Organic interferences and their elimination in the 2,4-xylenol spectrophotometric method for nitrate

The 2,4-xylenol spectrophotometric method for nitrate involves formation of 6-nitro-2,4-xylenol, which is steam-distilled into an ammonia—water—isopropanol mixture. The yellow color of the ammonium salt of 6-nitro-2,4-xylenol is measured at 455 nm. A detailed study of the possible interferences from 123 representative organic compounds is described; 61 compounds interfered (when present in amounts of 0.1 g in the original sample). The interfering compounds can be classified according to their mode of interference: (1) compounds that are readily nitrated or oxidized by nitrate in the sulfuric acid medium used cause low results; (2) compounds containing the ONO₂ group that hydrolyze to nitrate cause high results; (3) compounds that steam-distil to produce colored solutions; (4) compounds that steam-distil to produce turbid solutions; (5) compounds that hydrolyze, either in water or sulfuric acid solution, to produce inorganic ions or compounds (e.g. Cl^-, S^2-, and H₂O₂) that repress the color development. Three procedures are described for the elimination of the interferences: (1) oxidation of the organic compound with permanganate, reduction of the excess of permanganate with hydrogen peroxide, and destruction of the peroxide by boiling in the presence of Fe(III) catalyst (this is unsuitable for organic compounds containing nitrogen, as there is invariably some oxidation to nitrate); (2) extraction of interfering organic compounds with methyl isobutyl ketone; (3) precipitation—adsorption method involving treatment with zinc sulfate and sufficient sodium hydroxide to precipitate most of the zinc as zinc hydroxide, addition of 3 g of activated carbon, digestion at 55–65°C for 20 min. cooling, dilution, and filtration. Method (3) is applicable to all organic compounds tested except formaldehyde. The amount of organic compound used to test the methods was normally 0.25 g in the solution being treated.     

Fabrication of a Sensitive Cholesterol Biosensor Based on Cobalt‐oxide Nanostructures Electrodeposited onto Glassy Carbon Electrode

Electrodeposited cobalt oxide (CoOx) nanomaterials are not only used for immobilization of cholesterol oxidase (ChOx) but also as electron transfer mediator for oxidation of H₂O₂ generated in the enzymatic reaction. Voltammetry and flow injection analysis (FIA) were used for determination of cholesterol. FIA determination of cholesterol with biosensors yielded a calibration curve with the following characteristics: linear range up to 50 μM, sensitivity of 43.5 nA μM^?1 cm^?2 and detection limit of 4.2 μM. The apparent Michaelis‐Menten constant and the response time of the biosensor are 0.49 mM and 15 s, respectively. This biosensor also exhibits good stability, reproducibility and long life time.     

Reactions of Copper(II) Chloride in Solution: Facile Formation of Tetranuclear Copper Clusters and Other Complexes That Are Relevant in Catalytic Redox Processes

Mixing CuCl₂ ? 2 H₂O with benzylamine in alcoholic solutions led to an extremely colorful chemistry caused by the formation of a large number of different complexes. Many of these different species could be structurally characterized. These include relatively simple compounds such as [Cu(L¹)₄Cl₂] (L¹=benzylamine) and (HL¹)₂[CuCl₄]. Most interestingly is the easy formation of two cluster complexes, one based on two cluster units Cu₄OCl₆(L¹)₄ connected through one [Cu(L¹)₂Cl₂] complex and one based on a cubane‐type cluster ([Cu₄O₄](C₁₁H₁₄)₄Cl₄). Both clusters proved to be highly reactive in a series of oxidation reactions of organic substrates by using air or peroxides as oxidants. Furthermore, it was possible to isolate and structurally characterize ([Cu(L¹)Cl]₃ and [Cu(benz₂mpa)₂]CuCl₂ (benz₂mpa=benzyl‐(2‐benzylimino‐1‐methyl‐propylidene)‐amine), two copper(I) complexes that formed in solution, demonstrating the high redox activity of the cluster systems. In addition, it was possible to solve the molecular structures of the compounds Cu₄OCl₆(MeOH)₄, [Cu(MeOH)₂Cl₂], [Cu(aniline)₂Cl₂], and an organic side product (HC₁₃H₁₉NOCl). In fact all determined structures are of a known type but the chemical relation between these compounds could be explained for the first time. The paper describes these different compounds and their chemical equilibria. Some of these complexes seem to be relevant in catalytic oxidation reactions and their reactivity is discussed in more detail.     

