224
Anal. Chem. lg82, 5 4 , 224-228
Room-Temperature Phosphorescence of Hydroxyl-Substituted Aromatics Adsorbed on Solid Surfaces R. A. Dalterlo and R. J. Hurtubise* Chemistry Department, The Universiv of Wyoming, Laramie, Wyomlng 8207 1
Room-temperature phosphorescence (RTP) is a rapidly developing new analytical technique, as evidenced by a number of publications in recent years (1-10). Parker, Freedlander, and Dunlap (11,12)have published a review of RTP covering the physical aspects of the phenomenon and practical analytical considerations. Hurtubise (13)has discussed, in detail, instrumentation for RTP, some interactions responsible for RTP, and analytical applications. Hydroxyl-substituted aromatic compounds have been found in treated and untreated waters (14) and in plant tissues (15). They are used as food-grade antioxidants in foodstuffs (16) and as antioxidants in oils and oil additives (17)and in plastics (18). They are also present in coal-derived samples (19) and other fossil fuels. Hydroxyl-substituted aromatic compounds are the subject of much interest for development of new analytical approaches for identification and quantitation. In the present work several polymer-salt mixtures were examined as surfaces for inducing RTP from hydroxyl-substituted aromatic compounds. Ford and Hurtubise (1)found the salt of poly(acrylic acid), a binding agent in certain brands of silica gel chromatoplates, was the component largely responsible for inducing strong RTP from nitrogen heterocycles adsorbed on these plates. In this work, a sample-holding plate, originally designed by von Wandruszka and Hurtubise (20), was modified to accommodate 22 powder or filter paper circle samples for RTP measurement. A comparison of the RTP of hydroxyl-substituted aromatic compounds adsorbed on 1% PAA-NaBr (w/w) and on filter paper circles was made. The two solid surfaces were also compared with respect to reproducibility of the RTP signal, relative ease of handling of the solids, and decrease in RTP after drying.
to the long edge with 0.5 cm between edges of the depressions. The plate was blackened to a dull, nonreflecting finish. Phosphorescence excitation and emission spectra were obtained with a Farrand MK-2 spectrofluorimeter fitted with a phosphorescence rotary chopper. Metal slits giving a bandwidth of 10 nm were used at the entrance and exit positions of both the excitation and emission monochromators. Source radiation was provided by a 150-W xenon lamp and the detector was a 1P28-B photomultiplier tube. Powdered samples were placed in a quartz tube, sealed at one end, and held in the sample compartment of the spectrofluorimeter with a clamp provided with the Dewar assembly. Reagents. Absolute ethanol and water were purified by distillation. 4-Phenylphenol, p,p'-biphenol, 2-naphthol, 2,3-dihydroxynaphthalene, a-naphthoflavone, 2-hydroxy-5,6,7,8tetrahydrophenanthrene, 9-phenanthrol, and chrysin were purchased from Aldrich Chemical Co. and recrystallized from absolute ethanol. p-Hydroxybenzoic acid was 99+ % from Aldrich Chemical Co. and used as received. NaC1, NaBr, and NaI were analytical reagent grade. The polymers examined were purchased from Scientific Polymer Products Inc., Ontario, NY, and were used as received. The filter paper emplo$ed was Whatman No. 31 and was used as received. Polymer-salt powders were mixed in a ball mill (Norton Co., Chemical Process Products Division, Akron, OH) for 1 h to ensure uniformity. Procedures. Samples were prepared for calibration curves using 1% PAA-NaBr (w/w) mixtures. Aliquots of 15 pL of ethanol were introduced into 40 X 4 mm test tubes from a micropipet and 0.5-10 pL volumes of ethanolic sample solutions were added with a 10-pL Hamilton syringe. A fixed amount of PAANaBr was then added to each tube ( 10 mg) with a measuring spoon that had the same volume as the depressions in the plate described above. The tubes were then placed in an oven at 80 OC for 25-30 min to evaporate all the solvent. The powder was then transferred to the depressions in the brass plate and smoothed over with a spatula, taking care that all of the powder was in the boundaries of each depression. Other samples were prepared for calibration curves using filter paper circles. Filter paper circles were precut with a sharpened no. 1cork borer and placed into depressions in the brass sample holder. Sample solutions were prepared so that 2 pL of the solution contained 350 pg of NaBr and 0-500 ng of sample. The solvent was ethanol/water, 80:20 (v:v). The 2-pL volume was added all at once to the fiiter paper with a 10-pLHamiIton syringe and dried at 100 "C for 15 min. After the samples were dried, the brass plate was positioned on the scanning stage of the spectrodensitometer, the phosphoroscope was positioned, the excitation and emission monochromators set to the appropriate wavelengths, and the RTP was measured in the single beam reflection mode.
