Anal. Chem. 1985, 57, 1101-1106
1101
Analysis of Binary and Ternary Mixtures of Titanium, Zirconium, and Hafnium by Derivative Synchronous Fluorescence Spectrometry Soledad Rubio, Agustina G6mez-Hens, and Miguel Valclrcel* Department of Analytical Chemistry, Faculty of Sciences, University of Cdrdoba, Cdrdoba, Spain
The appllcatlon of derlvatlve synchronous fluorescence spectrometry to the analysls of mlxtures of tltanlum, zlrconlum, and hafnlum at the ng/mL concentratlon range has been studled. Thelr determlnatlon Is based on the formation of fluorescent complexes wlth blacetyl monoxlme nlcotlnylhydrazone In an acldlc medlum. The use of second-derlvatlve synchronous fluorescence spectra permlts the determlnatlon of binary and ternary mlxtures of these Ions and Improves the ratlo In which one of them can be determlned In the presence of one of the others.
The application of luminescence techniques to the analysis of complex mixtures is particularly attractive thanks to the high sensitivity achieved. The simplest form of emission spectrometric analysis involves studying a conventional emission spectrum recorded a t a fixed excitation wavelength. This method has an extremely restricted scope of application to the analysis of complex mixtures since its selectivity is reduced by the extensive spectral overlap, although it can be substantially improved by using synchronous ( I ) and derivative ( 2 ) luminescence spectrometric techniques. Synchronow fluorescence spectrometry, a methodology first used by Lloyd (1)to identify a number of polynuclear aromatic hydrocarbons, involves the simultaneous scan of the excitation and emission monochromators, which are synchronized in such a fashion that a well-defined relationship is maintained between the two wavelengths: either a constant wavelength (AX) (1)or a constant energy (AY) (3) difference. The frequency range over which a given component of the fluorescent mixture may emit is made narrower to an extent dependent on the magnitude of AX or Au. Vo-Dinh (4)has reported an excellent description of the principles of synchronous luminescence spectrometry. Although this technique has been used for the analysis of different organic samples such as crude oil (5-9), polynuclear hydrocarbons (10,11), and pharmaceuticals (12), it has not yet been applied to the simultaneous determination of inorganic ions. The application of derivative techniques to luminescence spectrometry was first proposed by Green and O'Haver (2). Examples of the increased detail displayed by the derivative presentation of fixed excitation-emission spectra have been reported both by these authors and by Eastwood et al. (13). John and Soutar (7) have pointed out that there is an obvious potential in combining synchronous and derivative fluorimetry to enhance minor spectral features, and Lloyd (8) has given an example of a derivative synchronous fluorescence spectrum in a sample of motor oil. Second-derivative synchronous fluorescence spectra of several polycyclic aromatic hydrocarbons have been studied by Vo-Dinh (14) and applied to the analysis of an extract of an atmospheric sample (15). The use of the traditional fluorescence technique for the analysis of inorganic ion mixtures by the formation of
fluorescent complexes has been very scarce so far owing to spectral overlap. In this work, the combination of the excellent band-narrowing features of derivative spectrometry with synchronous fluorescence spectrometry for the simultaneous determination of ion mixtures is assessed. We haven chosen the fluorescent complexes formed between titanium, zirconium, and hafnium and biacetyl monoxime nicotinylhydrazone (BMNH) (16) which have very similar fluorescent characteristics, but whose maxima are sufficiently different as to allow their binary mixtures to be resolved. In an earlier paper we studied the fluorescent behavior of these complexes (16) and reported procedures for the analysis of their binary mixtures. However, it was necessary to prepare several samples and run a number of calibration graphs to carry out their determination. With second-derivative synchronous fluorescence spectra it is possible to perform their complete analysis with only one scan. The results obtained show that the association of both techniques leads to a rapid and straightforward method for analyzing ion mixtures with similar characteristics without resorting to separation techniques. The only technique involving no separations that has been used to determine mixtures of metal chelates having similar fluorescence spectra is that based on the difference in fluorescence