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Fluorescence and metallic valency states
Amdyf
icn Chistica Acfn
Blscvicr
Publishing Company, Printed in Tbc Netherlands
FLUORESCENCE
503
Amsterdam
AND
PART IV. AROMATIC DETECTION AGENTS
METALLIC
CARBOXYLIC FOR COPPER
VALENCY
STATES
ACIDS AS NEW AND VANADLUM
FLUORESCENT
K. J. ICOW ANI) D. E. RYAN* Defiartntenl
of Clmnislry.
(Rcccivcd June qth,
Dalhousie
U7tivevsily.
Hdifax.
Nova
Scolia
(CUM&~)
1970)
Continuing investigation of fluorimetric methods for transition mcta_lsr-3 leas shown that aromatic carboxylic acids give characteristic fluorescent reactions with copper and vanadium in the presence of reducing agents. Fluorimetric determination of copper (G p.p.m.) with thiamine has recently been reported+E; copper (x5400 p.p.b.) has also been determined” with r,r,g-tricyano-2-amino-x-propene as a reagent. Copper can be detected at the 20 p.p.b. level by the method proposed here and xoo-fold amounts of most cations (including cobalt and nickel) do not interfere. Picogram amounts of copper have been detected under controlled conditions with a spectrophotofluorimeter. No detection method based on fluorescence production has been reported for vanadium; methods are either calorimetric (0.1-2.5 p.p.m.) or precipitation (0.05-0.25 p,p.m.) spot tests’ subject to many interferences. By the procedure proposed, 0.2 p.p.m. of vanadium can be detected in the presence of most common cations. EXPERIMENTAL
Ap+aratus and reagents A 230-W mercury ultraviolet lamp, Hanovia type IGIOG (excitation il,,,,, ~360 nm), was employed for visual observations and an Aminco Bowman spectrophotofluorimeter was used for obtaining excitation and emission spectra. Stock reagent solutions (0.2 and 1%) were prepared. The aromatic carboxylic acids were dissolved in 2-5 ml of concentrated ammonia liquor, IO ml of doubly distilled water were added and the solutions were adjusted to PH 5.5 with hydrochloric acid before dilution to IOO ml with distilled water. Both uncrystallized and recrystallized reagents gave the same reaction with copper and vanadium. The acetate buffer, pH 5.2, contained IOO m.l of I M sodium acetate and 20 ml of I M hydrochloric acid in a volume of 250 ml. The 10% (w/v) solution of hydroxylamine hydrochloride was stored in an amber glass bottle. The zinc amalgam was made by heating 15 g of pure zinc (20 mesh) with 25 ml of mercury and 15 ml of I + I hydrochloric acid for I h on a water bath in a well ventilated fume hood. The amalgam, after cooling, was washed several times with dilute hydrochloric acid and the liquid amalgam was separated from the solid with a + To whom all corrcspondencc should bc addressed. Anal.
Clhn.
Acta,
52 (1970)
503-506
K. J. KOH,
504
D. E.
RYAN
separatory funnel. The amalgam was stored in contact with acetate buffer to prevent oxide formation. A standard copper solution was prepared by dissolving 0.~5 g of pure copper wire in a small amount of I + I nitric acid. After boiling to remove oxides of nitrogen, the solution was diluted to 250 m.l with distilled water. This solution contained 1,000 p.p.m. of copper; I and IO p.p.rn.. copper solutions were made as required from this stock solution. The standard vanadium solution contained 1.0 mg of vanadium per ml. Vanadiumpentoxide (0.4464gof analytical reagent) was dissolved in I-Z ml of concentrated ammonia liquor which was then neutralized with dilute hydrochloric acid to a pH of IX. 5.5 ; the solution was then diluted to 250 ml with distilled water. Other solutions (I, IO and IOO p,p.m.) were made as required from this stock solution.
