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Gold nanoclusters decorated hollow ZIF-8 encapsulating iron-catecholates (Fe-HHTP@HZIF-8@ AuNCs) was formed through self-assembly of Fe3+ and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP), in situ embedding of ZIF-8, and Au3+-Zn2+ exchange reaction. Its morphology and structure were fully characterized by high-resolution transmission electron microscopy, X-ray diffraction, transmission electron microscopy element mapping, and X-ray photoelectron spectroscopy. Additionally, its oxidase-like activity was explored with Km of 0.21 mM and Vmax of 1.74 × 10−6 M·s−1 toward 3,3′,5,5′-tetramethylbenzidine (TMB). Due to its excellent catalytic activity and nitrite mediated diazotization of oxTMB, a ratiometric colorimetric method for nitrite detection was established and validated with wide linear range (2.0–400.0 μM), low LOD (0.12 μM), high accuracy (recovery of 95.11–102.14%), and good selectivity. This method was then utilized to determine the nitrite content in sausages and tap water. This study provided a new idea for developing efficient nanozymes and offered an accurate approach for nitrite determination. [ABSTRACT FROM AUTHOR]

In this work a simple and rapid automated analytical method for the determination of sulfur dioxide in wines by employing a sequential automatic analyser was validated. The methodology is based on the reaction of sulfur dioxide with 5,5′-dithiobis-(2-nitrobenzoic acid) in an alkaline medium followed by photometric detection. The linearity of the calibration curve was excellent (R2 = 1.000) and the LOQ (2.00 mg L−1) was well suited for the monitoring of regulatory limits. The accuracy and precision were evaluated with reference materials, providing highly successful results (RSD% < 3.8 for precision and R2 = 0.99 of correlation between the obtained and declared values). The method was applied to the analysis of commercial samples of wines ensuring compliance with legislation. The results found were compared to those obtained with the spectrophotometric method recommended for beers, implemented in a flow system, showing that there are no statistical differences between them (α ≤ 0.05). When compared with conventional methods, the proposed methodology showed to be fast, with minimum handling of the sample and small sample and reagents volume requirement, which together with a minimum maintenance, involves a considerable reduction in laboratory costs. [ABSTRACT FROM AUTHOR]

In situ enzymatic generation of bimetallic nanoparticles, mainly Au/Pt, overcomes the drawbacks (continuous absorbance drift, modest LOQ, and long-time reaction) observed when AuNP alone are produced. In this study, Au/Pt nanoparticles have been characterized by EDS, XPS, and HRTEM images using the enzymatic determination of tyramine with tyramine oxidase (TAO) as a model. Under experimental conditions, the Au/Pt NPs show an absorption maximum at 580 nm which can be related to the concentration of tyramine in the range 1.0 × 10-6M to 2.5 × 10-4M with a RSD of 3.4% (n = 5, using 5 × 10-6M tyramine). The Au/Pt system enables low LOQ (1.0 × 10−6 M), high reduction of the absorbance drift, and a significant shortening of the reaction time (i.e., from 30 to 2 min for a [tyramine] = 1 × 10−4M); additionally, a better selectivity is also obtained. The method has been applied to tyramine determination in cured cheese and no significant differences were obtained compared to a reference method (HRP:TMB). The effect of Pt(II) seems to involve the previous reduction of Au(III) to Au(I) and NP generation from this oxidation state. Finally, a three-step (nucleation-growth-aggregation) kinetic model for the generation of NPs is proposed; this has enabled us to obtain a mathematical equation which explains the experimentally observed variation of the absorbance with time. [ABSTRACT FROM AUTHOR]

It has been shown that 2-methyl-4-chlorophenoxyacetic acid (MCPA) forms an ionic associate (IA) with the polymethine dye Astrafloxin FF (AF). The energy efficiency of IA formation is substantiated by the method of mathematical modeling. The molecular modeling of MCPA– + AF+ systems and related calculations are performed by using the HyperChem 8.0 software package in various initial variants for the mutual arrangement of counterions ("single point" procedure). The geometric optimization of ions is carried out by the molecular mechanics method MM+. The obtained IA is quite well extracted by various aromatic hydrocarbons. The maximum IA extraction from the aqueous phase is attained at pH = 6–12. The effect of the dye concentration on the optical density of the toluene extracts of MCPA–AF ionic associates is studied. The IA extraction attains a maximum at a dye concentration of (1.6–2.8) × 10–4 M. Extraction equilibrium is reached for 50–60 s. The stoichiometry of the MCPA–AF ionic associate is established by the spectrophotometric methods of isomolar series and equilibrium shift; the ratio of components is 1 : 1. The IA formation and extraction scheme is proposed. The conditional molar absorption coefficient of the ionic associate is 1.1 × 105. The calibration dependence of the optical density of extracts on the MCPA concentration is described by the linear equation a = 0.0116 + 0.0613 within the MCPA concentration range of 0.9–45.6 μg/cm3. The MCPA detection limit calculated by the 3s criterion (n = 5, P = 0.95) is 0.8 μg/cm3. The disperancy of the plotted calibration curve for the detection of 2-methyl-4-chlorophenoxyacetic acid is estimated by using the Cochran test G. The calculated Cochran criterion (n = 5, P = 0.95) is lower than its tabular value, i.e., Gcalcd = 0.25 < Gtab = 0.64 to evidence variance homogeneity. The method for the photometric extraction detection of 2-methyl-4-chlorophenoxyacetic acid in water and bottom sediments has been developed. [ABSTRACT FROM AUTHOR]