decay times of the chelates (17,18),which is an admittedly expensive technique. EXPERIMENTAL SECTION Apparatus. All fluorometric measurements were performed with a Perkin-Elmer fluorescence spectrophotometer, Model MPF-43A, fitted with 1-cm cells and a xenon-arc source. The spectrofluorometer cell compartment was thermostated by circulating water at 20 "C. A spectral band-pass of 5 nm was set for the excitation and emission monochromators. For synchronous fluorescence measurements, both excitation and emission monochromators were locked together and scanned simultaneously at a rate of 4 nm/s. Derivative spectra were obtained by electronic differentiation of the signal from a Perkin-Elmer derivative accessory, Model H 200-0507. Six differential time constants, selected by the mode switch, were available. For the second derivative, the gain increases approximately by a factor of 4 with each constant, while the response speed decreases by the same factor. The mode selector was set in position 6 for all measurements. The response the spectrofluorometer (time constant) was set at 0.3 s for the titanium-zirconium and titanium-hafnium mixtures and at 1.5 s for the zirconium-hafnium ones. A set of fluorescent polymer samples was used daily to adjust the spectrofluorometer to compensate for changes in the source intensity. No correction was made of the instrumental response. Reagents. Biacetyl monoxime nicotinylhydrazone (BMNH) 5.5 X M in ethanol. The synthesis and properties of this reagent have been described elsewhere (16). The reagent solution is stable for at least 1 month. A standard Ti(1V) solution was prepared by dissolving 1.000 g of titanium metal in 1 L of 3 M HC1. A standard Zr(1V) solution was obtained by dissolving 3.532 g of ZrOC12.8H20(hafnium free) in 3 M HCl and standardized gravimetrically by precipitation with ammonia and ignition to Zr02 (19). A standard Hf(1V) solution was prepared by dissolving hafnium chloride in 3 M HCl, and standardized similarly to that of zirconium. Lower concentrations
0003-2700/85/0357-1101$01.50/00 1985 American Chemlcal Society
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 6, MAY 1985
of standard solutions were prepared daily by diluting with 3 M HCl. All solvents and reagents used were of Analytical Reagent Grade. Procedures for the Determination of Binary Mixtures. Titanium-Zirconium Mixtures. A sample containing 0.10-0.90 pg of Ti(1V) and 0.12-1.50 pg of Zr(1V) was placed in a 25-mL standard flask. Three milliliters of 5.5 X lo4 M BMNH solution and 1.2 mL of 0.1 M Na2S0, solution were then added and the pH of the solution was adjusted to 3.0 with hydrochloric acid or sodium hydroxide. The volume was made up to the mark with distilled water and the mixture was allow to stand for 1 h. The second-derivative spectrum, obtained by synchronous fluorescence, was recorded by scanning both monochromators together with a 70-nm constant difference between them. The excitation monochromator was scanned from 330 to 530 and the emission monochromator from 400 to 600 nm. The instrumental parameters were as above. Second-derivativemeasuremenk were carried out peak to peak (20), Le., by measuring the difference between the derivative signal at two wavelengths corresponding to an adjacent maximum and minimum, given as relative fluorescence intensity and expressed as AI. Titanium and zirconium measurements were made at 535-545 nm and 465-475 nm, respectively. The fluorescence intensities of these derivative signals are directly related to the concentration of each ion whose concentration is determined from the calibration curves previously plotted. Titanium-Hafnium Mixtures. Samples were prepared as described for the titanium-zirconium mixtures and measured by the same procedure. The range of hafnium concentration in the sample must be between 0.12 and 1.90 pg. The derivative signal is obtained by measuring the fluorescence intensity between the maximum at 460 nm and the minimum at 470 nm. Zirconium-Hafnium Mixtures. A sample volume containing Zr(1V) (0.12-2.25 pg) and Hf(1V) (0.12-2.25 pg), 3 mL of 5.5 X lod M BMNH solution, and 1mL of 0.1 M Na2S04solution were mixed in this order in a 25-mL standard flask, pH being adjusted to 1.5with hydrochloric acid or sodium hydroxide and the resulting volume being made up to the mark with distilled water. The second-derivative synchronous fluorescencespectrum was recorded by scanning both monochromators simultaneously with a constant 50-nm difference between them. The excitation monochromator was scanned from 350 to 500 nm and the emission one from 400 to 550 