Add 3 ml of a I o/o solution of 1,3-benzenedicarboxylic acid to 3 ml of acetate buffer in a IO-ml test tube. Mix thoroughly and divide into two equal portions. Add I drop of unknown solution, and 3 drops of 10% hyclroxylamine hydrochloride to one portion ; add the same amount of hydroxylamine hydrochloride to the second portion which serves as a blank. Mix thoroughly and observe under the ultraviolet lamp after 5 min. If copper (> zo p.p.b.) is present a strong blue fluorescence is observed; . the blank solution exhibits only a weak fluorescence. Copper is selectively detected with all the aromatic carboxylic acids studied: 20 p.p.b. were detected in the’ presence of roe-fold amounts of alkali and alkaline earth ions, Cd2-+, Co2-I-, Hga+, Mns+, X2+, Pb”+, Pde+, Zn2+, Als+, Bia+, Cra+, Rhs-I-, Hf4+, 1+-C, OS+‘-, Th4+, %rd+, UO+ and W”+; a IO-fold amount of Ce”+, Sri++, Ti”+ and V”-’ did not interfere. Common anions such as acetate, halides, nitrate, perchlorate, phosphate and sulphate also caused no interference. Cyanide quenched the fluorescence. Procc~ZureJoy va?tadiznn To cu. 0.5 ml of the amalgam in a IO-ml test tube add I drop of unknown solution (pi 4-7), 3 drops of o.So/, 1,3_benzenedicarboxylic acid solution and 3 drops of TABLIS RELATIVE
I INTENSITY
OF
TIIX
FLUORESCl3NCE
Acid
Excitation
Bonzoic q-Cyanobcnzoic I ,2-Bcnzcncdicarboxylic I ,3-Benzencdic:wboxylic I ,4-Bcnzcncdicarboxylic
325 320 325 335 3x5 355 315 325
,2,3-Benzcnetricarboxylic x,2,4-Benzcnetricarboxylic I
n Tho relative
intensity
(R.I.)
auininc sulnhitto stanclarcl.
is the intensity
~o.02°/, Glution. C 1.0% solution.
Anal.
Clbim. Acta, 52 (1970)
503-506
017 TllE
il
REACTION
Bmissioa
SYSTP,M
il
COPPER
R.1.n
1.3
455 445
0.02b
0.3 0
440 460 440 540 425 450
of the reaction
WITH
2.0
0.5 o-3 0.4 product
compnrcd
with
a
I
p,p.m.
FLUORESCENT
DETECTION
OF
COPPER
AND
505
VANADIUM
acetate buffer; mix thoroughly for I rnin and add a further I ml of reagent. If vanadium is present a blue fluorescence is observed under the ultraviolet lamp; a reagent blank should be run concurrently. Vanadium (0.2 p.p.m.) was easily detected; Ioo-fold amounts of the ions listed above for copper, including copper and cerium(IV), did not interfere. Vanadium was easily detected in the presence of a IO-fold amount of titanium(W) and a so-fold amount of iron(III) could be tolerated in the presence of phosphate. Similar fluorescent reactions were observed with all of the aromatic carboxylic acids investigated (Table I) ; with I ,4-benzenedicarboxylic acid, however, the fluorescence was yellow in color. RESULTS
AND
DISCUSSION
Factors
affecting fluorescence With the exception of the x,4-acid, the fluorescence spectra (Table I)’ showed excitation maxima from 315 to 335 nm and emission maxima from 420 to 4Go ntn. For the I,q-acid two characteristic excitation (315 and 355 ntn) and emission (440 and 540 nm) spectra were observed. The results given in Table I are for I p.p.m. of copper in solutions containing equal volumes (2.5 ml) of 0.20/~ reagent and acetate buffer with 0.5 ml of 5% hydroxylamine hydrochloride added; measurements were made after 30 min against a reagent blank. The fluorescence intensity increased gradually as the PH was increased from 4.7 to 6.5; rapid fluorescent reactions were observed at PH 65 in phosphate-buffered solutions but high reagent blanks were also obtained. Results were good, however, in acetate buffered solutions (PH 5.2) ; the reaction rate was satisfactory and the blank showed only a’weak fluorescence. Below pH 5, most of the reagents precipitated as the water-insoluble acids. The fluorescence intensity increased markedly as the concentration of the reagent was increased; at high reagent concentrations the reaction was very sensitive for copper but the fluorescence intensity of the blank was also increased. Reagent concentrations of 0.2-1~/~ are therefore recommended for easy detection. Nature
of reaction The fluorescent reaction products obtained on reacting aromatic carboxylic acids with metallic ions in reduced valency states are not formed unless oxygen is present. Reagent solutions that were degassed with nitrogen before addition of copper(1) chloride showed no fluorescence but, on contact with air, fluorescence was initiated at the surface and slowly spread throughout the body of the solution; similar results were obtained for degassed reagent solutions containing copl>cr(II) and hydroxylamine hydrochloride or vanadium and zinc amalgam. Radiolysis of reagents with a cobalt-6o y-ray source and electrolytic reduction of aqueous reagent solutions produced similar fluorescence to that obtained with reduced valency states of the metal ions. Dihydrocarboxylic acids are formed, via protonated intermediate alcohols, when aromatic carboxylic acids are electrolytically reduced8 and it has also been suggested that the dihydro acid is formed on reduction of phthalic (x,z-benzenedicarboxylic) acido. These results suggest that the fluorescence product is formed, in the presence Anal.