EXPERIMENTAL SECTION Apparatus. Calibration curves and relative RTP intensity measurements were obtained with a Schoeffel SD 3000 spectrodensitometer, with a modified reflection mode assembly and phosphoroscope attachment (21). The spectrodensitometer, reflection mode assembly and phosphoroscope were employed as described in ref 21, except that a R928 photomultiplier tube (Hamamatau Corp., Middlesex, NJ) was used in the present study. The samples measured with the spectrodensitometer were placed in a series of 22 circular depressions of 4.76 mm diameter and 1.0 mm depth for powder adsorbenta and 0.20 mm depth for filter paper adsorbenta. The depressions were milled into a brass plate, 25.5 cm long by 7.5 cm wide by 0.5 cm deep! along a line parallel
RESULTS AND DISCUSSION Polymer Mixtures a n d Other Solid Surfaces Examined as Adsorbents for RTP. Several polymers containing polar functional groups were examined as surfaces for inducing RTP. In no instance did a polymer alone induce RTP from the adsorbed compound. The polymers examined had to be mixed with an inorganic salt for them to be an effective material for inducing RTP. Volumes of 5 pL of ethanol solutions containing 300 ng of 4-phenylphenol, 300 ng of 2naphthol, and 300 ng of 2,7-dihydroxynaphthalenewere adsorbed individually onto 10 mg of polymer-salt mixture and dried at 80 "Cfor 15 min (Table I). The phosphorescence
Several polymer-salt mixtures were examlned as solld surfaces for room-temperature phosphorescence (RTP). A variety of hydroxyl-substltuted aromatlc compounds were observed to glve RTP when absorbed on poly(acry1ic acid) (PAA)-sodlum hallde mixtures and fllter paper. A solld-sample holdlng plate was used wlth a spectrodensltometer for solld surface luminescence detection of components on powder and fllter paper adsorbents. RTP analytlcal data, Including linear ranges of cailbratlon curves and limits of detection for several compounds, were compared for 1% PAA-NaBr powder and fllter paper.
0003-2700/82/0354-0224$01.25/0
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0 1982 American Chemlcal Society
ANALYTICAL CHEMISTRY, VOL. 54,
Table I. Solids Examined To Induce RTP with Model Compounds (Solid Mixtures, w/w%) material RTP 5% poly(viny1 fluoride)-NaC1 5% poly( acry1amide)-NaCl 5% poly(viny1 alcohol) (88% hydrolyzed)-NaCl 5% hydroxypropylcellulose-NaC1 5% cellulose triacetate-NaC1 2% poly(acrylonitri1e)-NaBr 1%ammonium salt of poly(acry1ic acid)-NaBr 1%poly(acry1ic acid) (secondary
-
standard)-NaBr 1%poly(acry1ic acid) (uncharacterized mol wt)-NaBr phosphorylized cellulose soluble starch
No Yes Yes No No No No Yes
Yes Yes Yes
~~
Table 11. Compounds Showing RTP on 5%Poly(acry1ic acid)-NaC1 Mixture compounda
RTP
