Flow Titration Research Articles

Precipitation titrations using an automatic titrator based on a multicommutated unsegmented flow system

An automatic flow titrator based on a multicommutated unsegmented flow system was used to perform precipitation titrations with potentiometric detection. The titration approach is based on sequential introduction of increasing titrant and decreasing titrand volumes into a mixing chamber. The system allows the attainment of complete curves, the titration end point being determined by the Gran method, as is usually employed in batch potentiometric titrations. The theoretical model for the analytical process is presented and discussed and the determination of titrand concentration is performed without any prior calibration. The automatic flow titrator developed was applied to chloride determination in bottled natural waters and the results obtained were reproducible (RSD 3.2 and 3.8% for repeatability and reproducibility, respectively) and in good agreement with those given by the reference procedure (relative deviation within the range from −4.6 to 4.8%).

Gradient flow titration for the determination of fluoride ion in natural waters

The determination of fluoride ions in water samples was accomplished by using a gradient flow titration. A standard commercial combined electrode is used in a cell configuration that combines the gradient chamber and the electrode in a single unit. The methodology developed gives results with a relative standard deviation of about 3%. The average recoveries after spiking natural samples with fluoride are in the range 100–102%. The method was used successful in determining the fluoride concentration in water samples.

Analytical options for control of acids and bases in hydrometallurgical processes

The most common procedures for the determination of acids and bases in hydrometallurgical process liquors are reviewed and compared. Automated batch titrations, performed by stepwise addition of titrant and using Gran plots for evaluation are reliable but slow compared to flow techniques. Continuous flow titrations are grouped into three classes: Flow Injection Titration, Single Point Flow Injection Titration, and Triangle-programmed Flow Titrations. Furthermore, Sequential Injection Analysis is also considered for process applications. Each one of these methods has advantages and drawbacks. An overview of the most common application problems, and the way they are solved with each methodology, is given. The analytical characteristics of the described procedures are given as well as a guide for the choice of technique for a given application.

A Monosegmented Flow Titration for the Spectrophotometric Determination of Total Acidity in Vinegar

A monosegmented flow system involving sample and titrant sequential injections and the establishment of a tandem plug between two air bubbles is proposed for automated titrations. The end point is found after successive variations of the sample and titrant volumes, determined by an algorithm based on the one-dimensional optimization method of Fibonacci. The set up includes a multi-port solenoid valve with four inlets and one outlet. The feasibility of the system was demonstrated in the spectrophotometric determination of the total acidity in vinegar with NaOH and phenolphthalein used as the titrant and indicator, respectively. The sample throughput was ca.30 h-1 and consumption of the sample and titrant was about 0.7 ml. The results were in agreement with the expected values, with relative errors lower than ±0.4%. After 12 successive analyses of typical samples with a 47.1–53.4 total acidity, expressed as g l-1 acetic acid, the relative standard deviations of the results were estimated within the 1.2–2.1% range.

Automatic potentiometric titration in monosegmented flow system exploiting binary search

An automatic monosegmented flow system (MSFA) based on the binary search concept to perform potentiometric titration is proposed. A tubular hydrogen ion-selective electrode without inner reference solution, consisting of a conducting epoxy cylinder machined with an axial hole coated with tridodecylamine (TDDA) was employed as a sensor. The titration procedure was implemented by exploiting the binary search approach, after each analytical cycle data were evaluated to decide the variation of the titrant volumetric fraction to be inserted for the next cycle. The flow network comprised three-way solenoid valves controlled by a microcomputer running software in QUICKBASIC 4.5. Combination of binary search and MSFA resulted in an automatic system providing possibilities to perform flow titrations without any operator assistance. The main features of the proposed system were verified by titrating hydrochloric and acetic acid solutions and the feasibility of the approach was ascertained by analyzing vinegar, coke, lemon soda, isotonic, industrial and natural orange juice samples. Results were in agreement with those obtained with a conventional potentiometric titration, and no significant difference at 95% confidence level was observed. A 1% standard deviation ( n=9) in results was also observed.

Titulador potenciométrico automatizado baseado em sistema de fluxo monossegmentado

A new automated system for acid-base flow titrations is proposed. In the operation mode, several sample to titrant volumetric ratios are injected in an air segmented plug. Five three way solenoid valves and three acrilic junctions, assembled in a hidrodynamic injection system, were accountable for the monosegmented reagents plug formation. A turbulent flow reactor was used for a perfect mix of reagents in the plug. The detector system employed a glass combined electrode fitted in an acrilic holder. Titrations of hydrochloric, nitric and acetic acids, in several concentrations, were performed with standard sodium hidroxide, for evaluation of the efficiency of the system. The relative standard deviation of the determinations was about ±0,5% and each titration was carried out in 3-4 minutes. A Quick BASIC 4.5® program was developed for the titrator control.