nm. The instrumental parameters were as detailed in Apparatus. Peak-to-peak measurements were carried out over the ranges 501-507 nm for Zr(1V) and 492-497 nm for Hf(1V). The concentration of each ion in the mixture was determined from their corresponding calibration graphs previously run under conditions analogous to those of the mixture. RESULTS AND DISCUSSION Biacetyl monoxime nicotinylhydrazone (BMNH) forms a fluorescent binary complex with Ti(1V) (A, 430, A, 540 nm) and ternary complexes with Zr(1V) (Aex 415, A,, 505 nm) and Hf (IV) (Aex 400, A,, 500 nm) in the presence of sulfate ions. Several sensitive methods have been proposed (16) for the individual determination of these ions. Discerning between two of them in a mixture is a more difficult task because of strong overlap between their conventional fluorescence spectra, shifted with respect to each other by only a few nanometers. The resolution of binary mixtures of these ions with BMNH requires running several calibration graphs and preparing samples a t different pH values, which is time-consuming. As the methods described for these ions with BMNH are very selective and sensitive, we have chosen them to be applied to the second derivative of the synchronous signal, thus developing fast and straightforward methods for the simultaneous determination of these binary mixtures. All possible two-component combinations of the titanium, zirconium, and hafnium complexes were studied. Three spectra were recorded for each of these ions as follows: (1) exciting at the maximum excitation wavelength and scanning the emission wavelength (usual method); (2) scanning both the excitation and emission wavelength a t a constant AX
30
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Flgure 1. Emission spectra of titanium (1) and hafnium (2) complexes at the maximum excitation wavelength for titanium (430 nm) (A) and for hafnium (400 nm) (B); synchronous fluorescence spectra (C) for both complexes at AX = 70 nm. Second-derivative synchronous fluorescence spectra for titanium (D) and hafnium (E) complexes, and for their mixture (F). Concentration of each ion was 40 ng/mL.
(synchronous spectrum); (3) recording the second-derivative synchronous fluorescence spectrum. Figure 1 shows the spectra obtained for titanium and hafnium complexes. When using a fixed excitation wavelength a t 430 nm (Figure 1A) and 400 nm (Figure lB), the fluorescence spectra recorded consist of broad spectral bands overlapping one another. It is practically impossible to simultaneously determine mixtures of these ions by studying their emission spectra alone. However, if a constant difference is maintained between the excitation and emission wavelengths (AA = 70 nm), it is possible to obtain a spectrum (Figure 1C) showing a wavelength range over which only the titanium complex exhibits fluorescence and another one where only that of hafnium is fluorescent. Hence, the values obtained from the synchronous spectrum afford significant improvement in selectivity, but the sensitivity for the hafnium complex, very similar to that of the titanium complex, is decreased as a result if its measurements are not carried out a t its fluorescence maximum. However, the signal is increased about 4-fold for the titanium complex (Figure 1D) and 5-fold for the hafnium complex (Figure 1E) when second-derivative synchronous fluorescence spectra are employed. The second-derivative spectrum of the mixture of both complexes (Figure 1F) shows two peaks, the fluorescence intensity corresponding to each complex being independent of each other. It has been checked that the peak height for the complex whose concentration is kept constant does not change as the concentration of the other complex is modified. The titanium and zirconium systems behave similarly, with no systematic interactions. The usefulness of second-derivative synchronous spectra becomes more ostensible in the simultaneous determination
30
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 6, MAY 1985
1103
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Figure 3. (A) Effect of AA on the wavelength corresponding to the peaks for which the contribution of titanium (1) and zirconium (2) is maximum. (B) Effect of AA on the relative fluorescence intensity obtained for the zirconium complex at its peaks of maximum contributlon (1) and at those of maximum contribution of the titanium complex (3);effect of AA on the relatlve fluorescence intensity obtained for the titanium complex at its peaks of maximum contributioH (2) and at those of maximum contribution of the zirconium complex (4).