4-phenylphenol 3-phenylphenol 2-phenylphenol o,o'-dihydroxybiphenyl p,p'-dihy droxybiphenyl 2,3-dihydroxynaphthalene 1,3-dihydroxynaphthalene 1,5-dihydroxynaphthalene 1,7-dihydroxynaphthalene 2,6-dihydroxynaphthalene 2,7-dihydroxynaphthalene 1-naphthol 2-naphthol 1,l'-bi-2-naphthol phenol p-cresol 2,6-di-tert-butylphenol 4-ethylphenol (with 0.1 M NaOH) chrysin (5,7-dihydroxyflavone) 9-phenanthrol 1,4,9)10-tetrahy droxyanthracene fisetin (3,3',4',7-tetrahydroxyflavone) rutin ( 3',4', 5,7-pentahydroxy-
strong moderate weak weak strong moderate weak weak weak weak moderate weak moderate weak very weak very weak very weak weak weak weak very weak weak very weak
flavone-3-rutinoside )
2-hy droxy-5,6,7,8-tetrahy dromoderate phenanthrene 01 aaphthoflavone strong p-hydroxy benzoic acid moderate 4-hydroxy-3-methoxybenzoic acid weak 5-hy.droxy-2-indolecarboxylic acid weak 5,6,7,8-tetrahydro-l-naphthol very weak 1,2-dihydroxybenzene (with 0.1 M NaOH) weak 1,2,3-trihydroxybenzene weak (with 0.1 M NaOH) a
1 f i g adsorbed, ~~
~
~~~~
~~
was detected visually as an afterglow upon removal of the exciting radiation from an ultraviolet handlamp. Both shortand longwave ultraviolet radiation were used to excite the samples. It was found that poly(acry1ic acid) (secondary standard, mol wt 2000000) induced the strongest RTP from model compounds and was used in this work to obtain analytical data for several compounds. Table I shows that several polymer-salt mixtures did not induce R T P from the model compounds. Poly(acrylamide) and poly(viny1 alcohol) induced weak RTP signals from the model compounds but impurities present in these polymers caused background RTP. These polymers cannot be useful analytically unless the background phosphorescence is reduced. The various types of poly(acrylic acid) examined also showed a small background R T P due to impurities in the polymer. An attempt was made to purify these
NO. 2,
FEBRUARY 1982
225
Table 111. Compounds Not Showing RTP When Adsorbed on 5% Poly( acrylic acid)-NaC1 anthrarobin (1,2,10anthracenetriol) hydroquinone 5-hydroxyquinoline p-aminophenol salicylic acid p-hydroxy cinnamic
acid 2,6-dihydroxybenzoic acid
5-hydroxytryptophan 3-hydroxytyramine p-hydroxyphenylacetic acid 2,3-dihydroxybenzoic acid 1,2-dihydroxynaphthalene 5-indanol 9-anthraceneme thanol
m-hydroxy benzoic acid
p-hydroxyphenylpyruvic acid
5-hydroxyindole-3acetic acid 1-hydroxy-9-fluorenone o -cresol
5-hydroxy uridine
m-cresol
L-tyrosine 5,6,7,8-tetrahydro-2naphthol
Table IV. Effects of Type of Salt Mixed with Poly(acry1ic acid) on RTP Intensity of Model Compounds
surface 0.5% poly(acry1ic acid)-NaCl 1.0% poly(acry1ic acid)-NaBr 1.0%poly(acry1ic acid)-NaI
re1 RTP intens 4-phenyl- p,p'-biphenola phenolb 1.5 2.3 none
a 150 ng adsorbed, average of two samples. adsorbed, average of two samples.
