Taianta, 1966. VoL 13, pp. 92s to 928. Perganwa m Ltd. Printed in Northern Ireland

TITRIMETRIC DETERMINATION OF HYDROGEN PEROXIDE IN ALKALINE SOLUTION

W. H. MCCURDY JR. and H. F. BELL Brown Laboratory, University of Delaware, Newark, Delaware, U.S.A.

(Received 5 January 1966. Accepted 15 February 1966)

Summary-Direct titration of hydrogen peroxide in alkahne bromide media has been a~omplish~ with sodium h~~o~te, The relative standard deviation is O-2 %. A photometric end-point is recommended for the determination of Oslo-1.0 mequiv of peroxide. Larger sampfes are evaluated by use of Bordeaux Red as visuaf indicator. The hypo- chlorite procedure compares favourably with iodometry and permanga- nate in the analysis of commercial peroxides.

TITRIMETRIC procedures for hydrogen peroxide employ iodometry,l permanganate2 or cerium(IV)3 in acidic media. No simple procedure of comparable accuracy has been described for the direct determination of peroxide in alkaline solution. Potentiometric titration with potassium hexacyanoferrate(II1) has been proposedP Several procedures use hypochlorite or hypobromite in dilute alkali. Campe et al.,5 recommend a reaction time of 1 hr in OG4M sodium hydroxide containing excess of hypobromite, and an iodometric finish. Excess hypobromite has been back-titrated with arsenite after addition of potassium iodide and Brasilin indicator in bicarbonate medium.6 In a study of amperometric titrations with hypochloriteP unsatisfactory results obtained in the direct titration of peroxide were attributed to slow reaction kinetics. Recently, Norkus and Valsiuniene6 reported the titration of peroxide with hypochlorite in the presence of potassium bromide using a potentiometric end-point. Depending on titration time and electrode surface area, heterogeneous decomposition of hydrogen peroxide at platinum electrodes9 may vitiate accurate results by electrometric end-point techniques.

A careful investigation of the hypobromite oxidation of hydrogen peroxide was undertaken to resolve the difference of opinion concerning the utility of this reaction. It is shown that satisfactory determination of O-10-3*0 mequiv of hydrogen peroxide may be a~omplished by direct titration in alkaline bromide solution with sodium hypochlo~te, detecting the end-point photometricalIy or visually.

Reagents EXPERIMENTAL

Distilled deionised water and reagent-grade chemicals, if obtainable, were used in all solutions. Sodium hypochlorite. A O-IN stock solution was prepared from reagent-grade calcium hypo-

chlorite by precipitation with a slight excess of sodium carbonate, filtration and dilution to volume. This solution was standardised every three or four days against arsenic(III) oxide in bicarbonate buffer.lO

Potassium bromide. 10 % Solution. Bu& (pH 9.2). A O*lM solution of sodium borate decahydrate. Peroxkfe samples. Sodium perborate (Baker and Adamson), 30 % hydrogen peroxide and 3 %

hydrogen peroxide (J. T. Baker) were used to prepare O*lN stock solutions. The peroxide content was determined before use, by iodometry.’ ~ios~lphate was standardised against potassium iodate; ~~an~nate used in comparison studies was standardised against arsenic(fI1) oxide.18

Zndicatur. A 0.2% sohttion of Bordeaux Red (C. I. No. 16180).

925

926 W. H. MCCURDY, JR. and H. F. BELL

dpparatris:

Photometric titrations were performed in a 2.0 x 5-O x S-O-cm rectangular cell constructed from Vitreosil tubing (Thermal American Fused Quartz Co., Montville, N.J.). Optical density measure- ments were made with a Beckman DU spectrophotometer with photomultiplier. The cell chamber was enlarged slightly by inserting a fibre-board spacer. Titrations were performed with a 5-ml microburette with teflon stop-cock. All burettes and pipettes were calibrated.