Chim. Acta, 52 (x970) 503-506
K.
506
J. KOH,
D.
E. RYAN
of oxygen, through an electron transfer process from the reduced state of the metallic ion to the aromatic carboxylic acid. Whether the intermediate so formed is directly responsible for the fluorescence of whether a further reaction with oxygen is also involved is not yet clear. Further studies are in progress. This work was supported by grants from the National Research Council and Defence Research Board. It is a pleasure for I<. J. I<. to thank Dalhousie University for the award of a Killam graduate scholarship. SUMMARY
Copper (20 p.p.b.) in solution is selectively and simply detected with aromatic carboxylic acids by observing, under the ultraviolet lamp, the fluorescence produced in the presence of reducing agents. Vanadium (0.2 p.p.m.) can also be detected, without interference from copper, if zinc amalgam is used as the reducing agent. Few ions interfere.
Le cuivre en solution (20 p.p.b.) peut etre d&e16 facilement et selectivement a l’aide d’acides aromatiques carboxyliques en examinant dans l’ultraviolet la fluorescence produite en presence d’agents reducteurs. Le vanadium (0.2 p.p.m.) peut egalement Stre decele, sans interference du cuivre, en utilisant un amalgame de zinc comme reducteur. Peu d’ions g&rent. ZUSAMMENFRSSUNC
Kupfer (20 p.p.b.) wird in Lijsung selektiv und einfach bonsauren nachgewiesen, indem unter der Ultraviolettlampe Reduktionsmitteln auftretende Fluoreszenz beobachtet wird. (0.2 p.p.m,) ohne Stijrung durch Kupfer nachgewiesen werden, Reduktionsmittel verwendet wird. Wenige Ionen storen.
mit aromatischen Cardie in Gegenwart von Es kann such Vanadin wenn Zinkamalgam als
REFERENCES I 2 3 4 5 6 7 8 g
I>. 13. B. Y. Y. I<. 17. C. N.
Amzl.
E. RYAN ANI) 13. I<. PAL, Awsl. Chiwt. Acta, 44 (rg6g) 385. II;. PAL AND D. E. RYAN, A,wnl. Claim. Ackc, 47 (xg6g) 35. I<. PAL AND II.E. RYAN, Arcal. Chim. Acta, 48 (1969) 227. YAMANB, Y. YAMNDA AND S. KUNIHIRO, Jafian A.nalyst, 17 (1968) 973. YAMANE, M. MIYAZAKI AND M. OHTAWA. Ju$xan Awdyst, 18 (1969) 750. Rmxm AND J. HAI~RIS, A,nnl. C&m., 4x (1gGg1 163. FI~,ICL, Spot Tests i~t Iwwgawic Analysis, Elsevicr. New York, 1958, p. 127~ METTLER, Ber., (1906) 2933. I-1. FURIVIAN, JO Amer. Chcm. Sot., 64 (1942) GGo. Chinr. Acta,
52 (1970)
503-506
icn Chistica Acfn
Blscvicr
Publishing Company, Printed in Tbc Netherlands
FLUORESCENCE
503
Amsterdam
AND
PART IV. AROMATIC DETECTION AGENTS
METALLIC
CARBOXYLIC FOR COPPER
VALENCY
STATES
ACIDS AS NEW AND VANADLUM
FLUORESCENT
K. J. ICOW ANI) D. E. RYAN* Defiartntenl
of Clmnislry.