1.0 1.8
none 300 ng
polymers by successive reprecipitation from ethanol-water solution with chloroform, but the impurities were not noticeably reduced. However, poly(acry1ic a c i d h a l t mixtures were still very good solid surfaces for inducing RTP. Compounds Examined f o r R T P on 5 % Poly(acry1ic acid)-NaC1 Mixture. Table I1 lists compounds that gave RTP when adsorbed on 5% poly(acry1ic acid)-NaC1 from absolute ethanol solutions. Table I11 lists compounds examined which did not show RTP when adsorbed on 5% poly(acrylic acid)-NaC1. The afterglow of phosphorescence was detected visually after removal of the exciting radiation from an ultraviolet handlamp. Both short- and longwave ultraviolet radiation were used to excite the samples. As indicated in Table I1 31 compounds gave RTP. Also, poly(acry1ic acid) mixed with NaBr elicits more intense RTP from hydroxyl aromatics than poly(acry1ic acid)-NaC1 mixtures. For this reason, some of the compounds that did not show RTP on poly(acry1ic acid)-NaC1 may show the effect on poly(acry1ic acid)-NaBr. R T P Intensity vs. Weight Percent Poly(acry1ic acid) Mixed with Sodium Halide Salts. The relative proportions and type of inorganic salt mixed with poly(acry1ic acid) were found to have a large effect on the RTP. A series of mixtures of poly(acry1ic acid) and NaCl were prepared and examined for RTP with model compounds. A mixture of 0.5% poly(acrylic acid)-NaC1 was found to yield the most intense RTP signals. Poly(acry1ic acid)-NaBr mixtures were examined similarly and a mixture of 1.0% poly(acry1ic acid)-NaBr showed the most intense RTP (Figure 1). NaI-poly(acry1ic acid) mixtures yielded no RTP. From Figure 1,it can be seen that for 50 and 100 ng of 2-naphthol, 0.5% PAA-NaBr gave the strongest RTP. At 150 ng of 2-naphthol, 0.5% and 1.0% PAA-NaBr show equal RTP and a t 300 ng of 2-naphthol, 1.0% PAA-NaBr gives the strongest RTP. Table IV compares RTP intensities of model compounds adsorbed on various
226
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2, FEBRUARY 1982
Table V. Effect of Sodium Halide Salts on RTP Intensity of 4-PhenylphenolAdsorbed on Filter Papera salt
RTP re1 intens*
None NaCl
9.6
1.0
salt
RTP re1 intensb
NaBr NaI
12 17
a A 2-pL aliquot of solution containing 100 ng of 4phenylphenol and 2 pmol of various sodium halide salts in Average of two ethano1:water (80:ZO) was adsorbed. samples.
Table VI. Effect of RTP Intensity on Amount of NaBr Added to Filter Paper amtof RTPrel amtof RTPrel NaBr, p g intensa NaBr, pg intensa 0 50 100 150 200 a
1.0 4.5 9.5 14 16
250 300 350 400
22 19 19 19
I
I
I
05
IO
I
I
duplicate samples.
optimal poly(acry1ic acid)-sodium halide salt mixtures. From Table IV it can be seen that 1% PAA-NaBr gives the strongest RTP from the model compounds. Effect of Sodium Halide Salts on RTP Intensity of Compounds Adsorbed on Filter Paper. The RTP intensity of 4-phenylphenol adsorbed on filter paper varies with the type and amount of sodium halide salt absorbed into the filter paper matrix. As shown in Table V, NaI induced the largest RTP signal. This is in contrast to the results in Table IV. The increase in RTP intensity caused by absorbing sodium halide salts into the filter paper is not likely the result of only heavy-atom enhancement, since NaCl causes nearly a 10-fold RTP increase over untreated paper. The salt may be contributing to a matrix packing effect by which the phosphor molecules become more rigidly held within the matrix and consequently less prone to collisional deactivation of the triplet state (22). The RTP intensity of 4-phenylphenol adsorbed on filter paper also depends upon the amount of salt absorbed onto the filter paper. For example, 2 pL of solution containing 100 ng of 4-phenylphenol and varying amounts of NaBr were absorbed onto filter paper and the RTP was measured. The data are shown in Table VI. Ethanokwater (8020) was used as a solvent to prepare NaBr stock solution from which dilutions were made with 100% ethanol. As indicated in Table VI, the maximum RTP was obtained with 250 pg of N d r . From 300 to 400 pg of NaBr, the RTP
