Determination of sulphuric acid in process effluent streams using sequential injection titration

Sulphuric acid in process effluent streams from an electrorefining copper plant was analysed with a sequential injection (SI) titration system using sodium hydroxide as titrant. In the proposed SI titration system a base titrant, acid analyte and base titrant zone were injected sequentially into a distilled water carrier stream in a holding coil and swept by flow reversal through a reaction coil to the detector. The base zones contained bromothymol blue as indicator and the endpoint was monitored spectrophotometrically at 620 nm. The influence of carrier stream flow rate, acid and base zone volumes and titrant concentration on the linear range of the method was studied to obtain an optimum. A linear relationship between peak width and logarithm of the acid concentration was obtained in the range 0.006-0.178 mol l(-1) of H(2)SO(4) for a NaOH concentration of 0.002 mol l(-1). The results obtained for the SI titration of process samples were in good agreement with a standard potentiometric method with an RSD<0.75% and a sample frequency of 23 samples h(-1).     

The principles and theory of high-speed titrations by flow injection analysis

The highly reproducible concentration gradients formed between an injected sample zone and the carrier stream in flow injection analysis are exploited for titrations based on measuring the time span between points of identical gradient dispersion. Comparison of the experimental data with theoretical models, has made it possible to locate the position and physical dimension of a single mixing stage, which at medium dispersion of the sample zone allows the entire titration cycle, including sampling and washout periods, to be completed within less than 30 s. The capability of this high-speed titration technique is demonstrated for acid—base, compleximetric and iodimetric titration procedures.     

Gran's plot titration and flow injection titration of sulfate in ground and drinking water with a barium ion-selective electrode

The application of a barium ion-selective electrode for the determination of sulfate is reported. Titrations in the batch mode using the Gran's plot method [1] have been carried out. In the presence of a lithium acetate buffer and after the addition of isopropanol it has been possible to determine sulfate with a relative standard deviation (RSD) of 1.5%. The concentration range of the samples was 5–400 mg sulfate/l. Interfering ions were separated by cation-exchange. This indirect titration constituted the basis of a flow injection titration (FIA titration) system for the continuous determination of sulfate. By plotting the peakwidth vs. the logarithm of the sulfate concentration of the injected samples, linear calibration graphs in the range of 50–200 mg sulfate/l were obtained. In this system, the sample stream was pumped through an ion-exchange column, mixed with a buffer stream of lithium acetate and injected in a reagent stream of a BaCl₂ solution. The resulting free Ba(II) concentration was monitored with a barium ion-selective electrode. The content of sulfate in ground and drinking water samples has been determined with a RSD between 1.2% and 1.3%.     

Pulsed reagent introduction through a membrane reactor for flow-injection systems

A method of intermittent reagent introduction, functionally equivalent to stop-go pumping, is described. A pneumatically pressurized reagent reservoir is used to deliver liquid through a high-speed on/off valve to the outer channel of an annular tube assembly. Except for this single entry point, the outer channel is otherwise sealed. The inner flow channel bearing the principal flow stream contains a short microporous membrane tube. When the reagent delivery valve is activated, reagent flows radially inward through the membrane into the principal flow stream.     

Flow-injection determination of ammonia in kjeldahl digests by gas diffusion and conductometry

A flow injection/conductometric method is proposed for determing ammonia in solutions obtained from Kjeldahl digestion. The method is based on diffusion of ammonia through a PTFE membrane from an alkaline (NaOH/EDTA) medium to a deionized water stream. The change in conductance of the deionized water stream is proportional to the ammonia concentration present in the digest. The effects of flow parameters, temperature and potential interferences are reported. Approximately 100 samples can be injected per hour; the precision is about 1%. Results for total nitrogen in vegetable tissues, animal feeds and fertilizers are in good agreement with those obtained by the usual distillation/titration method.     

An Alkalinity Experiment for Nonscience Majors

his article describes a simple experiment that is designed to illustrate the concepts of buffer capacity and alkalinity, while also focusing on the geological factors that influence the susceptibility of a body of water to the effects of acid rain. The students perform a semiquantitative titration of four different water samples with a dilute solution of sulfuric acid. The titrations are monitored with a pH meter. Streams flowing through regions rich in limestone have naturally high alkalinities due to the formation of bicarbonate ions from the dissolution of calcium carbonate. The focus of the experiment is to compare the buffer capacities of water samples taken from a stream that flows through a limestone-rich region with those obtained from a stream near its source at a limestone-deficient location. Students plot the pH vs. the number of drops of dilute acid added to each of the samples. The relative buffer capacities are determined from the number of drops required to reach a pH of about 4.4. Tap water and water taken from a major river that flows through central Pennsylvania were found to have fairly large buffer capacities, while deionized water and water taken from a smaller stream near its source were found to have very low buffer capacities. The results show that different bodies of water can have vastly different susceptibilities to the effects of acid rain, depending on the concentration of the bicarbonate ion. The examination of the titration curves enable students to appreciate the sudden drop in pH that occurs once all of the bicarbonate ions have been consumed.     

