Condition optimization of amperometric determination of chemical oxygen demand using boron-doped diamond sensor

The amperometric determination of chemical oxygen demand (COD) reported by Quan Xie??s group (Electrochem Commun 9:2281, 14), was a rapid, green and simple COD evaluation method. This work focused on testing and verifying this method by using a home-made boron-doped diamond (BDD) film as anode and optimizing the experiment conditions. The BDD thin film electrode was employed as anode and the electrochemical process was run with different experimental parameters including counter electrode, electrode gap, applied potential, electrolyte pH, and temperature. Standard samples were determined in the optimum conditions, a linear range of 19.2?C11,600?mg l^?1 COD and a low detection limit of 0.192?mg l^?1 COD were well established with the present approach. The COD value of the simulated organic wastewater determined by this method agreed well with the standard dichromate method, and it showed good accuracy, stability, and reproducibility.     

Determination of the chemical oxygen demand (COD) using a copper electrode: a clean alternative method

A clean alternative method for the determination of chemical oxygen demand (COD) was developed using a copper electrode as an electrocatalytic sensor. The measuring principle is based on oxidation current of organic compounds in the wastewater. The effects of important experimental conditions, such as electrolytic solution concentration and potential scan rate, on analytical performance have been investigated. Analytical linear range of 53.0–2,801.4 mg l⁻¹ COD with detection limit of 20.3 mg l⁻¹ COD was achieved. The procedure was successfully applied to the COD determination in wastewater from soft industries. The results obtained using the proposed method were in good agreement with those obtained using the conventional (i.e., dichromate) COD method. In this fashion, the COD value of a sample can be determined in a simple, rapid, accurate manner, and the end products do not contain toxic metals.     

Treatment of textile desizing wastewater by pilot scale nanofiltration membrane separation

Desizing wastewaters from the bleaching and dyeing industry of Hong Kong were treated by nanofiltration (NF) membrane separation on a pilot scale in the pressure controlled region. The two brown colored wastewaters had chemical oxygen demand (COD) of 14,000 mg l⁻¹ and 5430 mg l⁻¹, respectively. Permeate flux and COD retention were investigated in relation to transmembrane pressure drop, temperature, and feed-solution concentration. The permeate flux was found to increase significantly with transmembrane pressure drop and to decrease with feed concentration. Higher permeate flux was found for wastewater with higher pH. A minor increase in COD retention was found for the increase in transmembrane pressure drop as well as operating temperature. The COD retention was about 95% for wastewater with pH 10.2, and 80–85% for wastewater with pH 5.5. The difference in the results obtained for the two kinds of wastewater was attributed to their compositional difference that resulted from the desizing operation. Fouling of membrane is not a big concern for the NF membrane tested in treating this type of wastewater. The quality of the permeate is all above the discharge standard for foul sewer in Hong Kong. The experimental results are consistent with the theoretical analysis.     

Determination of residual chlorine by derivatisation with 2,6-dimethylphenol and gas chromatographic separation

Residual chlorine in aqueous solution is converted to 4-chloro-2,6-dimethylphenol, which is extracted into hexane and determined by gas chromatography. Relative standard deviations (n = 5) are 0.36–1.1% for chlorine concentrations of 8.6–0.01 mg l^-1 and chlorine recoveries are 99.2–101%. In the presence of dichromate (30 mg l^-1), relative standard deviations (n = 5) are 1.19–2.71% for chlorine concentrations of 9.3–0.1 mg l^-1. Oxidants and coloured solutes do not interfere.     

Chemiluminescence system for automatic determination of chemical oxygen demand using flow injection analysis

A novel chemiluminescence (CL) system for automatic determination of chemical oxygen demand (COD) combined with flow injection analysis is proposed in this paper. In this system, potassium permanganate is reduced to Mn²⁺ which is first adsorbed on a strongly acid cation-exchange resin mini-column to be concentrated during chemical oxidation of the organic compounds at room temperature, while the excessive MnO₄⁻ passes through the mini-column to be waste, then the concentrated Mn²⁺ is eluted reversely and measured by the luminol-H₂O₂ CL system. The calibration graph is linear in the range of 4-4000 mg l⁻¹ and the detection limit is 2 mg l⁻¹. A complete analysis could be performed in 1.5 min including washing and sampling, giving a throughout of about 40 h⁻¹. The relative standard deviation was 4.4% for 10 mg l⁻¹ COD (n=11), 4.8% for 100 mg l⁻¹ COD (n=11). This CL flow system for determination of COD is very simple, rapid and suitable for automatic and continuous analysis. The presented system has been applied successfully to the determination of COD of water samples.     