i / Iv/ i
I
50
I
I
I
100
I
150
3 20 285 295 330 290 3 10 300 329 264
I
I
I
200
I
250
I
L
300
NANOGRAMS
Figure 2. Calibration curve for 4-phenylphenol adsorbed on 1% poly(acrylic acid) in NaBr: XEx = 285 nm, XEm = 478 nm. was relatively constant. This is important analytically because changes in the amount of NaBr within this range do not affect the RTP signal. Additional Analytical Data. Analytical data, obtained for several compounds adsorbed on filter paper and 1% PAA-NaBr, are listed in Table VII. These compounds were chosen to include those which gave strong, moderate, and weak RTP signals. A typical calibration curve for 4-phenylphenol adsorbed on 1% PAA-NaBr is shown in Figure 2. Com-
9
2-hydroxy-5,6,7,8-tetrahydrophenanthrene
40
t
Table VII. RTP Analytical Data for Compounds Adsorbed on 1%PAA-NaBr and Filter Paper filter papera hex hex, linear nm nm range,ng LODb -naphthoflavone 4-phenylphenol p , p '-biphenol
I
I
Figure 1. Variatlon in RTP intensity of 2-naphthol as a function of percentage of poly(acrylicacid) in NaBr: XEx = 290 nm, XEm = 510 nm, (V)300 ng, (0) 150 ng, (A)100 ng, (0)50 ng.
100 ng of 4-phenylphenol adsorbed; average of
01
I
1
15 20 2.5 30 3 5 %POLYACRYLIC ACID, N a B r
520 478 488 570 510 510 520 530 406
0-85 0-310
0-190 0-220 0-350 0-330 0-350 no RTP 0-135
0.8
1.1
0.6 1.6 1.7 1.1 0.9
1% PAA-NaBr
linear range, ng 0-95 0-170 0-145 0-250 0-270 0-140 0-75 0-240
LOD 1.8
7.9 9.4 10
22 2-naphthol 16 2,3-dihy&oxynaphthalene 3.9 9-phenanthrol 27 chrysin 2.7 0-180 0.7 p-hydroxybenzoic acid LOD = limit of detection a A 2 pL solution applied to 3hG in. filter paper circle; solution contains 175 p g NaBr/pL. (ng); amount of sample needed to give a SIN of 3.
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2, FEBRUARY 1982
Table VIII. Effect of Layer Thickness on RTP of 4-Phenylphenol Adsorbed on 5% PAA-NaCI layer layer thickre1 RTP thickre1 RTP ness, mm intensa ness, mm intensa 0.25 0.50 1.0 1.5
0.67 1.0
1.0 0.99
2.0 2.5 3.0 3.5
0.97 0.97 0.95 1.0
a 4-Phenylphenol adsorbed at 200 ng/lO mg of adsorbent.
pounds adsorbed on filter paper showed more intense RTP than the corresponding compound adsorbed on 1% PAANaBr. The stronger RTP from filter paper results in lower detection limits for filter paper compared to 1% PAA-NaBr, but similar linear ranges were observed for both substrates. As shown in Table VII, the linear ranges and limits of detection are in the nanogram region. It is likely that many of the compounds listed in Table I1 would also give similar analytical data, since even compounds with relatively weak RTP signals gave good limits of detection and useful linear ranges. Good analytical data were obtained for each compound, except chrysin, on both adsorbents used. Linear ranges and limits of detection are comparable for the two solid surfaces examined. 2-Naphthol initially showed nonreproducible results. However, 2-naphthol is volatile in ethanol vapor. The ethanol was evaporated a t lower temperature (55 "C) and this approach yielded reproducible results. 9-Phenanthrol is airsensitive and the RTP data were also scattered. The problem was alleviated by using a fresh solution immediately and by evaporating the solvent at a lower temperature (55 "C).
