Method For Determination Of Phosphate Research Articles

Comparison of different preparation methods for oxygen isotope determination of phosphate in mammal tooth enamel

AbstractWe tested several sample pre-treatment protocols for the study of oxygen isotope ratios in the phosphate phase of mammalian enamel of ten different fossil samples. We investigated the effect of different pre-treatment methods and the duration of the hydrogen fluoride treatment on enamel samples from skeletal phosphate with known δ18O values. The samples had been measured previously, so we could compare the ratios measured in our laboratory with the previous values to choose the best chemical preparation procedure. Four pre-soaking methods and two different time intervals of 2 mol dm−3 hydrogen fluoride treatment were compared during our experiments. In our experimental conditions, the distilled water wash and the 6 h of soaking in hydrogen fluoride gave the closest results to the expected δ-values. The steps of the tested preparation processes were repeated at least three times on each sample, so the reproducibility of the process could be also investigated.

Effects of Huoxiang Zhengqi Oral Liquid on intestinal barrier function in rats with dampness obstructing spleen-stomach syndrome

The aim of this paper was to investigate the effect of Huoxiang Zhengqi Oral Liquid on intestinal barrier functions in rats with dampness obstructing spleen-stomach syndrome and primarily explore the mechanism. The rat model of dampness obstructing spleen-stomach syndrome was established, and then the modeled rats were randomly divided into the model control group, Huoxiang Zhengqi Oral Liquid high and low dose groups, and natural recovery group according to gender and body weight, with 10 rats in each group. Another 10 rats were taken as blank control group. After each group received the corresponding treatment for 7 days, rat serum was isolated. D-lactic acid content was detected by the MTT method, and diamine oxidase(DAO) activity was detected by the rate method. Colon tissues of the rats were isolated to detect Na~+-K~+-ATPase activity and Ca~(2+)-Mg~(2+)-ATPase activity by phosphate determination method, glutathione peroxidase(GSH-Px) activity was detected by spectrophotometry, catalase(CAT) activity was detected by ammonium molybdate, superoxide dismutase(SOD) activity was detected by hydroxylamine, the expression of occludin protein and ZO-1 protein was detected by immunofluorescence, and the expression levels of occludin protein and ZO-1 protein were detected by Western blot. RESULTS:: showed that low dose Huoxiang Zhengqi Oral Liquid could improve the body weight, diet, stool and urine state of rats with dampness obstructing spleen-stomach syndrome obviously. The D-lactic acid content and the DAO activity in the serum of rats with dampness obstructing spleen-stomach syndrome were reduced obviously. The activities of Na~+-K~+-ATPase, Ca~(2+)-Mg~(2+)-ATPase, GSH-Px, CAT and SOD in rat colon tissues were increased obviously. The occludin proteins and ZO-1 protein expression levels in rat colon tissues were raised obviously. The differences in the above indexes between Huoxiang Zhengqi Oral Liquid group and the model control group were statistically significant(P<0.05). Huoxiang Zhengqi Oral Liquid could effectively restore the intestinal barrier function in rats with dampness obstructing spleen-stomach syndrome and its mechanism may be related to the repair of intestinal mechanical barrier function.

Association between activities of SOD, MDA and Na+-K+-ATPase in peripheral blood of patients with acute myocardial infarction and the complication of varying degrees of arrhythmia