(Rcccivcd June qth,
Dalhousie
U7tivevsily.
Hdifax.
Nova
Scolia
(CUM&~)
1970)
Continuing investigation of fluorimetric methods for transition mcta_lsr-3 leas shown that aromatic carboxylic acids give characteristic fluorescent reactions with copper and vanadium in the presence of reducing agents. Fluorimetric determination of copper (G p.p.m.) with thiamine has recently been reported+E; copper (x5400 p.p.b.) has also been determined” with r,r,g-tricyano-2-amino-x-propene as a reagent. Copper can be detected at the 20 p.p.b. level by the method proposed here and xoo-fold amounts of most cations (including cobalt and nickel) do not interfere. Picogram amounts of copper have been detected under controlled conditions with a spectrophotofluorimeter. No detection method based on fluorescence production has been reported for vanadium; methods are either calorimetric (0.1-2.5 p.p.m.) or precipitation (0.05-0.25 p,p.m.) spot tests’ subject to many interferences. By the procedure proposed, 0.2 p.p.m. of vanadium can be detected in the presence of most common cations. EXPERIMENTAL
Ap+aratus and reagents A 230-W mercury ultraviolet lamp, Hanovia type IGIOG (excitation il,,,,, ~360 nm), was employed for visual observations and an Aminco Bowman spectrophotofluorimeter was used for obtaining excitation and emission spectra. Stock reagent solutions (0.2 and 1%) were prepared. The aromatic carboxylic acids were dissolved in 2-5 ml of concentrated ammonia liquor, IO ml of doubly distilled water were added and the solutions were adjusted to PH 5.5 with hydrochloric acid before dilution to IOO ml with distilled water. Both uncrystallized and recrystallized reagents gave the same reaction with copper and vanadium. The acetate buffer, pH 5.2, contained IOO m.l of I M sodium acetate and 20 ml of I M hydrochloric acid in a volume of 250 ml. The 10% (w/v) solution of hydroxylamine hydrochloride was stored in an amber glass bottle. The zinc amalgam was made by heating 15 g of pure zinc (20 mesh) with 25 ml of mercury and 15 ml of I + I hydrochloric acid for I h on a water bath in a well ventilated fume hood. The amalgam, after cooling, was washed several times with dilute hydrochloric acid and the liquid amalgam was separated from the solid with a + To whom all corrcspondencc should bc addressed. Anal.
Clhn.
Acta,
52 (1970)
503-506
K. J. KOH,
504
D. E.
RYAN
separatory funnel. The amalgam was stored in contact with acetate buffer to prevent oxide formation. A standard copper solution was prepared by dissolving 0.~5 g of pure copper wire in a small amount of I + I nitric acid. After boiling to remove oxides of nitrogen, the solution was diluted to 250 m.l with distilled water. This solution contained 1,000 p.p.m. of copper; I and IO p.p.rn.. copper solutions were made as required from this stock solution. The standard vanadium solution contained 1.0 mg of vanadium per ml. Vanadiumpentoxide (0.4464gof analytical reagent) was dissolved in I-Z ml of concentrated ammonia liquor which was then neutralized with dilute hydrochloric acid to a pH of IX. 5.5 ; the solution was then diluted to 250 ml with distilled water. Other solutions (I, IO and IOO p,p.m.) were made as required from this stock solution.
