Oligosaccharide dehydrogenase-modified graphite electrodes for the amperometric determination of sugars in a flow injection system

Enzyme electrodes for the determination of sugars based on solid graphite electrodes modified with oligosaccharide dehydrogenase "wired" with an osmium-based one-electron (no proton) acceptor redox hydrogel were studied as sensors in a flow injection system. The enzyme and a poly(1-vinylimidazole) (PVI) where every tenth mer is complexed with osmium (4,4'-dimethylbpy)(2)Cl, (denoted PVI(10)dmeOs) were cross-linked with poly(ethylene glycol) (diglycidyl) ether. The electrodes were active for l-arabinose, d-xylose, d-galactose, d-fructose, d-glucose, d-mannose, cellobiose, lactose, maltose, and maltooligosaccharides up to a degree of polymerization of 7. The highest relative response found was for glucose (100%) followed by maltose (40.6%) and lactose (40.6%). Fructose and isomaltotriose gave the lowest responses (<1%). Calibration curves for glucose were strictly linear in the range between 30 and 500 μM with sensitivity and apparent Michaelis-Menten constant (K(m)(app)) of 23.0 ± 1.4 μA mM(-)(1)cm(-)(2) and 4.26 ± 0.95 mM, respectively.     

Development of a flow amperometric enzymatic method for the determination of total glucosinolates in real samples

The first amperometric flow analyzer, based on the biosensor concept, capable of determining total glucosinolates in real samples, is described. Myrosinase was immobilized on aminopropyl-modified controlled pore glass, which was then used for the construction of a packed-bed reactor. Myrosinase catalyzes the hydrolysis of glucosinolates (sinigrin) to glucose (among the other products), which is then oxidized by the action of glucose oxidase to produce hydrogen peroxide. The glucose enzyme electrode is based on a multimembrane architecture and was mounted on an amperometric flow cell (hydrogen peroxide detection at a platinum anode poised at +0.65 V vs Ag/AgCl/3M KCl). Different membrane types and different activation procedures were tested. The system was optimized to various working parameters, either as a glucose electrode or as a glucosinolate analyzer. The interference effect of various compounds was also investigated. Application of the method to real samples was carried out using glucose/glucose, hydrolyzed sinigrin and glucose/sinigrin solution as calibrators of the glucose electrode and the glucosinolate analyzer. Deviations due to the enantioselectivity of glucose oxidase to the beta-glucose anomer were observed, and a data elaboration protocol is proposed. The possibility of the simultaneous determination of glucose and glucosinolates is also demonstrated.     

UV resonance raman spectroscopic detection of nitrate and nitrite in wastewater treatment processes

The 204- and 229-nm excited UV resonance Raman spectra of wastewater solutions containing sodium nitrite and nitrate were measured in the concentration range 7 microM to 3.5 mM (0.1-50 ppm nitrogen). The other chemical species present in wastewater do not interfere with Raman measurements of NO2-/NO3- bands. We observe detection limits of < 14 microM (< 200 ppb) for both NO2- and NO3-. UV resonance Raman spectroscopy appears to be an excellent tool for on-line monitoring of NO2-/NO3- in wastewater for the real-time control of water treatment plants.     

连续流动注射法测定水中总磷的不确定度评估

本文从标准曲线拟合、磷标准溶液配制、重复性、标准系列溶液配制、示值误差、测量环境条件和操作人员影响等六个方面对连续流动注射法测定水中总磷的不确定度进行分析计算,合成标准不确定度（U）和扩展不确定度（U）。     

Biosensor based on self-assembling acetylcholinesterase on carbon nanotubes for flow injection/amperometric detection of organophosphate pesticides and nerve agents