LO
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30
20
10
420
500
580
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500
580
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500
580
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Flgure 2. Emission spectra of zirconium (1) and hafnium (2) complexes at the maximum excitation wavelength for hafnium (400 nm) (A) and for zirconium (415 nm) (B); synchronous fluorescence spectra (C) for both complexes at AA = 50 nm; secondderivative synchronous fluorescence spectra for zirconium (D) and hafnium (E) complexes, and for their mixture (F). Concentration of each ion was 40 ng/mL. of zirconium-hafnium mixtures. Figure 2 shows the conventional fixed excitation fluorescence spectra (Figure 2A,B) and the synchronous fluorescence spectra (Figure 2C) of both complexes. Owing to the overlap of the emission bands, the simultaneous determination of this mixture by conventional fluorometry is unfeasible. We should note that the use of synchronous fluorescence spectra did not result in a more precise determination for any AA tested. Therefore, the possibility of applying derivative techniques to carry out the direct analysis of this mixture has a great potential interest. Figure 2, parts D and E, shows the individual second-derivative synchronous fluorescence spectra of zirconium and hafnium complexes, while Figure 2F shows the spectrum of their mixture (AA = 50 nm). No interaction is observed over a short range of wavelengths, which corroborates the feasibility of the simultaneous determination of these ions. It has been also checked that the direct determination of this mixture is not viable by using the second derivative of the conventional emission spectra of these complexes. This requires the association of both techniques in order to carry out the simultaneous analysis of the mixture. Effect of Variables on t h e Titanium-Zirconium a n d Titanium-Hafnium Systems. The systems were optimized by changing one variable at a time while keeping the others constant. The optimum value taken for each variable was that for which the following requirements were met: (1) The fluorescent signal for each complex should not depend on the signal of the other complex present in the mixture. (2) The
signal for each peak (AITi, AIzr, and A I H J should be as high as possible. Therefore, the response function selected (F(i)) was AlTi41zr for the first system and A I T ~ ~for I Hthe ~ second one. AI was assessed as described above. In order to modify the spectral bandwidth of the synchronous signal, AA and Stokes shift parameters were varied experimentally. The most important parameter in the simultaneous analysis of mixtures is the selection of the optimum wavelength difference between both monochromators. Second-derivative synchronous fluorescence spectra were obtained over a range of AA from 20 to 140 nm. The results found for the titaniumzirconium mixture are shown in Figure 3 from which the following considerations can be made: (1)The spectral distribution is a function of AA. Secondderivative synchronous fluorescence spectra were compressed or expanded by decreasing or increasing respectively this experimental parameter to which the number of peaks is also related. Therefore, we have studied the peaks obtained for each AA value at which the conditions for the optimization of the system are fulfilled. Figure 3A shows the variation with AA of the wavelength corresponding to the minimum of the derivative peak at which the contribution of titanium and zirconium complexes is maximum. As can be seen, this wavelength changes almost linearly for the titanium complex, whereas it remains unchanged for the zirconium complex up to a value of AA = 75 nm. Above this value, a small shoulder appears in the synchronous spectrum which results in the appearance of a new peak in the derivative spectrum, around A 480 nm, and hence in a decrease in the AI value. (2) The fluorescence intensity depends strongly on AA. Figure 3B lists the values of AI obtained at the wavelengths shown in Figure 3A. As can be observed, the signal obtained (All for each complex does not show its maximum value when the value chosen for AA equals the difference betwen the wavelengths of the excitation and emission maxima obtained from the conventional fluorescence spectra (110 nm for the titanium complex and 90 nm for the zirconium complex). This is always the case when only the synchronous fluorescence Bpectrum is recorded, but many other factors result in nonmaximum AI values for the second derivative of the synchronous fluorescence spectrum under these conditions. There is an appreciable extent of spectral overlap for AA C 65 nm