Determination of total and inorganic mercury in biological and environmental samples with on-line oxidation coupled to flow injection-cold vapor atomic absorption spectrometry

A method for determination of inorganic and total mercury by flow injection-cold vapor atomic absorption spectrometry (FI-CVAAS) with on-line oxidation was developed. Potassium peroxodisulphate and sulphuric acid were used as oxidizing agents so that decomposition of organomercury compounds could be achieved. Depending on the temperature selected, inorganic or total mercury could be determined with the same FI manifold. In order to assess the method performance, synthetic wastewater, wastewater, urine and saline water samples were spiked with inorganic mercury, methylmercury and phenylmercury. Quantitative recoveries were obtained for the three mercury species, except with the synthetic wastewater when the chemical oxygen demand value was higher than 1000 mg l⁻¹. In most cases, the standard addition method was usually needed for calibration. LODs calculated as 3 σ/m were 0.47 μg l⁻¹ for inorganic mercury and 0.45 μg l⁻¹ for total mercury. R.S.D. values corresponding to peak height measurements were 1.5 and 2.2% for inorganic mercury and total mercury, respectively. The accuracy of the method was tested by analyzing 5 mol l⁻¹ hydrochloric acid extracts of seven biological and environmental CRMs. LODs in the solid CRMs ranged from 0.032 to 0.074 μg g⁻¹.     

Flow-injection spectrophotometric determination of aluminium in water with pyrocatechol violet

Optimum conditions for the adaptation of the spectrophotometric pyrocatechol violet method for aluminium to a flow-injection system are described. The detection limit is 3 μg Al l^?1 and calibration graphs are linear up to 3 or 10 mg l^?1 (with 200-μl or 10-μl injection loops, respectively). The relative standard deviation is 〈 2% at 0.1 mg Al l^?1. Potential interferences of 40 common inorganic ions and of 20 organic substances, including fulvic acid, are reported. With the use of conventional masking agents and predigestion of samples with high organic content, the method is suitable for determining total aluminium in natural waters.     

纳米TiO2膜用于光催化氧化测定化学需氧量的研究

A photocatalytic oxidation method for determination of chemical oxygen demand （COD） using nano-TiO2 film, based on the use of a nano-TiO2-Ce（SO4）2 system and electrochemical detection, was proposed. The technique was originated from the direct determination of the Ce（Ⅲ） concentration change resulting from photocatalytic oxidation of organic compounds. Ce（Ⅲ）, which was produced by photocatalytic reduction of Ce（SO4）2, could be measured at a multi-walled carbon nanotubes （MWNT） chemically modified electrode （CME）. The COD values by this method were calculated from the differential pulse voltammetry （DPV） current of Ce（Ⅲ） at the CME. Under the optimal operation conditions, the detection limit of 0.5 mg·L^-1 COD with the linear range of 1-600 mg·L^-1 was achieved. This method was also applied to determination of various COD of ground water and wastewater samples. The resuits were in good agreement with those from the conventional COD methods, i.e., permanganate and dichromate ones.     

Amperometric determination of chemical oxygen demand using boron-doped diamond (BDD) sensor

A new application of boron-doped diamond (BDD) electrode was developed for detecting chemical oxygen demand (COD) by amperometric method. The effects of some basic experimental parameters including pH and applied potential on the response of the BDD electrode were investigated and the optimal operating conditions were obtained. In the COD tests of standard samples, a wide linear range of 20–9000 mg l⁻¹ COD and a low detection limit of 7.5 mg l⁻¹ COD were well established with the present approach. Additionally, the BDD sensor was successfully employed to determine the COD of real samples from various chemical or pharmaceutical wastewaters and the performance still kept stable after over 400 measurements. The results obtained indicated that, as compared with the conventional COD determination techniques, the proposed sensor was an environmentally friendly method with the advantages of short analysis period, simplicity, and no requirement of complicated sample pretreatment even for a sample containing relatively high concentration of organic pollutants.     

Analysis of organic amines and acids for water

Conventional methods for the determination of cyanide in effluents associated with steel-making procedures are compared with a method based on a cyanide-selective electrode. For cyanide levels above 1.0 mg l^-1, the standard argentimetric titration and electrode method give similar results. At lower levels (0.1–1.0 mg l^-1 and 0.01–0.10 mg l^-1), the potentiometric method is compared with pyridine-pyrazolone and pyridine—barbituric acid colorimetric procedures; the pyrazolene method tends to give higher results than the other two methods. Synthetic standards and actual effluent samples are discussed. Problems associated with the determination of cyanide in effluents containing complex iron cyanides and sulphides are examined. Sulphide removal with lead carbonate or cadmium carbonate above pH 11 should not be done until after the distillation.     

