospinal fluid, sweat, saliva, breast milk and human tissues. Finally, ion chromatography shows promise as a more precise and sensitive method for measurement of total acid-labile sulfoesters and thiosulfate.

The determination of inorganic sulphate in serum and synovial fluid by high performance ion chromatography

A method for the determination of inorganic sulphate based on high performance ion chromatography is presented. The separation was performed on an anion-exchange column with a 1.8 mmol/l sodium carbonate/ 1.7 mmol/l sodium hydrogen carbonate-buffer, pH 10.35. Conductivity of the eluate was monitored after suppression of the background conductivity caused by the eluent-buffer. Serum and synovial fluid samples were prepared by ultrafiltration through membranes with a molecular mass cutoff of M(r) 10,000. The viscosity of the synovial fluids was reduced by treatment with hyaluronate lyase before ultrafiltration. The method showed a linear response for sulphate concentrations between 0.5 and 1000 mumol/l. The limit of detection was 1 mumol/l for aqueous standards. For serum the coefficient of variation within-run was 2.3%-2.4%, the coefficient of variation between days 2.9%-3.1%. For synovial fluids the coefficient of variation within-run was 3.1%-3.4%, the coefficient of variation between days 4.6%-5.7%. Standard recovery experiments performed by spiking pools of human sera containing low sulphate concentrations with sulphate concentrations between 5 mumol/l and 40 mumol/l showed recoveries between 98.9% and 100.6%. The corresponding experiments with pools of synovial fluids showed recoveries of 98.3% to 100.9%. As determined from 127 serum samples the reference range for sulphate was 262 mumol/l-420 mumol/l, with a mean value of 314 mumol/l. No dependence on age or sex was observed. The sulphate concentration in 36 synovial fluids from knees affected by inflammatory processes showed a mean value of 424 mumol/l and a standard deviation of 70 mumol/l. In 41 synovial fluids from knees affected by chronic degeneration joint disease, the sulphate concentrations were statistically significantly lower, with a mean of 374 mumol/l and a standard deviation of 58 mumol/l. The concentrations of sulphate in the synovial fluids were statistically significantly higher than those in the serum samples used for determination of the reference range. Following the oral application of a subtoxic single dose of acetaminophen (32.5 mg/kg body weight-62.5 mg/kg body weight) to 4 healthy volunteers, there was a significant decrease in the concentration of sulphate in serum with a minimum at 4-5 h after application of the drug. The cumulative concentration decrease of sulphate in serum and the kinetic constant of the sulphate depletion were not correlated with the applied acetaminophen dose normalized for body weight.

Determination of nitrite and nitrate in human serum

A simple and effective assay for nitrite and nitrate in human serum has been developed using ion chromatography. Initial experiments using isocratic carbonate-bicarbonate elution with conductivity detection on a Dionex QIC system with an AS4A-SC column showed promise but were unsatisfactory because of co-elution problems with nitrite. Carbonate and chloride were investigated as eluents using a gradient system, and direct UV detection at 214 nm was used in place of conductivity detection. Dionex AS4A, AS9A, AS12, Nucleopac PA-100 and Carbopac PA-100 columns were compared for selectivity and resistance to overload. The final method, using a chloride concentration gradient, pH buffering and direct UV detection with a Carbopac PA-100 column, shows good resolution, does not suffer from chloride overload and is simple to use. The method is being used in an investigation of the role of nitric oxide in pre-eclampsia, a hypertensive disorder during pregnancy.

The role of nitric oxide in cancer. Improved methods for measurement of nitrite and nitrate by high-performance ion chromatography

The short lifetime of nitric oxide (NO) in vivo impedes its quantitation directly; however, the determination of nitrite and nitrate ions as the end-products of NO oxidation has proven a more practical approach. High-performance ion chromatographic analysis of nitrite in biological fluids is hampered by the large amount of chloride ion (up to approximately 100 mmol/l) which results in insufficient peak resolution when utilizing conductimetric detection. Analysis of both anions in small sample volumes is also constrained by the need to minimise sample handling to avoid contamination by environmental nitrate. We report a means to remove Cl- ions from small sample volumes using Ag+ resin which facilitates quantitation of either nitrite and nitrate anions in biological samples, using silica or polymer based ion-exchange resins with conductimetric or electrochemical and spectrophotometric detection. Including a reversed-phase guard column before the anion-exchange guard and analytical column also greatly extends column lifetime.

