Kinetic study of the cyanogen bromide-pyridine reaction applied to thiocyanate determinations in serum

Landis, J. B.; Rebec, Monica; Pardue, Harry L.

doi:10.1021/ac50014a029

Anal. Chem.

1977

DOI: 10.1021/ac50014a029

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Kinetic study of the cyanogen bromide-pyridine reaction applied to thiocyanate determinations in serum

J. B. Landis¹,

Monica Rebec²,

Harry L. Pardue³

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Cited by 20 publications

(14 citation statements)

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“…In an earlier report, we used propagation of error theory to show that the relative standard deviation of the rate of a first-order reaction is zero at t = 1/k = and presented experimental evidence verifying this result (6). Three assumptions were made in that development: (1) the reaction of interest is first order or pseudo first order, (2) sources of error other than variation in the rate constant are negligible, and (3) the rate can be estimated by instrumental or numerical methods at any time during the reaction.…”

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confidence: 96%

“…When the integrals of eq 6 are evaluated, we obtain eq 7. Two important consequences result from this equation: (1) the computed rate differs from the true rate by a constant factor that depends only on At/ , and (2) the relationship is valid for any time during the reaction. It is not obvious that eq 7 is in general a good approximation for the true rate Rt, however.…”

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Improvement of reaction rate measurement precision using the temporally optimized fixed-time ratemeter

Engh¹,

Holler²

1988

Anal. Chem.

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The domain of application of the flxed-time integrating ratemeter method is extended to ail times during first-order and pseudo-first-order reactlons. Propagation of error theory is applied to rate expressions to glve the optimum tlme for rate measurement as a function of Integration wldth. The maximum integration wldth consistent with the optimum measurement time is determined. Experimental data collected with a stopped-flow mixer uslng the iron( I I I)-thlocyanate reaction show excellent agreement with theory. The relative standard deviation of concentration of flve determlnations of a thlocyanate unknown was 0.16% under conditions of random varlabie temperature.It has been shown previously that the precision of reaction rate measurements can be improved by selection of the optimum time at which to make these measurements (1-6). To make best use of an optimum time for measurement, a reliable method of obtaining the rate at a single time is needed. The fixed-time integrating ratemeter method (7) gives an estimate of the rate a t a time at the center of an interval over which the reaction curve can be considered to be linear. In contrast to many methods of rate estimation, this approach is highly resistant to instrumental noise. In this paper we will show that this method is valid under first-order and pseudo-firstorder conditions at any time during the reaction, that the precision of the rate obtained by this method can be temporally optimized, and that there is a maximum integration width consistent with temporal optimization. Finally, we present experimental verification of temporal optimization and signal-to-noise-ratio enhancement resulting from optimum use of the integrating ratemeter.Several strategies have been proposed to temporally optimize reaction rate measurements. Landis et al. (I) recognized that a measurement time o f t = l / k = T is optimum, where k is the first-order or pseudo-first-order rate constant for the reaction, but only used this result for error analysis. Davis and Renoe (2) developed equations to obtain optimum times for wide-interval fixed-time rate measurements. Davis and Pevnick (3) considered coupled enzyme reactions and obtained optimum times for several cases of variations in one or both of the rate constants. Most recently, Wentzell and Crouch presented a two-rate method (4) and compared the accuracy and precision of their method and several other methods under various conditions (5). In an earlier report, we used propagation of error theory to show that the relative standard deviation of the rate of a first-order reaction is zero at t = l / k = 7 and presented experimental evidence verifying this result (6). Three assumptions were made in that development: (1) the reaction of interest is first order or pseudo first order, (2) sources of error other than variation in the rate constant are negligible, and (3) the rate can be estimated by instrumental or numerical methods at any time during the reaction. To take full advantage of the simplicity of a single-rate measurement at t ...

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confidence: 96%

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confidence: 99%

Improvement of reaction rate measurement precision using the temporally optimized fixed-time ratemeter

Engh¹,

Holler²

1988

Anal. Chem.

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“…These approaches range from control of experimental variables such as pH and temperature (1)(2)(3)(4) to numerical correction of data for variations in such variables (5,6). There have also been studies on the limitations of different methods of kinetic analysis (7)(8)(9)(10)(11).…”

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confidence: 99%

Application of temporal optimization to enzyme-based reaction rate methods

Calhoun¹,

Holler²

1988

Anal. Chem.

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“…Thus, traditional single-component reaction-rate methods, such as the fixed-time (1, 9,10), variable-time (1,11-13), and derivative (14-18) methods, require careful control of the experimental conditions. Several methods have been suggested to alleviate this constraint (19)(20)(21)(22)(23), but most of these, while reducing the rate constant dependence, do not eliminate it.…”

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confidence: 99%

“…A method developed by Cornell (19) in 1962 for fitting exponentials through partial sums is also applicable to the problem of between-run variations in the rate constant. While the Cornell method has been extended to other kinetic systems by Kelter and Carr (20)(21)(22), it has not appeared extensively in the analytical chemistry literature and in this sense its application to reaction-rate methods of analysis is fairly recent. Wentzell and Crouch (23) have introduced a new method, the two-rate method, which attempts to eliminate the dependence on between-run variations in the rate constant by using rate measurements made at two times during the course of the reaction.…”

mentioning

confidence: 99%

Reaction-rate method of analysis insensitive to between-run changes in rate constant

Wentzell¹,

Crouch²

1986

Anal. Chem.

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Kinetic study of the cyanogen bromide-pyridine reaction applied to thiocyanate determinations in serum

Cited by 20 publications

References 14 publications

Improvement of reaction rate measurement precision using the temporally optimized fixed-time ratemeter

Improvement of reaction rate measurement precision using the temporally optimized fixed-time ratemeter

Application of temporal optimization to enzyme-based reaction rate methods

Reaction-rate method of analysis insensitive to between-run changes in rate constant

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