Aim. To develop a new method, which has a good reproducibility of the experimental results, is fast, cheap and provides safe working conditions during the analysis, in order to determine the activity of cholinesterase. Experimental part. The light absorption of the test and control samples was measured using a CPhC-3-01 photoelectric photometer (420 nm, l = 3 cm). The reaction rate was characterized by the value of the optical density of the solution in 10 min (the fixed time method). Measurements were performed at +37 °C, the temperature of the reaction mixture was maintained by thermostatіng in water, the pH of the solutions was monitored potentiometrically using a glass electrode. The determination was repeated five times with each solution of a certain concentration of the enzyme. According to the average values obtained, the calibration graph of the specific activity of the enzyme (in international units – activity unit (AU/mg) – kmol/min to 1 mg of the substance) on the optical density of the solution was constructed. Using the mean value of five measurements of the optical density of the test solution the specific activity of the enzyme (U) was found by the calibration graph. Results and discussion. The essence of the method is the photometrical measurement of the rate of the enzymatic hydrolysis of acetylcholine in a buffer medium using 3,3′,5,5′-tetramethylbenzidine (TMB). The enzymatic hydrolysis reaction of the substrate was performed at pH 8.3, and in 10 min after the start the rate of enzymatic hydrolysis of acetylcholine was measured. The linear dependence of the optical density on the specific activity of the enzyme (U) was observed in the range of 3.5 – 28 AU/mg (activity unit/mg). The activity of the enzyme, according to the average results of 5 measurements, was 27.9 AU/mg. The declared activity the enzyme in accordance with the quality certificate was 28 AU/mg. The limit of quantification was 0.2 AU/mg. Metrological characteristics of the method were as follows: RSD = 1.8 % (n = 5; P = 0.95), accuracy – 0.45 %. These values indicate that the method proposed for determining the activity of cholinesterase is characterized by high sensitivity, reliability and reproducibility of the results. At the same time, it was proven that there was no systematic error in determining the activity of cholinesterase by the method developed. Conclusions. As a result of the research conducted a new method for determining the activity of the cholinesterase enzyme has been developed; it is characterized by high sensitivity, reliability and reproducibility of the results, and also provides safe working conditions during the analysis.

Aim. To develop a principally new method, which would allow achieving the necessary accuracy and reproducibility of the analysis results, for determining the activity of the blood cholinesterase; to create safe working conditions when performing the analysis. Results and discussion. The kinetic method proposed for determining the activity of cholinesterase consists in photometric measurement of the rate of the enzymatic hydrolysis of the acetylcholine substrate (by its residue) in the phosphate buffer using p-phenetidine as an indicator. The rate of the enzymatic hydrolysis of acetylcholine was determined by the tangent of the inclination angle of the linear part of the kinetic curve in the А–t coordinates at a wavelength of 358 nm. The linear dependence of the conditional reaction rate (tgα) on the enzyme concentration was observed in the concentration range of 0.12 – 0.36 mg/mL. Metrological characteristics of the method developed were: RSD = 2.0 % (n = 5; P = 0.95), correctness 0.4 %. These values indicate that the method for determining the activity of blood cholinesterase is sensitive, reliable and reproducible. Experimental part. The experiments on determining the rate of the enzymatic hydrolysis were repeated three times with a specific concentration of the enzyme. Using the data obtained the kinetic curves were constructed in the А–t coordinates; on their basis the tangents of the angles of inclination in min-1 were calculated. The calibration graph was constructed using the average values of the tangents of the angles of inclination, which corresponded to a certain concentration of the solution of the working standard sample of the enzyme. The equation of the calibration dependence of tgα-enzyme concentration was calculated by the method of least squares and found to be tgα (min-1) = –0.17с + 9.13 (r = 0.999). Conclusions. As a result of the studies conducted, a new method for determining the activity of the cholinesterase enzyme has been developed. The method is characterized by a high sensitivity, reliability and reproducibility and provides safe working conditions when performing the analysis.

