- Email: [email protected]
Reactions of metallochromic indicators on micelles—II1
‘rahttta. 1g65, vol. 12, pp. 437 to 440. Pergamon Press Ltd. F’rinti in Northem Ireland
REACTIONS OF METALLOCHROMIC ON MLCELLES-IIt
INDICATORS
APPLICATION OF XYLENOL ORANGE TO CHELATOMETRIC TITRATIONS IN AN ALKALINE MEDIUM* V. CHRO& and V. SVOBODA Institute of Pure Chemicals, Bmo, Czechoslovakia (Received 7 July 1964. Accepted 5 January 1965) Suxumsry-Xylen& Orange in the presence of ~tylpyridinium bromide has been applied as a metallochromic indicator for the complexometric determination of some metal cations in an alkaline medium, Precise successive determinations of some pairs of metals in the same solution are possible. IN the introductory communi~tio~ of this series,l the behaviour of alkaline Xylenol Orange solutions in the presence of micelle-forming cationic detergents has been described. From the analytical point of view, the most interesting property of the aggregates formed is their ability to form coloured complexes with various cations. Some of them react practically instantaneously with EDTA solution, so that their successful application in ~omplexometric titrations could be expected. In preliminary experiments, among the metals forming sufficiently stable complexes with EDTA in the alkaline region, the most promising results have been obtained in the titration of calcium(II), magnesium(Ii), cadmium(II), zinc(H) and manganese(I1). The extension of the working range of Xylenol Orange to alkaline solutions allows the successive determination of some pairs of metals in the same solution. The results of such determinations are presented in this paper. EXPERIMENTAL Reagents EDTA. NJ25 and 0.05M solutions were prepared from disodium ethylenediaminetetra-ac&ate (Chelaton 3, Lachema, Czechoslovakia) and standard&d in the usual manner. Metal ions. 0.025M solutions of calcium, magnesium, cadmium, zinc lead and manganese were prepared from appropriate salts and standardised by means of conventional EDTA titrations. Buffers. Ammoniacal buffer solution of pH 10.5 and solid hexamethylenetetramine were used for pH adjustment. Indicufor. Xylenol Orange was used as a 1: 100 solid mixture finely ground with potassium chloride. Cetylpyridinium bromide. Used in the form of a saturated solution in 20% aqueous methanoi. Nitric acid. 10 % Aqueous solution. All chemicals used in this work were of reagent-grade purity. Procedure Determination of single metal ions. Dilute the sample solution to 100 ml, and add 10 ml of pH 10-5 buffer solution followed by 1 ml of detergent solution and Xylenol Orange mixture. Titrate with EDTA to the end-point colour change. t Part I: see reference 1. * Presented in part before the Section of Analytical Czechoslovak Chemical Society, glina, July, 1963. 431
Chemistry
at the XXth Meeting of the
438
V. &ROM+ and V. SVOBODA
Determination of pairs of metal ions. The metal ion pairs are selected so that one ion may be titrated in acid and the other in alkaline solution. Acidify the solution to be titrated with a few drops of nitric acid, then add the indicator and solid hexamethylenetet~mine. Titrate with EDTA till the solution changes from dark red to clear lemon-yeUow.*~a Adjust the pH to 10.5 with IOml of ammoniacal buffer solution,.add l-2 ml of detergent solution and titrate the second cation with EDTA. RESULTS
Determination of single metal ions
The results of the determination of individual cations in an alkaline medium are given in Table I. All the tabulated values are the means of ten determinations. TABLE L-TITRATION
Ion
Taken,
Mn*+ Mge+ Cd?+
Found, mg
Standard deviation, mg
*0*01 I
5.06”
5.06
10-I 1”
IO.1 1
50.010
20.33b 562~ 11.24” 33.106 5.84” 11.71a 28.25* 6.14b 12.280 12.71b 31.78*
20.32 5.62 11.23 33.09 5.86 11.71 28.25 6.14 12.28 12.69 31.80
10.017 zlzo.014 ho.016 ho.028 *0@07 -to.010 :k 0.029 *OGl6 & 0.007 i 0.042 kO.053
c-k”Zn2+
mg
OF INDIVIDUAL CATIONS
4 0.025M EDTA used. * O*OSMEDTA used.
