pyromellitein indicators : adsorption indicators

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ANALYTICA CHIMICA ACTA 221 PYROMELLITEIN INDICATORS II. ADSORPTION INDICATORS JOHN A. BISHOP .Vewatk College of Ettgrneerrng. Newark, NJ. (tf S.A.) (Rccclvcd July mnd, rgsg) The first paper * of this series introduced a new group of indicators prepared from pyromellitic dianhydridc by condensing four phenolic molecules with one molecule of the dianhydride. Among these are two which resemble fluorescein ; one containing four rcsorcinol groups and the other containing two resorcinol and two phenol groups. Two additional indicators were prepared from these by bromination, in the same manner by which eosin is made from fluorescein. There were therefore four possible adsorption indicators to work with, which will be designated in this article as roman numerals as follows: I. Tctra-resorcinol pyromellitein ; II. Diresorcinol diphenol pyromcllitcin ; III. Brominated product of I. IV. Brominated product of II. Preliminary tests had determined that the other ind.icators listed in the first paper did not adsorb on silver halide precipitates. At the start of the study being discussed here, it was dcterrmncd that compound IV did not adsorb, and that compound II, from which it was prepared, adsorbed very weakly, it being necessary to use so much of this indicator that it was considered that the pink color on silver chloride might be due to impurity (compound I). As a comparison method, it was decided to titrate the soluble halides using 0.x N AgNOs by Fajans method 2, and to compare the results obtained with those using dichlorofluorescein. The effect of acidity was determined by adding 3 iJ2 HNOs to some solutions, and titrations rn the presence of colored ions were carried out in I ilf HNOa solutions. Eosin was included for comparison purposes. The results of these experiments may be summarized as follows: A. For llze tztraticm of ch!mides, indicator I gives results identical with %ose obtained in neutral and slightly acid solutions using dichlorofluorescein, but indicator II gives poor results. For the chloride titration in more acid solutions, however, where di- chlorofluorescein cannot be used, indicator II gives good results, even in the presence of highly colored ions such as Cr+ 8, Fe+s, Cu+z, Ni+*, and Co+* in I Al HNOa. In the absence of colored ions an excellent end-point was obtained in an acidity as high as I A4 HNOs. B. For the tztratim of bromides, indicator II gave excellent results over a wide range of acidities, from neutral to I Jl!Z HNOn, while indicator I gave results similar to those of &chlorofluorescein wrth brormdes. C. For the titration of iodides, indicator II also gave excellent results over a wide range of acidities, while indicator I gave results similar to those of dichlorofluo- rescein with bromides. Anal. Chime Acta, 22 (1960) 227422

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ANALYTICA CHIMICA ACTA 221

PYROMELLITEIN INDICATORS

II. ADSORPTION INDICATORS

JOHN A. BISHOP

.Vewatk College of Ettgrneerrng. Newark, NJ. (tf S.A.)

(Rccclvcd July mnd, rgsg)

The first paper * of this series introduced a new group of indicators prepared from pyromellitic dianhydridc by condensing four phenolic molecules with one molecule of the dianhydride. Among these are two which resemble fluorescein ; one containing four rcsorcinol groups and the other containing two resorcinol and two phenol groups. Two additional indicators were prepared from these by bromination, in the same manner by which eosin is made from fluorescein. There were therefore four possible adsorption indicators to work with, which will be designated in this article as roman numerals as follows: I. Tctra-resorcinol pyromellitein ; II. Diresorcinol diphenol pyromcllitcin ; III. Brominated product of I. IV. Brominated product of II.

Preliminary tests had determined that the other ind.icators listed in the first paper did not adsorb on silver halide precipitates. At the start of the study being discussed here, it was dcterrmncd that compound IV did not adsorb, and that compound II, from which it was prepared, adsorbed very weakly, it being necessary to use so much of this indicator that it was considered that the pink color on silver chloride might be due to impurity (compound I).