ObjectiveTo investigate the changes of ambulatory electrocardiography and peripheral blood SOD, MDA and Na+-K+-ATP enzymes in patients of acute myocardial infarction (AMI) complicated with arrhythmia. MethodsFrom January 2012 to March 2015, 135 cases AMI complicated with arrhythmia in our hospital were divided into 2 groups: 70 cases in the AMI uncomplicated with arrhythmia and 65 cases in the AMI complicated with arrhythmia. 62 cases volunteers accepted physical examination in our hospital in the same period were collected as the control group. 24 hour-electrocardiogram detected by ambulatory electrocardiogram (AECG), SOD and MDA in peripheral blood detected by diagnostic reagent kit and Na+-K+-ATP enzymes in peripheral blood detected by malachite green Kit Method phosphate determination method were collected. ROC curve was used to evaluate the prognostic value of SOD, MDA and Na+-K+-ATP enzymes in AMI patients. ResultsCompared with the control group, the patients had unusual ambulatory electrocardiography had increased (P <0.05), peripheral blood SOD and Na+-K+-ATP enzymes had decreased, peripheral blood MDA had increased in 2 AMI groups (P <0.05). Compared with AMI uncomplicated with arrhythmia group, the patients had unusual ambulatory electrocardiography had increased (P <0.05), peripheral blood SOD and Na+-K+-ATP enzymes had decreased, peripheral blood MDA had increased in AMI complicated with arrhythmia group (P <0.05). Among 135 cases AMI patients, 120 (88.9%) survived and 15 (11.1%) died, of whom 11 cases were AMI complicated with arrhythmia group, 4 cases were AMI uncomplicated with arrhythmia group. Compared with the AMI uncomplicated with arrhythmia group, the dead patients were more in the AMI complicated with arrhythmia group (c2 = 4.287, P = 0.038). Compared with the survival group, the SOD and Na+-K+-ATP enzymes were significantly lower (P <0.05) and MDA significantly higher (P <0.05) in the death group. The area under the ROC curve of SOD, MDA and Na+-K+-ATP enzymes were 0.958, 0.954 and 0.993 respectively, and the cut-off values were 30.66 ng/ml, 576.70 nmol/ml and 57.42 nmol/mgh, respectively. ConclusionAmbulatory electrocardiography has a close relationship with the peripheral blood SOD, MDA and Na+-K+-ATP enzymes in AMI patients complicated with arrhythmia, which might predict AMI condition.

Genetic Algorithm Based Wavelengths Selection Coupled with Partial Least Squares for Simultaneous Spectrophotometric Determination of Phosphate and Silicate in Detergent Products

Background: Phosphate and silicate are very important in a variety of compounds such as mineral resources, underground water, detergents and cleaners. Phosphate and silicate in water positively influence the metabolism of plants and animals. They have led to an environmental problem. This problem can have serious consequences because phosphate and silicate are widely utilized in water softening, surfactants and a large number of other applications. Methods: Genetic algorithm (GA) is an appropriate method for selecting wavelengths for PLS (partial least squares) calibration of mixtures which have almost identical spectra without losing prediction capacity using spectrophotometric method. In this paper, we have described a simple, sensitive and selective spectrophotometric method for the simultaneous determination of phosphate and silicate based on the formation of phospho- and silicomolybdenum blue complexes in the presence of ascorbic acid. Results: The complexes of phosphate and silicate with a reagent in the presence of ascorbic acid have been simultaneously determined by genetic algorithm- partial least squares (GA-PLS) although they showed a spectral overlap. The calibration curve was linear over a concentration range of 0.01-2.00 and 0.01-3.80 µgmL-1 for phosphate and silicate, respectively. The root mean square error (RMSE) for phosphate and silicate was 0.372 and 0.301, respectively. Conclusion: The present study indicates that the GA can be a good method for feature selection in spectral data sets. Results show that GA-PLS is an excellent calibration method for the determination of phosphate and silicate. In the end the proposed method was successfully applied for the simultaneous determination of phosphate and silicate in synthetic detergents. Keywords: Phosphate, silicate, spectrophotometry, GA-PLS, detergent products, surfactants.

Assessing Resistance and Bioremediation Ability of Enterobacter sp. Strain Saw-1 on Molybdenum in Various Heavy Metals and Pesticides

One of the most economical approaches for removal of toxic compounds is bioremediation. In the long term, bioremediation is economic and feasible compared to other methods, such as physical or chemical methods. A bacterium that can efficiently reduce molybdenum blue was isolated from polluted soil. Biochemical analysis revealed the identity of the bacterium as Enterobacter sp. strain Saw-1. The growth parameters for optimal reduction of molybdenum to Mo-blue or molybdenum blue, a less toxic product, were determined around pH 6.0 to 6.5 and in the range of 30 to 37 ℃, respectively. Glucose was selected as preferred carbon source, followed by sucrose, maltose, l-rhamnose, cellobiose, melibiose, raffinose, d-mannose, lactose, glycerol, d-adonitol, d-mannitol, l-arabinose and mucate. Phosphate and molybdate were critically required at 5.0 mM and 10 mM, respectively. The scanning absorption spectrum acquired to detect the development of complex Mo-blue showed similarity to previously isolated Mo-reducing bacteria. In addition, the spectrum closely resembled the molybdenum blue from the phosphate determination method. Heavy metals, including mercury, copper (II) and silver (I), inhibited reduction. Moreover, the bacterium also showed capability of exploiting the pesticide coumaphos as an alternative carbon source for growth. As the bacterium proved its ability to detoxify organic and inorganic xenobiotics, the usefulness of this microorganism for bioremediation is highlighted.