Introduction. Soy pulp, or okara, is a soy milk by-product. It contains a complex of valuable macro- and micronutrients, including fat-soluble vitamins. Recently, there has been a growing interest in replacing synthetic antioxidants with a mix of natural tocopherols. Soy beans and their by-products contain vitamin E and therefore can be used in food production, cosmetic, etc. Study objects and methods. The present research featured soy pulp. The content of tocopherols in the soy product was determined by high performance liquid chromatography using Sigma Aldrich standards and corresponding calibration dependencies. The research also involved spectrophotometry for determining tocopherols in standard solutions followed by chromatographic separation using fluorimetric detection. Results and discussion. To determine tocopherols in the okara, the test samples were treated with hexane. The filtered solution was exposed to low temperatures, after which the phases formed by centrifugation were separated. The samples were tested for all forms of tocopherols with the exception of β- and γ-forms. The chromatographic separation of the peaks of these forms was difficult due to the fact that their structural formulas were similar and differed only in the arrangement of methyl groups, i.e. the ortho- and paraposition. As a result, it was decided to determine the sum of the β- and γ-forms, which did not affect the objectivity of the analysis, since, according to published data, the content of β-tocopherol in soy products stays within 5%. Conclusion. The proposed method for sample preparation made it possible to improve the separation of the lipid fraction, which had a positive effect on the results of the analysis. The method also determined not only the quantitative, but also the qualitative content of tocopherols in the product. This reduced the risk of malfunctioning chromatographic equipment: the method proved more economical in terms of labor and reagent use. The obtained results corresponded to the existing scientific data on the content of tocopherols in soy products. The content of tocopherols in soy okara was 109 mg%.

Copper aspartate nanofibers were facilely prepared based on aspartic acid and copper (CuAsp nanofibers). It is found that the prepared CuAsp nanofibers have catalytic activities of five enzymes, including peroxidase, laccase, catalase, ascorbate oxidase, and superoxide dismutase mimetic activities. The kinetic and catalytic properties of CuAsp nanofibers were systematically investigated, showing their high catalytic activity, excellent stability, and reusability. The laccase mimetic activity of nanofibers could be used to detect catechin in the range 20–1200 µM with a detection limit of 5.88 µM. In addition, a sensing platform for glutathione with a detection limit of 0.25 µM and a detection range of 1–50 µM was established based on CuAsp nanofibers which have the peroxidase-mimicking activity. The sensor had good selectivity and could detect glutathione in actual samples of human serum. Therefore, CuAsp nanofibers with multi-enzyme activity have broad application prospects such as biosensing, environmental management, and disease diagnosis. [ABSTRACT FROM AUTHOR]

A novel visual detection mode is proposed to improve the detection sensitivity for the determination of ochratoxin A (OTA). The mode is based on aptamer recognition and the signal amplification of rolling circle amplification (RCA) products self-assembled DNA hydrogel. Moreover, gold nanoparticles (AuNPs) were directly assembled inside the DNA hydrogel by adjusting the padlock probe sequences to achieve a stronger binding force between the DNA hydrogel and AuNPs; this avoids the need for modification of AuNPs with DNA sequences. In the presence of OTA, DNA hydrogel is formed. With higher concentrations of OTA, a larger amount of DNA hydrogel is formed. When AuNPs are added to the DNA hydrogel, AuNPs can be enclosed inside the DNA hydrogel. With more DNA hydrogel, there is less AuNPs in the supernatant. Thus, the absorbance of the supernatant is anti-correlated with the concentration of OTA. After optimization of the experimental conditions, the change in the absorbance of the supernatant was linearly correlated with the concentration of OTA, in the range 0.05 to 10 ng/mL; the limit of detection was 0.005 ng/mL. The good specificity of the developed biosensor was confirmed in the presence of other mycotoxins that are coexistent with or analogues of OTA. By comparing the developed method with the ELISA method, the accuracy and stability of this new method were also verified, with good performance obtained in real samples. [ABSTRACT FROM AUTHOR]

This paper presents a novel miniaturized analytical method for the determination of carminic acid, a natural red food dye, in complex food and pharmaceutical matrices by microchip electrophoresis (MCE) with photometric detection. MCE has become a very attractive microscale separation technique because it offers high-speed, high-throughput, small sample injection volume and low reagents consumption. Fast determination of carminic acid in less than 5 min was achieved on a poly(methyl methacrylate) microchip in anionic separation mode at pH 6. Photometric detector based on light-emitting diode technology was set to a wavelength of 490 nm. Using a sample injection volume of 900 nL, a limit of detection of 69 nmol L−1 was achieved. A wide linear dynamic range over four orders of magnitude (from nmol L−1 to mmol L−1) was observed for peak area. Developed method provided favorable intra- and inter-day repeatability of the migration time (up to 2.5% RSD), as well as the repeatability of the peak area (less than 1.9% RSD), regardless of the sample type. The content of carminic acid was determined in various foodstuffs and pharmaceuticals, such as candies, saffron, non-alcoholic drink, and sore throat lozenges with good recoveries (92.5–104.0%).