Determination of the total acidity in soft drinks using potentiometric sequential injection titration

A potentiometric SI titration system for the determination of total acidity in soft drinks is proposed. The concept is based on the aspiration of the acid soft drink sample between two base zones into a holding coil with the volume of the first base zone twice to that of the second one and channelled by flow reversal through a reaction coil to a potentiometric sensor. A solution of 0.1 mol l⁻¹ sodium chloride is used as ionic strength adjustment buffer in the carrier stream. The system has been applied to the analysis of some South African soft drinks having a total acidity level of about 0.2–0.3% (w/v). The method has a sample frequency of 45 samples per h with a linear range of 0.1 and 0.6% (w/v). It is easy to use, fully computerised, and gives the results that are comparable to both automated batch titration and manual titration.     

The direct spectropolarimetric titration of palladium(II) ion with d-(-)-1,2-propylenediaminetetraacetic acid

A direct spectropolarimetric titration of palladium(II) at 40°C with the optically active ligand D-(—)-1,2-propylenediaminetetraacetic acid (D(—)PDTA) is described. The optical rotation is monitored with a modified photoelectric polarimeter, and both the palladium-D(—)PDTA complex and the titrant serve as optically active indicators. End-points are obtained by extrapolations. The proposed titration is compared with the visual back-titration method.     

Cationic membranes for phenols production

Ionic Substitution by Electrodialysis is a good alternative to the industrial conversion of sodium salts of phenols into undissociated phenols, conventionally performed through acidification by strong acids. The acidification through electromembranes combines the possibility to achieve high conversion values with the advantage of keeping the process stream separated from the acid stream. The process is performed through cationic membranes; conversion can be obtained also in the absence of electric current, even if slightly better performances can be achieved by applying an electric field. Process feasibility as well as membrane resistance is tested, for the case of model solutions reproducing the main features of the real process streams. Maximum conversion and process rate are greatly affected by the ratio between protons in the acid solution and sodium ions in the process solution. Phenol losses into the acid stream and chloride contamination of the process stream can be reduced by working with diluted process and acid streams.     

Flow injection analysis : Part IX. A New Approach to Continuous Flow Titrations

Studies of dispersion patterns in nonsegmented streams, flowing through narrow open tubes, show that it is possible to obtain highly reproducible concentration gradients within a sample zone injected into the moving stream. By varying the geometry of the flow path, low, medium and high dispersion patterns can be achieved; the high dispersion pattern forms the basis for a new approach to continuous flow titrimetry. In this type of titration, discrete samples are passed through a gradient device and are then mixed with a continuously flowing stream of titrant of fixed concentration. The new technique has been tested for potentiometric as well as spectrophotometric end-point indication. A simple one-channel system allows titrations to be performed automatically in less than 1 min.     

The Chemical Behavior of Active Nitrogen

Active nitrogen, which is formed on passage of an electric discharge through a stream of nitrogen, is detected by a characteristic yellow afterglow. It can be determined quantitatively, e.g. by gas phase “titration” with nitric oxide. Active nitrogen reacts with many chemical elements, as well as with organic and inorganic compounds. Although nitrogen atoms are responsible for many of the reactions of active nitrogen, electronically excited molecules also play a role.     

Complexometric titration of Aluminium

A procedure is given for the complexometric titration of aluminium. A known volume of a standard solution of EDTA is added to the sample solution, and the excess is back-titrated with a zinc sulphate solution, dithizone being used as indicator. The titration is performed at pH = 4.0 — 4.5 and 40 — 50% alcohol is added as solvent for the indicator.The theoretical basis of the method is developed, and the theoretical titration error with various amounts of aluminium and zinc is calculated.The results of some titrations are given.     

Coulometric titration with air transported sample

Air transported samples of a mixture containing the analyte and a supporting electrolyte are consecutively propelled into a microconduit system through a titration cell, a coil and a detector cell. Different amounts of electrochemically generated titrant are obtained in the separate samples while they are passing through the titration cell. Various quantities of the titrant are achieved by changing the duration of the titrant generating process that is done by various time for the sample solution staying in the titration cell (different sample movement rate). The titrated sample is then homogenised in the coil and detected in an electrochemical detector cell that supplies necessary data for the analyte determination. The declared method is experimentally verified on coulometric titration of hydrochloric acid (HCl) with electrogenerated sodium hydroxide and a titration of aniline with bromine generated in a bromide solution.     