Procedure

Photometric method. Mix samples of peroxide with one-thud their volume of buffer and one- tenth their volume of 10% potassium bromide solution in the photometric titration cell. The total volume of the solution is 25-40 ml. Adjust the spectrophotometer to read 04Ml absorbance at a wavelength of 330 mp. Add standard hypochlorite with stirring until the first increase in absorbance occurs. Make several additional 0*20-ml increments of h~~orite, measure the absorbance and locate the end-point in the usual manner.

V&al j~jcator rnet~~. Peroxide samples larger than 1 mequiv may be determined by dirxt titration with sodium hypochlorite in a solution containing 50 ml of buffer, 10 ml of 10% potassium bromide and l-2 drops of Bordeaux Red indicator. A fresh drop of indicator should be added just before the end-point. A blank correction (OGOS ml/drop indicator) should be applied.

RESULTS AND DISCUSSION

Optimum conditions of pH and bromide concentration were investigated as well as several possible sources of interference. Hypochlorite is rapidly converted into hypobromite in bromide solutions at pH 869.5. l1 Any concentration of potassium bromide between O-5-2*0 g/lo0 ml of solution was found to yield a satisfactory titra- tion and sharp end-point at pH 9.2. By monitoring the absorbance of hypobromite at 330 rnp, it was readily shown that reaction of hydrogen peroxide with hypochlorite is complete within a few seconds at this PH. Calculated times for 99% reaction based on rate studies by Connickla lead to the same conclusion. It is interesting to note that the colour of the stable free radical 2,2-diphenyl-l-picrylhydr~l (DPPH) dissolved in methanol is unchanged by intermediates or products of the hypochlorite-peroxide reaction at pH 9.2. This result indicates probable absence of free-radical side reactions at pH 9.2. DPPH does change colour when hypochlorite is added to an excess of per- oxide in acidic media.

When sodium hypochlorite was standardised against thiosulphate iodometrically, a normality about 0.5% higher than the normality against arsenic(II1) oxide was obtained. This was undoubtedly caused by the hypochlorite containing chlorite, as impurity, which reacts with iodide in acid but not with arsenic(II1) or peroxide in alkaline rnedia.s Therefore arsenic(II1) oxide is recommended as primary standard for sodium hypochlo~te in this determination, Comparison of Bordeaux Red, ~aranth, Quinoline Yellow and Tartrazine revealed a distinct superiority of Bordeaux Red. The photometric end-point is more time-consuming than the indicator method but possesses the advantage of eliminating the indicator blank correction in the analysis of small samples of peroxide. Results illustrating the determination of hydrogen peroxide in alkaline media by both procedures are presented in Table I, (A) and (B).

Slightly high results shown in Table I (A) appear to balance slightly low results in Table I (B), indicating that Bordeaux Red indicator may be changing colour before the true equivalence point. However, least squares regression analysis of data from both hypochlorite procedures failed to show significance bias at the 95% confidence level. Standard deviations of O*OOlO and 0$013 in slopes and 0+004 and O@O27 mequiv of peroxide in intercepts were calculated for photometric and visual indicator methods respectively. A comparison of results in titration of several commerical

Titrimetric determination of hydrogen peroxide in alkaline solution 927

TABLE I.-ANALYSES OF PEROXIDE SAMPLES

Taken, Found, Number of mequiv mepiv trials

(A) Photometric Method* 0.0834 0.1802 0.3076 0.3603 1.168

0.0837 0.1803 0.3084 0.3604 1.170

Error, %

1 0.4 2 0.1 2 0.3 2 0.0 1 0.2

Rel. std. dev. 0.2%

* Results based on standardisation by hypochlorite visual indicator method.

(B) Visual Indicator Method? 0.9786 1.469 1.950 2443 2.934

0.9770 2 -0.2 1.467 2 -0.1 1.951 2 0.0 2440 -0.1 2.926

; -0.3

Rel. std. dev. 0.2%

t Results based on iodometric standardisation.