RTP Reproducibility with Filter Paper and Poly(acrylic acid)-NaBr Mixture. Six identical samples of 100 ng of 4-phenylphenol adsorbed on 1.0% PAA-NaBr powder were run in duplicate. The relative average deviation from the mean was 3.8% for the first run and 4.6% for the second. Ten identical samples of 100 ng of 4-phenylphenol and 350 pg of NaBr adsorbed on 0.48-cm filter paper circles were run in duplicate. The relative average deviation from the mean was 6.4% for the first set and 4.6% for the second. The greater deviation in RTP measurements with the filter paper adsorbent may be due to slight inconsistencies in the thickness or texture of the paper. The 1% PAA-NaBr powder is very homogeneous and, when applied to the sample holder with care, can give quite consistent RTP measurements. Effect of Layer Thickness for Poly(acry1icacid)-Salt Mixture. To determine the dependence of layer thickness on RTP signals, we measured the RTP from layers of varying thickness. 4-Phenylphenol was adsorbed onto the PAA-salt mixture at a constant weight-weight ratio as described in the Experimental Section, The powder was placed in depressions of a blackened brass plate with varying depths (Table VIII). The data in Table VI11 indicate that a layer thickness greater than 0.50 mm should be used for reproducible data. Relative Ease of Sample Handling for Poly(acry1ic acid)-Salt Powder and Filter Paper. A factor to consider in deciding which solid surface to use for RTP work is the ease with which the sample can be applied to the solid and then be examined for RTP. In this respect, filter paper has an advantage over powder adsorbents because the step of transferring the powder from a glass test tube to the depression in the sample-holding plate is not needed. A savings of approximately 2 min per sample in analysis time results with the use of filter paper as an RTP adsorbent. By use of the sample holding plate and spectrodensitometer described in the Experimental Section as many as 44 samples can be
227
examined for RTP in 30 min, when either filter paper or PAA-salt mixtures are used.
Change in RTP Intensity after Drying for Poly(acrylic acid)-NaBr Powder and Filter Paper. RTP intensity of compounds adsorbed on PAA-NaJ3r powder has been observed to increase 2040% 24 h after removal from the drying oven. After the initial increase in RTP intensity, visual inspection showed the RTP remained constant for several days. The RTP intensity of compounds adsorbed on filter paper decreases slowly with time after removal from the drying oven. No special precautions have been taken to exclude oxygen or moisture when making quantitative measurements of RTP for either adsorbent. PAA-NaBr mixtures take somewhat longer to prepare than filter paper samples for RTP measurement, but PAA-NaBr shows less sensitivity to normal laboratory conditions such as moisture. Room Temperature Phosphorescence from Solid Surfaces and Micellar Solutions. Micelle-stabilized RTP (IO) and solid surface RTP (1-9) can be used for organic trace analysis at the nanogram level. In addition, it has been shown that the selectivity of solid-surface RTP is very good (4,20) and this should be true for micelle-stabilized RTP. To induce micelle-stabilized RTP, a detergent concentration above the critical micelle concentration must be used, heavy atoms must be present, the solution must be deoxygenated for about 15-30 min, an organic solvent in which the phosphor is dissolved is evaporated before adding the detergent solution, and the phosphor must be excited at an appropriate wavelength (10, 23). To induce solid-surface RTP, a solution (may or may not contain a heavy atom) of the phosphor must be applied to the surface, the phosphor-solid surface must be dried for 10-30 min, and the phosphor must be excited at an appropriate wavelength (1-9). Some samples adsorbed on fiiter paper have shown moisture sensitivity, but even in these situations, once the sample is dried, strong, reproducible RTP signals can be obtained (3, 6). Sodium acetate and silica gel chromatoplates (with a salt