A highly sensitive flow injection amperometric biosensor for organophosphate pesticides and nerve agents based on self-assembled acetylcholinesterase (AChE) on a carbon nanotube (CNT)-modified glassy carbon (GC) electrode is described. AChE is immobilized on the negatively charged CNT surface by alternatively assembling a cationic poly(diallyldimethylammonium chloride) (PDDA) layer and an AChE layer. Transmission electron microscopy images confirm the formation of layer-by-layer nanostructures on carboxyl-functionalized CNTs. Fourier transform infrared reflectance spectrum indicates the AChE was immobilized successfully on the CNT/PDDA surface. The unique sandwich-like structure (PDDA/AChE/PDDA) on the CNT surface formed by self-assembling provides a favorable microenvironment to keep the bioactivity of AChE. The electrocatalytic activity of CNT leads to a greatly improved electrochemical detection of the enzymatically generated thiocholine product, including a low oxidation overvoltage (+150 mV), higher sensitivity, and stability. The developed PDDA/AChE/PDDA/CNT/GC biosensor integrated into a flow injection system was used to monitor organophosphate pesticides and nerve agents, such as paraoxon. The sensor performance, including inhibition time and regeneration conditions, was optimized with respect to operating conditions. Under the optimal conditions, the biosensor was used to measure as low as 0.4 pM paraoxon with a 6-min inhibition time. The biosensor had excellent operational lifetime stability with no decrease in the activity of enzymes for more than 20 repeated measurements over a 1-week period. The developed biosensor system is an ideal tool for online monitoring of organophosphate pesticides and nerve agents.     

Nitroprusside and methylene blue methods for silicone membrane differentiated flow injection determination of sulfide in water and wastewater.

Hydrogen sulfide evolved from an acidified sample is pre-concentrated by permeation in a stationary alkaline acceptor solution enclosed in a silicone rubber sample loop. Depending on the sample volume pre-concentrated, the applicable analytical range spans low micrograms/L to tens of mg/L for both methods. The methylene blue method is more sensitive by a factor of approximately 30 and actually permits practical determinations in the sub-micrograms/L levels. The limit of detection (LOD) for the nitroprusside method ranges from 20 micrograms/L for a 20 microL sample by conventional flow-injection determination (no membrane, throughput 30 samples/h) to less than 2 micrograms/L for 12 mL sample pre-concentrated in the membrane system (throughput 5 samples/h). The membrane is highly resistant to fouling and permits analysis of untreated wastewater samples bearing suspended solids, oil, grease, etc. without any pretreatment. No significant interference is observed with either chemistry. Although the nitroprusside chemistry is less sensitive, it does not involve the use of concentrated aggressive reagents and is recommended unless ultratrace determinations are essential. Viable reaction mechanisms are proposed for both of these chemistries.     

A method for screening total mercury in water using a flow injection system with piezoelectric detection

An automatic microgravimetric screening system based on piezoelectric detection and the use of acidic stannous chloride as reductant was developed for the fast detection and determination of total mercury in water. Reduced mercury is detected as an amalgam by using a gold-coated piezoelectric crystal, the sensor subsequently being regenerated by passing it through a peroxydisulfate solution. The gold-coated piezoelectric crystal is a highly efficient retention unit for the main soluble mercury species (inorganic, complexed, and organometallic) previously reduced to elemental mercury and is free of interferences from other metal ions. This detector exhibits good sensitivity: it allows the determination of mercury at sub-parts-per-billion concentration levels (0.30-1.00 microg/L). The precision, expressed as relative standard deviation, was +/- 2.7% (n = 11; P = 0.05) at 0.5 microg/L total mercury. The proposed method was successfully used as a rapid screening method for mercury monitoring in natural waters.     

Automated flow injection analyzer with on-line solid-phase extraction and chemiluminescence detection for the determination of dodecylamine in diesel fuels

This paper describes the development of a portable, automated flow injection-chemiluminescence (FI-CL) analyzer incorporating on-line solid-phase extraction (SPE) for the determination of dodecylamine (detergent) in diesel fuels. The method is based on the peroxyoxalate/sulforhodamine 101 chemiluminescence reaction, with SPE required to remove indigenous compounds within the diesel fuel matrix that interfere with the CL response. The automated analyzer achieved a detection limit of 2.9 mg L(-1) and a linear range of 2.9-50 mg L(-1), which was suitable for determinations of dodecylamine at levels typically present in fully formulated diesel fuels (40 mg L(-1)). Analyses of base fuels from five different sources demonstrated that an automated FI-CL-SPE system could provide a portable instrument for monitoring the presence/absence of dodecylamine in diesel fuels.     