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 6, MAY 1985
which increases with decreasing AX. Above this AA value the fluorescence intensity for each complex, obtained at its corresponding wavelength, is independent of the fluorescence intensity of the other complex. The decrease in the fluorescent signal above AA = 75 nm for the zirconium complex is due to the appearance of the aforementioned further peak. AA = 70 nm was chosen for the simultaneous analysis of the titanium-zirconium mixture. The hafnium complex shows a similar behavior to that of the zirconium one. Therefore, the Ah value selected for the determination of the titanium-hafnium mixture was the same as the titanium-zirconium one. The Stokes shift can be varied by changing the solvent environment. Various solvents with different dielectric constants (dimethylformamide > methanol > ethanol > acetone) were tried. The spectral distribution and fluorescence intensity a t the peak of interest did not show significant differences for a given percentage of organic solvent, an increase of which results in a decrease in the fluorescence intensity of the titanium complex, whereas no variation is observed for those of zirconium and hafnium. Second-derivative synchronous fluorescence spectra are strongly dependent on three instrumental variables on which the time factor has an important effect: wavelength scanning speed, differentiation constant, and the spectrofluorimeter response (time constant). A decrease in the wavelength scanning speed exerts two distinct effects on the spectrum of the titanium-zirconium complexe mixture. First, the spectral resolution is increased. Second, the relative intensities of the main peaks are decreased. For a scanning speed of 8 nm/s the spectra of both complexes overlap and the spectrum of their mixture exhibits only one peak, thus rendering the mixture resolution impossible. Scanning speeds from 4 to 1 nm/s do permit this determination, whereas for lower speeds the spectra do not show definite peaks. The mixture of titanium-hafnium complexes behaves similarly. A scanning speed of 4 nm/s was chosen for both systems. The study of the effect of the differentiation constant of the second-derivative synchronous fluorescence spectra showed that a decrease in the response speed degrades the resolution and increases the relative intensities of the peaks of interest. The response function of both complexes is optimum when the response speed is minimum because the spectral resolution is adequate for the determination of both complexes and the fluorescence intensity is maximum. Constants of 0.3, 1.5, and 3.0 s have been tested in order to study the effect of the spectrofluorimeter response (time constant). Although the spectral resolution does not change appreciably, the relative intensity of the peak increases as the time constant decreases. Increasing the slit width in both monochromators causes a decrease in the resolution and an increase in the derivative signal. As can be inferred from this study, there is a variety of instrumental parameters affecting second-derivative synchronous fluorescence spectra. This fact endows this technique with a great versatility which facilitates its application to the simultaneous analysis of mixtures. The rate of formation of the titanium complex is highly dependent on the pH, increasing progressively with it. For the zirconium and hafnium complexes the maximum stability is obtained a t low pH values. The drop in intensity of these complexes over time above pH 3.0 is probably due to their progressive hydrolysis. The fluorescence intensity of the three complexes does not show significant changes over a pH range of 2.5-3.0 at times longer than 1h. The optimum pH range is different for each ion: titanium (2.7-3.2), zirconium (0.7-1.5), and hafnium (0.5-1.5). The response function for
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Flgure 4. (A) Effect of Ah on the wavelengths corresponding to the peaks for which the contribution of zirconium (1) and hafnium (2) complexes is maximum; (B) effect of Ah on the relative fluorescence intensity obtained for the zirconium complex (1) at its peak of maximum contribution and on that due to the hafnium complex (2) at the same peaks: (C) effect of AA on the relative fluorescence intensity obtained for the hafnium complex (1) at its peaks of maximum contribution and on that due to the zirconium complex (2) at the same peaks.