Potentiometric flow titration of iron(II) and chromium(VI) based on flow rate ratio of a titrant to a sample

A new potentiometric flow titration has been proposed based on the relationship of the flow rates between titrant and sample solutions. A sample solution is pumped at a constant flow rate. The flow rate of the titrant solution is gradually increased at regular time intervals and a flow rate for the titrant solution in the vicinity of the equivalence point is obtained. The concentration of the sample is calculated by C S (mol l −1)=( R T (ml min −1)× C T (mol l −1))/ R S (ml min −1), where C S, C T, R S, and R T denote the unknown sample concentration, titrant concentration in the reservoir, the flow rate of the sample solution which is a constant rate, and the flow rate of the titrant solution at an inflection point, respectively. The potentiometric flow titration of iron(II) with cerium(IV) and of chromium(VI) with iron(II) has been presented. The titration time of the proposed method is about 10 min per sample. An R.S.D. of the method is 0.77% for seven determinations of 1×10 −3 mol l −1 iron(II). Similarly, the flow titration of chromium(VI) with iron(II) is carried out over the range 1×10 −4–1×10 −3 mol l −1 chromium(VI) and is successfully applied to the determination of chromium in high carbon ferrochromium.

Automated flow‐rate meter for flow‐analysis systems

An automated flow-rate meter easy to construct and operate is described. This is controlled by a microcomputer connected to an analog/digital converter interface and by a control software. It uses two acrylic flow cells, each comprising a bicolor light-emitting diode and a phototransistor placed on opposite sides. The performance of this flow-rate meter was evaluated by applying it to three flow manifolds: one monosegmented flow titration system by binary sampling; one conventional monosegmented flow system, and one single-line FIA system. The FIA system flow rate was assessed by means of a Vanderslice's expression. The time range of measurement of the flow rates was of 3.5–19.5 seconds and relative errors of 0.2–2.6% as well as relative standard deviations from 0.4 to 3.1% were attained. The flow-rate meter allows one to optimize precision and velocity of measurements just by changing one of its parameters. Moreover, the flow-rate meter can be used with flow systems, therefore allowing one to perform on-line measurements, which facilitates a quick and effective control of the channels flow rate.© 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 97–104, 1999

Study on the implementation of flow titrations in sequential injection analysis

Several variables that affect flow spectrophotometric titrations in sequential injection analysis (SIA) systems were studied by using titration of a strong acid with a strong base as a model; blue bromothymol was used as an indicator and distilled water was used as a carrier. Both possibilities of performing titrations on SIA systems according to the aspiration sequences (a) titrant B/sample/titrant A and (b) titrant/sample are considered. In case (a) the possibilities regarding the use of different volumes and/or different concentrations of titrant reagents were studied and are discussed. The established methodology allows hydrochloric acid determinations with 0.1 M sodium hydroxide within the range 32–1000 mM by means of logarithmic calibration curves. The analysis rate is of 5 min/sample. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 207–216, 1999

Automated flow-rate meter for flow-analysis systems

An automated flow-rate meter easy to construct and operate is described. This is contralled by a micracomputer connected to an analog/digitai converter interface and by a contrai software. It uses two acrylic flow cells, each comprising a bicolor light-emitting diode anda phototransistor piaced on opposite sides. The performance of this flow-rate meter was evaiuated by appiying it to three flow manifoids: one monosegmented flow titration system by binary sampling; one conventionai monosegmented flow system, and one singie-iine FIA system. The FIA system flow rate was assessed by means of a Vanderslice's expression. The time range of measurement of the flow rates was of 3.5-19.5 seconds and relative errars of 0.2-2.6% as well as relative stanCorrespondence to: Mario Cesar U. Araujo. © 1999 John Wiley & Sons, Inc. CCC 0895-7533/99/020097-08 dard deviations fram 0.4 to 3.1 % were attained. The flow-rate meter allows one to optimize precision and velocity of measurements just by changing one of its parameters. Moreover, the flow-rate meter can be used with flow systems, therefore ailowing one to perform on-line measurements, which facilitates a quick and effective contrai of the channeis flow rate. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 97-104, 1999

