Acetate Buffer Medium Research Articles

DFT and electrochemical determination of Hg2+ and Pb2+ in water using polyaniline–quinoxaline composite modified GCE electrode

In this study, we designed and synthesized a new class of donor–acceptor conjugated polymers containing the polyaniline-quinoxaline [Acenaptho [1, 2 -b] quinoxalin-9-amine] (PAni-QUA) composite, and we subsequently utilized it as an electrochemical sensor to detect Hg2+ and Pb2+ ions with good selectivity and sensitivity. Energy dispersive X-ray analysis spectroscopy (EDAX), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and UV–Vis spectroscopy (UV–Vis) were employed to analyze the structural and morphological characteristics of the resulting composite. The electrochemical characteristics of the electrode modifiers were analyzed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Several sensitivity-influencing factors, including chemical and electrochemical parameters like pH and the impact of the supporting electrolyte medium, were also identified to improve the efficiency of the developed sensor. In the presence of different hazardous metal ion species, the interference ability of the proposed sensor was also examined. They were also used to conduct individual and simultaneous sensing studies of various metal ions in different supportive electrolyte media utilizing the differential pulse voltammetry technique (DPV). The PAni-QUA composite modified GCE sensor shows remarkable selectivity and sensitivity towards Hg2+ and Pb2+ ions over the other heavy metal ions in 1 to 20 µM ranges, respectively. The detection limits (3σ/m) were 1.28 nM and 5.91 nM for Hg2+ and Pb2+ ions. Density Functional Theory (DFT) was used in the present study to accomplish the adsorption mechanism of the suggested sensors. The DFT calculation demonstrated that the PAni-QUA composite was formed with a lower band gap energy than QUA and DD PAni. These results showed that the suggested sensor (PAni-QUA) had the lowest detection limit in the acetate buffer medium compared to the specified electrolyte media. Based on these findings, it is possible to use this technology to identify harmful metal ions (Hg2+ and Pb2+) with high sensitivity in real water samples.

An electrochemical voltammetric response of Hg2+ and Pb2+ ions using polyaniline-benzothiazole composite modified GCE electrode: Synthesis, characterization and quantum chemical calculation

An efficient electrochemical sensor based on polyaniline-benzothiazole [(3,5-bis (benzo[d]thiazol-2-yl)-[1,1–biphenyl]-4-ol)] (PAni-BEN) composite was designed and synthesized in this study, and it was employed as an electrochemical sensor to detect Hg2+ and Pb2+ ions with good selectivity and sensitivity. Fourier transform-infrared spectroscopy, UV–Vis spectroscopy, scanning electron microscopy, and energy dispersive X-ray analysis spectroscopy were employed to examine the morphology and structure of the produced composite. The electrochemical characteristics of the electrode modifiers were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Also, they were employed to perform both individual and simultaneous sensing studies of various metal ions using the differential pulse voltammetry technique (DPV) in a different supporting electrolyte (acetate buffer (pH 5), phosphate buffer (pH 7), and 0.1 M HCl) mediums. The PAni-BEN composite modified GCE sensor shows remarkable selectivity and sensitivity towards Hg2+ and Pb2+ ions over the other heavy metal ions in 1 to 24.84 µM, respectively. The limits of detection (S/N = 3) were 1 nM and 4.6 nM for Hg2+ and Pb2+ ions. Density Functional Theory (DFT) was used in the present study to accomplish the adsorption mechanism of the suggested sensors. The DFT calculation demonstrated that the PAni-BEN composite was formed with a lower band gap energy than BEN and DD PAni. These findings showed that the suggested sensor (PAni-BEN), which may used to detect Hg2+ and Pb2+ ions, had the lowest detection limit in the acetate buffer medium compared to the proposed electrolyte medium.

Simple colorimetric assay using pectin hydrogel reagent coupled with camera-based photometry for trace arsenic determination.

