Microdetermination of alizarine red S

XfICROCIIEhfICAL

JOURNAL

13, 671-673 ( 1968)

Microdetermination

of Alizarine

Red S

0. C. SAXENA Chemical Laboratories, University of Alluhabad, Alluhabad, India Received May 14, 196S INTRODUCTIOS

Literature has failed to give any information towards the denomination of alizarin red S. Its oxidation with alkaline periodate and alkaline ferricyanide (1) results in the formation of 1,2,9,10-anthracenetetrone-3-sulfonate, is reported in the literature. Hence an attempt is made to determine it. The present method deals with the determination of alizarin red S in micro quantities by oxidizing with ceric sulfate. The oxidation products were mainly phthalic acid and formic acid but not the above mentioned tetrone. The main products of oxidation were isolated, detected, and confirmed by specific tests. The present method is quick and accurate. EXPERIMENTAL

METHOD

Reagants employed. Alazarin red and N-phenyl anthranilic acid (B.D.H. grade); ceric sulfate (Technical B.D.H. grade); ferrous ammonium sulfate, sulfuric acid and potassium dichromate (ANALAR B.D.H. grade). The 0.01 M ferrous ammonium sulfate (in 1 N H,SO, ) solution is standarized by titrating against a standard solution of potassium dichromate using N-phenyl anthranilic acid as indicator. The 0.0041 M ceric sulfate (in 5 N H,SO,) solution is standarized by titrating against a standard solution of ferrous ammonium sulfate (in 1 N H,SO,) using N-phenyl anthranilic acid as indicator. PROCEDURE

A known volume (prepared by exact weighing) of alizarin red S solution is taken by a micropipette in a beaker containing a standard solution of a known excess of ceric sulfate (in 8 N H,SO+). The reaction mixture thus prepared, is boiled for about 2-3 minutes. After cooling 671

672

ALIZARIN

RED

S

at room temperature the remaining solution of ceric sulfate is titrated against a standard solution of ferrous ammonium sulfate (in 1 N H,SO, ) using N-phenyl anthranilic acid as indicator. At the sharp end point the brown red color vanishes. TABLE MICHODETEHMINATION

1 OF ALIZARIN RED S

Amount of alizarin red S Amount of ( O.tO(&M) Ce( SO,), FeSO,* ( NH,),SO,FeSO,* (NH,),SO,alizarin red 0.0041 M 0.01 M 0.01 M S found Error (ml) (mg/liter) (ml) (mg/liter) (%) (ml) (ml) 0.25 0.50 0.75 1.00 1.75 2.00

0.1801 0.3602 0.5403 0.7205 0.2610 1.4410

20.0 20.0 20.0 20.0 20.0 20.0 20.0

8.20 7.48 6.80 6.12 5.42 3.30 2.62

0.78 1.40 2.08 2.78 4.90 5.58

0.1851 0.3602 0.5353 0.7151 1.2610 1.4357

2.7 0.0 0.9 0.7 0.0 0.3

RESULTS AND DISCUSSION

Results are shown in Table 1. The range in which alizarin red S has been estimated varies from 0.1851 to 1.4357 mg/liter. The reaction between alizarin red S and ceric sulfate takes place at 14 equivalence, i.e., seven oxygen atoms are required for oxidation up to this stage. Oxidation results in the formation of phthalic acid and formic acid. Probably the following reaction takes place 2 0 OH OH SOsNa

673

SAXENA

0 + 28 Ce( S04)z + 26H20+ COOH COOH + 12HCOOH

+ Na2S04 + 15HzS04

+ 14Cen( SOd)3. From the results obtained the maximum experimental error was 2.7%. From these results it appears that the method is accurate, simple, and less time consuming. SUMMARY Alizarin red S is determined by oxidation with ceric sulfate. Oxidation results in the formation of phthalic acid and formic acid at 14 equivalence. Maximum error observed was + 2.7%. ACKNOWLEDGMENT The author is grateful to Dr. M. P. Singh for his kind interest; and also to the C.S.I.R. (Government of India) for providing financial assistance. REFERENCE

1.

RAMCHANDRAN, K. K., AND SARMA, P. S., Periodate taining the hydroquinone (1951).

grouping.

J. Sci. Ind.

oridation of dyes conRes. (India) lOB, 147