A robust multisyringe system for process flow analysis

A robust multichannel manifold involving a multisyringe piston pump used for performing process flow analysis is proposed. The simultaneous sequential determination of two analytes with a sampling frequency of 97 injections per hour is demonstrated. A robust and rapid continuous flow titration system, including a predilution step, was developed. A quantitative dilution, avoiding the need for diluting the standards too, is achieved in two steps by first splitting the concentrated sample stream and further dilution in a mixing chamber. A wide range of dilution grades (from 80 to 1150) can be easily implemented by software instructions, without the necessity of mechanical reconfiguration of the manifold. The resulting system gives medium or low dispersion peak signals with a sampling frequency of over 75 injections per hour for off-line diluted samples, and more than 33 injections per hour for concentrated samples. The proposed assemblage allows the automation of the single point flow injection titration procedure for the assay of acids and bases in concentrated process solutions. Recoveries of 97.5–103% were found with a maximum RSD value of 5%.

Study on the implementation of flow titrations in sequential injection analysis

Several variables that affect flow spectrophotometric titrations in sequential injection analysis (SIA) systems were studied by using titration of a strong acid with a strong base as a model; blue bromothymol was used as an indicator and distilled water was used as a carrier. Both possibilities of performing titrations on SIA systems according to the aspiration sequences (a) titrant B/sample/titrant A and (b) titrant/sample are considered. In case (a) the possibilities regarding the use of different volumes and/or different concentrations of titrant reagents were studied and are discussed. The established methodology allows hydrochloric acid determinations with 0.1 M sodium hydroxide within the range 32–1000 mM by means of logarithmic calibration curves. The analysis rate is of 5 min/sample. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 207–216, 1999

Study of the determination of acetylcholine after enzymatic hydrolysis by triangle programmed coulometric flow titration

A new method for the determination of acetylcholine is introduced and studied. The method uses enzymatic hydrolysis of acetylcholine carried out in a flow-through analytical reactor column, while for the detection triangle programmed coulometric flow titration is employed. The flow-through coulometric titration system and the preparation of the enzyme reactor are described. The operation conditions for the hydrolysis and for the titration were optimized. The flow-through coulometric titration technique offers a better precision for the determination of acetylcholine in small concentration ranges than methods based on the detection of pH change. Working conditions of the system can be easily adjusted for different sample concentration ranges. The limit of detection for the determination of acetylcholine was found to be 8×10 −5 M. The method described could be advantageously used for indirect determination of acetylcholinesterase inhibitors.

Time-division multiplex technique for producing concentration profiles in flow analysis

A technique is described which uses computer controlled solenoid valves for creating concentration profiles for various flow-based methods of analysis. These profiles can be quickly selected through software and, similarly, parameters such as the volume of the sample, carrier and reagents can be set and altered when required with minimal changes to the hardware. The technique has been demonstrated for flow titration and flow injection but is equally applicable to other methods. In all these methods, only a single channel pump is required to draw the mixed solutions through the detector and individual solutions are introduced into the flowing stream by selection through solenoid operated valves. Results are presented for the determination in water samples of calcium using potentiometric titration and orthophosphate by flow injection using the molybdenum blue method. The technique uses only small volumes of solutions and is fully automated and so is ideal for use in portable instrumentation.

Pulsed flow chemistry. A new approach to the generation of concentration profiles in flow analysis

Pulsed flow chemistry (PFC) is described as a new approach to automated on-line analytical chemistry. In contrast to existing flow-based analytical chemistry methods, PFC is characterized by pulsed flow, turbulent mixing and low axial dispersion. The PFC system is fully computerized and all operations are under software control. Consequently, most flow analysis methods (e.g., flow injection, continuous flow, flow titration, etc.) can be selected with a simple click of the mouse. The system is easily miniaturized and portable which makes it particularly suited to field instrumentation. The system has been tested using several flow-based techniques including on-line titration for the determination of calcium in waters with potentiometric detection and a calcium ion sensor.

Analyzing nitrogen and sulphide elimination from leachate by coulometric continuous flow titration