Humans mainly ingest arsenic through contaminated drinking water, causing serious health effects. The World Health Organization (WHO) has set the permissible limit of arsenic in drinking water at 0.01 mg/L and concentrations should be regularly determined to ensure a safe supply. In this study, a leucomalachite green (LMG) pectin-based hydrogel reagent was prepared that selectively reacted with arsenic over other metals including manganese, copper, lead, iron, and cadmium. Pectin, optimized at 0.2% (w/v), was used to form the hydrogel matrix. Arsenic reacts with potassium iodate in sodium acetate buffer medium to liberate iodine that then oxidizes LMG entrapped in pectin hydrogel to form a blue product. Camera-based photometry/ImageJ software was used to monitor the color intensity, eliminating the need for a spectrophotometer. The intensity of gray in the red channel was chosen as optimal for the red, green, and blue (RGB) analysis. The colorimetric assay revealed a dynamic detection range toward arsenic solution standards of 0.003-1 mg/L, covering the WHO recommendation of below 0.01 mg/L arsenic in drinking water. The assay gave recovery rates between 97 and 109% at a 95% confidence interval, with precision of 4-9%. Concentrations of arsenic in the spiked drinking water, tap water, and pond water samples monitored by the developed method agreed well with conventional inductively coupled plasma optical emission spectrometry. This assay showed promise for on-site quantitative analysis of arsenic in water samples.

СОРБЦИЯ ВОЛЬФРАМА(VI) НА МОДИФИЦИРОВАННОМ МОНТМОРИЛЛОНИТЕ

The aim of the work was to find conditions for the most adsorption of tungsten by a composite sorbent based on montmorillonite. It is shown that montmorillonite modified by magnetite particles adsorbs up to 99 % of tungsten from 10 mg/l W(VI) solution. The maximum difference in adsorption of W(VI) and Mo(VI) on the initial montmorillonite in an acetate buffer medium at pH = 5,4 was bserved. Desorption of tungsten from the surface of montmorillonite was 98 %.

Adsorption of Cr(VI) by Nanosized Rutile under the Action of UV Radiation

the properties of nanosized sorbents prepared by high-energy milling from microcrystalline powder of titanium dioxide of rutile modification have been studied. It was established that milling to an average crystallite size of ~30 nm and ultraviolet illumination significantly improved the sorption properties of rutile with respect to chromium compared with those of the starting material and the ability of Cr(VI) to be reduced to Cr(III) in its presence. The maximum removal of Cr(VI) from aqueous solutions with a concentration of 50 mg/L was achieved under UV illumination in an acetate buffer medium at pH 4–5 and a content of ground rutile of 16.7 g/L. A mechanism of adsorption was proposed.

Analytical optimization of liquid–liquid extractive spectrophotometric assessment protocol for tetravalent platinum: Analysis of environmental samples and cisplatin

An easy and reliable method is optimized for extractive spectrophotometric assessment of platinum(IV) with 4-(4′-nitrobenzylideneimino)-3-methyl-5-mercapto-1,2,4-triazole as an extractant. The basis of this method is the formation of red platinum(IV) complex with the above reagent in acetate buffer medium (pH 5.0) and extraction in chloroform. Good linearity with regression equation as y = 1.011 × 104 × + 0.002 having correlation coefficient (R2) of 0.998 over concentration up to 17.5 µg mL−1 of platinum(IV) was achieved with apparent molar absorptivity of 1.011 × 104 L mol−1 cm−1. The limit of detection (0.22 µg mL−1), limit of quantification (0.73 µg mL−1) and Sandell’s sensitivity (0.0193 µg cm−2) were also estimated. The interference of various cations was removed by using proper masking agents and consequently by using EDTA and citrate to mask certain transition metals, the method becomes highly specific for platinum(IV), including the effects of platinum group metals. The method is effectively used for determination of platinum(IV) from environmental and real samples such as alloys, catalysts, thermocouple wire and pharmaceutical sample.

Method development for the voltammetric determination of nitrite in diverse matrices

Catalytic electroreduction of nitrite ion in presence of thioglycollic acid in ammonium acetate buffer medium shows the posiibility of devising an analytical method for determination of nitrite at low concentration. A wide linear range of 0.9 µg/ml to 9µg/ml was obtained. The limit of quantification was 0.7µg/ml using differential pulse polarography. The method has successfully been applied for the analysis of nitrite content in marine waters and industrial wastes.