Photometric detection plays a significant role in microfluidics technology. However, the mismatch between the solution concentration and the optical path length will increase detection error. In this study, we proposed a round microfluidic chip for concentration detection to obtain the continuous gradient distribution of concentration. The optimum absorbance can be found by dynamic accurately searching. The solution concentration will be accurately calculated finally according to the relationship between arc length and solution concentration. The overall detection process runs automatically. Under the optimization of injection velocity and concentration, the experimental result shows that the compensation ratio increases as the solution concentration increases. The compensation ratio in the detection of pesticide residue has already reached 14.22% and the reproducibility is acceptable. Therefore, this novel method lays the theoretical foundation for the research of high precision microfluidic photometric detection equipment. [ABSTRACT FROM AUTHOR]

The BTEX detector employs the emission band of an ultraviolet light-emitting diode at 260 nm as monochromatic light source and photodiodes for the deep UV-range as reference and signal detectors. Optical fibres are used for coupling the light to the absorption cell of 40 cm length as well as to the reference photodiode. The use of an integrated circuit log-ratio amplifier allows the direct determination of absorbance values according to Lambert-Beer’s law. Linear calibration curves over two orders of magnitude, between about 1 ppm and 100 ppm, were obtained for benzene, toluene, ethylbenzene, o -xylene, m -xylene and p -xylene. There is some variation of the sensitivity between the six species, which correlate with differences in the absorption spectra, with toluene, ethylbenzene, o -xylene and m -xylene showing close values between 150 μAU/ppm and 185 μAU/ppm, while benzene with 62 μAU/ppm has a somewhat lower and p -xylene with 235 μAU/ppm a somewhat higher sensitivity. The limits of detection were determined as approximately 1 ppm. [ABSTRACT FROM AUTHOR]

The article describes a simple method for the rapid photometric and visual detection of sulfide in water samples. Silver nanoparticles were capped with chitosan (chit-AgNPs) and then characterized by absorption spectroscopy, high resolution transmission electron microscopy and zeta potential measurements. Chit-AgNPs exhibit a strong surface plasmon resonance band at 404 nm which disappears in the presence of increasing concentrations of sulfide. This is accompanied by color change from yellow to colorless and attributed to the formation of silver sulfide on the surface of the chit-AgNPs. This was corroborated by HR-TEM and zeta potential measurements. The method is fairly selective for sulfide even in the presence of 100-fold higher concentrations of interferents such as common anions and thiol containing molecules. The method can be applied to quantify sulfide in the 0.80 to 6.40 × 10 mol dm concentration range with a 0.35 × 10 mol dm detection limit (at an S/N ratio of 3). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: A simple and efficient microfluidic chip-based analytical system for rapid screening of photocatalysts was developed. The catalyst screening system consisted of a microchip with multiple channels for parallel reactions, a UV light source, and a CCD camera-based photometric detection system for monitoring the photocatalytic reaction. A novel microfluidic introduction method for loading particle samples into chip microchannels was established using dry sample powders and wedge-structure channel design. With this method, multiple different photocatalyst samples could be quickly introduced into the microchip with good reproducibility without the need of additional pumps or valves. We applied the present system in the rapid screening of doping TiO2 photocatalysts in terms of their activity for methylene blue (MB) degradation under UV light irradiation. Ten parallel photocatalyst screening reactions were achieved within 15min in the multi-channel chip. We also examined nine element doped TiO2 materials to investigate the doping effects of different elements on TiO2. Compared with conventional systems, the photocatalyst consumption (0.1mg) in the present system was significantly reduced at least 100 times. High reaction rate in chip microreactors was obtained with an increase of two orders of magnitude over bulk reactors. The miniaturization of the photocatalytic reaction on the microchip significantly improves the reaction rates, reduces the sample and reagent consumptions, and increases the throughput of screening for multiple catalyst samples in parallel. The present work provides a novel application for microfluidic chip-based analytical systems, as well as a rapid, highly-efficient and low-consumption method for screening of photocatalysts. [Copyright &y& Elsevier]

A determination method for gold (Au) ion in river water has been developed by reversed phase HPLC. The Au(III) ion was quantitatively extracted into benzene from a weak alkaline solution as 2-thiazolidinethione, 4-(1-methylethyl)-, (4S)- (TTM) chelate. The extracted Au-TTM chelate was then separated on a C18 column with an eluent of methanol/ethanol/ 0.01 mol/L TTM (70:30:0.1, v/v) and detected at 270 nm. The correlation coefficients of the calibration curves obtained with 5 mL Au standards were more than 0.999 in the range of 1 µg/mL (ppm) to 10 ppm. The detection limit of the Au ion in 5 mL of water was estimated as 0.08 ppm, by a signal-to-noise ratio (S/N) = 3. Relative standard deviations of peak areas (n = 6) for 5 ppm Au standards was 1.0%. The recoveries with a spiked river water sample for 5 ppm Au ion (n = 6) was 99.2 ± 0.6%. Effects of foreign ions on the determination of 2 ppm Au were investigated with 57 metal ions. Almost none of the ions interfered except for Ag(I), Cd(II), and Ti(IV) ions. [ABSTRACT FROM AUTHOR]

