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Fluorescence enhancement of the europium-yttrium-diphacinone-ammonia system
Analytlca Chlmrca Acta, 231 (1990) 295-298 Elsevter Sctence Pubhshers B.V., Amsterdam
295 - Pnnted
m The Netherlands
Short Communication
Fluorescence enhancement of the europium-yttrium-diphacinone-ammonia GUIYUN
ZHU
Department
*, ZHIKUN
SI, XIUHONG
of Applied Chemistry (Received
WANG
and WENJING
system ZHU
Shandong Umversrty, Jman (Chma)
29th September
1989)
ABSTRACT A study of the enhanced (ca. 100 x ) fluorescence mtenstty of the Eu3+ -dtphacmone-ammoma system by Y3+ was made usmg a collotdal suspension The excitation and emission wavelengths were 330 and 612 nm, respectively. The fluorescence mtenstty was a hnear functton of the concentratron of europmm 111the range 6.0 X IO-“-8 0 x lo-’ M. The detection hrmt was 8 0 X lo-l4 M The standard additron method was used for the determmatton of europium in rare earth oxtdes, wtth satisfactory results.
The study of enhanced luminescence has attracted recent attention [l-5]. For example, the sensitivity and selectivity of the Eu3+-thienoyltrifluoroacetone (TTA)-phenanthroline and Sm3+-TTA-phenanthroline systems in Triton X100 micelles were increased by the addition of La3+, Gd3+, Tb3+, Lu3+ or Y3+. The mechanism of this “co-1ummescence” effect has also been reported [6]. 2-(Diphenylacetyl)indan-1,3-dione (diphacinone, DPN) is an anticoagulant rodenticide, but the fluorescence system of europium with diphacinone has not been reported. We have found that the complexes formed by the reaction of europium or samarium ions with DPN and ammonia are fluorescent, and the intensity can be increased by the addition of yttrium ions. In thts communication, the fluorescence characteristics of the europium complex with DPN and ammonia in the presence of yttrium are reported, and a rapid and sensitive method for the spectrofluorimetric determination of europium is described. Experrmental Apparatus All fluorescence measurements were made on an RF-540 fluorescence spectrophotometer in l.O-cm quartz cells. 0003-2670/90/$03
50
0 1990 Elsevter Sctence
Publishers
B.V
Reagents. Analytical-reagent grade chemicals were used and distilled water was used to prepare the solutions. The lanthanide oxides were obtained in purities of 99.9% or better. Stock lanthanide solutions (0.01 or 0.001 M) were prepared by dissolving the appropriate amount of the oxide in hydrochloric acid and working solutions were prepared by dilution with water. The sodium salt of the DPN was purified by dissolution in hot water, filtration and cooling of the filtrate. The yellow crystalline sodium salt of DPN was obtained. A 1.0 X lop4 M solution of DPN was prepared by dissolving the appropriate amount of the sodium salt in a few ml of ethanol and diluting to volume with water. Ammonia-ammonium chloride solution (2.0 M) of pH 9.0 was used as a buffer. A 0.1% (m/v) Triton X-100 solution was used.
General procedure To 25 ml test-tubes, solutions were added in the following order: standard europium solution, yttrium solution, DPN, buffer and Triton X-100. The mixture was diluted to 10 ml with distilled water and after 5 min the fluorescence intensity
G ZHU
296
was measured at excitation and emission lengths of 330 and 612 nm, respectively.
wave-
Results and discussron Spectral charactenstlcs. Figure 1 shows the excitation and emission spectra of the Eu3+-DPNNH,-Triton X-100 and Eu3+-Y3+-DPN-NH,Triton X-100 systems at pH 9.0. It can be seen that the intrinsic Eu3+ emission of the Eu3+DPN-NH,-Triton X-100 complex is weak, but the addition of Y 3+ causes a large increase in intensity (about lOO-fold at 612 nm). The emission line at 612 nm was the most intense, so this wavelength was used in subsequent experiments. Under the described experimental conditions, the
ET AL
Y 3+-DPN-NH3-Triton X-100 system did not exhibit any fluorescence. High-purity yttrium oxide was used, which ensured that any enhancement effect observed was actually caused by yttrium rather than by europium present as an impurity in the yttrium oxide. Effect of PH. The fluorescence intensity of a 5.0 X lop9 M europium solution containing 5.0 X 10V7 M yttrium was measured over the pH range 7.0-11.0 by using ammonia-ammonium chloride buffer solution and adjusting the pH with hydrochloric acid or sodium hydroxide solution. The maximum fluorescence intensity was obtained at pH 8.5-9.5.