Improved methods to measure end products of nitric oxide in biological fluids: nitrite, nitrate, and S-nitrosothiols

The aim of this study was to compare and improve standard methods to determine nitrite (NO2-), nitrate (NO3-) and S-nitrosothiol (RSNO) levels in cell culture supernatants, sera, and urine. We modified the conventional Griess reaction by replacing sulfanilamide with dapsone (4,4'-diamino-diphenylsulfone) and compared the NO2- levels in our study samples with a commercially available NO2- assay kit. Our modification, along with ultrafiltration of the samples, resulted in an enhanced sensitivity to measure NO2- down to 0.2 microM. The detection limit was further improved to 0.02 microM when NO2- was identified by the fluorochrome 2,3-diaminonaphthalene (DAN). To measure the stable end product NO3- by the Griess reaction or the DAN method, this anion must be reduced to NO2-. We compared the capacity of bacterial nitrate reductase with the reducing metal cadmium to convert NO3- to NO2-. After reduction, NO2- levels were determined either by the DAN method or by our modified Griess reaction. We found that there was a high correlation (r2 = 0.998) in total NO2- concentrations in the study samples using both methods for reducing NO3- to NO2-. The simultaneous determination of NO2- and NO3- was achieved by using anion-exchange chromatography (HPLC; Polyspher IC AN-1 column). The detection limit of this assay for each anion is 0.5 microM, and it can be applied equally well to sera, urine, and culture media. We also adapted the DAN method to determine RSNO levels in our study samples. Using this approach, we were able to measure RSNO levels down to 0.15 microM. As result we discovered that RSNO levels were markedly increased in urine from septic patients and in supernatants from cytokine-stimulated human tumor cell lines. L-Citrulline, a coproduct of NO biosynthesis, was measured using a colorimetric assay with a sensitivity limit of 3.0 microM. Increased L-citrulline levels in media from cultured cells, but not in sera or urine, correlated with increased NO production. Although all methods studied were suitable for quantifying end products of NO in biological fluids and media, the use of bacterial reductase and the modified Griess reaction proved successful to provide the greatest sensitivity and linear range for routine measurements of NO2- and NO3-.

Determination of nitrite in human blood by combination of a specific sample preparation with high-performance anion-exchange chromatography and electrochemical detection

All photometric or HPLC methods described to date have been unable to detect nitrite, a reliable marker of NO synthase activity, in human blood because of its rapid metabolism within the erythrocytes. We now elaborate on method to prevent nitrite degradation during sample preparation which in combination with high-performance anion-exchange chromatography and electrochemical detection allows a sensitive measurement of nitrite. A linear current response in the concentration range of 10-1000 nmol/l nitrite was observed yielding a correlation coefficient of 0.99. In addition, the combination of the electrochemical with a UV detector allowed us to simultaneously quantify nitrate within one analytical run, which is the end product of NO/nitrite metabolism. Basal levels for nitrate and nitrite in human blood were determined with 25 +/- 4 mumol/l and 578 +/- 116 nmol/l (n = 8), respectively and thus were in the same concentration range as expected from NO measurement in saline perfused isolated organs or cultured endothelial cells. Therefore, the presented method may be used to assess activity of endothelial constitutive NO synthase in humans under physiological and pathophysiological conditions.

Nitric oxide in biological fluids: analysis of nitrite and nitrate by high-performance ion chromatography

The analysis of nitric oxide-derived nitrite and nitrate ions in biological fluids represents a proven strategy for determining nitric oxide participation in a diverse range of physiological and pathophysiological processes in vivo. In this article we describe a versatile method for the simultaneous measurement of NO2- and NO3- anions in both plasma and isolated tumour models based on anion-exchange chromatography with spectrophotometric detection (214 nm). This method compares well with the capillary electrophoresis technique, exhibiting an equivalent sensitivity for NO2-/NO3- anions and short run-times, i.e. not greater than 4 min. Comparisons are also made with two alternative but less satisfactory methods which employ ion-exchange or reversed-phase ion-pair chromatography with conductimetric as well as spectrophotometric detection. Technical problems associated with each method, particularly those arising from nitrate contamination, have been addressed.