Add 3 ml of a I o/o solution of 1,3-benzenedicarboxylic acid to 3 ml of acetate buffer in a IO-ml test tube. Mix thoroughly and divide into two equal portions. Add I drop of unknown solution, and 3 drops of 10% hyclroxylamine hydrochloride to one portion ; add the same amount of hydroxylamine hydrochloride to the second portion which serves as a blank. Mix thoroughly and observe under the ultraviolet lamp after 5 min. If copper (> zo p.p.b.) is present a strong blue fluorescence is observed; . the blank solution exhibits only a weak fluorescence. Copper is selectively detected with all the aromatic carboxylic acids studied: 20 p.p.b. were detected in the’ presence of roe-fold amounts of alkali and alkaline earth ions, Cd2-+, Co2-I-, Hga+, Mns+, X2+, Pb”+, Pde+, Zn2+, Als+, Bia+, Cra+, Rhs-I-, Hf4+, 1+-C, OS+‘-, Th4+, %rd+, UO+ and W”+; a IO-fold amount of Ce”+, Sri++, Ti”+ and V”-’ did not interfere. Common anions such as acetate, halides, nitrate, perchlorate, phosphate and sulphate also caused no interference. Cyanide quenched the fluorescence. Procc~ZureJoy va?tadiznn To cu. 0.5 ml of the amalgam in a IO-ml test tube add I drop of unknown solution (pi 4-7), 3 drops of o.So/, 1,3_benzenedicarboxylic acid solution and 3 drops of TABLIS RELATIVE
I INTENSITY
OF
TIIX
FLUORESCl3NCE
Acid
Excitation
Bonzoic q-Cyanobcnzoic I ,2-Bcnzcncdicarboxylic I ,3-Benzencdic:wboxylic I ,4-Bcnzcncdicarboxylic
325 320 325 335 3x5 355 315 325
,2,3-Benzcnetricarboxylic x,2,4-Benzcnetricarboxylic I
n Tho relative
intensity
(R.I.)
auininc sulnhitto stanclarcl.
is the intensity
~o.02°/, Glution. C 1.0% solution.
Anal.
Clbim. Acta, 52 (1970)
503-506
017 TllE
il
REACTION
Bmissioa
SYSTP,M
il
COPPER
R.1.n
1.3
455 445
0.02b
0.3 0
440 460 440 540 425 450
of the reaction
WITH
2.0
0.5 o-3 0.4 product
compnrcd
with
a
I
p,p.m.
FLUORESCENT
DETECTION
OF
COPPER
AND
505
VANADIUM
acetate buffer; mix thoroughly for I rnin and add a further I ml of reagent. If vanadium is present a blue fluorescence is observed under the ultraviolet lamp; a reagent blank should be run concurrently. Vanadium (0.2 p.p.m.) was easily detected; Ioo-fold amounts of the ions listed above for copper, including copper and cerium(IV), did not interfere. Vanadium was easily detected in the presence of a IO-fold amount of titanium(W) and a so-fold amount of iron(III) could be tolerated in the presence of phosphate. Similar fluorescent reactions were observed with all of the aromatic carboxylic acids investigated (Table I) ; with I ,4-benzenedicarboxylic acid, however, the fluorescence was yellow in color. RESULTS
AND
DISCUSSION
Factors
affecting fluorescence With the exception of the x,4-acid, the fluorescence spectra (Table I)’ showed excitation maxima from 315 to 335 nm and emission maxima from 420 to 4Go ntn. For the I,q-acid two characteristic excitation (315 and 355 ntn) and emission (440 and 540 nm) spectra were observed. The results given in Table I are for I p.p.m. of copper in solutions containing equal volumes (2.5 ml) of 0.20/~ reagent and acetate buffer with 0.5 ml of 5% hydroxylamine hydrochloride added; measurements were made after 30 min against a reagent blank. The fluorescence intensity increased gradually as the PH was increased from 4.7 to 6.5; rapid fluorescent reactions were observed at PH 65 in phosphate-buffered solutions but high reagent blanks were also obtained. Results were good, however, in acetate buffered solutions (PH 5.2) ; the reaction rate was satisfactory and the blank showed only a’weak fluorescence. Below pH 5, most of the reagents precipitated as the water-insoluble acids. The fluorescence intensity increased markedly as the concentration of the reagent was increased; at high reagent concentrations the reaction was very sensitive for copper but the fluorescence intensity of the blank was also increased. Reagent concentrations of 0.2-1~/~ are therefore recommended for easy detection. Nature
of reaction The fluorescent reaction products obtained on reacting aromatic carboxylic acids with metallic ions in reduced valency states are not formed unless oxygen is present. Reagent solutions that were degassed with nitrogen before addition of copper(1) chloride showed no fluorescence but, on contact with air, fluorescence was initiated at the surface and slowly spread throughout the body of the solution; similar results were obtained for degassed reagent solutions containing copl>cr(II) and hydroxylamine hydrochloride or vanadium and zinc amalgam. Radiolysis of reagents with a cobalt-6o y-ray source and electrolytic reduction of aqueous reagent solutions produced similar fluorescence to that obtained with reduced valency states of the metal ions. Dihydrocarboxylic acids are formed, via protonated intermediate alcohols, when aromatic carboxylic acids are electrolytically reduced8 and it has also been suggested that the dihydro acid is formed on reduction of phthalic (x,z-benzenedicarboxylic) acido. These results suggest that the fluorescence product is formed, in the presence Anal.