8
300
400
550
650
Wavelength
Ag 1 Fluorescence spectra: (A) excltatlon, (B) emmton Curves. (1) Y3+-DPN-NH3-Tnton 5.0 X 10e9 M Eu3+, 6 0 X lo-’ X-100, (3) Eu3+-Y3+-DPN-NH,-Tnton X-100 Condltlons NH,, 0 01% Tnton X-100, pH 9 0 Gam (1) 9, (2) 9; (3) 7
X-100; (2) Eu3+-DPN-NH3-Tnton M Y3+, 6 0 X 10e6 M DPN, 0 4 M
FLUORESCENCE
ENHANCEMENT
OF THE
EUROPIUM-YlTRIUM-DIPHACINONE-AMMONIA
Effect of DPN and NH, concentration. The effect of the DPN concentration on fluorescence intensity at fixed concentrations of europium (5.0 x lop9 M) and yttrium (6.0 X lo-’ M) was studied. A maximum and constant fluorescence intensity was obtained between 5.0 X 10e6 and 8.0 x lop6 M of DPN. In the absence of DPN the intrinsic europium emission was not observed. The effect of the concentration of the buffer solution on the fluorescence intensity at fixed concentrations of europmm (5.0 x lop9 M), yttrium (6.0 x lo-’ M) and DPN (6.0 x 10e6 M) was studied. When the ammonia concentration was increased, the fluorescence intensity also increased up to an ammonia concentration of 0.4 M, above which it remained maximum and constant. Effect of yttrium concentratron. The variation in the fluorescence intensity was investigated as a function of the concentration of yttrium in the presence of a fixed amount of europium (Fig. 2). The europium concentrations tested were 5.0 X low9 and 5.0 x lo-’ M. When the yttrium concentration was increased the fluorescence intensity of the system also increased, and the maximum
0
1 0
20
SYSTEM
mtensities were reached at the same concentration of yttrium, ca. 6.0 x lo-’ M. From Fig. 2, it can be seen that the degree of enhancement of the fluorescence by yttrium was the same at different concentrations of europium. Effect of Trlton X-100 concentratzon. The effect of Triton X-100 concentration on the fluorescence intensity was investigated. In the presence of 0.01% Triton X-100, the fluorescence intensity of the system was maximum and remained stable for at least 30 min. AnalytIcal charactenstlcs. The fluorescence intensity was a linear function of the concentration of europium in the range 6.0 x lo-“-8.0 lo-’ M, the straight line through the origin. detection limit (signal-to-notse ratio 2) was x lo-l4 The effect of foreign ions on the fluorescence intensity of the Eu 3+-Y 3+-DPN-NH3-Triton X-100 system was studied for 1.0 X lop9 M europium. The tolerance allowed in the vanation of the fluorescence intensity was f5%. The other trivalent lanthanide ions were examined, and it was found that the following maximum molar
I
40
60
297
L 80
100
C (x10-‘M)
Fig. Effect of yttnum concentration 0 01% Tnton X-100, pH 9 0
Curves.