The average recoveries of the determined cations agree well with the amounts taken. The standard deviations, show, especially in the case of determinations of calcium, magnesium and manganese, the excellent reproducibility of individual results. The results obtained for cadmium(I1) are less satisfactory; nevertheless, even in this case the results compare favourably with those from previously published methods. In all the determinations, the end-point colour change was distinct and sharp, within 1-2 drops of the titrant solution. The colours of the indicator-metal complexes vary with the metal ion; those of magnesium and zinc are red; that of manganese is violet; and those of calcium and cadmium are blue-violet. At the equivalence-point these colours change to colourless or pale grey, depending upon the amount of the indicator added. With calcium and cadmium, the colour change passes through a sky-blue shade close to the equivalence-point, which makes the colour change more remarkable, Determination of pairs of metals
The presence of a metal of the alkaline earth metal group does not interfere with the first determination in acid solution, and the accuracy is unimpaired. As described in the preceding paper: mineral salts affect the formation of the indicator-detergent complex. Therefore, in these determinations, after the adjustment of pH, a greater amount of the detergent solution is necessary in order to obtain satisfactory results.
Reactions of metallochromic indicators on micelIes-
439
In all the titrations of the second cation in the alkaline region, the end-point colour change of the indicator is much better than that obtained when the corresponding metal ions are alone. This phenomenon is probably explained by the following reaction taking place, at least to some extent, Pb-EDTA + Ca-In $ Pb-In + Ca-EDTA so that at the end-point the lead-indicator complex is being titrated with consequent improvement in colour change. TABLE IL-TITRATION
Taken, mg
OF PAIRS OF METALS
Found, qg
95 % Confidence interval, rng
Zn
%
Zn
Mg
Zn
3.31 9.92 16.53 23.15 29.76
10.99 8.55 6.11 3.66 1.22
3.3f 9-87 16.54 23.16 29.78
10.98 8.54 6-11 3.66 1.23
*IO*016 *0*033 10.033 *0.016 rto.033
%0*012 10.012 10.012 f0.012 f0.012
Pb
Ca
Pb
Ca
Pb
Ca
10.58 31.55 52.58 73.61 94.64
18.13 14.10 10.07 6.04 2.01
10.51 31.57 52.56 73.60 94.63
18.13 14.11 lO*O? 6.05 2.02
iO~OJ5 xto.053 ztO*lOS &to.053 f0*160
%
*0.041 *a021 i 0.020 io.020 +0*020
Table II shows the results of titrations of the metal pairs zinc-magnesium and leadcalcium. The titrations were performed for various ratios of cations. The values given in the table are averages of five determinations. The Dean-Dixon method,6 which has been recommended for the statistical evaluation of data based on a small number of observations, was used. As may be seen from the tabulated values of confidence intervals, the results of individual titrations of the second cation have good precision. DISCUSSION
Among the large number of metallochromic indicators used in complexometric titrations, Xylenol Orange is outstanding. However, its application has been limited by its own acid-base indicator properties, to the acid region. The interaction of Xylenol Orange with cation-active detergents permits the extension of its useful range to pH 11, where it behaves like its “acid’ form, giving with many cations “normal” complexes (cJ?*~). The titrations described in this communication represent only a few examples of the cases in which Xylenol Orange can be used in the presence of cationic detergents. For most of these determinations, of course, other, more or less suitable indicators have been proposed todate. Nevertheless, because of the excellent colour properties of Xylenol Orange which are retained even in these instances, one can suppose that these new possibilities will find a very wide practical application in complexometric analysis.
440
V.
CHROM+
and V.
SVOB~DA
Zu~~nfass~-Xylenolor~ge wurde als ~et~lfarbindikator in Gegenwart von Cetylpyridiniumbromid zur komplexometrischen Bestimmung einiger Kationen in alkalischer Losung angewendet. Es ist mijglich gewisse Metallp~~ in derselben Liisung aufeinander folgend sehr genau zu bestimmen. Resume-Le Xylenol Orange en presence de bromure de cetylpyridinium a tte applique, en tam qu’indicateur metallochrome, au dosage complexometrique de quelques cations dans un milieu al&in. I1 est possible d’effectuer les dosages successifs prtfcis de quelques paires de mctaux dans la meme solution. REFERENCES
f V. Svoboda and V. Chromjt, Takmta, 1965,12,431. a J. Klirbl and R. Pfibil, Ch~rn~~f-Analyst,1956,45, 102. ., 9 J. Kiirbl, R. Pfibil and A. Emr, CoN. Czech. Cbent. Comm., 1957,2Z, 961. 4 J. Kiirbl and R. PPibil, Ind. Chemist, 1958,34,616. 5 J. Korbl and V. Svoboda, Talanta, 1960, 3, 370. 8 R. 3. Dean and W. J. Dixon, Analyf. Chem., 19X23,636.