Chim. Acta, 52 (x970) 503-506
K.
506
J. KOH,
D.
E. RYAN
of oxygen, through an electron transfer process from the reduced state of the metallic ion to the aromatic carboxylic acid. Whether the intermediate so formed is directly responsible for the fluorescence of whether a further reaction with oxygen is also involved is not yet clear. Further studies are in progress. This work was supported by grants from the National Research Council and Defence Research Board. It is a pleasure for I<. J. I<. to thank Dalhousie University for the award of a Killam graduate scholarship. SUMMARY
Copper (20 p.p.b.) in solution is selectively and simply detected with aromatic carboxylic acids by observing, under the ultraviolet lamp, the fluorescence produced in the presence of reducing agents. Vanadium (0.2 p.p.m.) can also be detected, without interference from copper, if zinc amalgam is used as the reducing agent. Few ions interfere.
Le cuivre en solution (20 p.p.b.) peut etre d&e16 facilement et selectivement a l’aide d’acides aromatiques carboxyliques en examinant dans l’ultraviolet la fluorescence produite en presence d’agents reducteurs. Le vanadium (0.2 p.p.m.) peut egalement Stre decele, sans interference du cuivre, en utilisant un amalgame de zinc comme reducteur. Peu d’ions g&rent. ZUSAMMENFRSSUNC
Kupfer (20 p.p.b.) wird in Lijsung selektiv und einfach bonsauren nachgewiesen, indem unter der Ultraviolettlampe Reduktionsmitteln auftretende Fluoreszenz beobachtet wird. (0.2 p.p.m,) ohne Stijrung durch Kupfer nachgewiesen werden, Reduktionsmittel verwendet wird. Wenige Ionen storen.
mit aromatischen Cardie in Gegenwart von Es kann such Vanadin wenn Zinkamalgam als
REFERENCES I 2 3 4 5 6 7 8 g
I>. 13. B. Y. Y. I<. 17. C. N.
Amzl.
E. RYAN ANI) 13. I<. PAL, Awsl. Chiwt. Acta, 44 (rg6g) 385. II;. PAL AND D. E. RYAN, A,wnl. Claim. Ackc, 47 (xg6g) 35. I<. PAL AND II.E. RYAN, Arcal. Chim. Acta, 48 (1969) 227. YAMANB, Y. YAMNDA AND S. KUNIHIRO, Jafian A.nalyst, 17 (1968) 973. YAMANE, M. MIYAZAKI AND M. OHTAWA. Ju$xan Awdyst, 18 (1969) 750. Rmxm AND J. HAI~RIS, A,nnl. C&m., 4x (1gGg1 163. FI~,ICL, Spot Tests i~t Iwwgawic Analysis, Elsevicr. New York, 1958, p. 127~ METTLER, Ber., (1906) 2933. I-1. FURIVIAN, JO Amer. Chcm. Sot., 64 (1942) GGo. Chinr. Acta,
52 (1970)
503-506