of poly(acry1ic acid) as binder) appear to show less moisture sensitivity than filter paper (I,@. Solid surface RTP is more simple procedurally than micelle-stabilized RTP when a solution of the phosphor is applied directly to the surface. Also, less sample is required for solid surface analysis and the sample is recoverable. If the sample is applied to a powdered adsorbent, such as a polymer-salt mixture which is described in this work, then possibly the micelle and solid surface approaches are roughly equivalent procedurally. Readily available commercial equipment can be used to measure both micelle-stabilized and solid surface RTP. Our views on the procedural simplicity and ready use of commercial equipment in regards to micelle-stabilized RTP vs. solid-surface RTP are in contrast to recently published comments (IO, 23). LITERATURE CITED (1) Ford, C. D.; Hurtubise, R. J. Anal. Chem. 1980. 5 2 , 656. (2) Paynter, R. A.; Wellons, S. L.; Wlnefordner, J. D. Anal. Chem. 1974, 46, 736. (3) Parker, R. 1.;Freedlander, R. S.; Schuiman, E. M.; Dunlap, R. B. Anal. Chem. 1979, 57, 1921. (4) Vo-Dinh, T.; Hooyman, J. R. Anal. Chem. 1979, 5 1 , 1915. (5) Meyers, M. L.; Seybold, P. G. Anal. Chem. 1979, 5 7 , 1609. (6) Schulman, E. M.; Parker, R. 1.J . Phys. Chem. 1977, 81, 1932. (7) de Lima, C. G.; Nlcola, E. M. M. Anal. Chem. 1978, 5 0 , 1658. ( 8 ) von Wandruszka, R. M. A.; Hurtubise, R. J. Anal. Chem. 1977, 49, 2164. (9) Bower, E. L.; Winefordner, J. D. Anal. Chlm. Acta 1978, 702, 1. (10) Cline Love, L. J.; Skrilec, M.; Habarta, J. G. Anal. Chem. 1980, 52, 754. (11) Parker, R. T.; Freedlander, R. S.; Dunlap, R. B. Anal. Chlm. Acta IS80, 179, 189. (12) Parker, R. T.; Freedlander, R. S.; Dunlap, R. B. Anal. Chim. Acta 1980, 720, 1. (13) Hurtubise, R. J. "Solld Surface Lumlnescence Analysis: Theory, Instrumentation, Applicatlons"; Marcel Dekker: New York, 1981; Chapters 3, 5, and 7.
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Anal. Chem. 1982, 54, 228-231
(14) Chrlswell, C. D.; Chang, R. C.; Fritz, J. S. Anal. Chem. 1975. 47. 1325. (15) Court, W. A. J . Chromatogr. 1977, 130, 287. (16) Jayaraman, S.; Vasundhara, T. S.; Parihar, D. B. Mlkrochim. Acta 1978. II.365. (17) Coates, J. P. J. Insf. Pet. 1971, 57, 209. (18) Schabron, J. F.; Fenska, L. E. Anal. Chem. 1980, 52, 1411. (19) Schabron, J. F.; Hurtubise, R. J.; Sliver, H. F. Anal. Chem. 1979, 51, 1426. (20) von Wandruszka, R. M. A.; Hurtubise, R. J. Anal. Chem. 1978, 48, 1784.
-.
(21) Ford. C. D.: Hurtubise. R. J. Anal. Chem. 107Q. 51. - , 659 --(22j Niday, G. J:; Seybold, P. G. Anal. Chem. 1978, 50, 1577. (23) Cline Love, L. J.; Skrilec, M. Am. Lab. (FalrfleM, Conn.) 1981, 13 (No. a), 103.
RECEIVED for review June 22,1981. Accepted November 9, 1981. Financial support for this project was provided by the Department of Energy, Division of Basic Energy Sciences, Contract No. DE-AC02-80ER10624.
Spectrophotometric, Potentiometric, and Gravimetric Determination of Lanthanides with perbDihydroxynaphthindenone Saad S. M. Hassan*l and W. H. Mahmoud Department of Chemistry, Faculty of Science, Ain Shams University, Cairo, Egypt
Sensltlve and reasonably selectlve methods are descrlbed for the spectrophotometrlc, potentlometrlc, and gravlmetrlc determfnatlon of lanthanldes using perl-dlhydroxynaphthlndenone as a novel chromogenlc and preclpltatlng reagent. The reagent forms a stable 1:2 (metakreagent) type of complex wlth light lanthanides at pH 2-7 In 1:l ethanol-water mlxture. Low metal concentratlons ( < I O pg/mL) develop 580-590 nm, emax (4-6) X lo4 L mol-' colored specles (A, cm-')whlch obey Beer's law. Quantltatlve preclpltatlonof the complexes from metal solutlons of concentratlons >100 pg/mL permlts both gravlmetrlc quantltatlon by lgnltlng the preclpltatesto the metal oxides and potentlometrlc tltratlon of the excess reagent. Results wlth an average recovery of 98% (standard devlatlon 0.7%) are obtainable for 0.1 kg to 200 mg of all light lanthanldes. Many forelgn Ions naturally occurrlng or frequently assoclated wlth lanthanldes do not Interfere or can be tolerated.