Determination of humic acid by chemiluminescence

The analytical utility of the chemiluminescence resulting from the reaction of humic acid with permanganate is investigated. The chemiluminescence response curve rises sharply to a peak value at about 0.5 s after mixing and decays somewhat more slowly. The peak signal for a fixed humic acid concentration is shown to pass through a maximum near a permanganate concentration of 17 μmol l^-1 and to increase continuously with potassium hydroxide concentration up to 2.0 mol l^-1. Calibration plots of peak signal vs. humic acid concentration exhibit complex behaviour, being approximately linear up to about 20 mg l^-1, curving slightly toward the concentration axis up to about 40 mg l^-1, and then curving away from the concentration axis above 40 mg l^-1. The detection limit for humic acid is about 0.7 mg l^-1. No interference is observed for thirteen common inorganic species at typical levels in water samples. Substantial differences are observed for humic acid in selected samples determined by the chemiluminescence and visible absorption procedures.     

Sequential injection lab-on-valve simultaneous spectrophotometric determination of trace amounts of copper and iron

A sequential injection (SI) method in a lab-on-valve (LOV) format for simultaneous spectrophotometric determination of copper and iron has been devised. The detection chemistry is based on the complex formation of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline (5-Br-PSAA) with copper(II) and/or iron(II) at pH 4.6. Copper(II) reacts with 5-Br-PSAA to form the complex which has an absorption maximum at 580 nm but iron(III) does not react. In the presence of a reducing agent only iron(II)-5-Br-PSAA complex is formed and detected at 558 nm. Under the optimum experimental conditions, the determinable ranges are 0.1-2 mg l⁻¹ for copper and 0.1-5 mg l⁻¹ for iron, respectively, with a sampling rate of 18 h⁻¹. The limits of detection are 50 μg l⁻¹ for copper and 25 μg l⁻¹ for iron. The relative standard deviations (n = 15) are 2% for 0.5 mg l⁻¹ copper and 1.8% for 0.5 mg l⁻¹ iron when determined in standard solutions. The recoveries range between 96 and 105% when determining 0.25-2 mg l⁻¹ of copper and 0.2-5 mg l⁻¹ of iron in artificial mixtures at copper/iron ratios of 1:10 to 5:1. The proposed SI-LOV method is successfully applied to the simultaneous determination of copper and iron in multi-element standard solution and in industrial wastewater samples.     

Study on photocatalytic oxidation for determination of chemical oxygen demand using a nano-TiO2-K2Cr2O7 system

A photocatalytic method for the determination of chemical oxygen demand (COD) using a nano-TiO₂-K₂Cr₂O₇ system is described. The measuring principle is based on direct determination of the change of Cr(III) concentration resulting from photocatalytic oxidation of organic compounds and simultaneous photocatalytic reduction of stoichiometrically involved K₂Cr₂O₇ in the solution. The operation conditions were optimized. The determinative COD value using this method was calculated from the absorbance of Cr(III). The operational characteristics of this method were demonstrated by use of a standard glucose solution as substrate. This method was also applied to the determination of the COD of wastewater samples. The results were in good agreement with those from the conventional (i.e., dichromate) COD methods.     

An atomic absorption spectrometric method for the determination of non-ionic surfactants

A method is described for the determination of non-ionic surfactants in the concentration range 0.05–2 mg l^-1.Surfactant molecules are extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate(II) and the determination is completed by atomic absorption spectrometry. With a 150-ml water sample, the limit of detection is 0.03 mg l^-1(as Triton X-100).The method requires a single phase separation step, is applicable, without modification, to fresh, estuarine and sea-water samples and is relatively free from interference by anionic surfactants; the presence of up to 5 mg l^-1 of anionic surfactant (as LAS) introduces an error of no more than 0.07 mg l^-1 (as Triton X-100) in the apparent non-ionic surfactant concentration.     

Determination of cobalt in biological materials by RNAA via induced short-lived 60mCo

A chemiluminescence (CL) micro-flow system is presented for rapid determination of chemical oxygen demand (COD) in water at room temperature. In this system, potassium dichromate is reduced to Cr³⁺ in 2 mol L⁻¹ H₂SO₄ during the chemical oxidation of COD substances in the sample, and Cr³⁺ can be measured with the help of the luminol-H₂O₂ CL system. The polymethyl methacrylate micro-flow chip with discrete microdroplet sampling was used here. Effects on COD determination (such as pH, concentrations, the channel length, and interference) were investigated. The linear range for COD determination was 0.27–10 g L⁻¹, and the detection limit was 100 mg L⁻¹. The method was successfully applied to the determination of COD in wastewater samples. The data obtained with the present method were in fairly good agreement with those obtained by the titrimetric method. Correspondence: Zhujun Zhang, Key Laboratory of Analytical Chemistry for Life Science of Shaanxi Province, School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an 710062, P.R. China; Department of Chemistry, Institute of Analytical Science, Southwest University, Beibei, Chongqing 400715, P.R. China     