过硫酸盐活化高级氧化新技术

过硫酸盐在热、光、过渡金属催化等条件激活下产生强氧化性的硫酸根自由基·SO₄^-。基于·SO₄^-的过硫酸盐活化“高级氧化技术”在环境污染治理领域的应用,是刚刚发展起来的崭新的研究方向,具有广阔的应用前景。本文在分析其基本原理的基础上,综述了过硫酸盐活化技术在国内外土壤地下水有机污染原位修复、难降解有机废水处理等环境污染治理方面的研究进展,并就存在问题进行了研究展望。     

A Simple Strategy for Simultaneous Determination of Paracetamol and Caffeine Using Flow Injection Analysis with Multiple Pulse Amperometric Detection

In this work, we report a simple and novel strategy for simultaneous analysis using flow injection analysis with multiple pulse amperometric (FIA‐MPA) detection. The proposed strategy was successfully used for simultaneous determination of paracetamol and caffeine (model analytes) in pharmaceutical formulations. A sequence of potential pulses (waveform) was selected in such a way that PA is selectively oxidized at E₁ (+1.20 V/50 ms) and both compounds (PA+CA) are simultaneously oxidized at E₂ (+1.55 V/50 ms); hence, current subtraction (using a correction factor) can be used for the selective determination of CA. The proposed FIA method is simple, cheap, fast (140 injections h^?1), and present selectivity for the determination of both compounds in pharmaceutical samples, with results similar to those obtained by HPLC at a 95 % confidence level.     

Liquid chromatography/mass spectrometry stable isotope analysis of dissolved organic carbon in stream and soil waters

A commercial interface coupling liquid chromatography (LC) to a continuous‐flow isotope ratio mass spectrometry (CF‐IRMS) instrument was used to determine the δ¹³C of dissolved organic carbon (DOC) in natural waters. Stream and soil waters from a farmland plot in a hedgerow landscape were studied. Based on wet chemical oxidation of dissolved organics the LC/IRMS interface allows the on‐line injection of small volumes of water samples, an oxidation reaction to produce CO₂ and gas transfer to the isotope ratio mass spectrometer. In flow injection analysis (FIA) mode, bulk DOC δ¹³C analysis was performed on aqueous samples of up to 100 μL in volume in the range of DOC concentration in fresh waters (1–10 mg C.L^–1). Mapping the DOC δ¹³C spatial distribution at the plot scale was made possible by this fairly quick method (10 min for triplicate analyses) with little sample manipulation. The relative contributions of different plot sectors to the DOC pool in the stream draining the plot were tentatively inferred on the basis of δ¹³C differences between the hydrophilic and hydrophobic components. Copyright © 2011 John Wiley & Sons, Ltd.     

Analytical methods for the speciation of selenium compounds: a review

Selenium, like sulphur, exists in the environment in several oxidation states and as a variety of inorganic and organic compounds. Dissolved inorganic selenium can be found in natural waters as selenide Se (–II), as colloidal elemental selenium Se (0), as selenite anions HSeO ₃ ^– and SeO ₃ ^2– i.e. Se (+IV) and as the selenate anion (SeO ₄ ^2– ) i.e. Se (+VI). Organic forms of selenium that may be found in organisms, air or in the aqueous environment, are volatile (methylselenides) or non volatile (trimethylselenonium ion, selenoamino acids and their derivatives). Knowledge of the different chemical forms and their environmental and biomedical distribution is important because of the dependence of bioavailability and toxicity on speciation. This paper reviews the different analytical methods used for the speciation of selenium compounds, with special attention to inorganic selenium and organoselenium species.     