Chemometrics-assisted cross injection analysis for simultaneous determination of phosphate and silicate

ABSTRACTThis work presents a novel method for simultaneous spectrophotometric determination of phosphate and silicate by using a cross injection analysis (CIA) coupled with the use of partial least squares (PLS) for data evaluation. The detection principle is based on the well-known ‘molybdenum blue’ method. The molybdate ions in the presence of stannous chloride in acidic medium give phosphomolybdenum blue and silicomolybdenum blue as products. In this work, all the liquids, including sample and reagents were simultaneously introduced into a CIA platform by using two peristaltic pumps for controlling the x-channel and y-channel flow which was automatically manipulated by using in-house control board. Crossflow provides sufficient mixing inside the platform prior detection of the absorption spectra of blue complexes in the wavelength of 400–900 nm. Since spectra of the blue colour product of phosphate and silicate are resemblant, these two analytes therefore reciprocally interfere with one another. This results in difficulty in simultaneous analysis of phosphate and silicate. In this work, PLS was utilised as assistor of CIA system for simultaneous analysis of phosphate and silicate using molybdenum blue reaction without using any modification of reagents and addition of selective masking agent. The calibration ranges are 0.1–6 mgP L−1 and 5–100 mgSi L−1 for phosphate and silicate, respectively. By using CIA coupled with PLS for data evaluation, the analysis of two analytes was achieved within 1.5 min with only single injection. The developed system was applied to natural water samples and the system was validated with the conventional methods. By statistical paired t-test, there was no evidence of significant difference at 95% confidence level (tstat = 2.28, tcritical = 2.31 and tstat = 0.62, tcritical = 2.31 for phosphate and silicate, respectively). This implied that the chemometrics-assisted CIA system was successfully developed for simultaneous spectrophotometric determination of phosphate and silicate.

Electrochemical Determination of Phosphate in Freshwater Free of Silicate Interference

This paper proposes an electrochemical method for phosphate determination with oxalic acid as masking agent to eliminate silicate interference in freshwater. An electrochemical cell including electrochemical threeelectrode system, reaction zone, inlet and outlet was designed and fabricated to detect phosphate by Sequential Injection Analysis (SIA). The influence of the masking agent and its concentration on the determination of phosphate were investigated. With 0.01% oxalic acid as masking agent, better signal amplitude and less signal distortion were displayed. The reason may be that the oxalic acid replaces molybdosilicate easier than molybdophosphate. In this way, oxalic acid inhibits silicate interference and shows less influence on phosphate determination. The linear ranges of phosphate from 0 to 1.0 mg/L were displayed with oxalic acid as mask reagent in freshwater. For natural samples, the deviation between spectrophotometric and LSV methods is less than 10%. The experimental results indicated that the proposed method can be applied to in situ monitoring of phosphate.

Isolation and characterization of a molybdenum-reducing and orange G-decolorizing &lt;i&gt;Enterobacter&lt;/i&gt; sp. strain Zeid-6 in soils from Sudan

Chemical toxins and organic contaminants such as hydrocarbons and dyes are major global contaminants with countless tones of those chemicals are created yearly with a significant amount release to the environment. In this work we screen the ability of a molybdenum-reducing bacterium isolated from contaminated soil to decolorize various azo and triphenyl methane dyes independent of molybdenum reduction. Biochemical analysis resulted in a tentative identification of the bacterium as Enterobacter sp. strain Zeid-6. The bacterium was able to decolorize the azo dye Orange G. The bacterium reduces molybdate to Mo-blue optimally at pH between 5.5 and 8.0 and temperatures of between 30 and 37 oC. Other requirements include a phosphate concentration of 5 mM and a molybdate concentration of 20 mM. The absorption spectrum of the Mo-blue produced was similar to previous Mo-reducing bacterium, and closely resembles a reduced phosphomolybdate. Molybdenum reduction was inhibited by copper, lead, mercury and silver which showed 36.8, 16.9, 64.9 and 67.6% inhibition to Mo-reducing activity of Enterobacter sp. strain Zeid-6, respectively. The resultant molybdenum blue spectrum closely resembles the spectrum of molybdenum blue from the phosphate determination method. The ability of this bacterium to detoxify molybdenum and decolorize azo dye makes this bacterium an important tool for bioremediation.