Abstract: In this work, hydrolysis of three different hexafluorophosphate salts in purified water was investigated. Aqueous samples of lithium hexafluorophosphate (LiPF6), sodium hexafluorophosphate (NaPF6) and potassium hexafluorophosphate (KPF6) were prepared and stored for different times. Ion chromatography (IC) with UV as well as non-suppressed and suppressed conductivity detection was used for the analysis of the reaction products. For the detection and identification of the formed decomposition products, an IC method using IonPac AS14A 250mm×4.0mm i.d. column and 2.5mM KHCO3–2.5mM K2CO3 eluent was established. Besides hexafluorophosphate, four other anionic species were detected in fresh and matured aqueous solutions. The hydrolysis products fluoride (F−), monofluorophosphate (HPO3F−), phosphate (HPO4 2−) and difluorophosphate (PO2F2 −) were found and were unambiguously identified by means of standards or electrospray ionization mass spectrometry (ESI-MS). It was shown that stability of hexafluorophosphate solutions depends on the nature of the counter ion and decreases in the order potassium>sodium>lithium. [Copyright &y& Elsevier]

The photometric detection of urea with the use of p-dimethylaminobenzaldehyde as a reagent has been develeped. The method allows one to reliably determine 10 mg/L of urea with the volume of an aliquot of 10 mL. The method has been applied for the determination of urea in river water. [ABSTRACT FROM AUTHOR]

In this paper, flow injection analyser with photometric detection has been examined for the possibility of monitoring of ammonium ions in water and wastewater samples. Ammonium ions determination (even trace amounts) in environmental samples with great matrix differentiation (mainly with complex or atypical composition) seemed to be workable after appropriate sample pre-treatment and due to in-line separation and preconcentration by gas diffusion. Established method shows low limit of detection, good precision and good correctness. The described full automatic method takes effect in short-time analysis, small sample volume and waste restriction. Proposed flow injection system comply with requirements and, therefore it may be applied in monitoring studies, as well as in the routine analysis of real samples of water and wastewater from different sources. [ABSTRACT FROM AUTHOR]

general procedure is presented for the fabrication of miniaturized continuous flow analytical microsystems based on photometric detection using the low temperature co-fired ceramics technology. Optical elements such as light emitting diodes and photodiodes (all in the size of a few hundred micrometers) are integrated by means of an off-chip approach. A simple procedure is demonstrated to integrate a glass window after the ceramic sintering in order to minimize the decrease in sensitivity due to the reduction of the optical path length when scaling down. A flow cell with a shape of a bubble has been used to increase the area of the light beam. The device is robust, affordable, and small-sized. It enables absorbance measurements to be performed in-situ or for continuous monitoring of environmental samples. Specifically, a microsystem is introduced for colorimetric determination of chromium (VI) ion in waters based on the diphenylcarbazide reagent as a model. Under the optimized conditions, a linear response is obtained for the concentration range from 0.1 to 20 mg L, with a detection limit of 50 μg L. [ABSTRACT FROM AUTHOR]

Abstract: A mixture of 29 organic acids (OAs) occurring in urine was analyzed by capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4D) and UV photometric detection. The optimized analytical system involved a 100cm long polyacrylamide-coated capillary (50μm i.d.) and the background electrolyte of 20mM 2-morpholinoethanesulfonic acid (MES)/NaOH+10% (v/v) methanol, pH 6.0 (pH is related to the 20mM MES/NaOH buffer in water). The LOD values obtained by C4D for the OAs which do not absorb UV radiation range from 0.6μM (oxalic acid) to 6.8μM (pyruvic acid); those obtained by UV photometry for the remaining OAs range from 2.9μM (5-hydroxy-3-indoleacetic acid) to 10.2μM (uric acid). The repeatability of the procedure developed is characterized by the coefficients of variation, which vary between 0.3% (tartaric acid) and 0.6% (5-hydroxy-3-indoleacetic acid) for the migration time and between 1.3% (tartaric acid) and 3.5% (lactic acid) for the peak area. The procedure permitted quantitation of 20 OAs in a real urine sample and was applied to monitoring of the occurrence of the inborn metabolic fault of methylmalonic aciduria. [Copyright &y& Elsevier]

