A coulometric titrator using potentiometric end-point determination

129

A novel, totally electrochemical pH-stat has been constructed and evaluated. The system has a minimum time constant of 2-3 s at which no overshoot or ringing is observed and has a current efficiency of nearly 100% over a wide range of conditions. The applicability of the device to the measurement of reaction rates was tested by determining the hydrolysis rate of a reasonably rapid reaction, namely the hydrolysis of ferfbutyl chloride In water at pH 7 (k = 0.041 ± 0.0007 s~1). It was further tested by assaying the activity of the enzyme penicillinase over the range 0.4 to 26IU, by measurement of the enzyme's pH profile and pH optimum (7.2) and by determining the Michaells constant of the substrate penicillin G (88 µ ). The slat may be used as a controlled current coulometric acid-base analyzer. Good precision and coulometric current efficiency were obtained when mineral acid, In amounts from 0.02 to 5 µ , was rapidly added to a 50-ml electrolysis vessel or when the acid was added slowly from a constant rate buret at rates ranging from 0.1 to 22 µ /min. Amounts of penicillin G ranging from 0.15 to 3.2 µ were also measured by direct enzymic hydrolysis in the electrolysis vessel. In general, the device Is sufficiently fast to permit approximately 100 determinations of acid or base, or about 20 rate determinations per hour.

Section: Figure 2 Details Of the Ph-stat Electrolysis Vesselmentioning

confidence: 99%

“…A number of methods are available for the determination of the sulfite ion (or sulfur dioxide) (1-23). Among these are a method based on the redox reaction between sulfite and iodine (1) as well as several spectrophotometric methods (6,8,9,11). Two potentiometric methods are available for the analysis of the sulfite ion.…”

mentioning

confidence: 99%

Electrochemical pH-stat and controlled current coulometric acid-base analyzer

Adams¹,

Betso²,

Carr³

1976

129

“…Coulometric generation of reagents offers the interesting possibility of controlling the current with the potential difference between a reference potential and the indicator electrode's potential, as was demonstrated by Takahashi and Sakurai (226). Johansson (92) extended the control by making it bilateral: if the sample is overtitrated, the current is reversed.…”

Section: Schonebaum and Breeklandmentioning

confidence: 99%

Potentiometric Titrations

Roe¹

1966

review includes potentiometric titrations and related de-velopments which became available during the period from December 1963 (14S) through November 1965. Publications are grouped into six major categories on the basis of emphasis alone.General reviews of the subject include a book by Ashworth (9) on organic analysis and a report by Headridge, Pierce, and Anderson (79). Redox methods were briefly covered byStephen ( 212), and to a greater extent by Zyka (244,245). TITRATION CURVES AND THEIR INTERPRETATIONAcid-Base Titrations. A fresh approach to the mathematical treatment of mono-and diprotic weak acidstrong base titration curves was developed by Stokes (213). He formu-

“…The thermostat, provided with thyristor regulation and refrigerator was placed in a thermostated room, the temperature of which was 25.0 ± 0.1 °C. In this way, the temperature constancy of the permeation tubes was 25.0 ± 0.03 °C. The tubes were normally weighed every fourth day with a semimicro Mettler balance.…”

mentioning

confidence: 94%

Comparison of high precision coulometric and West-Gaeke methods with the gravimetric method for preparation of standard sulfur dioxide gas blends using permeation tubes

Cedergren¹,

Wikby²,

Bergner³

1975

A high precision coulometric method has been developed to determine the permeation rate of sulfur dioxide from FEP permeation tubes. The relative standard deviation of the method was about 0.04% for titrations performed during a couple of hours. The relative standard deviation of titrations performed on different occasions over a period of one month was 0.1-0.2% which corresponds to a temperature control better than f0.02 OC during the whole period. The coulometric method has been compared with a modified West-Gaeke method according to Scaringelll ef a/. and with a gravimetric method. Some anomalities observed in the West-Gaeke method were explained from the kinetic behavior of the involved reactions. The relative standard deviation of the modified West-Gaeke method was found to be 3 % and this procedure was shown to constitute a significant improvement of the original West-Gaeke method. A comparison between the mean values obtained by the modified West-Gaeke and the coulometric methods and the mean value obtained gravimetrically gave ratios of 97.2 and 99.9 %, respectively. Because of its accuracy, the coulometric method made it possible to detect significant dlfferences in permeation rates for environmental gases such as nitrogen, oxygen, and air.