Determination of phosphate in soil extracts in the field: A green chemistry enzymatic method

Measurement of ortho-phosphate in soil extracts usually involves sending dried samples of soil to a laboratory for analysis and waiting several weeks for the results. Phosphate determination methods often involve use of strong acids, heavy metals, and organic dyes. To overcome limitations of this approach, we have developed a phosphate determination method which can be carried out in the field to obtain results on the spot.This new method uses:•Small volumes.•An enzymatic reaction.•Green chemistry.First, the soil sample is extracted with deionized water and filtered. Next, an aliquot of the soil extract (0.5mL) is transferred to a disposable cuvette, containing 0.5mL of reaction mixture [200mM HEPES, pH 7.6, 20mM MgCl2, with 80nmol 2-amino-6-mercapto-7-methylpurine ribonucleoside (MESG) and 1 unit of recombinant purine nucleoside phosphorylase (PNP; EC 2.4.2.1)], mixed, and incubated for 10min at field temperature. Absorbance of the completed reaction is measured at 360nm in open-source, portable photometer linked by bluetooth to a smartphone. The phosphate and phosphorus content of the soil is determined by comparison of its absorbance at 360nm to a previously prepared standard phosphate curve, which is stored in the smartphone app.

Simultaneous spectrophotometric flow injection determination of phosphate and silicate

A method for the simultaneous determination of phosphate and silicate based on spectrophotometric measurement at 385nm of a single peak using a flow injection system with two component calibration is described. In the system, a stream of sample containing both analytes is merged with a stream of ammonium molybdate to form (at 1<pH<2) molybdophosphoric and molybdosilicic acids. Total absorbance of the compounds is registered in a form of a constant signal. Simultaneously, oxalic acid solution is injected into a carrier stream (H2SO4) and then merged with the stream of sample containing the mixture of heteropolyacids. A characteristic peak is registered as a result of selective decomposition of molybdophosphoric acid by oxalic acid. The area (or the absorbance measured at the constant signal) and the absorbance measured at the minimum of the peak can be used as measures corresponding to the phosphate and silicate concentrations, respectively. The time of the peak registration is about 3min. Two-component calibration with the use of four standard solutions of the phosphate/silicate concentrations established in accordance with 22 factorial design was applied. Phosphate and silicate can be determined within the concentration ranges of 0.20–15.00 and 0.20–20.00mg L−1, with precision less than 2.7 and 0.9% (RSD), respectively and accuracy better than 6.2% (RE). The detection limit is 0.054 and 0.092mg L−1 for phosphate and silicate, respectively. The method was applied to determination of the analytes in certified reference materials of groundwater, wastewater, and river water giving results consistent with the certified values.

Reagentless and silicate interference free electrochemical phosphate determination in seawater

An electrochemical method for phosphate determination in seawater was based on the oxidation of molybdenum in order to form molybdates and protons and subsequently, to create the phosphomolybdic complex electrochemically detectable by means of amperometry at a rotating gold disk electrode [J. Jońca et al., Talanta 87 (2011) 161]. To avoid silicate interferences, the method required an appropriate ratio of protons over molybdates equal to 70. Since the ratio of protons over molybdates created during molybdenum oxidation is only 8, the previous method still needed addition of sulfuric acid and thus was not free from addition of liquid reagents. In the present work, this aspect is solved by modification of the electrochemical cell construction. The method is now totally free from addition of any liquid reagents and gives a possibility to determine phosphate by amperometry in the concentrations range found in the open ocean with a detection limit of 0.11μM. Having in mind the energy savings for future in situ sensor development, amperometry at rotating gold disk electrode was replaced by differential pulse voltammetry at static one. Phosphate can then be determined with a detection limit of 0.19μM. Both methods are characterized by good reproducibility with an average measurements precision of 5.7% (amperometry) and 3.8% (differential pulse voltammetry). Results also show a good accuracy with an average deviation from theoretical values of phosphate concentration of 3.1% for amperometry and 3.7% for differential pulse voltammetry.

Sequential injection system exploring the standard addition method for phosphate determination in high salinity samples: interstitial, transitional and coastal waters

A sequential injection system for phosphate determination within a wide concentration range was developed for water samples with high salinity levels. The determination is based on molybdenum blue chemistry using the standard addition quantification method. The detection system included a multi-reflective flow cell coupled to a light emitting diode, enabling the minimization of the schlieren effect. The developed system gave a LOD of 0.3 μmol P L−1 and LOQ of 1.1 μmol P L−1 with a sample consumption of 125 μL. A determination rate of about 30 h−1 was obtained, and the developed method was effectively applied to interstitial, transitional and coastal waters.