Flow-injection spectrophotometric determination of glucose in blood plasma with bindschedler's green leuco base as color reagent

The hydrogen peroxide produces in the oxidation of glucos in an immobilized glucose oxidase reactor is determined by using Bindschedler's green (leuco base) as color reagent with iron(II) as catalyst; the increase in the absorbance at 725 nm is measured. For 100-μl samples, calibration was almost linear in the range 0–2.5 mg l^?1 glucose; the relative standard deviation for 1 mg l^?1 glucose was 0.6% (n=10) and the detection limit (S/N= 2) was 0.02 mg l^?1. The injection rate was 20 h^?1. Glucose was determined satisfactorily in control sera and in real blood sera.     

环境水中化学需氧量的FI分光光度法自动在线检测

本文将流动注射分光光度法用于环境废水中化学需氧量（ＣＯＤ）的自动在线检测，方法线性范围在０－１００ｍｇ／Ｌ之间，相对标准偏差＜２％以葡萄糖和苯二甲酸氢钾混合液制备标准溶液，对标准参考水样ＣＯＤ含量（Ｃｒ值）的测定结果表明两者有良好的相关性（Ｒ＝０．９８８０）对环境水样中ＣＯＤ含量的动态变化连续１０ｈ模拟试验，自制的在线过滤装置稳定，未发生堵塞现象；该系统可以较好地跟踪水样中ＣＯＤ浓度的实际变化     

Determination of Ammonia in Water Using Flow Injection Analysis with Automatic Pervaporation Enrichment

Abstract

An automated ammonia monitoring system has been developed by putting a pervaporation unit in an enrichment cycle used in flow injection analysis mode. In the proposed system, an enrichment cycle was equipped to enable the adjustment for the measuring range of ammonium by controlling the duration of the enrichment circulation. Therefore, the system was capable to determine ammonia in both the surface water with low ammonia concentration and the ammonia-rich wastewater with the linear dynamic range of 0.05–15 mg l^?1 and 15–50 mg l^?1, respectively. The relative standard deviations were less than 1.9% and the quantification limit is as low as 0.03 mg l^?1. The sampling frequency is 8–10 h^?1.     

Determination of dissolved boron in fresh,estuarine, and geothermal waters by d.c. argon-plasma emission spectrometry

A d.c. argon-plasma emission spectrometer is used to determine dissolved boron in natural (fresh and estuarine) water samples. Concentrations ranged from 0.02 to 250 mg l^-1. The emission—concentration function is linear from 0.02 to 1000 mg l^-1. Achievement of a relative standard deviation of ? 3% requires frequent restandardization to offset sensitivity changes. Dilution may be necessary to overcome high and variable electron density caused by differences in alkali-metal content and to avoid quenching of the plasma by high solute concentrations of sodium and other easily ionized elements. The proposed method was tested against a reference method and found to be more sensitive, equally or more precise and accurate, less subject to interferences, with a wider linear analytical range than the carmine method. Analyses of standard reference samples yielded results in all cases within one standard deviation of the means.     

The spectrophotometric determination of arsenic in sea water,potable water and effluents

Procedures are described for the determination of arsenic in sea water, potable waters and effluents. The sample is treated with sodium borohydride added at a controlled rate. The arsine evolved is absorbed in a solution of iodine and the resultant arsenate ion is determined photometrically by a molybdenum blue method. The time required for a complete analysis is about 90 min, but of this only 15 min is operator time. For sea water the range, standard deviation, and detection limit are 1–4 μgl^-1, 1.4 % and O.14 μg l^-1, respectively; for potable waters they are 0–800 μg l^-1, about 1 % (at 20μg l^-1 level) and 0.5μg l^-1, respectively. Silver and copper cause serious interference at levels of 0.5 mgl^-1, and nickel, cadmium and bismuth interfere at concentrations of a few tens of mg l^-1; however, these elements can be removed either by preliminary extraction with a solution of dithizone in chloroform or by ion exchange. Arsenic present in organo-arsenic compounds is not directly determinable, but can be rendered reactive either by photolysis with ultraviolet radiation or by oxidation with permanganate or nitric—sulphuric acid mixture. Arsenic(V) can be determined separately from total inorganic arsenic after extracting arsenic(III) as its pyrrolidine dithiocarbamate into chloroform.