REACTIONS OF METALLOCHROMIC ON MLCELLES-IIt
INDICATORS
APPLICATION OF XYLENOL ORANGE TO CHELATOMETRIC TITRATIONS IN AN ALKALINE MEDIUM* V. CHRO& and V. SVOBODA Institute of Pure Chemicals, Bmo, Czechoslovakia (Received 7 July 1964. Accepted 5 January 1965) Suxumsry-Xylen& Orange in the presence of ~tylpyridinium bromide has been applied as a metallochromic indicator for the complexometric determination of some metal cations in an alkaline medium, Precise successive determinations of some pairs of metals in the same solution are possible. IN the introductory communi~tio~ of this series,l the behaviour of alkaline Xylenol Orange solutions in the presence of micelle-forming cationic detergents has been described. From the analytical point of view, the most interesting property of the aggregates formed is their ability to form coloured complexes with various cations. Some of them react practically instantaneously with EDTA solution, so that their successful application in ~omplexometric titrations could be expected. In preliminary experiments, among the metals forming sufficiently stable complexes with EDTA in the alkaline region, the most promising results have been obtained in the titration of calcium(II), magnesium(Ii), cadmium(II), zinc(H) and manganese(I1). The extension of the working range of Xylenol Orange to alkaline solutions allows the successive determination of some pairs of metals in the same solution. The results of such determinations are presented in this paper. EXPERIMENTAL Reagents EDTA. NJ25 and 0.05M solutions were prepared from disodium ethylenediaminetetra-ac&ate (Chelaton 3, Lachema, Czechoslovakia) and standard&d in the usual manner. Metal ions. 0.025M solutions of calcium, magnesium, cadmium, zinc lead and manganese were prepared from appropriate salts and standardised by means of conventional EDTA titrations. Buffers. Ammoniacal buffer solution of pH 10.5 and solid hexamethylenetetramine were used for pH adjustment. Indicufor. Xylenol Orange was used as a 1: 100 solid mixture finely ground with potassium chloride. Cetylpyridinium bromide. Used in the form of a saturated solution in 20% aqueous methanoi. Nitric acid. 10 % Aqueous solution. All chemicals used in this work were of reagent-grade purity. Procedure Determination of single metal ions. Dilute the sample solution to 100 ml, and add 10 ml of pH 10-5 buffer solution followed by 1 ml of detergent solution and Xylenol Orange mixture. Titrate with EDTA to the end-point colour change. t Part I: see reference 1. * Presented in part before the Section of Analytical Czechoslovak Chemical Society, glina, July, 1963. 431
Chemistry
at the XXth Meeting of the
438
V. &ROM+ and V. SVOBODA
Determination of pairs of metal ions. The metal ion pairs are selected so that one ion may be titrated in acid and the other in alkaline solution. Acidify the solution to be titrated with a few drops of nitric acid, then add the indicator and solid hexamethylenetet~mine. Titrate with EDTA till the solution changes from dark red to clear lemon-yeUow.*~a Adjust the pH to 10.5 with IOml of ammoniacal buffer solution,.add l-2 ml of detergent solution and titrate the second cation with EDTA. RESULTS
Determination of single metal ions
The results of the determination of individual cations in an alkaline medium are given in Table I. All the tabulated values are the means of ten determinations. TABLE L-TITRATION
Ion
Taken,
Mn*+ Mge+ Cd?+
Found, mg
Standard deviation, mg
*0*01 I
5.06”
5.06
10-I 1”
IO.1 1
50.010
20.33b 562~ 11.24” 33.106 5.84” 11.71a 28.25* 6.14b 12.280 12.71b 31.78*
20.32 5.62 11.23 33.09 5.86 11.71 28.25 6.14 12.28 12.69 31.80
10.017 zlzo.014 ho.016 ho.028 *0@07 -to.010 :k 0.029 *OGl6 & 0.007 i 0.042 kO.053
c-k”Zn2+
mg
OF INDIVIDUAL CATIONS
4 0.025M EDTA used. * O*OSMEDTA used.