A pilot plant for the treatment of lemon industry wastewater

A pilot plant with a 10-m³ airlift reactor, a settler and a 300-m³ pond were developed for the treatment of the lemon processing industry wastewater. The aim of this work is to evaluate reactor and pilot plant performance. We worked in a continuous system with activated sludge, using wastewater microorganisms and testing the most important parameters of the process (HRT, SRT, F/M, VRC, K _La). An outflow settler tube added to the reactor design increased sludge concentration in 25% at 200–500 l/h flow rates. At 600–800 l/h flow rates sludge concentration was 10–15% higher. Volumetric removal capacity of the suspended solid in the reactor was more than 6 kg BOD₅/m³ day with lesser than 17 h hydraulic retention time. Maximum BOD₅ removal was 92% with 200 l/h flow. The reactor had a good mixing performance and a satisfactory volumetric mass transfer coefficient. Efficient reactor design made foam disposal easy. The effluent came out of the pond with DBO = 50 mg/l, i.e. a total BOD removal of 99% with 600 l/h flow. The pond also had a very important function: it completely eliminated reactor produced biomass by using a natural degradation process.     

Direct determination of carbohydrates, amino acids, and antibiotics by microchip electrophoresis with pulsed amperometric detection

The separation and detection of underivatized carbohydrates, amino acids, and sulfur-containing antibiotics in an electrophoretic microchip with pulsed amperometric detection (PAD) is described. This report also describes the development of a new chip configuration for microchip electrophoresis with PAD. The configuration consists of a layer of poly(dimethylsiloxane) that contains the microfluidic channels, reservoirs, and a gold microwire, sealed to a second layer of poly(dimethylsiloxane). Example separations of carbohydrates, amino acids, and sulfur-containing antibiotics are shown. The effect of the separation and injection potentials, buffer pH and composition, injection time, and PAD parameters were studied in an effort to optimize separations and detection. Detection limits ranging from 6 fmol (5 microM) for penicillin and ampicillin to 455 fmol (350 microM) for histidine were obtained.     

不同消解方法对HG-AFS测定植物样品硒含量的影响

为研究不同消解方法对植物样品中硒含量测定的影响,分别采用电热板敞开消解、高压罐密闭加热消解和微波密闭消解3种方法对富硒荞麦的籽粒、茎叶和壳以及国家标准物质灌木枝叶(GSV-1、GSV-2、GSV-3)进行前处理。在氢化物原子荧光光谱法(HG-AFS)优化条件下,对样品中的硒含量进行测定。结果显示3种消解方法都能获得准确的结果,其中微波消解法的准确度、精密度和回收率最好;电热板敞开消解法波动性较大,但是该方法适合于大批量样品分析。在分析实践中,应根据样品量、硒含量和结果准确度要求选择合适的消解方法。     

Temperature effect on shear flow and thixotropic behavior of residual sludge from wastewater treatment plant

The temperature and shear rate effects on rheological behavior of residual sludge from wastewater treatment plant was investigated in this work. The model of Herschel–Bulkley was used to fit the shear rate dependence of the shear stress. The temperature increase induced not only an increase in the yield stress and the flow index of sludge but also a decrease of the consistency index of sludge. The temperature dependence of limit viscosity at high shear rate of the residual sludge was fitted by an Arrhenius equation. For constant shear rate applied on the sludge at 20 °C a thixotropic behavior was observed and analyzed using a modified model of Herschel–Bulkley in which a structural parameter λ was included in order to account for the time-dependent effect.     

Method development for the quantitative determination of lactulose in heat-treated milks by HPAEC with pulsed amperometric detection

A robust, rapid, and sensitive high-performance anion-exchange chromatographic method for the separation and quantitative determination of lactulose in heated milks, along with other common milk carbohydrates, has been developed. Complete separation of galactose, glucose, N-acetylgalactosamine, lactose, lactulose, and epilactose was isocratically accomplished in about 22 min by an anion-exchange column eluted with 10 mM NaOH spiked with 2 mM Ba(OAc)2. The within-day repeatability was lower than 2.1% for 10 repetitive injections. Under optimized conditions, there was no need either of post-column addition of strong bases to the eluent for enhancing detection sensitivity or, even more important, for column regeneration between chromatographic runs. Upon 100-fold sample dilution, the amperometric response of lactulose in milk samples was found to be linear up to 100 microM (r = 0.99935) with a limit of detection equal to 1.2 microM (S/N = 3). The lactulose content in ultrahigh-temperature (UHT) and sterilized milks was evaluated by a calibration graph using 2-deoxyglucose as the internal standard, making the proposed method very useful in discriminating among heat-treated milks. Whereas the mean value of lactulose in skimmed, partially skimmed, and whole UHT milks ranged from 10 to 90 mg/100 mL, lactulose content in bottle-sterilized whole milk (two samples) was higher than 140 mg/100 mL. The presence of epilactose, which is another isomer of lactose, was also ascertained in sterilized milk.     

