Talanro, Vol. 37, No. 6, PP. 595-598, 1990 0039-9140/w $3.00 + 0.00 Printed in Great Britain. All rights reserved Copyright 0 1990 Pergamon Press plc

DETERMINATION OF BROMINE IN ORGANIC COMPOUNDS BY HIGH-PERFORMANCE LIQUID

CHROMATOGRAPHY

ARCHANA JAIN, ARCHANA VERMA and KRISHNA K. VERMA*

Department of Chemistry, Rani Durgavati University, Jabalpur 482001, Madhya Pradesh, India

(Received 9 July 1989. Revised 26 September 1989. Accepted 24 October 1989)

Stunmnry-A method is proposed for the determination of bromine in organic compounds (which may also contain chlorine and iodine) by oxygen-flask combustion of the compound followed by pre-column reaction of bromide with acetanilide and 2-iodosobenzoic acid to form 4-bromoacetanilide which is then chromatographed on an ODS column with a mobile phase of methanol:water, 65: 35 v/v, detection at 240 nm, and 4-N-acetylaminotoluene as internal standard. The method is rapid and precise (RSD < 1%), and applicable to a variety of bromine-containing organic compounds; the limit of detection is 0.2 ng of bromine.

The determination of bromine in organic com- pounds requires (i) conversion of organic bro- mine into bromide, and (ii) determination of the bromide.’ The first step involves mineralization of the compound, e.g., by oxygen-flask combus- tion.* Determination of bromide by titratiot?” or spectrophotometry based on displacement reactions such as those with mercury(I1) chlor- anilate’ or mercury(I1) thiocyanate* is neither sensitive nor selective for bromide. A recently published method,9 which is based on the anion- exchange reaction of bromide or chloride with excess of solid silver chromate, and polaro- graphic determination of the liberated chro- mate, should also be applicable to iodide, but cannot be used if the sample contains more than one of these three halides, and is inapplicable to organometalic compounds of metals such as lead, which could yield a precipitate with the chromate liberated. Also, large amounts of phosphate produced by oxidation of phos- phorus, if present, may lead to a positive error. 2-Propanol has been used to reduce the effect of co-precipitation in the argentimetric potentio- metric titration of bromide and chloride.‘0 Oxygen-flask combustion, followed by bromide determination by ion-chromatography with conductivity detection has also been reported.”

Recent developments in precolumn deriva- tization reactions and high-performance liquid chromatography (HPLC)‘*-” led us to convert the bromide formed by oxygen-flask combus-

*Author for correspondence.

tion of organic bromo-compounds into 4-bro- moacetanilide, and to determine this by HPLC.

EXPERIMENTAL

Apparatus

The liquid chromatograph used consisted of a Shimadzu LC-5A pump, an SIL-1 A manual loop injector, a Shim-pack ODS column (particle size 5 pm; 150 x 6 mm i.d.), an SPD- 2A variable wavelength UV detector, and a Shimadzu C-R2AX integrator fitted with a printer-plotter. Peak areas were used for quantification.

Reagents

Acetanilide, 4-N-acetylaminotoluene and 4- bromoacetanilide were synthesized and purified by repeated recrystallization.‘* 2-Iodosobenzoic acid was synthesized by the method of Chinard and Hellerman.i9

The mixed reagent solution, prepared by dissolving 100 mg of acetanilide and 150 mg of 2-iodosobenzoic acid in 100 ml of methanol, was filtered through a 0.45~pm membrane filter. A sulphuric acid solution was made by diluting 1.2 ml of the analytical reagent grade con- centrated acid to 100 ml with methanol. A 63: 35 v/v mixture of methanol and water was used as the mobile phase.

Standards

All bromo-compounds analysed were of high purity. The internal standard was a

595

596 ARCHANA JAIN et al.

solution of 5 mg of pure 4-N-acetylamino- toluene (N-acetyl-4-toluidine) in methanol, diluted to volume in a 50-ml standard flask.

For calibration a standard 30+g/ml bromide solution was prepared by dissolving 223.1 mg of analytical grade potassium bromide in water and diluting to volume in a loo-ml standard flask, then accurately diluting 5 ml of this solution to 250 ml.

Procedures

Calibration. To portions of the calibration standard ranging from 200 to 1400 ~1(6-42 pg of bromide) add 200 ,ul of internal standard solution, 500 ~1 of mixed reagent solution and 200 ~1 of the sulphuric acid solution, dilute the mixture of volume in a lo-ml standard flask with mobile phase, shake the flask well for 1 min, and inject a lo-p1 portion into the HPLC column. Set the eluent flow-rate at 1 ml/min (column back pressure approximately 50 kg/cm*) and monitor the eluate with the detector set at 240 nm and a sensitivity of 0.04 absorbance for full scale deflection.

Determination of bromine in organic com- pounds. Burn a l-4 mg sample, accurately weighed, in the usual way in a 250-ml Schiiniger flask filled with oxygen and containing 10 ml of distilled water, 0.5 ml of 30% hydrogen per- oxide and 3 ml of 0.03M sodium hydrogen carbonate. After the combustion, shake the flask for 5-10 min, rinse the stopper and sample holder with about 10 ml of mixed water, and boil the solution gently to decompose the hydro- gen peroxide, until the volume is reduced to about 10 ml. Transfer the solution quantita- tively to a 25-ml standard flask and dilute to the mark with water. Pipette a 1 or 2 ml portion into a lo-ml standard flask, add 200 ~1 of internal standard solution, 500 ~1 of mixed reagent solution and 200 ~1 of the sulphuric acid sol- ution. Dilute to volume with mobile phase, mix well for 1 min, and chromatograph a lo-p1 portion as above.