(1) 5.0 X 10m9 M Eu3+, (2) 5 0 X lo-’
M Eu3+, 6 0 X 10K6 M DPN, 0 4 M NH,,
298
excesses of these ions caused no interference: Tb 20, Nd 20, Ho 20, Er 20, Tm 20, La 50, Ce 100, Dy 100, Sm 10, Pr 100, Y 50 and Lu 100. The new system was applied to the determination of trace amounts of europium in lanthanide oxides. The sample contained La,O, 27.11, CeO, 49.21, Pr,O,, 5.18, Nd,O, 16.75, Sm,O, 1.29, Eu,O, 0.23, Gd,O, 0.40, Tb407 0.03, Dy,O, 0.09, Y203 0.27, Er,O, 0.027, Ho,O, 0.023, Tm,O, 0.0085, Lu,O, 0.003, and Yb,O, 0.013%. The europium contents found were 0.23, 0.23, 0.24, 0.22, 0.22 and 0.25% (mean fs.d. = 0.23 f 1.2%). When 38.0 ng of europium was added, The amounts found were 38.0, 38.0, 39.5, 38.8 and 38.8 ng (mean f s.d. = 38.5 f 1.8 ng). Enhancement mechanum. Yttrium does not form a compound with Eu3+-DPN-NH Eu3+-DPNNH, and Y3+-DPN-NH, are bo?h formed and dissolve in the Triton X-100 micelles with the two complexes in close contact. The excited singlet states of DPN m these complexes undergo a radiationless transition to the triplet states. Europium can be excited both by intramolecular energy transfer from the excited triplet state of DPN in the Eu3+-DPN-NH, complex and by intermolecular energy transfer from the excited triplet state of DPN in the Y 3+-DPN-NH3 complex. Because
G ZHUETAL
the concentration of the yttrium complex is much greater than that of the europium complex in the Triton X-100 solution, each Eu3+-DPN-NH3 molecule is surrounded by many Y 3+-DPN-NH3 molecules, and the fluorescence of the europium is considerably enhanced. Yttnum cannot be excited by the excited triplet state of DPN because the structure of the yttnum molecule is stable. Triton X-100 also plays an important part in the dissolunon of both complexes and their protection against collision with solvent (water) molecules, which would cause a loss of energy.
REFERENCES
1 G.-Y. Zhu, J.-H. Yang Xuebao, 5 (1987) 79. 2 G.-Y. Zhu, J.-H. Yang, Chm. Umv
and W
L. Wang, Ge and
Zhongguo
L. Wang,
Xltu
Chem.
J
295 - Pnnted
m The Netherlands
Short Communication
Fluorescence enhancement of the europium-yttrium-diphacinone-ammonia GUIYUN
ZHU
Department
*, ZHIKUN
SI, XIUHONG
of Applied Chemistry (Received
WANG
and WENJING
system ZHU
Shandong Umversrty, Jman (Chma)
29th September
1989)
ABSTRACT A study of the enhanced (ca. 100 x ) fluorescence mtenstty of the Eu3+ -dtphacmone-ammoma system by Y3+ was made usmg a collotdal suspension The excitation and emission wavelengths were 330 and 612 nm, respectively. The fluorescence mtenstty was a hnear functton of the concentratron of europmm 111the range 6.0 X IO-“-8 0 x lo-’ M. The detection hrmt was 8 0 X lo-l4 M The standard additron method was used for the determmatton of europium in rare earth oxtdes, wtth satisfactory results.
The study of enhanced luminescence has attracted recent attention [l-5]. For example, the sensitivity and selectivity of the Eu3+-thienoyltrifluoroacetone (TTA)-phenanthroline and Sm3+-TTA-phenanthroline systems in Triton X100 micelles were increased by the addition of La3+, Gd3+, Tb3+, Lu3+ or Y3+. The mechanism of this “co-1ummescence” effect has also been reported [6]. 2-(Diphenylacetyl)indan-1,3-dione (diphacinone, DPN) is an anticoagulant rodenticide, but the fluorescence system of europium with diphacinone has not been reported. We have found that the complexes formed by the reaction of europium or samarium ions with DPN and ammonia are fluorescent, and the intensity can be increased by the addition of yttrium ions. In thts communication, the fluorescence characteristics of the europium complex with DPN and ammonia in the presence of yttrium are reported, and a rapid and sensitive method for the spectrofluorimetric determination of europium is described. Experrmental Apparatus All fluorescence measurements were made on an RF-540 fluorescence spectrophotometer in l.O-cm quartz cells. 0003-2670/90/$03
50
0 1990 Elsevter Sctence
Publishers
B.V
Reagents. Analytical-reagent grade chemicals were used and distilled water was used to prepare the solutions. The lanthanide oxides were obtained in purities of 99.9% or better. Stock lanthanide solutions (0.01 or 0.001 M) were prepared by dissolving the appropriate amount of the oxide in hydrochloric acid and working solutions were prepared by dilution with water. The sodium salt of the DPN was purified by dissolution in hot water, filtration and cooling of the filtrate. The yellow crystalline sodium salt of DPN was obtained. A 1.0 X lop4 M solution of DPN was prepared by dissolving the appropriate amount of the sodium salt in a few ml of ethanol and diluting to volume with water. Ammonia-ammonium chloride solution (2.0 M) of pH 9.0 was used as a buffer. A 0.1% (m/v) Triton X-100 solution was used.