The worldwide interest in lanthanides as fission products and their uses for production of some modified alloys, ceramics, optical crystals, and semiconductors have necessitated the development of suitable methods for their accurate determination. Among the various instrumental methods, spectrophotometry has shown to be a simple and reliable technique applicable for quantitation of a wide range of concentrations (1-17). However, many of these methods are not sensitive enough to permit accurate determination of trace levels of these metals, involve a time-consuming extraction step, develop unstable colors, and require a long time for full color development (6,8,10,13,16).On the other hand, metals frequently associated or naturally occurring as contaminants with lanthanides (e.g., alkaline earths, zinc, and aluminum) seriously interfere with most of these reagents (3, 6, 12, 14, 16,17).
In previous study, we have demonstrated that a-amino acids, ascorbic acid, and hydrazines quantitatively reduce Present address: Department of Chemistry, University of Delaware, Newark, Delaware 19711. 0003-2700/82/0354-0228$01.25/0
peri-naphthindane trione into peri-dihydroxynaphthindenone (18-20). The similarity between the structure of peri-dihydroxynaphthindenone and some of the lanthanide chromogens stimulated us to investigate the usefulness of this compound, which has never been used in analytical chemistry, for lanthanide quantitation. In the present paper, we wish to point out the potential usefulness of peri-dihydroxynaphthindenone as a novel multipurpose reagent for lanthanides. The keto-ene-diol chelating group of this reagent proved to be suitable for both separation and determination of light lanthanides by spectrophotometric, potentiometric, and gravimetric techniques. The reagent offers clear advantages in terms of sensitivity, selectivity, and wide applicability over many of the available chromogenic and precipitating reagents.
EXPERIMENTAL SECTION Reagents. All the reagents used were of analytical reagent grade unless otherwise stated. Twice distilled organic solvents and deionized water were used throughout. peri-Naphthindane trione hydrate was prepared from naphthalic anhydride according to the method of Errera (21). A 0.5 M aqueous solution of the trione was treated at 70 "C with an excess of 0.5 M ascorbic acid to precipitate peri-dihydroxynaphthindenone.The precipitate (red crystals, mp 258 "C) was recrystallized out from 1:l acetic acid-water mixture. The precise molecular weight obtained by mass spectrometry and elemental analysis conformed with the molecular formula C13H803.The infrared and nuclear magnetic resonance spectra conformed with the presence of a keto-ene-diol group substituted at the 1:8 position of the naphthalene nucleus. Working solutions of the reagent (5 X 10-1 and 5 X 10-3M) were prepared in 96% ethanol and standardized by potentiometric titration with standard iodine solution using a platinum-calomel electrode system. Lanthanide oxides of purity not less than 99.9% were obtained from Sigma Chemical Co. (St. Louis, MO). Stock 1mg/mL lanthanide(II1) perchlorate solutions of pH 3-5 were prepared and standardized by visual titration with EDTA (22). Cerium(II1) perchlorate was prepared from Ce(OH)3obtained by reaction of cerium(II1) nitrate with sodium hydroxide. Apparatus. The spectrophotometric measurements were carried out with a UNICAM SP 1800 spectrophotometer at 25 A 0.5 "C using 1.00-cm quartz cuvettes. The potentiometric measurements were made with a PYE UNICAM M-290 pH meter using an Orion combined platinum-calomel electrode (Model 96-78) and an Orion iodide ion selective electrode (Model 94-53) 0 1982 American Chemical Society