Study on photocatalytic oxidation for determination of the low chemical oxygen demand using a nano-TiO2-Ce(SO4)2 coexisted system

A new photocatalytic system, nano-TiO₂-Ce(SO₄)₂ coexisted system, which can be used to determine the low chemical oxygen demand (COD) is described. Nano-TiO₂ powders is used as photocatalyst in this system. The measuring method is based on direct determination of the concentration change of Ce(IV) resulting from photocatalytic oxidation of organic compounds. The mechanism of the photocatalytic oxidation for COD determination was discussed and the optimum experimental conditions were investigated. Under the optimum conditions, a good calibration graph for COD values between 1.0 and 12 mg l⁻¹ was obtained and the LOD value was achieved as low as 0.4 mg l⁻¹. When determining the real samples, the results were in good agreement with those from the conventional methods.     

Fluorometric Determination of Fructose, Glucose, and Sucrose Using Zirconyl Chloride

Zirconyl chloride upon hydrolysis in water to form Zr(OH)⁺ has been found to react to form a fluorescent derivative with not only a ketose such as fructose but also a hexose such as glucose and the disaccharide sucrose. When reaction conditions such as a temperature of 99°C and a time of 60 min are used, detection limits below 1 μg/mL are possible. All three zirconyl–sugar derivatives show very similar absorbance and fluorescence spectra, indicating a common mechanism involving formation of an enediol which can be complexed with ZrOH⁺ is likely. Because the reactivity order is glucose < sucrose < fructose, the reaction can be made selective for fructose at a lower reaction temperature and time such as 60°C at 5 min. Because interference from ascorbic acid and caffeine is also avoided, the fluorescent determination of fructose in soft drink samples after simply a dilution step is possible. We have also employed this reaction for flow injection analysis (FIA) using a polystyrene–divinylbenzene-packed HPLC column as a mixing device. Using a 0.01 M HClO₄ with 1% zirconyl chloride carrier, we obtained a linear calibration curve from 2 to 30 μg/mL with a correlation coefficient of 0.994. A detection limit less than 2 μg/mL was possible. A comparison of results for the FIA of soft drinks with the enzymatic method involving fructose-5-dehydrogenase confirmed the FIA method was quite specific for fructose.     

Minimization of Interferences in Flow Injection Amperometric Glucose Biosensor Based on Oxidation of Enzymatically‐produced H2O2

One of the major problems in amperometric biosensors based on detection of H₂O₂ produced by enzymatic reaction between oxidase enzymes and substrate is the interference of redox active compounds such as ascorbic acid (AA), dopamine (DA) and uric acid (UA). To minimize these interferences, sodium bismuthate was used for the first time as an insoluble pre‐oxidant in the flow injection (FI) amperometric glucose biosensor at a Glucose oxidase (GOx) immobilized Pt/Pd bimetallic modified pre‐anodized pencil graphite electrode (p.PGE). In this context, these interfering compounds were injected into a flow injection analysis (FIA) system using an injector which was filled with NaBiO₃. Thus, these interferents were converted into their redox inactive oxidized forms before reaching the electrode in the flow cell. While glucose was not influenced by the pre‐oxidant in the injector, the huge oxidation peak currents of the interferents decreased significantly in the biosensor. FI amperometric current time curves showed that the AA, DA and UA were minimized by 96 %, 86 %, and 98 % respectively, in the presence of an equivalent concentration of interferences in a 1.0 mM glucose solution. The proposed FI amperometric glucose biosensor exhibits a wide linear range (0.01–10 mM, R²=0.9994) with a detection limit of 2.4×10^?3 mM. Glucose levels in the artificial serum and two real samples were successfully determined using the fabricated FI amperometric biosensor.     

Enhancing selectivity in spectrofluorimetric determination of tryptophan by using graphene oxide nanosheets