WITHDRAWN: Synthesis, characterization, and cytotoxicity assessment of biotinylated carbon dots nanoparticles as camptothecin delivery system

Abstract Carbon dots (CDs) are one of the most highlighted carbon-based material for biological applications such as delivery of therapeutic payloads for cancer treatment mainly due to their excellent biocompatibility, low to no cytotoxicity, and unique optical properties. Camptothecin (CPT)-based drugs inhibit topoisomerase I, leading to destruction of DNA, and are currently being used clinically as important chemotherapeutic agents in treatment of cancer. However, different problems associated with cancer therapy hinder their anticancer activity. .In this work, we designed and synthesized two CPT prodrugs; compound I (CPT-biotin), compound II (CPT-CDs-biotin). These compounds are designed to selectivity deliver the active drug to the vitamin receptors overexpressed on tumor cell surface by using biotin as a navigational molecule. The smooth drug release from compound I and II via glutathione-triggered self-immolation of the disulfide linker and CDs used as nanocarriers in compound II. In vitro drug release of nanoparticles demonstrated acceptable stability in phosphate buffer saline (PBS) containing 100 μM GSH at pH 7.4, the accumulative drug release approximately 17.6%. However, in 10 mM GSH medium reached to 84.9% in acetate buffer medium at pH 5.8. In vitro cytotoxicity study (MTT assay) demonstrated that compound I showed higher inhibition ratios on biotin receptor overexpressed cell lines (MCF-7, HepG2) and lower cytotoxicity on normal cell lines (CHO). Compound II showed good activity against (MCF-7, HepG2), and much lower cytotoxicity on (CHO).

Spectrophotometric and Spectrofluorimetric Determination of Terazosin in Tablets by Eosin Y

Simple, sensitive and accurate two methods were described for the determination of terazosin. The spectrophotometric method (A) is based on measuring the spectral absorption of the ion-pair complex formed between terazosin with eosin Y in the acetate buffer medium pH 3 at 545 nm. Method (B) is based on the quantitative quenching effect of terazosin on the native fluorescence of Eosin Y at the pH 3. The quenching of the fluorescence of Eosin Y was measured at 556 nm after excitation at 345 nm. The two methods obeyed Beer’s law over the concentration ranges of 0.1-8 and 0.05-7 µg/mL for method A and B respectively. Both methods succeeded in the determination of terazosin in its tablets

Determination of Pb(II) and Cd(II) via anodic stripping voltammetry using an in-situ bismuth film electrode. Increasing the sensitivity of the method by the presence of Alizarin Red S

Using the differential pulse anodic stripping voltammetry technique and an in-situ bismuth film deposited on a glassy carbon electrode, a simple and sensitive method for rapid Pb(II) and Cd(II) quantification was developed. The effect of the presence of Alizarin Red S (ARS) was studied, and an increase in the sensitivity of the method was obtained. The developed method was compared to another reported method that uses a 0.1 mol L−1 acetate buffer medium (pH 4.5). The optimal experimental conditions are listed as follows: [CH3COOH]: 30.0 mmol L−1; [Bi(III)]: 0.75 mg L−1; [ARS]: 40.0 µmol L−1; [Fe(CN)64−]: 50.0 µmol L−1; Edep: −1.40 V; tdep: 60 s. Under these conditions, the detection limits were 0.16 and 0.09 µg L−1 and the linearity was maintained at values as great as 30.0 and 15.0 µg L−1 for Pb(II) and Cd(II), respectively. The effect of 35 foreign ions as possible interferents was studied. The method was validated using two certified reference materials (TMDW and TMDA-61.3) with satisfactory results. Finally, the method was applied for the analysis of four natural water samples.

The use of tetracyanoethylene as a photometric reagent in analysis of pharmaceutical preparations