RESULTS AND DISCUSSION

Several ion-chromatographic methods are available for the determination of bromide. The detection methods include spectrophotometric monitoring at 200-214 nm,20-22 indirect photo- metry at 240 nm by use of eluents containing species such as phthalate23 which absorb at this wavelength, conductimetry24v25 or ampero- metry. Pre-column derivatization reactions are

used to improve chromatographic separation and detection. Thus, conversion of halides into their arylmercury(I1) derivatives has been reported for their determination by reversed- phase HPLC and detection at 220 nm.26 In the present work, the pre-column derivatization is based on the oxidation of bromide with 2-iodo- sobenzoic acid in acid medium to produce bromine which then brominates acetanilide to form 4-bromoacetanilide and bromide. This sequence of oxidation and bromination reac- tions continues until all the bromide has been

i, ’ i ’ 1'0

Retention Time (min)

Fig. 1. Chromatogram of (a) reagent blank, and (b) pre- column reacted bromide (31 ng) with the same reagent and mixed with 4-N-acetylaminotoluene (5 1 ng) used as internal standard. Peaks: 1 = 2-iodosobenzoic acid 2 = 2-iodo- benzoic acid; 3 = extraneous matter; 4 = acetanilide; 5 = 4-N-acetylaminotoluene; and 6 = 4-bromoacetanilide.

Chromatographic condition as in the text.

Determination of bromine in organic compounds 597

Table I. HPLC determination of bromide

Bromide, fig/lo0 ml

Taken*

60.5” 81.4

128.1b 163.4c 208.2 241 .Sd 276.5 339.2’ 365.7’ 402.3

Found (n = 6)

61.3 80.2

129.5 161.7 210 237 279 336 369 406

RSD, %

0.5 0.3 0.4 0.5 0.4 0.6 0.6 0.6 0.8 0.7

*The aliquot injected also contained (a) 20 pg of trisodium phosphate; (b) 100 pg of potassium chloride; (c) 200 pg of sodium nitrate; (d) 10 pg of potassium iodide; (e) 100 peg of lead nitrate; (f) 50 pg of mercuric chloride.

converted into 4-bromoacetanilide. The acetyl- amino group (in acetanilide) is an ortho-para

director in electrophilic substitution reactions but its large size causes bromination at the ortho-position to be sterically hindered. Aceta- nilide was selected as the derivatization reagent because its bromination is particularly rapid and yields only 4-bromoacetanilide. In the internal standard, 4-N-acetylaminotoluene, the

para-position is already occupied by a methyl group and thus this substance does not undergo bromination. 2-Iodosobenzoic acid is a selective organic oxidizing agent.27-2g Its redox potential at 25” and pH 1 is 1.21 V.28

The best chromatographic separation (Fig. 1) was achieved under the conditions recom- mended, with detection at 240 nm, where most anilides absorb strongly. A calibration graph of peak area for 4-bromoacetanilide vs. amount of bromide injected was linear over the range 642 ng. A response factor of 0.593 for bromide (as 4-bromoacetanilide) relative to 4-N-acetyl- aminotoluene was calculated from the HPLC peak-area ratios for various concentration ratios of the calibration and internal standards. The percentage of bromine in the sample is calculated from

ACuD % Br = 59.3 AW IS

where A/As is the ratio of the peak areas for 4-bromoacetanilide and the internal standard, Cu the concentration of internal standard, W the weight of sample, and D the dilution factor. Results are given in Table 1 for the analysis of ten standard solutions of bromide, with or without the presence of various ions which may be formed during the oxygen-flask combustion

Table 2. HPLC determination of bromine in organic compounds

Bromine, %

Compound Theory Found (n = 5) RSD, %

CBromoacetanilide 3-Bromobenzoic acid 3-Bromocamphor 5-Bromo-2chlorobenzoic acid 5-Bromosalicyl-4’-chloroaniline 2-Bromoacetamido-2’, 5’-dichloro-

benzophenone 2-Bromoacetamido-5-chloro-2’-

fluorobenzophenone

37.33 37.2 0.5 39.75 39.9 0.5 34.61 34.5 0.6 33.97 33.8 0.7 24.50 24.6 0.6

20.71 20.7 0.7

21.58 21.7 0.8 5-Bromo-2-iodobenzoic acid 24.46 24.6 0.6

Table 3. Comparison of diverse HPLC methods for bromide determination

Method Detector LD* ULD* Reference

Liquid chromatography on Zipax SAX column 200 nm 10 ng 5 flcg 30

Anion-exchange chromatography 600nm 15 ng 160 ng 31 Ion-exchange chromatography 190 nm 1 ng/ml 100 ng/ml 32 Anion-exchange chromatography conductivity 20 ng - 33 Liquid chromatography on

aminopropylisilica 214 nm 1 ng 50 ng 34 Reversed-phase ion-interaction

chromatography 205-220 nm 24 ng - 35 Pre-column derivatization to

4-bromoacetanilide 240 nm 0.2 ng 42 ng This work

*LD = limit of detection; ULD = upper limit of detection.

598 ARCHANA JAIN et al.

of organic compounds and may interfere in other methods for determination of bromide. Large amounts of diverse ions such as phos- phate, chloride and nitrate can be tolerated. Other ions which do not interfere when present in up to 50-fold weight ratio to bromide include sulphate, calcium, barium, magnesium, zinc, copper(I1) and iron(II1). The present method is therefore simple and specific for the deter- mination of bromine in organic compounds (Table 2). The limit of detection is 0.2 ng of bromide injected (S/N = 2). A comparison of some HPLC methods with the present one in terms of detection limit and measurement range is given in Table 3.

Acknowledgements-Thanks are due to the Council of Scientific and Industrial Research, New Delhi, for a Research Associateship to A.J., and to the University Grants Commission, New Delhi, for financial assistance to K.K.V.

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