Reaction of formaldehyde with amino acids followed by oxidation with hydrogen peroxide to produce a fluorophore Norharman product is well known and was used for the spectrofluorimetric determination of l-tryptophan (Trp). This study aimed to use graphene oxide (GO) to enhance the selectivity and sensitivity of Trp in presence of other amino acids and possible interfering compounds. Different parameters such as pH, temperature, incubation time, and concentrations of formaldehyde, H₂O₂ and GO were studied to optimize the condition of determination. Experimental data showed that the maximum fluorescence intensity was achieved in pH 7.0–9.0 phosphate buffer mixed with 7–10% (v/v) formaldehyde and 1–2% (v/v) H₂O₂ as oxidizing agent at 60 ?C for 1 h. On the basis of calibration curve of various concentrations of Trp in the presence of 20 μg mL⁻¹ GO, the lower limit of detection (LOD) of Trp was determined as 0.092 nmol mL⁻¹ and the lower limit of quantification (LOQ) was 0.3 nmol mL⁻¹. The selectivity of Trp in presence of other amino acids and possible interfering compounds were studied with and without GO. The data obtained after inner filter effect corrections revealed that the selectivity of Trp in presence of amino acids and other possible interfering agents was improved in the range of 76–96%, compared with that in absence of GO. The enhancement of selectivity in the presence of GO indicates that the Trp and other amino acid and possible interfering compounds were adsorbed by GO, and the selective uptaking of Trp-by the reaction with formaldehyde followed by oxidation with H₂O₂ at 60 ?C with high selectivity and sensitivity was achieved successfully.     

Simple and Fast Determination of Warfarin in Pharmaceutical Samples Using Boron‐doped Diamond Electrode in BIA and FIA Systems with Multiple Pulse Amperometric Detection

This paper proposes the use of the boron‐doped diamond electrode (BDDE) in flow and batch injection analysis (FIA and BIA) systems with multiple‐pulse amperometric (MPA) detection for the determination of warfarin (WA) in pharmaceutical formulations. The electrochemical behavior of WA obtained by cyclic voltammetry (CV) in 0.1 mol L⁻¹ phosphate buffer shows an irreversible oxidation process at +1.0 V (vs Ag/AgCl). The MPA was based on the application of two sequential potential pulses as a function of time on BDDE: (1) for WA detection at +1.2 V/100 ms and; (2) for electrode surface cleaning at −0.2 V/200 ms. Both hydrodynamic systems (FIA‐MPA and BIA‐MPA) used for WA determination achieved high precision (with relative standard deviations around 2 %, n =10), wide linear range (2.0−400.0 μmol L⁻¹), low limits of detection (0.5 μmol L⁻¹) and good analytical frequency (94 h⁻¹ for FIA and 130 h⁻¹ for BIA). The WA determination made by the proposed methods was compared to the official spectrophotometric method. The FIA‐MPA and BIA‐MPA methods are simple and fast, being an attractive option for WA routine analysis in pharmaceutical industries.     

Synthesis,characterization and catalytic activity of novel Co(II) and Pd(II)‐perfluoroalkylphthalocyanine in fluorous biphasic system; benzyl alcohol oxidation

Tetrakis[heptadecafluorononyl] substituted phthalocyanine complexes were prepared by template synthesis from 4‐(heptadecafluorononyloxy)phthalonitrile with Co(CH₃COO)^·₂H₂O or PdCl₂ in 2‐N, N‐dimethylaminoethanol. The corresponding phthalonitrile was obtained from heptadecafluorononan‐1‐ol and 4‐nitrophthalonitrile with K₂CO₃ in DMF at 50 °C. The structures of the compounds were characterized by elemental analysis, FTIR, UV–vis and MALDI‐TOF MS spectroscopic methods. Metallophthalocyanines are soluble in fluoroalkanes such as perfluoromethylcyclohexane (PFMCH). The complexes were tested as catalysts for benzyl alcohol oxidation with tert‐butylhydroperoxide (TBHP) in an organic–fluorous biphasic system (n‐hexane–PFMCH). The oxidation of benzyl alcohol was also tested with different oxidants, such as hydrogen peroxide, m‐chloroperoxybenzoic acid, molecular oxygen and oxone in n‐hexane–PFMCH. TBHP was found to be the best oxidant for benzyl alcohol oxidation since higher conversion and selectivity were observed when this oxidant was used. Copyright © 2008 John Wiley & Sons, Ltd.     