General procedure To 25 ml test-tubes, solutions were added in the following order: standard europium solution, yttrium solution, DPN, buffer and Triton X-100. The mixture was diluted to 10 ml with distilled water and after 5 min the fluorescence intensity
G ZHU
296
was measured at excitation and emission lengths of 330 and 612 nm, respectively.
wave-
Results and discussron Spectral charactenstlcs. Figure 1 shows the excitation and emission spectra of the Eu3+-DPNNH,-Triton X-100 and Eu3+-Y3+-DPN-NH,Triton X-100 systems at pH 9.0. It can be seen that the intrinsic Eu3+ emission of the Eu3+DPN-NH,-Triton X-100 complex is weak, but the addition of Y 3+ causes a large increase in intensity (about lOO-fold at 612 nm). The emission line at 612 nm was the most intense, so this wavelength was used in subsequent experiments. Under the described experimental conditions, the
ET AL
Y 3+-DPN-NH3-Triton X-100 system did not exhibit any fluorescence. High-purity yttrium oxide was used, which ensured that any enhancement effect observed was actually caused by yttrium rather than by europium present as an impurity in the yttrium oxide. Effect of PH. The fluorescence intensity of a 5.0 X lop9 M europium solution containing 5.0 X 10V7 M yttrium was measured over the pH range 7.0-11.0 by using ammonia-ammonium chloride buffer solution and adjusting the pH with hydrochloric acid or sodium hydroxide solution. The maximum fluorescence intensity was obtained at pH 8.5-9.5.
8
300
400
550
650
Wavelength
Ag 1 Fluorescence spectra: (A) excltatlon, (B) emmton Curves. (1) Y3+-DPN-NH3-Tnton 5.0 X 10e9 M Eu3+, 6 0 X lo-’ X-100, (3) Eu3+-Y3+-DPN-NH,-Tnton X-100 Condltlons NH,, 0 01% Tnton X-100, pH 9 0 Gam (1) 9, (2) 9; (3) 7
X-100; (2) Eu3+-DPN-NH3-Tnton M Y3+, 6 0 X 10e6 M DPN, 0 4 M
FLUORESCENCE
ENHANCEMENT
OF THE
EUROPIUM-YlTRIUM-DIPHACINONE-AMMONIA
Effect of DPN and NH, concentration. The effect of the DPN concentration on fluorescence intensity at fixed concentrations of europium (5.0 x lop9 M) and yttrium (6.0 X lo-’ M) was studied. A maximum and constant fluorescence intensity was obtained between 5.0 X 10e6 and 8.0 x lop6 M of DPN. In the absence of DPN the intrinsic europium emission was not observed. The effect of the concentration of the buffer solution on the fluorescence intensity at fixed concentrations of europmm (5.0 x lop9 M), yttrium (6.0 x lo-’ M) and DPN (6.0 x 10e6 M) was studied. When the ammonia concentration was increased, the fluorescence intensity also increased up to an ammonia concentration of 0.4 M, above which it remained maximum and constant. Effect of yttrium concentratron. The variation in the fluorescence intensity was investigated as a function of the concentration of yttrium in the presence of a fixed amount of europium (Fig. 2). The europium concentrations tested were 5.0 X low9 and 5.0 x lo-’ M. When the yttrium concentration was increased the fluorescence intensity of the system also increased, and the maximum
0
1 0
20
SYSTEM