(C) Comparison Studyt: H,O, and rel. std. dev., % Sample Permanganate Iodometry Hypochlorite

3 % Hydrogen peroxide 3.452 0.4 % 3.401 0.10% 3.417 0.4 % 30 % Hydrogen peroxide 29.34 0.0, % 29.19 0.10% 29.20 0.0, %

Sodium perborate 2164 0.0, % 21.58 O.l,% 21.57 0.0, %

$ Each result is the average of at least 4 titrations.

peroxide samples by permanganate, iodometry and hypochlorite is given in Table I(C). Although equal precision was obtained by the three methods, all permanganate analyses are significantly higher than results by the other methods at the 99% confidence level. For the 3 y. hydrogen peroxide which contains O-01 y. of acetophenetidin as preserva- tive, the hypochlorite analysis is 0.5% higher than the iodometric results.

Other interferences encountered in determination of peroxide with hypochlorite are similar to those reported in the spectrophotometric evaluation of ammonia.ll In general all reduced forms of nitrogen and sulphur interfere to some extent. Quantitative determinations of peroxide in the presence of 0.1 g of sodium oxalate, sodium pyrophosphate, sodium stannate or sodium bromate, 10 ppm of acetanilide or 8-quinolinol or 1 ppm of disodium-EDTA were satisfactory.

Attempts to titrate organic peroxides such as benzoyl and succinyl peroxide in alkaline solution with the hypochlorite procedures were unsuccessful. These com- pounds either react very slowly with hypobromite or react directly with bromide to form hypobromite.

Acknowledgement-This work was supported in part by funds furnished under subcontract SU 603941/63 by Melpar, Inc., Falls Church, Virginia.

5

928 W. H. MCCURDY, JR. and H. F. BELL

Zusammenfassang-Die direkte Titration von Wasserstoffpcroxyd in alkalischen Bromid-Medien wurde mittels Natriumhypochlorit be- werkstelligt. Die relative Standardabweichung betrlgt 0,2x. Zur Bestimmung von O,lO-1,0 miiq Peroxyd wird photometrische Endpunktsbestimmung empfohlen. Gr613ere Mengen werden mit Bordeauxrot als visuellem Indikator titriert. Die Vorschrift mit Hypochlorit zeigt Vorteile vor der Jodometrie und der Permanganat- Titration bei der Analyse handelstiblicher Peroxyde.

R&un~On a realise le dosage direct de l’eau oxygenee en milieux alcalms en presence de bromure au moyen d’hypochlorite de sodium. L’ecart type relatif est de 0,2x. On recommande un point de virage photometrique pour le dosage de O,lO-1,O milliequiv. de peroxyde. On dose des echantillons plus eleves par l’emploi derougeBordeaux comme indicateur visuel. La methode a l’hypochlorite est favorablement com- parable a l’iodometrie et a la manganimetrie pour l’analysedeperoxydes commerciaux.

REFERENCES

1. I. M. Kolthoff, Z. anul. Chem., 1921,60,400. 2. C. E. Huckaba and F. G. Keyes, J. Am. Chem. Sot., 1948,70,1640. 3. E. C. Hurdis and H. Romeyn, .&al. C’hem., 1954,26,320. 4. J. Vulterin and J. Z$ka, Chem. Listy, 1954,48,619. 5. A. Campe, A. Claeys and J. Pijck, Bull. Sot. Chim. Be&es, 1964,73,622. 6. J. Bitskei, Acta Chim. Acad. Sci. Hung., 1955, 8,203. 7. H. A. Laitinen and D. E. Woerner. Anal. Chem.. 1955.27.215. 8. P. Norkus and J. Valsiuniene, Lietuoos TSR Mokslu Akad. Darbai Ser. B, 1962, No. 2, 37. 9. J. E. Harrar, Anal. Chem., 1963, 35, 893.

10. I. M. Kolthoff and R. Belcher, Volumetric Analysis, Vol. 3, pp. 282, 580, 75. Interscience, New York, 1957.

11. J. H. Howell and D. F. Boltz, Anal. Chem., 1964,36, 1799. 12. R. E. Connick, J. Am. Chem. Sot., 1947,69,1509.