A determination method for Copper (Cu) ion in river water has been developed by reversed phase HPLC combined with solvent extraction. The Cu(II) ion was quantitatively extracted into benzene from a weak acidic solution as 2-mercaptobenzothiazole (MBT) chelate. The extracted Cu-MBT chelate was then separated on a C18 column with an eluent of methanol/water (88:12, v/v) and detected at 275 nm. The correlation coefficients of the calibration curves obtained with 5 mL Cu standards were more than 0.999 over the range of 0.01 to 10 µg/mL (ppm). The detection limit of the Cu ion in 5 mL water was 3 ng/mL, which corresponded to 3 times the standard deviation (N = 8) of the blank peak area. Effects of foreign ions on the method were investigated with 0.4 ppm Cu standard and 57 metal ions. Almost none of the ions interfered except for Au(III), Pt(IV), V(V), and Zr(IV) ions. Recoveries with a spiked river water sample for 5 and 0.5 ppm Cu ion were 99.9 ± 0.5% and 99.8 ± 0.8%, respectively (N = 6). [ABSTRACT FROM AUTHOR]

A selective and sensitive determination method for mercury (Hg) ions in river water by reversed phase high performance liquid chromatography (HPLC) has been developed. Two mL of water sample containing Hg(II) ions was put into a 4 mL sample tube. To the sample tube, 500 µL of 2 mol/L (M) acetate buffer solution (pH 4.5), and 50 µL of 0.01 M 2-mercaptopyrimidine (MP) were added to form a neutral Hg chelate. The Hg chelate subsequently became preconcentrated in a reversed phase mini column. By switching the valve, the Hg chelate was separated and detected at 255 nm. These processes occur automatically, except for the addition of water samples, buffer, and MP solutions. The correlation coefficients of the calibration curves obtained with 2 mL of mercury standard were more than 0.999 over the range of 20 ng/mL (ppb) to 10 µg/mL (ppm). The detection limit of Hg ions in 2 mL solution was 1.6 ppb, which corresponded to 3 times the standard deviation (N = 10) of the blank peak area. Effects of foreign ions on the determination of 0.2 ppm Hg were investigated with 57 metal ions. Almost none of the ions interfered except for Au(III), Pd(II), Ag(I), and Co(II) ions. The recoveries with spiked river water samples for 5, 0.5, and 0.05 Hg ion (N = 7) were 99.7 ± 0.4%, 100.3 ± 0.3%, and 100.7 ± 0.7%, respectively. [ABSTRACT FROM AUTHOR]

Nowadays, there is a trend towards developing and fabricating (bio) analytical chemistry systems adopting additive manufacturing techniques, also known as 3D printing. These developments focuses on manufacturing flow detection cell, mixing system and electrochemical electrodes, but not to automation, portability and real time analytical systems. A new 3D printed opto-microfluidic analyzer was developed to implement an autonomous and miniaturized analytical process with auto-calibration controlled by wireless communication. The device integrated an RGB photodetection system to select the operating wavelength in the visible range. The system was initially evaluated using solutions dyes based on methyl red, methylene blue and later to determinate fluoride concentrations in groundwater samples. The results were comparable with those obtained with a commercial instrument. The device allowed decreasing instrumentation size, and reagents and energy consumption, which achieved significant advantages for an in-situ and real-time in a portable analytical system. With the implementing of other nodes, a wireless sensors network could be achieved with an application for internet of things IoT to generate and process analytical data. [Display omitted] • A 3D printing opto-microfluidic autonomous analyzer was developed using additive manufacturing technology. • The system allows defining three wavelengths of operation to photometric applications in environmental monitoring. • The analyzer presented a level of automation and portability not previously reported in devices for similar applications. • The 3D printing had advantages such as rapid prototyping, low cost, reduced size and the designs complex microfluidics. • The automation process was executed by wireless communication for measurements insitu, real time and application in IoT. [ABSTRACT FROM AUTHOR]

A selective determination method for Iron (Fe) ion in tap water has been developed by solvent extraction, followed by reversed phase HPLC with photometric detection. The Fe(III) ion was quantitatively extracted into chloroform over the pH range of 3.2 to 4.3 as 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine (DHOB) chelate. Job's method indicated that the Fe-DHOB chelate composition was Fe(DHOB)3. The molar absorptivity of the Fe-DHOB chelate was calculated as 7.6 × 103 at 430 nm. The extracted Fe-DHOB chelate was then separated on a phenyl column with an eluent of methanol/water/0.05 M DHOB (40:20:40, v/v) and detected at 500 nm. The correlation coefficients of the calibration curves obtained with 5 mL Fe standards were about 0.999 over the range of 10 ng/mL (ppb) to 10 µg/mL (ppm). The detection limit of the Fe ion in 5 mL water was estimated as 7 ppb, which corresponded to 3 times the standard deviation of the blank peak area. Effects of foreign ions on the determination of 0.2 ppm Fe ion were investigated with 57 metal ions. Almost none of the ions interfered, except for V(V), Sn(II), and Ti(IV) ions. The recovery with a spiked tap water sample for 0.5 ppm Fe ion (N = 4) was 99.2 ± 0.9%. [ABSTRACT FROM AUTHOR]

