Chemometrics characterisation of the quality of river water

Within the period from autumn 1990 to spring 1999 (from October to April in each period) 207 samples were collected and the measurement of 19 physical and chemical variables of the Mura river, Slovenia, were carried out. These variables are: river flow, water temperature, air temperature, dissolved oxygen, deficit of oxygen, oxygen saturation index, chemical oxygen demand (COD) in unfiltered and filtered samples, and biochemical oxygen demand after 5 days (BOD5) in unfiltered and filtered samples, pH, conductivity, ammonium, nitrite, nitrate, and phosphate concentrations, adsorbable organic halogens (AOX), dissolved organic carbon (DOC), and suspended solids. For handling the results of all measurements different chemometrics methods were employed: (i) the basic statistical methods for the determination of mean and median values, standard deviations, minimal and maximal values of measured variables, and their mutual correlation coefficients, (ii) the principal component analysis (PCA), and (iii) the clustering method based on Kohonen neural network. The influences of season, month, sampling site, and sampling time on the pollutant levels were examined. Before 1993, the pulp and paper industry was the main source of pollutants because of large amounts of chlorine emission as a consequence of industrial treatment, the leaching of cellulose. After the year 1993, the technology was changed and the quality of the river water has improved. The improvement could be detected 1 year after the change of technology. For one part of water samples the river quality classes based on biological parameters were also determined. The correlation between the biologically determined quality classes and chemical measurements was sought. Consequently, the biological classification for the water samples based on the chemical analyses was studied.     

The determination of chemical oxygen demand in waste-waters with dichromate by flow injection analysis

A simple method is described for the continuous determination of chemical oxygen demand (COD) in wastewater samples by flow injection analysis. Samples are injected into a water stream which merges with an acidic dichromate carrier solution. After reaction in a PTFE coil at 120°C, absorbances are measured at 445 nm. D-Glucose is satisfactory as a standard substance for COD in a variety of wastewaters. A sampling rate of 15 samples per hour can be achieved, and the detection limit and precision are 5 mg l^-1 as COD and 0.4%, respectively. Chloride concentrations of ? 100 mg l^-1 interfere slightly unless silver and/or mercury salts are added. COD values for various wastewater samples correlate well with those obtained by standard methods using dichromate or permanganate.     

Micropumping multicommutation turbidimetric analysis of waters

A micropumping multicommutation manifold to perform turbidity determinations in waters is described. The procedure is based on the use of a combination of hydrazine sulfate and hexamethylenetetramine, to obtain an external standard of nephelometric turbidity units (NTU), which could compare the absorbance measurements at high wavelengths for samples with a calibration line obtained from a concentrated formazine standard diluted on-line. To minimize sample and reagent consumption and waste generation, the flow system was designed with two solenoid micro-pumps, one of them for the alternative introduction of the formazine standard and samples and the other one for the water carrier. The multicommutation approach makes possible the on-line dilution of a single standard to obtain the external calibration. The linear response was ranged up to 160 NTU. The coefficient of variation was estimated as 1.6 and 3.2% for 10 and 100 mm flow cell, respectively, for solutions containing 40 NTU (n = 10). Approximately, 60 determinations can be carried out per hour with limit of detection values of 1 and 0.1 NTU, consuming only 160 or 240 μL formazine solution and generating 1.8 or 2.0 mL waste per determination, using measurement cells of 10 and 100 mm optical pathlength, respectively. The procedure was successfully applied to 11 different water samples. Recovery studies were carried out and results obtained were between 97.5 ± 0.2 and 100 ± 1%. The development of a homebuilt light emitting diode (LED)-based portable flow analysis instrument was checked for in situ turbidimetric measurements, providing this equipment a LOD value of 0.09 NTU working with a blue LED at 464 nm and a LOD value of 0.1 NTU working with an IR LED.     