A possibility of using tetracyanoethylene (TCNE) as a photometric reagent for determination of the dipyrone content in pharmaceuticals is considered. A photometric form was obtained in the aqueous phase in an acetate buffer medium (pH 3.13). The resulting π -complex revealed two absorption bands at (400 and 420) nm with molar absorption coefficients of 1.56 Ч 10 4 and 1.62 Ч 10 4 , respectively. Due to a high lability of the photometric reagent, the optical density of the complex thus formed must be measured immediately after preparation. The composition and possible mechanism of π -complex formation were determined using the methods of molar ratios and isomolar series: the active substance interacts with the reagent in a molar ratio 1:1. The calculated value of the stability constant of the formed π -complex was 1.42 Ч 10 6 . Proceeding from the obtained data, a spectrophotometric method of dipyrone determination in drugs is developed with a detection limit of 42.63 μg/ml (the error of determination being below 3.0%). The linear dependence of the analytical signal on the concentration of the active substance is observed in the range of 20 – 100 μg/ml. Testing of the spectrophotometric method for dipyrone determination was carried out on tablets and injection solutions manufactured in Russia. There is a good convergence between the results of dipyrone determination by the developed and arbitration methods (pharmacopoeia monograph 2.1.0003.15). The analysis revealed that the content of dipyrone in the dosage form corresponds to the declared. The developed technique is easy to use accessible in equipment and can be recommended for determination of dipyrone in conditions of a conventional analytical laboratory.

Kinetic and Mechanistic Studies on the Oxidation of DL-Aspartic Acid with Gold(III) in Aqueous and Micellar media

Kinetics of oxidation of DL-aspartic acid was studied at 30°C with Au(III) in sodium acetate–acetic acid buffer medium to investigate the mechanism of oxidation the presence and absence of nonionic micelle, Triton X-100. The rate of the reaction is fractional with respect to Asp and ionic strength has negligible effect. The rate of the reaction is inhibited by [Cl–] and [AuIII]. The reaction is accelerated initially by increase in pH and then showed a retardation over the value of 3.90, displaying that the rate depends on [H+]. This reaction is inhibited in the presence of Triton X-100. A mechanism involving zwitterionic species of aspartic acid and AuCl3OH– of oxidant has been proposed.

Multicomponent solid forms of the uric acid reabsorption inhibitor lesinurad and cocrystal polymorphs with urea: DFT simulation and solubility study.

Lesinurad (systematic name: 2-{[5-bromo-4-(4-cyclopropylnaphthalen-1-yl)-4H-1,2,4-triazol-3-yl]sulfanyl}acetic acid, C17H14BrN3O2S) is a selective uric acid reabsorption inhibitor related to gout, which exhibits poor aqueous solubility. High-throughput solid-form screening was performed to screen for new solid forms with improved pharmaceutically relevant properties. During polymorph screening, we obtained two solvates with methanol (CH3OH) and ethanol (C2H5OH). Binary systems with caffeine (systematic name: 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione, C8H10N4O2) and nicotinamide (C6H6N2O), polymorphs with urea (CH4N2O) and eutectics with similar drugs, like allopurinol and febuxostat, were prepared using the crystal engineering approach. All these novel solid forms were confirmed by XRD, DSC and FT-IR. The crystal structures were solved by single-crystal and powder X-ray diffraction. The crystal structures indicate that the lesinurad molecule is highly flexible and the triazole moiety, along with the rotatable thioacetic acid (side chain) and cyclopropane ring, is almost perpendicular to the planar naphthalene moiety. The carboxylic acid-triazole heterosynthon in the drug is interrupted by the presence of methanol and ethanol molecules in their crystal structures and forms intermolecular macrocyclic rings. The caffeine cocrystal maintains the consistency of the acid-triazole heterosynthons as in the drug and, in addition, they are bound by several auxiliary interactions. In the binary system of nicotinamide and urea, the acid-triazole heterosynthon is replaced by an acid-amide synthon. Among the urea cocrystal polymorphs, Form I (P-1, 1:1) consists of an acid-amide (urea) heterodimer, whereas in Form II (P21/c, 2:2), both acid-amide heterosynthons and urea-urea dimers co-exist. Density functional theory (DFT) calculations further support the experimentally observed synthon hierarchies in the cocrystals. Aqueous solubility experiments of lesinurad and its binary solids in pH 5 acetate buffer medium indicate the apparent solubility order lesinurad-urea Form I (43-fold) > lesinurad-caffeine (20-fold) > lesinurad-allopurinol (12-fold) ≃ lesinurad-nicotinamide (11-fold) > lesinurad, and this order is correlated with the crystal structures.