A determination method for palladium (Pd) ion in river water has been developed by reversed phase HPLC. The Pd(II) ion was quantitatively extracted into benzene from an acidic solution as 5-methyl-1, 3, 4-thiodiazole-2-thiol (MTT) chelate. The extracted Pd-MTT chelate was then separated on a phenyl ethyl column with an eluent of methanol/water/0.01 mol/L MTT (90:10:0.5, v/v) and detected at 270 nm. The correlation coefficients of the calibration curves obtained with 5 mL Pd standards were more than 0.999 over the range of 10 ng/mL (ppb) to 50 µg/mL (ppm). The detection limit of the Pd ion in 5 mL of water was estimated as 10 ppb by a signal to noise ratio of 3. Relative standard deviations of peak areas (N = 6) for 5, 0.5, and 0.05 ppm Pd standards were 1.5, 1.3, and 0.9%, respectively. The recoveries with a spiked river water sample for 5, 0.5, and 0.05 ppm Pd ion (N = 6) were 99.9 ± 1.0%, 99.5 ± 0.8%, and 94.0 ± 1.1%. Effects of foreign ions on the determination of 0.2 ppm Pd were investigated with 57 metal ions. Almost none of the ions interfered except for Cu(II), Ag(I), Ni(II), Cd(II), Co(II), and Ti(IV) ions. [ABSTRACT FROM AUTHOR]

A selective determination method for palladium (Pd) ion in river water by reversed-phase HPLC has been developed. The Pd ion was quantitatively extracted into 4-methyl-2-pentanone over the pH range of 0.5 to 4 as 5-chloro-2-mercaptobenzothiazole (CMBT) chelate. Job's method indicated that the Pd-CMBT chelate composition was Pd(CMBT)2. The molar absorptivity of the Pd chelate was determined as 1.58 × 10³ at 440 nm. The extracted Pd-CMBT chelate was then separated on a phenyl column with an eluent of methanol/2-propanol/1-hexanol/0.1 mol/L CMBT (40 : 50 : 9 :1, v/v) and detected at 440 nm. The correlation coefficients of the calibration curves obtained with 5 mL Pd standards were more than 0.999 over the range of 10 ng/mL (ppb) to 10 μg/mL (ppm). The detection limit of the Pd ion in 5 mL water was estimated as 5 ppb by a signal to noise ratio of 3. Relative standard deviations of peak areas (N=6) for 1 and 0.1 ppm Pd standards were 0.8 and 1.1%, respectively. The recoveries with a spiked river water sample for 5, 0.5, and 0.05 ppm Pd ion (N=5) were 100 ± 1%, 98 ± 1%, and 98 ± 4%. Effects of foreign ions on the method were investigated with 57 metal ions. Almost none of the ions interfered except for Hg(II), Ag(I), and Cu(II). [ABSTRACT FROM AUTHOR]

A selective determination method for nickel (Ni) ion in river water has been developed by solvent extraction, followed by reversed‐phase HPLC with photometric detection. The Ni(II) ion was quantitatively extracted into 4‐methyl‐2‐pentanone over the pH range of 7.5 to 9.0 as α‐furyl dioxime (FDO) chelate. The extracted Ni‐FDO chelate was then separated on an ODS column with an eluent of methanol/water (85:15, v/v) and detected at 435 nm. Job's method suggested that the Ni‐FDO chelate composition was Ni(FDO) 2 . The molar absorptivity of the Ni chelate was determined as 1.7×10 4 at 435 nm. The correlation coefficients of the calibration curves obtained with 5 mL Ni standards were more than 0.999 over the range of 1 ng/mL (ppb) to 1 µg/mL (ppm). The detection limit of the Ni ion in 5 mL water was estimated as 0.8 ppb, which corresponded to 3 times the standard deviation of the blank peak area. Relative standard deviations of peak areas (N=6) for 1 and 0.1 ppm Ni standards were less than 2%. The recoveries with a spiked river water sample for 500, 50, and 5 ppb Ni ion (N=5) were 100.5±1.5%, 101.2±1.5%, and 97.5±6.4%, respectively. Effects of foreign ions on the determination of 0.05 ppm Ni ion were investigated with 57 metal ions. Almost none of the ions interfered, except for Rh(III), Co(II), and Sn(II) ions. [ABSTRACT FROM AUTHOR]

Abstract: A novel HPLC method, using UV and fluorimetric serial detection, for the simultaneous determination of methotrexate (MTX), five disease marker pteridines, and the reference metabolic subproduct creatinine (CREA) in human urine was established. A previous oxidation process using 10−3 M KMnO4 (pH 5.0) and 35min of oxidation time was necessary to transform the analytes in the highly fluorescent pteridinic rings. CREA was not affected by the oxidative medium. Using Tris–HCl/NaCl buffer solution (pH 6.6) as mobile phase, MTX and the assayed pteridines were monitored by fluorescence at λ em =444nm and λ ex =280nm and creatinine was monitored by absorption measurements at λ abs =230nm. All components were well resolved in approximately 7min. Detection limits, according the criteria of Clayton and co-workers, were 10ngml−1 for MTX, less than 1ngml−1 for all of the pteridines, and 4μgml−1 for CREA. [Copyright &y& Elsevier]