Oxalate, phosphate and sulphate determination in serum and urine by ion chromatography

A rapid method for the determination of phosphate, sulphate and oxalate in serum by ion chromatography is described. Serum is deproteinized through a Centrifree filter by centrifugation and the ultrafiltrate directly injected into an ion chromatograph equipped with an anion exchange column and a conductivity detector. By this procedure the sample is not diluted and even small amounts of oxalate in biological fluids can be detected. Mean serum concentrations found in healthy individuals are: phosphate 1.07 mmol/l; sulphate 0.35 mmol/l; oxalate 21.02 mumols/l. Phosphate, sulphate and oxalate contents were also determined in urine from healthy individuals. Values found in serum and urine are in good agreement with those previously reported.

Assay of inorganic sulfate in biologic fluids by nonsuppressed (single-column) ion chromatography

An assay using nonsuppressed (single-column) anion chromatography was developed to determine the concentration of inorganic sulfate in biologic fluids. A conventional HPLC system with an anion-exchange column and conductimetric detector interfaced with an automatic injector and integrator was used. The mobile phase for the chromatography of urine and serum samples is 4 mM potassium hydrogen phthalate, pH 4.5, and potassium iodide is used as the internal standard. For cerebrospinal fluid samples, the mobile phase is modified by addition of 10% of a 4 mM phthalic acid solution. Results of the HPLC assay were found to correlate well (r = 0.991 and 0.999) with those of two commonly used spectrophotometric methods for urine and serum inorganic sulfate determinations. However, the concentrations determined by ion chromatography were 2.5 to 10% lower, possibly due to less assay interference by other substances following chromatographic separation of sulfate. Anion chromatography using a single-column system is a convenient and relatively inexpensive method with sufficient sensitivity for the determination of inorganic sulfate concentrations in urine, serum, and cerebrospinal fluid.

Determination of iodide and bromide by ion chromatography with post-column reaction detection

During an investigation into the mechanism of the biosynthesis of thyroid hormones, it became necessary to determine traces of iodide and bromide in biological matrices as well as in food. A vydac 302-IC anion-exchange column with methanesulphonic acid as the mobile phase was used for the ion chromatographic separation of iodide and bromide. A post-column reaction detector was developed based on the reaction between iodide or bromide, chloramine-T and 4,4'-bis(dimethylamino)diphenylmethane. Methods with minimal sample preparation are described for determination of iodide or bromide in serum, milk, salt and water. The detection limit is ca. 20 pg iodide and 15 ng bromide injected.

Determination of small quantities of sulfate (0-12 nmol) in serum, urine, and cartilage of the mouse

The colorimetric benzidine method of K. S. Dodgson and B. Spencer (1953, Biochem. J. 55, 436-440) for the measurement of inorganic sulfate can be scaled down about 100 times by using disposable 96-well microplates instead of individual cuvettes. Ten-microliter samples of serum and urine, derived from mice, can be analyzed in a simple, rapid, and reliable way without sacrificing the animals. Without prior isolation of sulfated glycosaminoglycans, ester sulfate in mouse patellar cartilage is liberated quantitatively as inorganic sulfate upon acid hydrolysis in 3 M HCl for 16 h at 80 degrees C. To this end the articular cartilage layer of the patella must be separated in toto from the underlying bone. Subsequent hydrolysis in polypropylene tubes gives accurate results. In contrast, hydrolysis in borosilicate glass vials is useless, since nanomoles of sulfate added cannot be recovered adequately. The thin patellar cartilage layer obtained from 10-week-old male mice contains about 5 nmol of sulfate, an amount easily measured with the developed microplate benzidine method.