微波消解-钼锑抗光度法测定蔬菜中总磷

采用微波消解-钼锑抗光度法测定蔬菜中的总磷,为获得最佳试验条件,对微波消解条件中的酸的种类、消解时间和消解温度等影响因素进行优化,结果表明:硝酸和过氧化氢(体积比7∶1)为最佳消解酸系,最高消解温度180℃,保持时间20 min。对紫外-可见光波长和显色时间对试验结果的影响进行探讨,结果表明710 nm和20 min为最佳试验条件。为评价该方法的可靠性,选用两种蔬菜标准物质GBW 10048和GBW 10049对该方法进行分析验证,测定值与标准值相符,相对标准偏差(RSD)分别为0.884%和0.938%,添加回收率大于89.93%,表明该方法拥有良好的准确性和精密度。微波消解-钼锑抗光度法具有简单、省时省力、试剂用量少等优点,能够满足蔬菜中总磷的测定。     

Raman spectroscopic analysis of cyanogenic glucosides in plants: development of a flow injection surface-enhanced Raman scatter (FI-SERS) method for determination of cyanide

Cyanogenic glucosides were studied using Raman spectroscopy. Spectra of the crystal forms of linamarin, linustatin, neolinustatin, amygdalin, sambunigrin, and dhurrin were obtained using a Raman spectrograph microscope equipped with a 532 nm laser. The position of the signal from the C identical with N triple bond of the cyanohydrin group was influenced by the nature of the side group and was above 2240 cm(-1) for the three cyanogenic glucosides that contain a neighboring aromatic ring, and below or partially below 2240 cm(-1) for the non-aromatic cyanoglucosides. Signals from the CN bond of linamarin/lotaustralin in leaves and roots from a medium cyanogenic cassava variety were obtained in situ using a Fourier transform near-infrared (FT-NIR) Raman interferometer with a 1064 nm laser, but the signal was very weak and difficult to obtain. A spectrum containing a signal from the CN bond of dhurrin in a freeze-dried sorghum leaf was also obtained using this instrument. Surface-enhanced Raman Spectroscopy (SERS) was demonstrated to be a more sensitive method that enabled determination of the cyanogenic potential of plant tissue. The SERS method was optimized by flow injection (FI) using a colloidal gold dispersion as effluent. Potential problems and pitfalls of the method are discussed.     

Ecotoxicological evaluation of the wastewater treatment process of the sewage treatment plant of Thessaloniki, Greece

The LUMISTox toxicity test was employed to assess the removal of municipal wastewater toxicity during the biological treatment with activated sludge in the wastewater treatment plant of Thessaloniki, Greece. Possible associations of toxicity data with chemical parameters of organic pollution of wastewaters, namely BOD(5), COD, DOC, SS and persistent organic pollutants (POPs) were also investigated. Toxicity and chemical parameters were concurrently measured at three sampling points of the treatment plant, the entrance of the unit (raw wastewater, RW), the effluent of the secondary sedimentation tank (SSE), and the final sewage sludge (FS). Substantial reduction of toxicity was observed from RW to SSE (mean+/-S.D. of bioluminescence inhibition 36+/-9.4% and 13+/-4.0%, respectively) indicating removal of toxicants during primary and secondary clarification, also suggesting that a large part of the toxicity measured is attributed to the biodegradable fraction of the organic content of wastewater. Significant positive correlations were observed between % inhibition values and wastewater parameters (BOD, COD, SS). In sludge, correlations were in general poor. Negative strong correlation was observed between EC(20/15) and TOC suggesting that the organic content of sludge contributes to the toxicity measured. Toxicity was positively correlated with the concentrations of certain POPs in RW, while weaker negative correlations were observed in SSE. Correlations in sewage sludge were less significant. It was concluded that toxicity testing is a useful tool supplementing chemical analyses in the evaluation of the potential hazard from effluent discharges and disposal of waste sludge.