As a comparison method, it was decided to titrate the soluble halides using 0.x N AgNOs by Fajans method 2, and to compare the results obtained with those using dichlorofluorescein. The effect of acidity was determined by adding 3 iJ2 HNOs to some solutions, and titrations rn the presence of colored ions were carried out in I ilf HNOa solutions. Eosin was included for comparison purposes. The results of these experiments may be summarized as follows:

A. For llze tztraticm of ch!mides, indicator I gives results identical with %ose obtained in neutral and slightly acid solutions using dichlorofluorescein, but indicator II gives poor results. For the chloride titration in more acid solutions, however, where di- chlorofluorescein cannot be used, indicator II gives good results, even in the presence of highly colored ions such as Cr+ 8, Fe+s, Cu+z, Ni+*, and Co+* in I Al HNOa. In the absence of colored ions an excellent end-point was obtained in an acidity as high as I A4 HNOs.

B. For the tztratim of bromides, indicator II gave excellent results over a wide range of acidities, from neutral to I Jl!Z HNOn, while indicator I gave results similar to those of &chlorofluorescein wrth brormdes.

C. For the titration of iodides, indicator II also gave excellent results over a wide range of acidities, while indicator I gave results similar to those of dichlorofluo- rescein with bromides.

Anal. Chime Acta, 22 (1960) 227422

222 J. A. BISHOP

D. In titrating thiocyanate sohtion, indicator II gave very good results both in dilute and strong acid, the end-points being sharp and the checks excellent. The color of colored thiocyanate ions (such as ferric), of course, interferes.

E:. In the titration of very d&&e sol&ions of all thee halides, indicator I gave results at least as good as those obtained with dichlorofluorescein in weak acid solutions, while indicator II gave better results for bromides and ioclides in weak acid solution, and very good results for all three halides in solutions of HNOl which were 0.05 IV or stronger.

The good results obtained for bromides and iodides may bc due to the fact that the color of indicator II on adsorption has a more purple tinge than that shown by dichlorofluorescein, eosin, and indicator I which are shades of pmk when adsorbed. The color changes of indicators I and II are listed in Table I.

Inillcator I Indicator II Indicator I Indlcatol II Indicator 11

Neutral Neutral o 05 N o 05 N IN

Green-Yellow fluorcvccncc Pmk Yellow Orange Orange

Ymk (coral) Purple Pmk (not at equlv pt ) Purple Purple (more pmk)

All indicator solutions in these tests were made up by dissolving 0.1 g of indicator in IOO ml HaO, one drop of G N NaOH being added to aid in dissolving the indicator.

When 0.1 N halide solutions were tested, five drops of indicator were used for a total final volume of about 50 ml. When very weak halide solutions were titrated, only one drop of indicator solution was used.

’ ACKNOWLEDGEMENT

The author wishes to acknowledge financial assistance from the National Insti- tutes of Health, (P.H.S. Grant RC&5736) and the receipt of ample supplies of PMDA from the E. 1. DuPont de Nemours Co.

SUNIMARY

Two new indlators have been made and tcstcd, one of them bcmg a substltutc for dlchloro- fluoresccln, tho other showing cxccllcnt end-points m modcratcly strong nltrlc acid solutions for chlorldcs, bromides, lod~dcs and thtocyanatcs cvcn in the presence of colored Ions

Rl%UMc

Des indicateuru ont btb prbpar6s par conclcnsatlon du dlnnhydrldc pyromclhquc avcc IQ r&or- cinol. 11s ont dtf5 cxammds cn vue dc lcur cmploi commc tndicatcurs d’adsorptlon

ZUSAMMENFASSUNG

Die Rcaktlonsproduktc von Pyromcllitstiurc-dmnhydrld mlt Resorcm wurden auf ihre Elgnung als Adsorptlonsmdlkatoren untersucht.

REFERENCES

1 J. A. BISHOP, Anal. CItttn AcXrt , 22 (Igbo) x17. 2 I<. FAJANS AND 0 HASSEL, Z. Elehtrochenr., zg (1923) t+g5#

Anal. Chw. Acla, 22 (1960) 221-222