Spectrophotometric Determination of Ru(IV) Using 5-Hydroxyimino-4-imino-1,3-thiazolidin-2-one as a Novel Analytical Reagent

The interaction of Ru(IV) ions with a novel analytical reagent - 5-hydroxyimino-4-imino-1,3-thiazolidin-2-one, by spectrophotometric method was investigated. The complex is formed at pH 5.0 in acetate buffer medium after heating in the boiling water bath (~371 K) for 25 min. The complex has maximum absorption at 350 nm and is stable for 24 h. Beer's law is valid over the concentration range of 0.5-6.1 μg mL-1 for Ru(IV). The molar absorptivity at μ = 350 nm is 6.21 × 103 L mol-1 cm-1. The limit of detection of this method is 0.2 μg mL-1. The interfering effect of various cations and anions on the spectrophotometric determination of the Ru(IV) were investigated. The proposed method was successfully applied to the determination of Ru(IV) in alloys.

Recycling of rare earth elements from FeNdB-Magnets via solid-state chlorination

Recycling of rare earths from magnetic alloys such as Fe14Nd2B is a widely studied field of research. However, with rare earth metal prices falling, leaching of magnet materials with mineral acids has become economically unfeasible. In order to circumvent high expenditures, solid-state chlorination offers an attractive alternative. Chlorination takes place via partial decomposition of NH4Cl at temperatures between 225 and 325 °C. Subsequently, dry HCl gas reacts with the magnet material in a rotary kiln to form water-soluble metal chlorides, which are dissolved in an acetic acid buffer medium. Here, spent Fe14Nd2B-magnets from a wind turbine served as starting material. For the first time, the solid-state chlorination process was optimised with the aid of statistical experimental design considering binary factor correlations. The global optimum was determined by varying the amount of NH4Cl, temperature, residence time and buffer mass in the subsequent leaching step. The maximum rare earth yield amounted to 84.1%. For dissolving rare earths quantitatively, the unreacted residue requires recirculation. In this respect, solid-state chlorination was compared to an optimised state-of-the-art process employing hydrochloric acid for digestion. The solid-state chlorination process was found to be superior in that consumption of chemicals was reduced by 45%, no costs for neutralisation incur and chemical costs were decreased by at least 51%.

Determination of amino acids in gym supplements using digital images and paper platform coupled to diffuse reflectance spectroscopy and USB device

New and reliable methodologies are described for the determination of amino acids in gym supplements, offering rapid and clean analysis, with low generation of waste. The proposed methods are based on the reaction between ninhydrin and amino acids in acetate buffer medium (pH 4.75). Experimental design tools were used to optimize the analytical conditions. The linear range obtained for both methodologies was 20.0–350.0 mg L−1. The detection (LOD) and quantification (LOQ) limits were 6.2 and 21.0 mg L−1, respectively, for diffuse reflectance using a paper filter with hydrophobic barriers to increase the sensitivity and homogeneity of the colored product, and 5.7 and 18.8 mg L−1, respectively, for digital image analysis. A USB device was used in the diffuse reflectance spectroscopy method for heating the filter paper, providing speed and portability for the developed methodology. The methods showed good results when applied to gym supplement samples, with recoveries in the range 93.1–110%.

Structural Changes of Poplar Wood Lignin in Hydrothermal pretreatment in Acetic Acid-Sodium Acetate system

Hydrothermal pretreatment of poplar wood chips was performed in an acetic acid/sodium acetate buffer medium. To characterize the structural changes of lignin in the pretreatment process, milled wood lignin (MWL) was isolated from both the un-treated and treated poplar wood chips, and analyzed by 1 H-NMR, 13 C-NMR, 31 P-NMR, FT-IR, and GPC-MALLS. Results showed that the lignin in the pretreated wood chips had more phenolic OH groups, less aliphatic OH groups, higher molecular weight, and narrower polydispersity, in comparison with the lignin in the un-treated wood. The acetic acid-sodium acetate buffer pretreatment facilitated the removal of -OCH 3 groups and the cleavage of the inter-unit linkages of β-O-4 bond in the lignin. Furthermore, the re-polymerization of lignin in the acetic acid-sodium acetate buffer pretreatment was found to be less than that in autohydrolysis.