Dichromate method for the determination of chemical oxygen demand

The oxidizability of organic substances of different classes was studied under the conditions of an official procedure for the determination of chemical oxygen demand (COD) with and without using Ag₂SO₄ as a catalyst. Organic substances can be divided into three groups: easily oxidizable compounds that are oxidized by 80–100% without a catalyst; medium-oxidizable compounds that are oxidized by 40–80% in the absence of a catalyst; and hardly oxidizable compounds that are oxidized by less than 40% without a catalyst. It was shown that, in the presence of a catalyst, not all organic substances are completely oxidized; therefore, the verification of the results of the determination of COD using easily oxidizable potassium hydrophthalate and glucose cannot be reliable in the presence of more hardly oxidizable substances. A standard mixture containing ethylene glycol, acetic acid, dimethylformamide, and nitrobenzene was proposed to verify the results of determining COD in waters of any type. The error in COD values found in a standard mixture varied in the range from 15 to 840 mg O/L. A modified procedure for the determination of COD in pure waters was proposed.     

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 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.     

Coagulation and UF treatment of pulp and paper mill wastewater in comparison

A study using coagulation-flocculation and ultrafiltration (UF)methods for pulp and paper mills’ wastewater (WW)was carried out. The reduction efficiencies of turbidity and chemical oxygen demand (COD), the removal efficiency of total suspended solids (TSS) and absorbance at 254 nm were the main evaluating parameters. Using coagulation-flocculation, the efficiencies of alum and polyaluminum chloride (PACl)were studied, when used alone and when coupled with flocculant aids. During the coagulation-flocculation process, use of a single coagulant, the coagulant dosage, and the pH, play an important role in determining the coagulation efficiency. At the optimum PACl dosage of 840 mg L⁻¹ and optimum pH of 9.0, turbidity reduction was found to be 94.5%. A combination of inorganic coagulant and flocculant, or polymer was applied, in which PACl was used coupled with the polyelectrolytes Organopol WPB20 and WPB40. PACl coupled with Organopol WPB20 by optimal pH 9 gave a 98.3% reduction of turbidity, 91.9% removal of TSS, and a 60.2% reduction in COD. Ultrafiltration trials were carried out on a pilot scale. A tubular module was used with ceramic membrane. This membrane is a multi-channel membrane with an active surface layer made of Al₂O₃ and ZrO₂. Within the acidic range, the turbidity and TSS were removed at above 99%.     

Hydrodynamic characteristics in aerobic biofilm reactor treating high-strength trade effluent

Four 3–L aerobic biofilm reactors (ABRI, 2, 3, and 4) treating a highstrength food–processing waste water (10 g chemical oxygen demand [COD]/L) were subject to reactor liquor recirculation rates of 1, 3,15, and 30 L/h, respectively. Treatment performance in terms of COD removal rates of ABRI, 2, and 3 were similar at hydraulic loads of 2.0 g COD/L/d and below. At higher organic loads, ABR3 could achieve a COD removal rate that was over two times higher than that of ABRI and 2. ABR3 could be operated at a maximum organic load that was two times higher than that of ABRI and 2. ABR4 experienced a biofilm sloughing from the packing medium at the beginning of operation. Tracer studies showed that recirculation rate of 1 L/h resulted in a plug–flow pattern in the packed bed of the reactor. On the other hand, recirculation rate of 15 L/h, which was equivalent to recirculating the reactor liquor five times per hour, provided effective mixing in the packed bed. Superior performance of ABR3 was attributed to the effective recirculation of reactor liquor, which diluted and distributed the influent, particularly the oil and grease components.     

Formation of photochemical π-cation radicals

We have monitored the spectra and kinetics of μ-oxo iron (III) tetraphenyl porphyrin. The spectral changes between 460 nm and 770 nm were observed after excitation with 25 ps fwhm, 355 nm pulse. Kinetic studies from — 100 ps to 4 ns suggest that after the immediate formation of the excited states a transient species is formed which we assign to the π-caion radical-ferrous porphyrin pair. This pair decays with a time constant of 600 ps ± 100 ps leaving a small amount of disproportionation reaction photoproducts. The spectra and kinetics of the transients, were not altered by concentration (0.15 OD – 1.0 OD at 571 nm), solvent or addition of oxygen.     

Colorimetric Estimation of Melatonin in Pharmaceutical Formulations

 Three simple and sensitive colorimetric methods (A–C) for the determination of melatonin in bulk samples and in pharmaceutical formulations are described. They are based on the formation of coloured species by reaction of ninhydrin with the drug (method A, λ_max 397 nm) by oxidation of the indol moiety in melatonin with potassium persulphate (method B, λ_max 450 nm) or by reduction of osmium (VIII) (method C, λ_max 516 nm). Regression analysis of Beer-Lambert plots showed good correlations in concentration ranges between 0.8–14.2, 70.0–140.0 and 2.0–40.0 μg/mL for methods A, B and C, respectively. The molar absorptivity, Sandell sensitivity and detection limit were calculated. For more accurate analysis, Ringbom optimum concentration ranges were calculated. The validity of the proposed methods was tested by analysing pharmaceutical formulations containing melatonin. The relative standard deviations were ≤ 0.95% with recoveries 99.0–101.33%. Received October 20, 1999. Revision February 10, 1999.     