the resolution of titanium-zirconium and titanium-hafnium mixtures is maximum a t pH 2.8. The effect of the sulfate concentration on these systems was studied over the 2 X 10" to M range. Sulfate ions form ternary complexes with zirconium-BMNH and hafniumBMNH, but do not affect the titanium-BMNH complex. The fluorescence intensity of the zirconium and hafnium complexes increases with increasing concentration of sulfate ion up to a value of 4 X M, keeping constant for greater concentrations. The influence of the BMNH concentration was assessed over the 2 X to 2 X lo4 M range. The complete formation of the titanium complex in the mixtures is restricted to reagent concentrations below 4 X M. On the other hand, the fluorescence intensity of the titanium complex decreases for concentrations higher than M. A 6.5 X M concentration was thus selected. The variation of the ionic strength (0-0.5 M range), adjusted with sodium chloride, and the order of addition of the reagents exert almost no influence on the response function of both mixtures. The effect of the temperature was checked over the 15-35 "C range. The variations in the percentage of fluorescence intensity per degree centigrade (temperature coefficient) were -0.6%, -1.5%, and -1.1% for the titanium, zirconium, and hafnium complex, respectively. Ethanol solutions of BMNH do not fluoresce a t any pH value and their second-derivative synchronous fluorescence spectra show no signal in the spectral region of interest under the optimum conditions for the resolutipn of both mixtures. Effects of Variables on the Zirconium-Hafnium System. The optimization on each variable was carried out according to the considerations made for the other systems. Therefore, the response function selected was F,, = h l z , . h l ~ p The effect of AA on the second-derivative synchronous fluorescence spectra of both zirconium and hafnium ternary complexes is shown in Figure 4 (similar to Figure 3), in which the wavelength corresponding to the minimum of the derivative peak of each complex and the fluorescence intensity obtained at these wavelengths are plotted as a function of AA. A bathochromic shift (Figure 4A) is observed for both complexes as the AA value increases. In this case, the peak selected for the analysis of these ions in the mixtures with titanium
ANALYTICAL CHEMISTRY. VOL. 57, NO. 6, MAY 1985
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Figure 5. Secondderivative synchronous fluorescence spectra obtained for several mixtures of zirconium and hafnium complexes: Zr:Hf ratio (ng/mL), (A) 20:20;(B) 10:40;(C)10:80; (D) 60:iO; (E) 805.
described above cannot be used for the zirconium-hafnium mixture since the contribution of both complexes to this peak is very similar. The hafnium complex does not affect the peak corresponding to the zirconium one at AX > 47 nm (Figure 4B), while the zirconium complex shows no influence on the peak of the hafnium one at AX 5 50 nm (Figure 4C). The maximum response function is obtained for AX = 50 nm. The solvent environment and its percentage in the samples do not affect spectral distribution and only causes small changes in the fluorescence intensity. Variations in the scanning speed of both monochromators and in the differentiation constants have effects similar to those described for the preceding systems. As far as the spectrofluorimeter time constants are concerned, a value of 0.3 s yields the maximum relative intensity, but the contribution of the zirconium complex to the maximum signal peak of the hafnium complex is rather significant. Both peaks are independent of each other for a value of 1.5 s, and the relative intensities obtained in this case are greater than those obtained for a constant of 3 s. The zirconium-hafnium complex mixture is not dependent on the pH over the 1.0-2.5 range, outside which the relative intensity for both peaks is decreased. Hence, a pH of 1.5 was chosen. The sulfate ion concentration has a marked effect both on the fluorescence of the two complexes and on the resolution of their mixture. The second-derivative synchronous fluorescence spectra of both ions (bihary complexes) overlap throughout the spectral region in the absence of sulfate ions. When the concentration of sulfate increases up to 2 X M, the fluorescence intensity of both complexes also increases due to the formation of the corresponding ternary complexes. Higher concentration do not affect either complex. The effect of the BMNH concentration on this mixture was studied over the 2 X to M range. Reagent concentrations below 5 X M result in spectral overlap in the peak corresponding to the maximum contribution of the zirconium complex. The peaks corresponding to both complexes are independent of each other for greater concentrations.