A selective method for determination of iron ions in river water and iron in standard bovine liver has been developed by reversed-phase HPLC. An Iron (Fe) ion was quantitatively extracted into 4-methyl-2-pentanone at pH 3.0&PlusMinus;0.5 as N -benzoyl- N -phenylhydroxylamine (BPHA) chelate. The extracted Fe-BPHA chelate was then separated on a ODS column with an eluent of methanol/water/0.2 mol/L BPHA (78:21:1), and detected at 443 nm. The correlation coefficients of the calibration curves obtained with 5 mL Fe standards were more than 0.999 over the range of 10 ng/mL (ppb) to 10 µg/mL (ppm). The detection limit of Fe ion in 5 mL water was 2 ppb, which corresponded to 3 times the standard deviation of the blank peak area. Relative standard deviations of peak areas (N=5) for 5, 0.5, and 0.05 ppm Fe standards were 0.9, 0.8, and 0.9%, respectively. Analytical results of Fe ion in river water obtained by the presented method, showed good agreement with those by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Fe concentration in standard bovine liver was determined to be 193 µg/g, which was coincident with the reference value (194&PlusMinus;20 µg/g). Effects of foreign ions on the method were investigated with 55 metal ions. Almost none of the ions interfered, except for V(V), Ti(IV), and Sn(II). [ABSTRACT FROM AUTHOR]

A dynamic system for the continuous leaching of Cr(VI) from sediment and soil based on both microwave assistance and iterative change of the flow direction of the extractant through the sample cell has been developed. The microwave-assisted extractor has been coupled to a photometric detector through a flow injection interface in order to develop a fully automated method. The Cr(VI) extracted was monitored after derivatization with 1,5-diphenylcarbazide. Two approaches are proposed which differ in the inclusion of a preconcentration minicolumn packed with a strong anion exchange resin. A 0.04 M ammonium buffer solution was used as extractant and 0.2 g of sample—river sediment spiked with 50 and 5 μg g-1 for the method without preconcentration (method A) and with preconcentration (method B)—was subjected to 8–14 min of 300 W microwave-assisted extraction. The within-laboratory reproducibility and repeatability were 2.6 and 1.9 for method A, and 4.0 and 2.6 for method B. The proposed methods have been compared with the reference EPA method 3060/7196. [Copyright &y& Elsevier]

A reverse flow injection method (rFIA) based on the Winkler titration chemistry, is reported for the determination of dissolved oxygen (DO) in natural waters. Manganese(II) sulfate is injected into a continuously flowing stream of sample and subsequently merges with a reagent stream of sodium hydroxide and sodium iodide. Manganese(II) hydroxide that is formed reacts with DO in the sample to form an oxidized manganese hydroxyoxide floc. Addition of 10% sulfuric acid dissolves this floc, and under acidic conditions, the triiodide ion formed is detected by photometry in a flow through cell at a wavelength of 440 nm. The method is rapid (48 measurements per h), repeatable (R.S.D. ca. 3%, n=3), and has a calculated detection limit of 0.25 mg l−1 (P=0.001). No interference from nitrite or ferrous ions was observed at concentrations typically found in natural waters. The method has been successfully applied to on-line measurement of DO in sediment respiration reactors. [Copyright &y& Elsevier]

The design, construction and validation of a compact, portable flow injection analysis (FIA) instrument for underway analysis of phosphate in marine waters is described. This portable system employs gas pressure for reagent propulsion and computer controlled miniature solenoid valves for precise injection of multiple reagents into a flowing stream of filtered sample. A multi-reflection flow cell with a solid state LED photometer is used to detect filterable reactive phosphate (0.2 μm) as phosphomolybdenum blue. All the components are computer controlled using software developed using the Labview™ graphical programming language. The system has the capacity for sample throughput of up to 380 phosphate analyses per hour, but in the mode described here was operated at 225 analyses per hour. Under these conditions, the system exhibited a detection limit of 0.15 μM, reproducibility of 1.95 % RSD (n=9) and a linear response (r2=0.9992) when calibrated in the field with standards in the range 0.81–3.23 μM. The system was evaluated for the mapping of phosphate concentrations in Port Phillip Bay, south eastern Australia, and during the course of a 150 km cruise, 542 analyses were performed automatically. In general, good agreement was observed between analyses obtained using the portable FIA system and those obtained from manual sampling and laboratory analysis. [Copyright &y& Elsevier]