Determination of chemical oxygen demand of nitrogenous organic compounds in wastewater using synergetic photoelectrocatalytic oxidation effect at TiO2 nanostructured electrode

Chemical oxygen demand (COD) is one of the most important parameters in water quality assessment and monitoring. The natural degradation of nitrogenous organic compounds (NOCs) in water requires significant amounts of oxygen. In the determination of standard COD however, NOCs are persistent compounds that cannot be completely oxidized even in the most oxidative chemical environments, i.e. the reaction media that contain high concentrations of dichromate in strong acid at high temperature. Consequently, the measured COD values of wastewater samples containing NOCs are commonly lower than theoretical COD values and do not reflect the actual oxygen demand of the water body. This problem is partially alleviated when the photoelectrochemical method for COD determination (PeCOD) based on nanostructured TiO₂ photoanode is utilized. To completely overcome this problem, a synergetic photoelectrochemical oxidation effect in thin layer cells is used to achieve complete oxidation of NOCs. This is done by the simple addition of a hydroxyl organic compound (i.e. glucose) into the test sample before the PeCOD measurement. Preliminary experimental results demonstrate that the synergetic PeCOD method provides an effective and reliable means to measure COD values of NOC-containing pollutants without the need for toxic or expensive reagents.     

纳米PbO2修饰电极安培检测器流动注射法快速测定化学需氧量

采用以纳米PbO₂修饰电极为工作电极的安培检测器,用流动注射法快速检测水体中的化学需氧量(COD).根据纳米PbO₂修饰电极催化氧化电流的大小测定样品的COD值,在50-1 200 mg/L COD的范围内,电流响应与标准水样中的COD_Cr值呈线性关系,检出限为20 mg/L.该法不需对水样进行预处理,不使用有毒试剂,无二次污染,具有快速、简便、进样量少及工作电极使用寿命长等优点,与COD_Cr国家标准分析法对比具有较好的相关性.     

Electrocatalytic Sensor for the Determination of Chemical Oxygen Demand Using a Lead Dioxide Modified Electrode

An amperometric method that makes use of a nano‐PbO₂ modified electrode as an electrocatalytic sensor for the determination of chemical oxygen demand (COD) is described. The sensor signal was observed as a result of the detection of the oxidation current due to electrocatalytic oxidation of organic compounds in the sample solution. This sensor responded linearly to the COD_Cr of standard samples in the range of 5–3 000 ppm and the detection limit was 2.5 ppm. When using the sensor to determine real samples, it displays short analysis time, simplicity and no sample pretreatment. The sensor was stable for over 20 days in real wastewater samples and has successfully been applied to the determination of COD in real wastewater samples.     

Determination of haptoglobin in human serum by high-performance gel-permeation chromatography

Summary A high-performance gel-permeation chromatographic (GPC) method is described for the determination of serum haptoglobin (Hp), based on the estimation of the haptoglobin-hemoglobin (Hp−Hb) complex. Hemoglobin (Hb) is added to the serum and the resulting Hp−Hb complex is separated by GPC and detected at 415 nm. The Hp−Hb complex separated chromatographically from serum migrated electrophoretically with the globulin fraction. It was found to be stable over a period of one week at 4°C. The total analysis time for a serum sample is approximately 20 min. The minimum detection limit is 30mg/L. Relative standard deviation values were below 1% (peak area). No interferences from bilirubin or from turbidity of samples were observed. The results of the GPC analysis correlate well with those obtained by nephelometric assay (r=0.996).     