AbstractThe process of leachate denitrification by populations of nitrifying and denitrifying bacteria was investigated. Leachate, derived from a local municipal landfill site, was nitrified in a continuously operating packed‐bed biofilm reactor and thereafter denitrified in an activated sludge bioreactor. To follow the progress of nitrogen elimination, ammonium, nitrite and nitrate concentrations were determined at all stages of the process. While the nitrite and nitrate concentrations were measured by conventional colorimetric methods, computer controlled coulometric titration with in situ generated hypobromite was used for ammonium determination, which had previously been selectively separated from the sample matrix by gas dialysis. The detection range of the method was from 1 × 10−6 to 1 × 10−3 M ammonium (relative standard deviation (RSD) = 2%, n = 6). No interference of the complex sample matrix was found in ammonium determination. The average ammonium concentration in the leachate was 409 mg/l (standard deviation (SD) = 142 mg/l, n = 55). The ammonium concentrations decreased to 1–5 mg/l during nitrification under continuous operating conditions. Increased ammonium concentrations after nitrification correlated with a decrease in the efficiency of nitrogen elimination by up to 45% due to the build‐up of high concentrations of nitrite. The concentration of sulphides, another source of pollution of the leachate, was also determined by triangle programmed coulometric titration. The average concentration of sulphides in the leachate was 221 mg/l (SD = 374 mg/l; n = 55). The sulphide concentrations decreased to concentrations below the detection limit of the coulometric titration (2 × 10−6M) during nitrification.

Selective determination of gas dialysable components in complex sample solutions using triangle programmed coulometric titration in continuous flow systems

A precisely and sensitively working coulometric flow titration procedure was developed to determine ammonium/ammonia and sulphide/hydrogen sulphide in leachate from a municipal waste landfill site. The selectivity of coulometric titration with electrogenerated hypobromite could be essentially improved by the combination with a continuously and quantitatively working thin layer gas dialysis cell, which was integrated in the flow titration setup in one measuring device. During the flow titrations both ammonium/ammonia and sulphide/hydrogen sulphide were quantitatively separated from the sample solutions. Both the commonly used biamperometric and the chemiluminescence flow detection could be applied to follow the titration course. By triangle-programmed coulometric titration ammonium/ammonia were detected in a linear range from 10 −3 to 10 −6 M (relative standard deviation (RSD) = 1%, n = 6, confidence level α = 0.05) using biamperometric detection and from 5 × 10 −4 to 10 −6 M (RSD = 3%, n = 6, α = 0.05) using chemiluminescence detection. Sulphide/hydrogen sulphide could be determined in a linear range from 5 · 10 −4 to 2 · 10 −6 M (RSD = 4%, n = 6, α = 0.05). Up to 30 flow titrations could be implemented per hour.

Binary search in flow titration employing photometric end-point detection

A binary search strategy is proposed and implemented in a continuous flow system to find the end-point titration by employing spectrophotometric detection. It takes advantage of the binary sampling process under a constant flow-rate. For this task an automated flow set-up based on solenoid valves was designed. A 386 microcomputer was employed to control the valves, and to perform data acquisition and data processing. The accuracy level can be previously settled as a software parameter. Samples with concentrations ranging within two orders of magnitude could be titrated by making use of the same flow set-up. Titration of hydrochloric acid with sodium hydroxide was performed to demonstrate the feasibility of the proposal. Titrations in triplicate, with 99.99% precision were carried out in 3 min with a solution consumption of 2 ml.

Continuous flow titration system for the generation of multivariate spectrophotometric data in the study of acid—base equilibria

In the present work a continuous flow system to carry out spectrophotometric titrations is developed. The titrant solution is generated on-line from mixing two different stock buffer solutions. The composition of the titrant agent is sequentially varied along the titration by changing the ratio of flow rates of both buffer channels, and therefore the pH can be modified. One spectrum is recorded at each pH value when the absorbance achieves the steady state. The spectral data have been treated by means of a recently developed self-modelling multivariate curve resolution method (SPFAC procedure). This method has been applied to the study of the acid-base equilibria of 1,2-naphthoquinone-4-sulfonate (NQS). Four titrations with concentrations of NQS ranging from 1.6 × 10 −4 to 7.3 × 10 −4 M have been performed, and, in every case, 24 spectra at different pH have been registered. Three species are detected in the range of pH studied (6.9–12.3). Their distribution plot with pH and their unit spectrum have been obtained.

Micro-batch Flow Titration

Two micro-batch flow titration assemblies are proposed in the present work. The first describes the use of a titration microchamber and an injection valve that joins two flow systems. Of the two flow systems, one uses an air carrier and the other a liquid carrier. The sensing elements are placed in the liquid carrier. The second assembly uses a titration microchamber with a miniature sensor placed inside. There is no need for calibrations when performing microtitrations in the two described assemblies. The air carrier moves the injected samples toward the titration chamber without dispersion. An automatic burette introduces a volume of titrant to the chamber. Acid-base volumetric analysis has been assayed using the microtitration flow injection system, yielding precise and reproducible results. These results are comparable to those obtained with discontinuous titrations.