Diffusional Microtitration of 20 μL Samples with Optical Indication

Hui, Kwong Yue; Gratzl, Miklós

doi:10.1021/ac9607976

Cited by 11 publications

(14 citation statements)

References 8 publications

(19 reference statements)

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“…The diffusion coefficient of ferricyanide ion (D = 6.3 × 10 -6 cm 2 /s) being almost 2 orders of magnitude lower than that of H + or OH -, diffusion cannot effectively homogenize even a 1 µL drop ECS Transactions, 19 (6) 65-70 (2009) during the delivery process. Yet, the voltammetric current measured by a spatially averaging Fermat's spiral electrode deposited onto a 2D substrate obtained in an unstirred solution is essentially identical with that in a stirred solution (2).…”

Section: Resultsmentioning

confidence: 78%

“…The length increments of a linear spiral in concentric cylindrical shells increase linearly with the radius similar to the volume of the individual shells themselves. [2] where α and β are geometry constants which influence the density, or in other words the length per angle of rotation of these spiral electrodes. Therefore, by changing the values of these geometry constants many different variants of 1D spiral SAEs can be obtained.…”

Section: Resultsmentioning

confidence: 99%

“…Continuous dosing or removal of a reagent or analyte into or from a microliter sample poses a similar problem. Inhomogeneous concentration distribution of H + /OH -ions develops in samples that are about 5µL or larger in volume despite their high diffusion rate, as seen in diffusional microtitration (1,2). To address this issue, we have developed and tested a novel design of electrodes that we call spatially averaging electrodes, SAE, that can report 3D spatially averaged bulk concentrations of inhomogeneous samples without the need for stirring (3).…”

Section: Introductionmentioning

confidence: 99%

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Spatially Averaging Electrodes

2009

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In contrast to many optical techniques, both the potentiometric and voltammetric measurement approach are only capable of reporting the concentration of the analyte of the sample solution that exists adjacent to the diffusion layer. Therefore, electrochemical measurement techniques in general cannot be used to assess 3D averaged bulk concentrations of inhomogeneous samples. This may pose a problem in very small samples which cannot be optically analyzed and where homogenization by stirring is difficult. We discuss the concept of spatially averaging electrodes that can, due to their designed geometry, report 3D spatially averaged bulk concentration of inhomogeneous samples that have some type of symmetry. Within a given type of symmetry an infinite variation of concentration distributions may exist. Electrode geometries for samples with two different types of symmetries, hemispherical and cylindrical, are discussed. Alternate designs with intrinsic redundancies to correct for any systematic errors in the measurement are also shown.

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Section: Resultsmentioning

confidence: 78%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spatially Averaging Electrodes

2009

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“…Presumably the above instrumentation could be adapted to the determination of pK a values but this has not been reported. Diffusional microtitration has been employed to conduct acid-base titrations in samples ranging in size from microliters to femtoliters [17][18][19][20] but, again, with endpoint detection as the primary aim. The determination of pK a values by diffusional microtitration may be complicated by the necessity to account for not only the diffusion of titrant but the back-diffusion of the titrated analyte species.…”

Section: Introductionmentioning

confidence: 99%

Microscale Titrimetric and Spectrophotometric Methods for Determination of Ionization Constants and Partition Coefficients of New Drug Candidates

Morgan

Liu

Anderson

1998

Journal of Pharmaceutical Sciences

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This study describes the adaptation of conventional titrimetric and spectrophotometric techniques to a microscale for the determination of drug ionization constants (pKa) and partition coefficients (log P). The apparatus for determining pKa and compound purity (or equivalent weight) consists of a three-port conical glass microvial maintained at 25 degrees C, a pH microelectrode, and a microinjection pump equipped with a 10 microL gastight syringe for titrant delivery. Sample mixing and protection from atmospheric CO2, which is particularly important at the microscale, is accomplished using a fine stream of water-saturated N2 bubbles. Simple titrimetric procedures combined with ionic equilibria models which allow the accurate determination of pKa and purity (or equivalent weight) using sample sizes in the microgram range and solution volumes of 10-100 microL were developed and validated using acetic acid and tromethamine. Simultaneous determinations of pKa, purity or equivalent weight, and octanol/water partition coefficient were shown to be possible from a single sample of a test solute by adapting the pH-metric technique to a microscale. Using benzoic acid as a model compound, a pKa of 4.24 and octanol/water partition coefficient of 64 were obtained, in close agreement with the literature values. The principles employed in titrimetric analysis were also applied to demonstrate the spectrophotometric determination of benzoic acid's pKa and partition coefficient using only 6 micrograms of compound. The microscale titration method was then used to determine the two pKa values of an "unknown" diprotic acid containing a carboxyl and an aromatic SH group. The phenyl thiol pKa was confirmed using the microscale spectrophotometric procedure.

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“…A different principle for dispensing titrant was reported by Gratzl, where the titrant was added to the sample by diffusion through a membrane. The method has been utilized in several applications, including complexometric, precipitation, and acid−base titrations of 1−20-μL sample volumes. − In a particular mode, where a miniaturized buret and a colorimetric detection was used, acid−base titrations of 1−10-pL sample volumes have been demonstrated.…”

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confidence: 99%

Nanoliter Titration Based on Piezoelectric Drop-on-Demand Technology and Laser-Induced Fluorescence Detection

1998

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An automated technique for fast acid−base titration of 9-nL sample volumes has been developed, based on the use of piezoelectrically driven pipets and laser-induced waveguide fluorescence detection. As an example, a standard titration of a H2SO4 solution with NaOH was examined by utilizing fluorescein as an indicator. The technique had reproducibility in quantitative determination on the order of 1%. The technique allows hundreds of individually executed unattended titrations to be performed in a few hours on an area less than 3 cm2. The lowest amount of acid titrated was ∼670 fmol.

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Diffusional Microtitration of 20 μL Samples with Optical Indication

Cited by 11 publications

References 8 publications

Spatially Averaging Electrodes

Spatially Averaging Electrodes

Microscale Titrimetric and Spectrophotometric Methods for Determination of Ionization Constants and Partition Coefficients of New Drug Candidates

Nanoliter Titration Based on Piezoelectric Drop-on-Demand Technology and Laser-Induced Fluorescence Detection

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