Continuous flow method for the simultaneous determination of phosphate/arsenate based on their different kinetic characteristics

This paper proposes a new automated spectrophotometric method for the simultaneous determination of phosphate and arsenate without pre-treatment, which is faster, simpler, less expensive and hazardous than other well-known methods used with water samples. Such method is based on the different kinetic characteristics of complex formation of phosphate and arsenate with ammonium molybdate. A flow system was used in order to achieve good mixing and to provide precise time control. All the measurements were performed at the isosbestic point wavelength (885nm). Chemical variables were optimized by factorial design (ammonium molybdate 0.015molL−1, potassium antimony tartrate 1×10−4molL−1, and sulphuric acid 0.7molL−1). An appropriate linear range for both analytes (0.50–8.00μmolL−1), good inter-day reproducibility (4.9% [P] and 3.3% [P+As]) and a sample throughput of 6h−1 were obtained. The detection limits are 0.4μmolL−1 P and 0.19μmolL−1 [P+As] (3.3Sy/x). The method was validated.

Application of a new potentiometric method for determination of phosphate based on a surfactant-modified zeolite carbon-paste electrode (SMZ-CPE)

A phosphate-selective electrode based on surfactant-modified zeolite (SMZ) particles into carbon-paste has been proposed (SMZ-CPE). The electrode was fully characterized in terms of composition, response time, ionic strength, thermal stability and usable pH range. The electrode containing 20% SMZ exhibited linear response range to phosphate species in the range of 1.58 × 10 −5 to 1.00 × 10 −2 M with a detection limit of 1.28 × 10 −5 M and a Nernstian slope of 29.9 ± 0.9 mV per decade of phosphate concentration. The electrode response to phosphate remains constant in the pH range of 4–12 and in the presence of 1 × 10 −4 to 4 × 10 −3 M NaNO 3. The response of the electrode reaches equilibrium within several seconds after immersing the electrode in phosphate solution. Common anions such as Cl −, Br −, I −, NO 3 −, SO 4 2− and Cr 2O 7 2− have little effect on the determination of phosphate but AsO 4 3− shows some interference. A successful application of the electrode for determination of phosphate in a fertilizer, using direct potentiometry, is presented. The electrode was also used for the potentiometric titration of phosphate. The validation of the obtained results in each case was proved by statistical methods.

An Autonomous Microfluidic Sensor for Phosphate: On-Site Analysis of Treated Wastewater

A microfluidic sensor for long-term monitoring of phosphate levels has been developed that incorporates sampling, reagent and waste storage, detection, and wireless communication into a compact and portable device. The sensor is based on the yellow method for phosphate determination, a simple colorimetric technique involving the formation of vanadomolybdophosphoric acid when a phosphate-containing sample is mixed with an acidic reagent containing ammonium molybdate and ammonium meta-vanadate. This paper describes the application of the phosphate sensor to the on-site analysis of effluent from a wastewater treatment plant. The data was validated by comparison with the plant's existing online monitor, and a good correlation between the two sets of data was achieved, showing that the phosphate sensor is capable of operating satisfactorily at low mg L-1 levels over extended periods of time.

Bifunctional Au-Fe3O4 Nanoparticles for Protein Separation

In this article, we report the synthesis of bifunctional Au-Fe(3)O(4) nanoparticles that are formed by chemical bond linkage. Due to the introduction of Au nanoparticles, the resulting bifunctional Au-Fe(3)O(4) nanoparticles can be easily modified with other functional molecules to realize various nanobiotechnological separations and detections. Here, as an example, we demonstrate that as-prepared Au-Fe(3)O(4) nanoparticles can be modified with nitrilotriacetic acid molecules through Au-S interaction and used to separate proteins simply with the assistance of a magnet. Bradford protein assay and sodium dodecyl sulfate-polyacrylamide gel electrophoresis were performed to examine the validity of the separation procedure, and the phosphate determination method suggested that the as-separated protein maintained catalytic activity. This result shows the efficiency of such a material in protein separation and suggests that its use can be extended to magnetic separation of other biosubstances. Moreover, this synthetic strategy paves the way for facile preparation of diverse bifunctional and even multifunctional nanomaterials.