Variations in the ionic strength and in the order of addition of the reagents do not affect the behavior of both complexes. The temperature coefficient found was about -0.970 per degree centigrade for the zirconium complex and -1.070for the hafnium one. Characteristics of the Analytical Methods, On the basis of the experimental work, several methods for the simultaneous determination of binary mixtures of titanium, zirconium, and hafnium are proposed. Linear calibration graphs are run by plotting A I against different concentrations of these ions. The analysis of samples containing various concentrations of two of these ions shows that the determination of their mixtures is feasible over the following concentration ranges: Ti(1V)-Zr(1V) mixture, Ti(1V) (4-35 ng/mL, 70RSD = f2.8), Zr(IV) (5-60 ng/mL, % RSD = f3.2); Ti(1V)-Hf(1V) mixture, Ti(1V) (4-35 ng/mL, 70RSD = f 2.81, Hf(1V) (5-75 ng/mL, % RSD = f4.2); Zr(1V)-Hf(IV) mixture, Zr(1V) (5-90 ng/mL, % RSD = f4.3), Hf(1V) (5-90 ng/mL, % RSD = k3.9). The effect of foreign ions on these systems, using this technique, has been studied and the results found are very similar to those obtained by conventional fluorometry (16). Simultaneous Determination of Titanium, Zirconium, and Hafnium in Synthetic Binary Mixtures. The association of second-derivative spectrometry and synchronous fluorescence techniques has been applied to the determination of several synthetic binary mixtures containing two of these ions in different ratios. Table I summarizes the results obtained and Figure 5 shows the second-derivative synchronous fluorescence spectra of various zirconium-hafnium mixtures. In view of the results obtained in the analysis of these mixtures both by this technique and by conventional fluorimetry (161, the following conclusions can be drawn: The ratio in which an ion can be determined in the presence of the other is increased. The highest ratio obtained for the three mixtures by conventional fluorimetry is k2.5. This ratio is increased up to 1:16 (Zr-Hf mixture) by this technique. The sensitivity obtained for the zirconium and hafnium determinations is similar for both techniques, but it is 5 times higher for the determination of titanium.
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Table I. Simultaneous Analysis of Synthetic Binary Mixtures of Titanium, Zirconium and Hafnium
mixture
Table 11. Analysis of Synthetic Ternary Mixtures of Titanium, Zirconium, and Hafnium
amt of amt of amt of Ti(IV), Zr ( W , Hf(IV), ng/mL ng/mL ng/mL ratio taken found" taken found" taken found'
ratio 1:l:l
Ti(1V)-Zr(IV)
5 20 30 5
6 22 28 5
5 20 30 20
10
10
50
3:2 3:1 4:1 6:1
5 30 30 20 30
5 29 33 22 31
50 20 10 5 5
1:1
5
4
5
5
1:2 3:7 2:7 1:4 1:5 2:1 3:1 41
20 20 30 20 5 10 10 30 20
22 20 30 18 5 12 9 28 20
20 40 70 70 20 50 5
20 43 74 72 24 50 6 9 4
1:l
1:4 1:5 1:lO
Ti(1V)-H-
6 19 28 17 53 52 21 10 4 4
1:2:2 1:2:3 3:1:4 1:4:2 3:1:2 3:l:l 1:4:4 2:l:l
F(IV)
Zr(1V)-Hf(IV)
1:l
1:4 1:8 4:1 6:1 16:l
10
5
5 20 50 80 5 10
4 20 45 81 5
10
10 78 63 82
80 60 80
10
5 20 50 80 20 40 80 20 10 5
5 19 51 82 20 38 77 18
8 6
" Average of three separate determinations. Only one scan is required, which results in shorter measurement times. Precision is slightly poorer, but this can be attributed to the intrinsic characteristics of the chemical systems involved rather than to the technique itself, because titanium is measured over a lower concentration range and the determinations of zirconium and hafnium are carried out at pHs other than the optimum ones for these complexes. The results obtained show that the combination of both techniques has a great potential in developing an efficient, fast, and straightforward method for the simultaneous determination of ion mixtures. Determination of Ternary Mixtures. The determination of ternary mixtures of these ions can be carried out by performing two scans, one for the determination of the Zr-Hf mixture under the same experimental conditions indicated in the procedure for this mixture, and another one for the determination of Ti under the conditions specified in the procedures for Ti-Zr and Ti-Hf mixtures, but adding an excess of reagent (10mL of 5.5x M solution) to achieve the complete formation of the Ti complex in the presence of the other two ions.