利用二次球形配位构筑疏水型隧道框架结构

质子化N,N,N',N'-四苄基乙二胺(L)可与[MCl4]2-(M=Mn, Co, Cu)形成二次球形配合物. 通过N—H…Cl相互作用构筑了1D带状和2D层状框架结构, 层中配体L的苄基通过C—H…Cl相互作用分别采取水平和垂直取向, 使1D带状和2D层状呈现凸凹交替排列. 通过层间凸凹部位的C—H…H—C相互作用, 形成了层间空穴, 进而构筑成了3D疏水型隧道框架结构, 乙醇分子能够填充于隧道之中. 在L·2H+·[CuBr4]2-晶体中, 由于[CuBr4]2-没有与配体L的苄基形成C—H…Br氢键, 使配体L的苄基采取了同向取向. 因而, 形成的2D层状框架结构是平展的, 未形成3D疏水型隧道框架结构, 也未发现与乙醇分子的包结现象.     

Determination of surfactant concentration using micellar enhanced fluorescence and flow injection titration

Flow injection titration was used for the determination of anionic, cationic, nonionic and zwitterionic surfactants. The procedure was based on the micellar-enhanced fluorescence of 1,8-anilino-naphthalene sulfonate (ANS). Samples were injected into a carrier stream of phosphate buffer and 1.0 mol l⁻¹ NaCl. The sample then passed through a mixing chamber which generated the exponential peak shape needed for the titration as well as diluted the sample in the carrier stream to control the pH and ionic strength of the sample. The peak width was linearly related to the logarithm of the surfactant concentration. The minimum detectable concentration was governed by the critical micelle concentration for anionic, zwitterionic and nonionic surfactants, but below the critical micelle concentration for cationic surfactants. The linear range extended for 1.5 orders of magnitude. Reproducibility ranged from 12% at the lower end of the calibration range to 1.1% at higher concentrations. For SDS recoveries of 82–108% were achieved in matrices as concentrated as 1 mol l⁻¹ in NaCl or Na₂SO₄.     

全自动电位滴定法测定锂电池原料碳酸锂中主成分的含量

采用全自动电位滴定法测定锂电池原料碳酸锂中主成分的含量,用盐酸标准溶液进行滴定,考虑自动电位滴定仪的灵敏性和准确度,通过多次对比实验,确定了仪器的最佳工作参数、滴定剂浓度和样品称样量等滴定条件;对两个不同品位试样分别进行了11次平行测定,相对标准偏差(RSD)均小于1％.在碳酸锂试样中加入基准物质无水碳酸钠进行碳酸根的...     

利用二次球形配位构筑亲水型隧道框架结构

质子化N,N,N’,N’-四苄基乙二胺可与[Fe(CN)6]3－, [SnCl6]2－和[TeCl6]2－二次球形配位分别形成可容纳客体分子的包结物晶体(1～3). 晶体1通过NH＋…NC－, NH＋…p(NC)和CH…p(NC)组合合成子, 构筑了亲水性层柱隧道结构, 孔径尺寸为1.03 nm×1.12 nm, 两个乙醇分子和两个水分子填充于隧道中; 晶体2通过CH…Cl－合成子, 构筑了亲水性层间隧道结构, 孔径尺寸为0.94 nm×0.73 nm, 三个水分子和两个氯离子填充于隧道中; 晶体3的结构与晶体2相似, 也是通过CH…Cl－合成子, 构筑了层间亲水性隧道结构, 孔径尺寸为0.94 nm×0.72 nm, 两个水分子填充于隧道中.     

A micro-heterometric determination of traces of iron (III) in alloys and salts with α-nitroso β-naphthol

Ferric iron constituting approximately 0.01% — 0.1% may be determined by a heterometric titration with α-nitroso-β-naphthol. The solution may contain 99.9% or more of calcium, barium, magnesium, aluminium, chromium, manganese, nickel, cadmium or lead salts. No previous separation is necessary. The α-nitroso-β-naphthol is dissolved in alcohol. The analysed solution must be acidified. No complexing agents are necessary. Citrate or tartrate must be absent. The maximum optical density values which are obtained at the end of the titration are proportional to the amount of iron which is analysed. These maximum values are entirely unaffected by the concentrated salt solutions. The heterometric sensitivity of the reaction between iron and α-nitroso-β-naphthol is three times higher in 50% alcoholic solution than in water. The titration takes about one hour. The error is 0.0—4%.     

Flow-injection extraction with a microvolume module based on integrated conduits

A self-contained module for liquid—liquid extractions is described. The module contains engraved conduits for mixing of sample and ragent, an engraved segmentor, a detachable extraction coil, a membrane separator, and a rinsing system for the flow cell. The membrane in the separator is supported by a teflon-coated steel grid and can be replaced rapidly. The segmented stream enters at the centre of the circular membrane and travels through an engraved, coiled channel in contact with the membrane before leaving the membrane area at the periphery. The volume of the receptor chamber for the organic phase is 10 μl. For a detector flow-cell volume of 8 μl, an aqueous flow rate of 2.0 ml min^?1 and an organic flow rate of 1.2 ml min^?1, the “loss factors” caused by analyte dispersion are 3.2 and 1.5 for caffeine sample volumes of 40 μl and 100 μl, respectively, compared with batch extraction. The system is also tested for extraction of anionic surfactants as their ion-pairs with methylene blue.