Dopamine sulfate formation and phenol sulfotransferase activity in dog and human platelets

High performance liquid chromatography with radioactive flow detection was used to examine the accumulation and sulfoconjugation of dopamine by human and dog platelets. Platelets from both species accumulated similar amounts of dopamine from the incubation medium, but only human platelets were found to convert 3H-dopamine to 3-H-dopamine sulfate. This difference between the two species was associated with a relative absence of phenol sulfotransferase activity in dog platelets as compared to human platelets. Dog platelets did not appear to contain an inhibitor of phenol sulfotransferase activity. Despite the apparent difference in the ability of platelets to form dopamine sulfate, conc concentrations of dopamine-3-O-sulfate and dopamine-4-O-sulfate were similar in dog and human plasma. These data suggest that platelets may represent a potential source of at least some of the dopamine sulfate found in human plasma, but not in dog plasma.

Sweat sulfate concentrations are decreased in cystic fibrosis

We have developed methods to measure inorganic sulfate in small volumes of sweat, and compared sulfate concentrations in sweat samples from CF patients and controls. In contrast to the increases in sweat chloride, sweat sulfate concentrations in 13 CF patients were reduced to 68 +/- 24% of control values (mean +/- SD, n = 25, p less than 0.001). Sulfate concentrations in sweat may depend on sweat rates, but the rates were not significantly different in the two study groups. Since we have observed a positive correlation between sweat sulfate and sweat chloride excretion in non-CF subjects in earlier studies, we suggest that the decreased sulfate in CF sweat may bear directly on the nature of the anion permeability defect present in the ductal epithelium of the CF sweat gland.

Liquid chromatographic determination of bromide in human milk and plasma

A liquid chromatographic method for the determination of bromide present in human body fluids at the level of 0.5-5.0 ppm is presented. The method involves liquid--liquid extraction of lipids and other lipophilic compounds, destruction of the aqueous phase and analysis of the residue on an aminopropyl bonded silica column with UV detection at 214 nm. The method was applied to the analysis of 278 samples of Dutch human milk. Comparison of the results obtained with those from a routinely used colorimetric procedure for plasma indicated excellent agreement. The ease of automation of the described procedure and its excellent reproducibility make it a good alternative to existing methods for bromide analysis in body fluids.

Determination of inorganic sulphate in plasma by reversed-phase chromatography using ultraviolet detection and its application to plasma samples of patients receiving different types of haemodialysis

The determination of sulphate in plasma is described, making use of reversed-phase high-performance liquid chromatography with ultraviolet detection. The concentration of inorganic sulphate determined in plasma of twenty healthy volunteers was 0.307 +/- 0.092 mmol/l (mean +/- S.D.). In one stable chronic dialysis patient the kinetics of plasma sulphate removal were monitored during and after one single pass dialysis. In addition, plasma sulphate concentrations were determined in three stable chronic dialysis patients during a consecutive scheme of two single pass dialyses, five Redy dialyses and three single pass dialyses. As expected, plasma sulphate accumulates in plasma to a high steady-state level under Redy dialysis, whereas during single pass dialysis sulphate is efficiently removed.

Determination of inorganic sulfate in human saliva and sweat by controlled-flow anion chromatography. Normal values in adult humans

Following the previous demonstration that low concentrations of inorganic sulfate (SO4) in human serum and cerebrospinal fluid can be accurately determined by controlled-flow anion chromatography, the assay has been extended to the quantitation of free SO4 in saliva and sweat by modification of the established methods of sample collection and preparation. Salivary secretions were ultrafiltered to remove macromolecular polyanions that bind irreversibly to the anion-exchange separator column and reduce resolution. Sweat was collected from 22 fasted adult volunteers using a method which utilizes absorbent filter pads applied to the forearm after secretion had been stimulated by pilocarpine iontophoresis. It was necessary to acid wash the filter pads to reduce sulfate contamination. Saliva ultrafiltrate or sweat was diluted and injected onto a Dionex D-10 Ion Analyzer using the standard anion column system. The mean inorganic SO4 concentration in saliva from seventeen adult fasting volunteers was 72 +/- 4 mumol/l (+/- S.E.); the mean SO4 concentration in sweat was 83 +/- 3 mumol/l. Both are significantly less than in matching serum, suggesting that SO4 is actively removed during formation of these glandular secretions. The ion chromatographic assay is shown to be capable of measuring SO4 in biological fluids at concentrations that are otherwise undetectable by conventional assay techniques.