mtensities were reached at the same concentration of yttrium, ca. 6.0 x lo-’ M. From Fig. 2, it can be seen that the degree of enhancement of the fluorescence by yttrium was the same at different concentrations of europium. Effect of Trlton X-100 concentratzon. The effect of Triton X-100 concentration on the fluorescence intensity was investigated. In the presence of 0.01% Triton X-100, the fluorescence intensity of the system was maximum and remained stable for at least 30 min. AnalytIcal charactenstlcs. The fluorescence intensity was a linear function of the concentration of europium in the range 6.0 x lo-“-8.0 lo-’ M, the straight line through the origin. detection limit (signal-to-notse ratio 2) was x lo-l4 The effect of foreign ions on the fluorescence intensity of the Eu 3+-Y 3+-DPN-NH3-Triton X-100 system was studied for 1.0 X lop9 M europium. The tolerance allowed in the vanation of the fluorescence intensity was f5%. The other trivalent lanthanide ions were examined, and it was found that the following maximum molar
I
40
60
297
L 80
100
C (x10-‘M)
Fig. Effect of yttnum concentration 0 01% Tnton X-100, pH 9 0
Curves.
(1) 5.0 X 10m9 M Eu3+, (2) 5 0 X lo-’
M Eu3+, 6 0 X 10K6 M DPN, 0 4 M NH,,
298
excesses of these ions caused no interference: Tb 20, Nd 20, Ho 20, Er 20, Tm 20, La 50, Ce 100, Dy 100, Sm 10, Pr 100, Y 50 and Lu 100. The new system was applied to the determination of trace amounts of europium in lanthanide oxides. The sample contained La,O, 27.11, CeO, 49.21, Pr,O,, 5.18, Nd,O, 16.75, Sm,O, 1.29, Eu,O, 0.23, Gd,O, 0.40, Tb407 0.03, Dy,O, 0.09, Y203 0.27, Er,O, 0.027, Ho,O, 0.023, Tm,O, 0.0085, Lu,O, 0.003, and Yb,O, 0.013%. The europium contents found were 0.23, 0.23, 0.24, 0.22, 0.22 and 0.25% (mean fs.d. = 0.23 f 1.2%). When 38.0 ng of europium was added, The amounts found were 38.0, 38.0, 39.5, 38.8 and 38.8 ng (mean f s.d. = 38.5 f 1.8 ng). Enhancement mechanum. Yttrium does not form a compound with Eu3+-DPN-NH Eu3+-DPNNH, and Y3+-DPN-NH, are bo?h formed and dissolve in the Triton X-100 micelles with the two complexes in close contact. The excited singlet states of DPN m these complexes undergo a radiationless transition to the triplet states. Europium can be excited both by intramolecular energy transfer from the excited triplet state of DPN in the Eu3+-DPN-NH, complex and by intermolecular energy transfer from the excited triplet state of DPN in the Y 3+-DPN-NH3 complex. Because
G ZHUETAL
the concentration of the yttrium complex is much greater than that of the europium complex in the Triton X-100 solution, each Eu3+-DPN-NH3 molecule is surrounded by many Y 3+-DPN-NH3 molecules, and the fluorescence of the europium is considerably enhanced. Yttnum cannot be excited by the excited triplet state of DPN because the structure of the yttnum molecule is stable. Triton X-100 also plays an important part in the dissolunon of both complexes and their protection against collision with solvent (water) molecules, which would cause a loss of energy.
REFERENCES
1 G.-Y. Zhu, J.-H. Yang Xuebao, 5 (1987) 79. 2 G.-Y. Zhu, J.-H. Yang, Chm. Umv
and W
L. Wang, Ge and
Zhongguo
L. Wang,
Xltu
Chem.
J