Fenton’s reagent for kinetic determinations

The use of the Fenton’s reagent (FR) (a mixture of H₂O₂ and Fe²⁺) for the kinetic determination of individual chemical species is proposed. The possibilities of the reagent arise from the oxidant power of intermediate species generated during the slow oxidation of Fe²⁺ by H₂O₂, but very few analytical applications of the reagent can be found. The oxidation of organic compounds (known as the Fenton reaction) is in fact an induced chain reaction that proceeds to an extension which is influenced by the reaction conditions. Experimental design has been used for optimization thinking of the analytical application. The pesticide atrazine has been used as analyte to test the analytical possibilities of the FR. Partial least squares regression (PLS), applied to reaction profiles between 206 and 270 nm, was used as algorithm to make the calibration model. Atrazine concentrations ranging from 0.46 to 13.4×10⁻⁵ M have been used for calibration, and mean errors under 2.5% both for calibration and validation have been found. Other classical methods of calibration such as those using absolute values of absorbance, initial rates, etc. gave poor results in the cases considered. According to the study of interferences, the main drawback of the reagent is the lack of selectivity, but some possible ways of improving it are discussed. The method was applied for the determination of atrazine in several commercial atrazine-based pesticide preparations. In general, good results were obtained when compared with those found by gas-liquid chromatography as a reference. Recovery studies also gave satisfactory results.     

Struktur und katalytische Eigenschaften von Molybdänoxid-Trägerkatalysatoren bei einigen Oxydationsreaktionen

Structure and Catalytic Properties of Molybdenum Oxide Supported Catalysts in Some Oxidation Reactions Molybdenum supported catalysts were prepared by using different precursor compounds such as Mo(π-C₃H₅)₄, [Mo(OC₂H₅)₅]₂, MoCl₅, (NH₄)₆Mo₇O₂₄, and their catalytic behaviour in some oxidation reactions was studied. During the preparation process, as a result of interaction between the molybdenum compound used and the support, different surface compounds with strongly differing catalytic properties have been formed. MoO₃ and supported catalysts with MoO₃ crystallites on the surface, catalyse the H₂ oxidation at temperatures above 400°C and the CO oxidation at temperatures of about 500°C. The reaction proceeds according to a redox mechanism. On surface compounds of molybdenum which exist on the surface if organic complexes are used as precursors, the catalytic H₂ oxidation occurs even at 100°C with a high reaction rate. The catalytic CO oxidation on these catalysts occurs at temperatures of about 300°C. An associative mechanism on coordinative unsaturated Mo^VI sites is discussed.     

The kinetics of oxidation of simple aliphatic sulphur compounds by potassium ferrate

Potassium ferrate (K₂FeO₄) is highly soluble in water and a very strong oxidizing agent^{(1, 2)}. Other properties include a strong bacteriacidal action which has been documented by Murmann and Robinson⁽¹⁾. These characteristics, and others, suggest that potassium ferrate would be useful in the advanced treatment of municipal waste water. The efficiency of oxidation of various organic compounds by potassium ferrate must be investigated before conclusions can be drawn.When K₂FeO₄ is placed into aqueous solution a purple colour is produced which disappears as K₂FeO₄ is reduced. At a spectrophotometric wavelength of 505 nm this affords a convenient method for measuring the decomposition kinetics of K₂FeO₄.Rate constants were obtained by algorithmic analysis of spectral absorbance data by the Cornell method⁽³⁾. This work will present a mechanism of reaction for oxidation of simple aliphatic sulphur compounds by potassium ferrate. The oxidation of simple aliphatic sulphur compounds produces the corresponding sulphoxide or sulphone^{(4, 5)} Compounds studied included dimethyl sulphoxide, diethylsulphide, dimethylsulphone, and 2,2-thiodiethanol.     

Oxidation State 10 Exists

In a recent paper, Wang et al. found an iridium‐containing compound with a formal oxidation state of 9. ⁵ This is the highest oxidation state ever found in a stable compound. To learn if this is the highest chemical oxidation state possible, Kohn–Sham density functional theory was used to study various compounds, including PdO₄²⁺, PtO₄²⁺, PtO₃F₂²⁺, PtO₄OH⁺, PtO₅, and PtO₄SH⁺, in which the metal has an oxidation state of 10. It was found that PtO₄²⁺ has a metastable state that is kinetically stable with a barrier height for decomposition of 31 kcal mol^?1 and a calculated lifetime of 0.9 years. All other compounds studied would readily decompose to lower oxidation states.     