Evaluation of preconcentration methods in the analysis of synthetic musks in whole‐water samples

According to the European Water Framework Directive, environmental assessment of organic compounds should be made in whole‐water samples, but due to their hydrophobicity and strong attraction to organic content these compounds can be found bound to suspended particle matter or in the dissolved fraction. In this work, the extraction of musk compounds was studied in whole‐water samples exhibiting different amounts of dissolved organic carbon and suspended particulate matter using polyethersulfone preconcentration technique. Matrix effects in estuarine and wastewater (both influent and effluent) were evaluated for filtered and unfiltered samples. For unfiltered samples, estuarine water exhibited matrix effects <20%, while for effluent it was up to 48% and for influent ranged from 85 to 99%. To compensate matrix effects and determine total concentrations in unfiltered samples, different quantification approaches were tested: the use of deuterated analogues and standard additions. Standard additions provided the best results for unfiltered samples. Finally, filtered and unfiltered samples were analyzed using both polyethersulfone preconcentration and membrane‐assisted solvent extraction and results showed a good agreement between the two methods. In both cases unfiltered samples provided concentrations 1.5–2.6 times higher than filtered samples.     

Sensitive and simple determination of the vasodilator agent dipyridamole in pharmaceutical preparations by phosphorimetry

The applicability of heavy atom-induced room-temperature phosphorescence to pharmaceutical samples is demonstrated in this work. Thus a new, simple, rapid, and selective phosphorimetric method for dipyridamole determination is proposed. The phosphorescence signals are a consequence of intermolecular protection when analytes are exclusively in the presence of heavy atom salts and sodium sulfite as an oxygen scavenger to minimize RTP quenching. The determination was performed in 0.1 mol L^–1 thallium(I) nitrate and 8 mmol L^–1 sodium sulfite at a measurement temperature of 20 °C. The phosphorescence intensity was measured at 635 nm, with excitation at 305 nm. Phosphorescence was easily developed; a linear concentration range was obtained between 0 and 100 ng mL^–1 with a detection limit of 940 ng L^–1, an analytical sensitivity of 2.5 ng mL^–1, and a standard deviation of 2.7% at 60 ng mL^–1 concentration. The method has been successfully applied to the analysis of dipyridamole in a unique Spanish commercial formulation containing 100 ng mL^–1 per capsule. The recovery was 101.6% with 6.5% standard deviation of analytical measurement. The method using the standard addition methodology has been validated.     

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     

Slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of Cr, Cd and Pb in plastics

Ultrasonic slurry sampling electrothermal vaporization dynamic reaction cell inductively coupled plasma mass spectrometry (USS–ETV–DRC–ICP–MS) for the determination of Cr, Cd and Pb in several plastic samples, using NH₄NO₃ as the modifier, is described. The influences of the instrumental operating conditions and the slurry preparation technique on the ion signals are investigated. A reduction in the intensity of the background at signals corresponding to chromium masses (arising from matrix elements) was achieved by using NH₃ as the reaction cell gas in the DRC. The method was applied to determine Cr, Cd and Pb in two polystyrene (PS) samples and a polyvinyl chloride (PVC) sample using two different calibration methods, namely standard addition and isotope dilution. The results were in good agreement with those for digested samples analyzed by ultrasonic nebulization DRC–ICP–MS. The precision between sample replicates was better than 17% with the USS–ETV–DRC–ICP–MS method. The method detection limits, estimated from standard addition curves, were about 6–9, 1–2 and 8–11 ng g⁻¹ for Cr, Cd and Pb, respectively, in the original plastic samples.     

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.     

Quantification of Teicoplanin in Human Plasma by Liquid Chromatography with Ultraviolet Detection

A simple high-performance liquid chromatographic method was developed for determining five major components of teicoplanin, designated A2–1, A2–2, A2–3, A2–4 and A2–5, in human plasma. Using piperacillin sodium as internal standard, teicoplanin in plasma samples was extracted by coextractive cleanup procedure. The extracts were injected into a Nova-Pak C₁₈ column maintained at ambient temperature. The mobile phase consisted of acetonitrile–0.1% trifluoroacetic acid (27:73, pH = 2.2), at a flow rate of 1.0 mL min⁻¹. The analytes were detected at the UV wavelength of 218 nm. The method was found to be linear over the concentration range of 2.5–50 mg L⁻¹ for teicoplanin (r = 0.9993 ± 0.0038), which covered the clinically expected trough plasma levels. The percentage error of the analytical method was below 9%. The intra- and inter-day reproducibility was adequate with coefficients of variation less than 7%. The chromatographic running time was 11 min. Thus, the method can be effectively applied to measure teicoplanin concentrations in clinical samples.