Multiple Standard Addition Research Articles

In SituMeasurement of Electrode Slope and Gravimetric Multiple Standard Addition Analysis by Ion Selective Potentiometry Without Prior Calibration of Electrode

Abstract Two methods of calculation for the determination of an unknown concentration by gravimetric multiple standard addition analysis using ion selective potentiometry without prior calibration of the electrode have been described. These are based on simple calculation procedures involving linear least square fitting to Gran's equation to evaluate first the actual electrode slope ‘in situ’, then the unknown concentration and the cell constant. One method is iterative and the other is noniterative. The applicability of the methods has been demonstrated by processing the experimental data obtained by using fluoride and uranyl ion selective electrodes.

Determination of volatile and non-volatile organic acids in technical sugar solutions by ion-exclusion chromatography

Volatile and non-volatile organic acids present in sugar process juices were separated by ion-exclusion chromatography on an HPICE-AS1 cation-exchange column (H + form) using both dilute hydrochloric acid and 2-propanol-water solutions of tridecafluoroheptanoic acid. Coupled with an anion-exchange micromembrane suppressor, a conductivity detector made it possible to reveal citric, tartaric, gluconic, malic, lactic, succinic, glycolic, formic, acetic and pyrrolidonecarboxylic acid in the presence of inorganic acids and non-ionic organic matter. In sugar process juices subjected to alkaline and/or oxidative treatment, increasing concentrations of the major acid components, i.e., acetic, formic and lactic acid, can be measured. The analysis is performed in the presence of sucrose and a simple clean-up by rapid batch treatment with a cation exchanger (H + form) is sufficient to remove proteins and cations. The multiple standard addition procedure is used for calibration.

Linearized multiple standard additions for the potentiometric determination of weak acids

The feasibility of potentiometric determination of weak monoprotic acids by the multiple standard addition method is examined. A standard solution of pure weak acid is added to the solution containing an unknown amount of the same weak acid, alone or mixed with its conjugate base. The experimental data are processed by Gran-type plots, for which rigorous and approximate equations are obtained. It is shown that weak acids can be determined by multiple standard additions with a precision comparable with that of the usual kinds of potentiometric addition-methods. The validity range of the approximate equations is established. Linear equations similar to those of Hofstee, Scatchard, Lineweaver and Burk, and Scott are also obtained, by which aciditity constants can be determined together with equivalence volumes. The effects of systematic and random measurement errors are examined.

Hybrid multiple standard additions-analyte addition method for ion-selective electrodes with integral calibration

A hybrid multiple standard additions-analyte addition method for ion-selective electrodes is described in which the calibration of the potentiometric cell and the determination of the unknown concentration of the sample are carried out in a single experiment. This ensures maximum constancy of the calibration characteristics, E°′ and S, of the cell. The proposed method allows the determination of trace amounts (100 µg) of a sample. The data treatment includes an iterative minimisation procedure using the least-squares sum method, which improves the accuracy and the statistical reproducibility of the results. The method can be automated by means of an automatic titrator, controlled by an HP-85B microcomputer. A BASIC program was constructed for this purpose. The method was tested by applying it to the determination of sodium, potassium, chloride and fluoride ions and the errors of the results were less than 1%. The limit of determination of the method was investigated by determining decreasing concentrations of fluoride ions. It was found that the method gives satisfactory results over the entire linear range of the ion-selective electrode.

Measurement in the non-linear region of the calibration graph of the fluoride ion-selective electrode by blank adjustment

A method is described that permits the determination of low levels of fluoride with a fluoride ion-selective electrode, in the non-linear response region, but avoids the use of non-linear calibration. An estimate of the background response of the fluoride ion-selective electrode is obtained by multiple standard additions. Adjustment of the fluoride standard values with this background estimate results in a linear calibration graph. Fluoride levels in samples are then easily determined by linear interpolation and correction for background response, irrespective of whether this is due to fluoride contamination of reagents or hydroxide interference from buffer pH.