Oxidation State 10 Exists

In a recent paper, Wang et al. found an iridium‐containing compound with a formal oxidation state of 9. ⁵ This is the highest oxidation state ever found in a stable compound. To learn if this is the highest chemical oxidation state possible, Kohn–Sham density functional theory was used to study various compounds, including PdO₄²⁺, PtO₄²⁺, PtO₃F₂²⁺, PtO₄OH⁺, PtO₅, and PtO₄SH⁺, in which the metal has an oxidation state of 10. It was found that PtO₄²⁺ has a metastable state that is kinetically stable with a barrier height for decomposition of 31 kcal mol⁻¹ and a calculated lifetime of 0.9 years. All other compounds studied would readily decompose to lower oxidation states.     

From the {FeIII2Ln2} Butterfly's Perspective: the Magnetic Benefits and Challenges of Cooperativity within 3 d–4 f Based Coordination Clusters

In this Review we discuss the tuning handles which can be used to steer the magnetic properties of Fe^III-4 f “butterfly” compounds. The majority of presented compounds were produced in the context of project A3 “Di- to tetranuclear compounds incorporating highly anisotropic paramagnetic metal ions” within the SFB/TRR88 “3MET”. These contain {Fe^III₂Ln₂} cores encapsulated in ligand shells which are easy to tune in a “test-bed” system. We identify the following advantages and variables in such systems: (i) the complexes are structurally simple usually with one crystallographically independent Fe^III and Ln^III, respectively. This simplifies theory and anaylsis; (ii) choosing Fe allows ⁵⁷Fe Mössbauer spectroscopy to be used as an additional technique which can give information about oxidation levels and spin states, local moments at the iron nuclei and spin-relaxation and, more importantly, about the anisotropy not only of the studied isotope, but also of elements interacting with this isotope; (iii) isostructural analogues with all the available (i. e. not Pm) 4 f ions can be synthesised, enabling a systematic survey of the influence of the 4 f ion on the electronic structure; (iv) this cluster type is obtained by reacting [Fe^III₃O(O₂CR)₆(L)₃](X) (X=anion, L=solvent such as H₂O, py) with an ethanolamine-based ligand L′ and lanthanide salts. This allows to study analogues of [Fe^III₂Ln₂(μ₃-OH)₂(L′)₂(O₂CR)₆] using the appropriate iron trinuclear starting materials. (v) the organic main ligand can be readily functionalised, facilitating a systematic investigation of the effect of organic substituents on the ligands on the magnetic properties of the complexes. We describe and discuss 34 {M^III₂Ln₂} (M=Fe or in one case Al) butterfly compounds which have been reported up to 2020. The analysis of these gives perspectives for designing new SMM systems with specific electronic and magnetic signatures     

Effects of exogenic chloride on oxidative degradation of chlorinated azo dye by UV-activated peroxodisulfate

Recently, the degradation of organic compounds in saline dye wastewater by sulfate radicals (SO₄⁻)-based advanced oxidation processes (AOPs) have attracted much attention. However, previous studies on these systems have selected non-chlorinated dyes as model compounds, and little is known about the transformation of chlorinated dyes in such systems. In this study, acid yellow 17 (AY-17) was selected as a model of chlorinated contaminants, and the degradation kinetics and evolution of oxidation byproducts were investigated in the UV/PDS system. AY-17 can be efficiently degraded (over 98% decolorization) under 90 min irradiation at pH 2.0–3.0, and the reaction follows pseudo-first order kinetics. Cl^‒ accelerated the degradation of AY-17, but simultaneously led to an undesirable increase of absorbable organic halogen (AOX). Several chlorinated byproducts were identified by liquid chromatography-mass spectrometry (LC–MS/MS) in the UV/PDS system. It indicates that endogenic chlorine and exogenic Cl^– reacted with SO₄⁻ to form chloride radicals, which are involved in the dechlorination and rechlorination of AY-17 and intermediates. The possible degradation mechanisms of AY-17 photooxidative degradation are proposed. This work provides valuable information for further studies on the role of exogenic chloride in the degradation of chlorinated azo dyes and the kinetic parameters in the PDS-based oxidation process.