Difference between the inflection point and the equivalence point in coulometric titrations of weak acids

Marinenko, George; Champion, Charles E.

doi:10.1021/ac60279a021

Cited by 7 publications

(6 citation statements)

References 10 publications

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“…Based on the result presented in Table 1 , the current efficiency is considered to be 101.1 ± 0.6%, within the limit of its experimental determination. As mentioned before, the coulometric determinations of strong acids or bases most nearly approach the ideal measurement situation [ 8 , 9 , 10 ] in aqueous media completely free of reactive impurities. A current efficiency of 100% is only obtainable for one type of electrode reaction: the electrolysis of a molten salt or of a pure solvent; and this only holds when the products of the anode and cathode reactions are prevented from reaching the other electrode.…”

Section: Resultsmentioning

confidence: 99%

“…[ 7 ]. The coulometric determination of strong acids or bases most nearly approaches the ideal measurement situation [ 8 , 9 , 10 ] in aqueous media completely free of reactive impurities. However, no matter what the working conditions are, at least one secondary reaction occurs in competition with the desired electrode reaction, even though it may be very slight.…”

Section: Introductionmentioning

confidence: 99%

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Accurate and precise coulometric determination of sulfur dioxide in compressed gas mixtures

Mitchell

Bell

1991

J. RES. NATL. INST. STAN.

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Coulometry has been established as an important and reliable method for the determination of acidic compounds. The analytical method and simple apparatus described here arc applied to the precise and accurate determination of sulfur dioxide in nitrogen, specifically in compressed gas cylinders at nominal concentrations of 50 and 100 µmol/mol (ppm). This method is constant current coulometry where the magnitude of the current is set by the balance between the electrochemical generation of OH−, the flow of SO2, and the chemical reaction of the solution. The method is direct, rapid, and can be refined further to provide analysis at the nanomol/mol level.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Accurate and precise coulometric determination of sulfur dioxide in compressed gas mixtures

Mitchell

Bell

1991

J. RES. NATL. INST. STAN.

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“…Since the acid was close to stoichiometric H :IB0 3 , this pH measurement was made in the (~pHI ~C)max region and thus in the region of maximum sensitivity. To determine the differe nce (in coulombs) between the pH at this final rinse point and the pH at (~pH/~C)max' a small amount of hydrochloric acid (10-20 fLeq) was added to the cell and the regenerated boric acid was retitrated differentially to establish pH at (~pHI ~C)m ax ' This process can be repeated several times to improve the evaluation of the inflection point (9). In practice, then, a correction of a few thousandths of a percent is applied at the end of the titration for the difference between the final pH and the pH at the inflection point.…”

Section: Methodsmentioning

confidence: 99%

“…The pH at the completion of the passage of charge through the cell at high current was 8.234 (point B on the graph), corresponding to an overtitration of 0.178 C. Thus, it is necessary to correct the total charge by -0.178 C, and the number of coulombs equivalent to the delivered sample of boric acid is 935.026 C. By Faraday's law this corresponds to 9.69069 meq of acid or the weight of boric acid of 0.599205 g. Since 0.599207 g of the acid was weighed out, the assay of th e material found in this titration is 99.9997 weight percent H :IB0 3 • In an earlier communication the error which resulted from the difference between the inflection point and the equivalence point in coulometric titration of boric acid was evaluated [9]. It was found that when cK" is 10 -9 , the error is 0.003 percent, and for larger cKa it is .…”

