University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Acidity, constants

@ ChemSpider@ NIST@ PubChem

Citations 5

"Spectrophotometric Determination Of PK(a) Values Based On A PH Gradient Flow Injection System"
Anal. Chim. Acta 2000 Volume 408, Issue 1-2 Pages 135-143
Javier Saurina, Santiago Hernández-Cassou, Romà Tauler and Anna Izquierdo-Ridorsa

Abstract: This paper describes a pH gradient flow injection method for fast spectrophotometric determination of acidity constants. The flow injection system consists of a three-channel manifold in which the sample bolus is injected between acidic and basic zones. Therefore, the front of the flow injection peak is made acidic while the tail of the peak is alkalinized, and consequently, a pH gradient from acidic to basic medium is generated along the flow injection peak in an easy and reproducible way. The whole procedure is composed of two steps; first, the in situ determination of the pH gradient profile by using a standard compound with a known pK(a) value, and second, this pH gradient profile is used to calculate the pK(a) of an unknown compound. An alternating least squares multivariate curve resolution method is used in both steps to resolve the concentration profiles of the acidic and basic species in the standard and in the unknown samples which are the basis of the calculations. The method is tested using several nucleic acid components. An additional advantage of the proposed method is that no pH experimental measurement is needed for the fast determination of pK(a) values. Results obtained using the proposed procedure are consistent with those listed in the literature.
Water Spectrophotometry pH gradient Titrations Multivariate calibration

"Spectrophotometric Determination Of Acidity-constants Of Unstable Compounds By Flow Injection Analysis"
Anal. Chim. Acta 1985 Volume 171, Issue 1 Pages 303-312
A. Ríos, M. D. Luque De Castro and M. Valcárcel

Abstract: Spectrophotometric methods of determining acidity constants of ligands in solution can be used satisfactorily for the determination of such constants of unstable ligands by flow injection analysis. The technique can also be used in the stopped-flow mode, to allow the extent of the reaction causing the instability to be established. The procedures are applied to glyoxal bis(2-hydroxyanil), 6-methylpicolinaldehyde azine, 2-hydroxy-benzaldehyde hydrazone and benzoylpyridine oxime.
Spectrophotometry Tecator

"Determination Of PH Gradients And Acidity Constants In Flow Injection Analysis Systems By Evolving Factor Analysis"
Anal. Chim. Acta 1991 Volume 255, Issue 1 Pages 143-148
Lars Nørgaard

Abstract: A general multivariate method for determining pH gradients in FIA systems was developed. A FIA system was constructed in which an injected sample merged with a non-linear pH gradient and the method was demonstrated by the injection of acid - base indicators with pKa from 3.4 to 8.9. The indicator responses were monitored by a photodiode-array spectrophotometer. By application of the evolving factor analysis multi-variate peak resolving technique it was possible to determine the concentration profiles of the acidic and basic forms of the indicators and using these profiles the pH gradient can be determined. The pH gradient can also be used to predict pKa values of unknown indicators. The prediction errors obtained are comparable to literature results. As an alternative, a multivariate calibration model (partial least-squares regression) was tested for empirically predicting the pKa values by using the evolving factor analysis concentration profiles as variables. The prediction errors obtained by this multivariate approach were also similar to literature results.
Spectrophotometry pH gradient Multivariate calibration Partial least squares

"Photometric Determination Of Acidity Constants By The Flow Gradient Technique Without PH Measurements"
Anal. Chem. 1990 Volume 62, Issue 20 Pages 2237-2241
Juliana Marcos, Angel Rios, and Miguel Valcarcel

Abstract: A simple photometric method for the determination of acidity constants without pH measurements is proposed. It is based on the establishment of a pH gradient in a flow system which is created by means of a flow gradient. The proposed method thus avoids other less accurate procedures for the establishment of pH gradients. Large pH gradients can be maintained over long periods. The acidity constants of various compounds were determined automatically from different parameters of the absorbance-time recordings. The proposed method allows more than one acidity constant for the same compound to be determined. The accuracy of the method is between 0.9% and 5.3%, in terms of relative standard deviation, and ±0.1 and ±0.4 in terms of confidence intervals.
pH Gradient technique

"PKa Determinations By Using A HPLC Equipped With DAD As A Flow Injection Apparatus"
J. Pharm. Biomed. Anal. 1997 Volume 16, Issue 1 Pages 31-37
Howard Y. Ando*, and Tycho Heimbach

Abstract: A semi-automated method to determine pKa values spectrophotometrically is described. The method uses the capabilities of a HPLC equipped with a diode array detector (DAD) as a flow injection apparatus. The advantages are low sample consumption, rapid sample throughput, high sensitivity, and precision. Experimental pKa values obtained for two model compounds, benzoic acid (approximately 4.0) and 2-aminopyridine (approximately 6.8), are consistent with literature values. Constant ionic strength was maintained for a wide pH range. Solubilized samples in non-aqueous solvents were also investigated. The weakening in pKa values, often seen when using non-aqueous solvents, was small (0.04- 0.40 pH units) compared to conventional methods.
Spectrophotometry Sensitivity