amt of Ti(IV), ng/mL taken found" 10 20 30 10 10
30 10 30 30 10
20
11 22 30 10 13 29 8 29 28 11 18
amt of Zr(IV), w/mL taken found" 10
20 30 20 20 10 40 10 10 40 10
10 19 35 23
20 11 35 12 11
42 9
amt of Hf(IV), ng/mL taken found' 10
20 30 20 30 40 20 20 10 40 10
9 18 27 19 31 38 21 23 9 39 12
'Average of three seDarate determinations. Several synthetic ternary mixtures of these ions have been analyzed by using this procedure, the results obtained being shown in Table 11. The direct simultaneous determination of ternary mixtures is impossible because the Zr-Hf mixture can only be resolved in a AA range of 47-50 nm, as shown in Figure 4,whereas the Ti-Zr and Ti-Hf mixtures require a AA value greater than 65 nm for their resolution (Figure 3). Therefore, no suitable value of Ah can be chosen for the simultaneous determination of the three ions. These species can be determined in different alloys, steels, clays, etc., thanks to the small number and low level of interferents encountered in the fluorometric determination proposed (16). Registry No.BMNH,91151-80-3; Ti, 7440-32-6; Zr, 7440-67-7; Hf, 7440-58-6. LITERATURE CITED (1) Lloyd, J. B. F. Nature (London) 1071, 237, 64. (2) Green, G. L.; O'Haver, T. C. Anal. Chem. 1074, 46, 2191. (3) Inman, E. L., Jr.; Winefordner, J. D. Anal. Chim. Acta 1982, 747, 241. (4) Vo-Dlnh, T. Anal. Chem. 1978, 50, 396. (5) Vo-Dinh, T.; Martin&, P. R. Anel. Chim. Acta 1081, 725, 13. (6) Eastwood, D.; Fortier, S. H.; Hendrlck, M. S. Am. Lab. (FairfieM, Conn.) 1078, 70, 45. (7) John, P.; Soutar, I. Anal. Chem. 1078, 48, 520. (8) Lloyd, J. B. F. Analyst (London) 1080, 705, 97. (9) Wakeham, S. G. Environ. Sci. Technoi. 1077, 7 1 , 272. (10) Vo-Dinh, T.; Gammage, R. B.; Martinez, P. R. Anal. Chem. 1981, 53, 253. (11) Vo-Dinh, T.; Gammage, R. 8.; Hawthorne, A. R.; Thorngate, J. H. Environ. Sci. Techno/. 1978, 72, 1297. (12) Andre, J. C.; Baudot, Ph.; Nlclause, M. Clln. Chim. Acta 1077, 76, 55. (13) Eastwood, D.; Fortier, S. H.; Hendrick, M. S. Int. Lab. 1078, July/August, 51. (14) Vo-Dinh, T. I n "Modern Fluorescence Spectroscopy", 1st ed.; Wehry, E. L., Ed.; Plenum Press: New York, 1981; Vol. 4, Chapter 5. (15) Vo-Dlnh, T. Appl. Spectrosc. 1982, 36, 576. (16) Cejas, M. A,; G6mez-Hens, A.; ValcBrcel, M. Anal. Chim. Acta 1084, 758, 287. (17) Lytle, F. E.; Storey, D. R.; Jurlcich, M. E. Spectrochim. Acta, Pert A 1973, 29, 1357. (18) Hirakl, K.; Morlshige, K.; Nishikawa, Y. Anal. Chim. Acta 1078, 9 7 , 121. (19) Erdey, L. "Gravimetric Analysis", 1st ed.; Pergamon Press: Oxford, 1965; Part 11, p 476. (20) O'Haver, T. C. Ciin. Chem. (Wlnston-Salem, N . C . ) 1070, 25, 1548.
RECEIVED for review September 6,1984.Accepted December 19,1984.