Section: Methodsmentioning

confidence: 99%

High-precision coulometric titrations of boric acid

Marinenko¹,

Champion²

1971

J. RES. NATL. BUR. STAN. SECT. A.

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An abso lute me th od wa s deve lope d for th e de te rmin a ti on of boric ac id by coulome tri c titrim etry. Th e prec is ion of th e me thod , ex pressed as th e s ta nd a rd de viation of a s in gle de te rmin ation is 0.0033 pe rcen t. C ha nges in th e inves ti gate d titration param ete rs produ ced no s ignifi cant effects on th e titrati o n res ult s. Indi c a ti ons are th a t within th e un ce rtainty of meas ure me nt s the me thod is b ias free.Key words: Acc ura te a na lys is; bori c a cid : co ulometri c titra ti on ; hi gh-p recision acid im e try; hi gh prec is io n co ul ome try. . IntroductionTh e National Bureau of Standard s condu cts a great deal of researc h towards es tabli s hm e nt of absolute standard s in all areas of th e meas ure me nt field . One ar ea whi ch e nables analyti cal quantifi cation of c he mical property on the absolute basis is co ulo me try. For thi s reason, ove r a numbe r of years, an inte nse effort has bee n mad e to d evelop me thods for precise analysis and to test the acc uracy of th ese methods [1 -5].1 This paper is one of a series of articles on th e de velopm e nt of pre cise coulometri c me th ods and th eir appli cation to c harac te rizati on of high purity standard refere nce materials (SRMs).Th e expanding use of boron and its co mpounds in nuclear tec hnology a nd th e NBS program co ncern ed with the iss uan ce of an SRM for ne utron flux monitorin g necessitated th e de ve lopme nt of a me thod for th e prec ise a nd acc ura te determination of thi s ele me nt. Th e mos t wid ely used me thod for the determination of milligram amounts of boron involves titration of boric acid in the presence of a polyol [6], us ually mannitol. Howe ver, thi s method is somewhat empirical in nature , partic ularly with re s pect to the amount of polyol required for titration and moreo ver, is generally precise to only a fe w parts p e r th ousand. Le Duigou and Lauer recently re ported a procedure for the coulome tric de te rmination of boron [7]. Th eir precision for l50-mg samples of boric acid was on th e orde r of 0.02 pe rce nt. Thus, th e m ethod appeared promising from the standpoint of precision, but th e di s turbin g fact is that these authors found a di screpancy of 0.1 perce nt be twee n the co ul ome tri c valu e a nd the va lue obtain ed b y conventional acidim e tri c titration . Referrin g to the coulo-* Presc nl ~Iddr~ss: \I c th ods Hesear('h a nd Tec hni(' a l Service Divi s ion. Eastrna n Kodak. Hoc hesle r, New Yo rk 14603. IFi gures in brackets indi cat e lit erature re fe rences at th e e nd of t hi s paper. me tri c me th od , th ese a uthors co ncluded that further studi es are necessary to improve its acc uracy. This co nclusion alone was s ufficie nt to a rouse our inte rest in the co ulometri c be havior of th e sys tem, particularly from th e s tandpoint of poss ible so urces of e rror whi c h apparently have not bee n ruled out in th e coulometric inves ti gation s of Le Duigo u and Lauer.W e th erefore und ertook inves ti gati on ...

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“…However, more than 0.1 M of mannitol was required for the production of normal anion chromatograms. Since the acid dissociation constant of the borate-mannitol complex becomes larger in proportion to the mannitol concentration, 13,14 the complex under this condition exhibits a strong acidic property and the background conductivity after suppression remained at a high level. The capacity gradient, starting with an initial mannitol concentration above 0.1 M, suffered from a large negative baseline drift.…”

Section: Disappearance Of the Ion-exchange Property On A Hydroxy Resi...mentioning

confidence: 99%

Characteristics of a column suitable for capacity gradient chromatography with a borate eluent

Yamamoto

Kodama

Matsunaga

et al. 2001

Analyst

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In capacity gradient elution, the gradient separation of ionic species is achieved by decreasing the ion-exchange capacity of a column during the course of the separation. Diol-type hydroxy groups on the resin surface form anionic complexes with borate as an eluting reagent. Thus, a chemically bonded anion-exchange column enriched with residual hydroxy groups allows the creation of a capacity gradient. An increase in the amount of the complex formed gradually brings about a decrease in the ion-exchange capacity of the column, and strongly bound analyte ions are eluted. We investigated the characteristics of a column suitable for this eluent system. The concentration of borate eluent required to remove the ion-exchange capacity depended inversely on the ratio of the residual hydroxy groups to functional groups. On a column in which this ratio was approximately 100, the ion-exchange capacity could easily be adjusted by using a low concentration of mannitol as a competing reagent. Use of this column led to very small baseline shifts during the borate-mannitol gradients, and to the simultaneous determination of anions with widely varying retention times.

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Difference between the inflection point and the equivalence point in coulometric titrations of weak acids

Cited by 7 publications

References 10 publications

Accurate and precise coulometric determination of sulfur dioxide in compressed gas mixtures

Accurate and precise coulometric determination of sulfur dioxide in compressed gas mixtures

High-precision coulometric titrations of boric acid

Characteristics of a column suitable for capacity gradient chromatography with a borate eluent

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