Liquid Chromatographic Determination of Benomyl in Wettable Powders

Abstract Pesticide formulations containing benomyl are extracted with acetonitrile containing 3% n-butyl isocyanate (BIC) and chromatographed on a reverse phase C-18 column. The equilibrium of benomyl degradation to methyl 2-benzimidazoIe carbamate (MBC) and BIC is driven toward benomyl. Thus, the method offers quantitation of benomyl in its intact form, using a mobile phase of acetonitrile-2% acetic acid (80 + 20) and detection at 290 nm. This assay was evaluated for linearity, precision, recovery, stability, and matrix effects. Linearity checks of standard solutions and spiked samples yielded coefficients of determination, r2, of 0.9996 and 0.9998, respectively. Quadruplicate analysis of 5 benomyl formulations gave an average relative standard deviation of 1.95%. A multiple standard addition plot revealed the absence of matrix effects. Mean recovery of standard from the sample pool was 95% with a standard deviation of 3.5%. Samples chromatographed 2 weeks after extraction indicated excellent analyte stability.

High Performance Liquid Chromatographic Determination of Dielofop-Methyl

Abstract Diclofop-methyl is diluted in acetonitrile-2% acetic acid (70 + 30) and chromatographed on a reverse phase C-18 column. The anaìyte is eluted by an acetonitrile- 2% acetic acid mobile phase and detected at 280 nm. The method was validated by testing precision, linearity, and recovery. Precision and linearity were excellent (% RSD = 0.55, r2 = 0.9997). A multiple standard addition to a pool of formulation samples showed the method to have excellent recovery (99%) and to be free of matrix interferences

Determination of selectivity coefficients of ion-selective electrodes by means of linearized multiple standard addition techniques

The application of multiple known-addition or dilution techniques to the evaluation of potentiometric selectivity coefficients of ion-selective electrodes is proposed. The validity of the common form of the Nikolskii—Eisenman equation is assumed and experimental data are processed by using Gran-type linear functions. Six possible methods are derived which make it possible to work under bi-ionic conditions for the electrode response. Optimization of the experimental procedures is discussed.

The precision of potentiometric measurements.

Widespread use of ion-selective electrodes and the growing possibility of using sophisticated computer technique in conjunction with the electrodes has made necessary to investigate the degree of precision attainable by potentiometric techniques. Results obtained by applying error propagation statistics to various potentiometric methodologies, like calibration, single and multiple standard addition, titration, etc. have been critically reviewed.

Determination of total zinc in soils by external-beam proton-induced X-ray emission spectrometry

A rapid non-destructive determination of total zinc in soils is reported. The 1 mm thick targets were prepared without a binder. Multiple standard additions were used for calibration. For a 10-μC irradiation with 2-MeV protons, the detection limit was about 2 ppm of zinc. The precision was within 5% and good agreement was found with spectrophotometric measurements of zinc.

Comparative study on the precision of potentiometric techniques applied with ion-selective electrodes: Part 2. Multiple standard addition

The errors in multiple standard addition techniques depend on whether or not the slope of the calibration graph is known. The precision obtainable by regression techniques with and without Gran transformation of the experimental data are compared. Monte Carlo simulation is used to estimate the precision of the result obtained by non-linear regression.

Novel computer evaluation of multiple standard addition with ion-selective electrodes

A novel method has been worked out for the computer calculation of unknown sample concentrations from the results of the multiple standard addition method. The program has been run on a desk computer.

Potentiometric determinations with the silver sulfide membrane electrode : Part I. Determination of cyanide

The possibilities of the silver sulfide membrane electrode for the determination of cyanide are described; determinations by multiple standard addition and titration have been studied, and interferences have been checked. The determination of cyanide in solutions containing various metal complexes, and the evolution method for separation of hydrogen cyanide are discussed. Automatic titration can be used for samples containing 1 p.p.m. cyanide, and the standard addition method for 1 p.p.b. cyanide.

Determination of Sodium and Potassium in Blood of Oceanic Fish by Emission Flame Spectrometry Using an Exponential Extrapolation with Multiple Standard Additions

A method is described for using multiple standard additions to determine sodium and potassium in samples of digested but unpurified blood of oceanic tuna fish whose flame emission responses are nonlinear. An exponential curve is fit in a rational manner to signals of the unknown and two or more spiked unknowns. Evidences are given suggesting that higher precision can be obtained in determination of these and similar elements in biological materials in a direct and simple manner.