Simultaneous Spectrophotometric Determination of Phosphate and Silicate by Using Principal Component Artificial Neural Network

A very sensitive, simple and selective spectrophotometric method for simultaneous determination of phosphate and silicate based on formation of phospho- and silicomolybdenum blue complexes in the presence of ascorbic acid is described. Although the complexes of phosphate and silicate with reagent in the presence of ascorbic acid show a spectral overlap, they have been simultaneously determined by principal component artificial neural network (PC-ANN). The PC-ANN architectures were different for phosphate and silicate. The output of phosphate PC-ANN architecture was used as an input for silicate PC-ANN architecture. This modification improves the capability of silicate PC-ANN model for prediction of silicate concentrations. The linear range was 0.01-3.00 microg mL(-1) for phosphate and 0.01-5.00 microg mL(-1) for silicate. Interference effects of common anions and cations were studied and the proposed method was also applied satisfactorily to the determination of phosphate and silicate in detergents.

A critical comparison of analytical flow systems exploiting streamlined and pulsed flows

Multipumping (MPFS) and multicommuted (MCFS) flow systems relying on pulsed and laminar flows were critically compared. The mixing conditions and dispersion associated with both systems were evaluated by simulating the sample with bromocresol green. The molybdenum blue method for phosphate determination in soil extracts was also implemented in both flow systems. Furthermore, laser-induced fluorescence (LIF) was applied to visualize the dispersing sample; rhodamine B was used as the fluorescent species. The pulsed flow enhanced the mixing of the solutions involved, thus reducing reagent consumption (48 and 96 microl for MPFS and MCFS), and improving sampling rate (67 and 144 h(-1) for MCFS and MPFS). For phosphate determination, results obtained with both systems were precise (r.s.d. < 0.5%; n = 10) and accurate. Analyses of the absorbance vs time/space LIF plots revealed that exploitation of pulsed flow led to a pronounced radial dispersion and to a limited axial dispersion, typical aspects of turbulent flows.

Novel indirect spectrophotometric methods for determination of phosphate and arsenate using polyoxometalates and micellar medium

Five various methods based on the use of polyoxometalates (POMs) have been developed for indirect spectrophotometric determination of phosphate or arsenate. Amplification procedure involving formation of the 12-molybdophosphate, its extraction with butyl acetate, and stripping with ammonia differs from known method by applying sensitive reaction of molybdenum(VI) with phenylfluorone in presence of the nonionic surfactant neonole at the last step of analysis. The calibration curve for phosphate is linear over the range of 2×10 −8 to 2×10 −7 M. The molar absorptivity was 1.68×10 6 l mol −1 cm −1 at 524 nm. Ion-exchange separation of metal ion excess from mixed POMs PMeW 11O 39 5− [Me–Co(II), Zn(II)] allows to realize indirect determination of phosphorus on metal atoms by means of spectrophotometry or atomic absorption spectrometry. Stability of POMs with Keggin structure is greatly increased by solubilization in micelles of nonionic surfactant. An explanation for this effect was proposed, and two analytical procedures based on this phenomenon were created. They include determination of phosphate or arsenate by means of measurement of absorbance in near UV and visible region of the spectrum as well as another amplification procedure which is based on destroying the molybdenum(VI) complexes with alizarin S or brompyrogallol red due to formation of POMs in the presence of phosphate. Finally, it was found that reaction of Keggin POMs with cyanine dyes leads to significant changes in colour of the ion associate by contrast with other dyes. The value of molar absorptivity is equal to 9.0×10 4 l mol −1 cm −1 at 580 nm.

Direct determination of phosphate in urine by sequential-injection analysis with single on-line dilution–calibration method and photometric detection

In this work we report a sequential-injection (SI) analysis method for the direct determination of phosphate in urine with on-line dilution and photometric detection. The developed SI manifold incorporated an additional dilution coil (DC) connected to one of the ports of the selection valve. On-line dilution was performed by aspirating a zone of sample with volume V S from the sample line into the holding coil (HC), transferring volume V T of that zone into the DC, and, finally, aspirating a portion of V T with volume V A back into the HC. This dilution introduces an additional dispersion of the initial sample zone represented by the effective dispersion coefficient D eff which can be tailored to the desired value by appropriate selection of the volumes V S, V T, and V A. Actual detection of phosphates was performed by the molybdenum blue method with detection at 690 nm. By employing an on-line dilution step with a D eff=100, the calibration curve for phosphate was linear in the range 0.05 × 10 −2 to 3 × 10 −2 mol L −1 which covers the actual phosphate concentration in urine samples. The regression coefficient was r 2=0.996, the relative standard deviation was s r=3.9% at the 1 × 10 −2 mol L −1 level ( n=10), and the injection frequency was 30 injections h −1. The method was applied to urine samples with recoveries >97%.