Mediator-free simultaneous determination of acetaminophen and caffeine using a glassy carbon electrode modified with a nanotubular clay

The authors describe a voltammetric method for the simultaneous determination of acetaminophen (ACOP) and caffeine (CAF) using a glassy carbon electrode modified with a Nafion® protected halloysite nanotubular clay (GCE). Enhanced electrocatalytic oxidation behavior was observed at pH 4.5 in acetate buffer medium, with oxidation peak potentials of + 0.21 V for ACOP and + 1.0 V for CAF. The peak potential window (~ 800 mV) is quite large and hence differential pulse voltammetry (DPV) can be applied for simultaneous determination of both analytes. The calibration plots of ACOP and CAF are linear in the concentration ranges from 0.6 μM to 14 μM and 0.6 μM to 20 μM, and the detection limits are 1.1 × 10−8 M and 1.73 × 10−7 M, for ACOP and CAF, respectively. The method was applied to the determination of both analytes in drug formulations and human urine samples.

Study of behaviour of Ni(III) macrocyclic complexes in acidic aqueous medium through kinetic measurement involving hydrogen peroxide oxidation and DFT calculations

The Cu(II) ion-catalysed kinetics of oxidation of H2O2 by [Ni IIIL] [where L = L1 (cyclam) and L2 (1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)] was studied in the pH range of 3.6–5.6 in acetic acid-acetate buffer medium at 25°C in the presence of sulphate ion. The ionic strength (I) was maintained at 0.5 M (NaClO4). The rate constants showed an inverse acid dependence and [Ni III L 2] was observed to be more stable than [Ni III L 1]. The rate of the reaction of both complexes with hydrogen peroxide shows contrasting behaviour at pH > 2.5 when compared to the same reaction in perchloric acid medium. DFT calculations performed on the complexes [Ni III L 1(SO4)(OAc)] and [Ni III L 2(SO4)(OAc)] reveal that both the acetate and sulphate ligands are axially coordinated to the metal centre. In addition, there is strong hydrogen bonding between the axial ligand and NH hydrogen of the macrocyclic ligand. The computed covalent bond orders in the aqueous medium predict that the acetate forms stronger coordinate bond with Ni ion than the sulphate ligand. The hydroxyl group present in one of the pendant groups of L2 forms a strong hydrogen bond with the sulphate ligand which leads to additional stability in [Ni III L 2(SO4)(OAc)]. The Cu(II) ion-catalysed kinetics of oxidation of H2O2 by [NiIIIL] [where L = L1 (cyclam) and L2 (1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)] was studied in the pH range of 3.6-5.6. The structure and bonding patterns of the [NiIIIL1(SO4)(OAc)] and [NiIIIL2(SO4)(OAc)] were studied using DFT calculations.

The influence of diesel-truck exhaust particles on the kinetics of the atmospheric oxidation of dissolved sulfur dioxide by oxygen.

The automobile exhausts are one of the major sources of particulate matter in urban areas and these particles are known to influence the atmospheric chemistry in a variety of ways. Because of this, the oxidation of dissolved sulfur dioxide by oxygen was studied in aqueous suspensions of particulates, obtained by scraping the particles deposited inside a diesel truck exhaust pipe (DEP). A variation in pH showed the rate to increase with increase in pH from 5.22 to about ∼6.3 and to decrease thereafter becoming very slow at pH = 8.2. In acetate-buffered medium, the reaction rate was higher than the rate in unbuffered medium at the same pH. Further, the rate was found to be higher in suspension than in the leachate under otherwise identical conditions. And, the reaction rate in the blank reaction was the slowest. This appears to be due to catalysis by leached metal ions in leachate and due to catalysis by leached metal ions and particulate surface both in suspensions. The kinetics of dissolved SO2 oxidation in acetate-buffered medium as well as in unbuffered medium at pH = 5.22 were defined by rate law: k obs = k 0 + k cat [DEP], where k obs and k 0 are observed rate constants in the presence and the absence of DEP and k cat is the rate constant for DEP-catalyzed pathway. At pH = 8.2, the reaction rate was strongly inhibited by DEP in buffered and unbuffered media. Results suggest that the DEP would have an inhibiting effect in those areas where rainwater pH is 7 or more. These results at high pH are of particular significance to the Indian subcontinent, because of high rainwater pH. Conversely, it indicates the DEP to retard the oxidation of dissolved SO2 and control rainwater acidification.