The average recoveries of the determined cations agree well with the amounts taken. The standard deviations, show, especially in the case of determinations of calcium, magnesium and manganese, the excellent reproducibility of individual results. The results obtained for cadmium(I1) are less satisfactory; nevertheless, even in this case the results compare favourably with those from previously published methods. In all the determinations, the end-point colour change was distinct and sharp, within 1-2 drops of the titrant solution. The colours of the indicator-metal complexes vary with the metal ion; those of magnesium and zinc are red; that of manganese is violet; and those of calcium and cadmium are blue-violet. At the equivalence-point these colours change to colourless or pale grey, depending upon the amount of the indicator added. With calcium and cadmium, the colour change passes through a sky-blue shade close to the equivalence-point, which makes the colour change more remarkable, Determination of pairs of metals
The presence of a metal of the alkaline earth metal group does not interfere with the first determination in acid solution, and the accuracy is unimpaired. As described in the preceding paper: mineral salts affect the formation of the indicator-detergent complex. Therefore, in these determinations, after the adjustment of pH, a greater amount of the detergent solution is necessary in order to obtain satisfactory results.
Reactions of metallochromic indicators on micelIes-
439
In all the titrations of the second cation in the alkaline region, the end-point colour change of the indicator is much better than that obtained when the corresponding metal ions are alone. This phenomenon is probably explained by the following reaction taking place, at least to some extent, Pb-EDTA + Ca-In $ Pb-In + Ca-EDTA so that at the end-point the lead-indicator complex is being titrated with consequent improvement in colour change. TABLE IL-TITRATION
Taken, mg
OF PAIRS OF METALS
Found, qg
95 % Confidence interval, rng
Zn
%
Zn
Mg
Zn
3.31 9.92 16.53 23.15 29.76
10.99 8.55 6.11 3.66 1.22
3.3f 9-87 16.54 23.16 29.78
10.98 8.54 6-11 3.66 1.23
*IO*016 *0*033 10.033 *0.016 rto.033
%0*012 10.012 10.012 f0.012 f0.012
Pb
Ca
Pb
Ca
Pb
Ca
10.58 31.55 52.58 73.61 94.64
18.13 14.10 10.07 6.04 2.01
10.51 31.57 52.56 73.60 94.63
18.13 14.11 lO*O? 6.05 2.02
iO~OJ5 xto.053 ztO*lOS &to.053 f0*160
%
*0.041 *a021 i 0.020 io.020 +0*020
Table II shows the results of titrations of the metal pairs zinc-magnesium and leadcalcium. The titrations were performed for various ratios of cations. The values given in the table are averages of five determinations. The Dean-Dixon method,6 which has been recommended for the statistical evaluation of data based on a small number of observations, was used. As may be seen from the tabulated values of confidence intervals, the results of individual titrations of the second cation have good precision. DISCUSSION
Among the large number of metallochromic indicators used in complexometric titrations, Xylenol Orange is outstanding. However, its application has been limited by its own acid-base indicator properties, to the acid region. The interaction of Xylenol Orange with cation-active detergents permits the extension of its useful range to pH 11, where it behaves like its “acid’ form, giving with many cations “normal” complexes (cJ?*~). The titrations described in this communication represent only a few examples of the cases in which Xylenol Orange can be used in the presence of cationic detergents. For most of these determinations, of course, other, more or less suitable indicators have been proposed todate. Nevertheless, because of the excellent colour properties of Xylenol Orange which are retained even in these instances, one can suppose that these new possibilities will find a very wide practical application in complexometric analysis.
440
V.
CHROM+
and V.
SVOB~DA
Zu~~nfass~-Xylenolor~ge wurde als ~et~lfarbindikator in Gegenwart von Cetylpyridiniumbromid zur komplexometrischen Bestimmung einiger Kationen in alkalischer Losung angewendet. Es ist mijglich gewisse Metallp~~ in derselben Liisung aufeinander folgend sehr genau zu bestimmen. Resume-Le Xylenol Orange en presence de bromure de cetylpyridinium a tte applique, en tam qu’indicateur metallochrome, au dosage complexometrique de quelques cations dans un milieu al&in. I1 est possible d’effectuer les dosages successifs prtfcis de quelques paires de mctaux dans la meme solution. REFERENCES
f V. Svoboda and V. Chromjt, Takmta, 1965,12,431. a J. Klirbl and R. Pfibil, Ch~rn~~f-Analyst,1956,45, 102. ., 9 J. Kiirbl, R. Pfibil and A. Emr, CoN. Czech. Cbent. Comm., 1957,2Z, 961. 4 J. Kiirbl and R. PPibil, Ind. Chemist, 1958,34,616. 5 J. Korbl and V. Svoboda, Talanta, 1960, 3, 370. 8 R. 3. Dean and W. J. Dixon, Analyf. Chem., 19X23,636.