Anal. Chem. 1988, 58. 547-551
in terms of the concentration and the elimination of interference. Moreover, an improvement of absolute detection limit of 1 order of magnitude, compared with previously reported work (In,was achieved by use of the amalgamation apparatus. The reasons for this improvement are likely to be as follows. (A) Separation of the large amount of water mist from the Hg vapor by the amalagamator might enhance the Hg emission in the plasma. (B) Separation of dissolved concomitants and gases might reduce the spectral interference at the Hg emission line, where nitrogen-containing compounds, especially, give a NO band emission (17). (C) Sharpening of the peak might give a higher concentration of Hg in the plasma excitation source. (D)The removal of contaminating Hg in the reducing reagent might reduce the blank. Contamination from marketing reagents corresponded to about 100 pg without purification. The detection limit obtained in this study (0.5 pg) was of the same order as that of methylmercury(I1) chloride by the gas chromatography-MIP system (24, 28). MIP emission spectrometry may have the detection capability of this order with gas-phase Hg introduction. Hg analysis a t levels below nanogram-per-liter was established with a suitable sample volume for natural water analysis, in this study. Research is continuing into the application of the technique reported here to the analysis of various kinds of environmental water samples.
ACKNOWLEDGMENT The authors thank K. Okamoto and T. Uehiro of the NIES, Japan, for their offering of CRM and valuable discussion. We also thank J. Edmonds of Marine Research Laboratories of Western Australia for his valuable comments. Registry No. Hg, 7439-97-6; water, 7732-18-5. LITERATURE CITED (1) Matsunaga, K.; Nlshimura, M.; Konishi, S. Nature (London) 1975, 258, 224-225.
547
(2) Mukherjl, P.; Kester, D. R. Science 1979, 204, 64-66. (3) Olafsson, J. "Trace Metals In Sea Water"; Wong, C. S.,Boyle, E., Bruland, K. W., Burton, J. D., Goldberg, E. D., Eds.; Plenum Press: New York, 1983;pp 475-485. (4) Matsunaga, K. Jpn. J . Limnol. 1976, 37, 131-134. (5) Fltzgerald, W. F.; Lyons, W. B.; Hunt C. D. Anal. Chem. 1974, 46,
iaa2-ia85. ( 6 ) Nishimura, M.; Matsunaga, K.; Konishi, S . Bunseki Kagaku 1975, 24,
655-658. (7) Yoshida, Y.; Murozuml, M. Bunseki Kagaku 1977, 26, 789-794. (8) Chou, H. N.; Naleway, C. A. Anal. Chem. 1984, 56, 1737-1738. (9) Bloom, N.; Crecelius, E. A. Mar. Chem. 1983, 74, 49-59. (10) Hawley, J. E.; Ingle, J. D., Jr. Anal. Chem. 1975, 47,719-723. (11) Tanabe, K.; Takahashi, J.; Haraguchi, H.; Fuwa, K. Anal. Chem. 1980, 52,453-457.
(12) Haraguchi, H.; Takahashi, J.; Tanabe, K.; Fuwa, K. Specfrochirn. Acta, P a r t s 1981, 368,719-726. (13) Braman, R. S.; Johnson, D. L. Environ. Sci. Techno/. 1974, 8, 996-1003. (14) Bricker, J. L. Anal. Chem. 1980, 52, 492-496. (15) Talmi, Y. Anal. Chim. Acta 1975, 74, 107-117. (16) Watling, R. J. Anal. Chim. Acta 1975, 75, 281-268. (17) Tanabe, K.; Chiba, K.; Haraguchl, H.; Fuwa, K. Anal. Chem. 1981, 53, 1450-1453. (18) Chiba, K.; Yoshida, K.; Tanabe, K.; Haraguchi, H.; Fuwa, K. Anal. Chem. 1983, 55, 450-453. (19) Wrembel, H. 2 . Specfrochlm. Acta, Part 8 1982, 378,937-946. (20) Estes, S. A.; Uden, P. C.; Barnes, R. M. Anal. Chem. 1981, 53,
1829-1837. (21) Okamoto, K.; Morita, M.; Quan, H.; Uehiro, T.; Fuwa, K. Clin. Chem. (Winston-Salem, N.C.) 1965, 37, 1592-1597. (22) Okamoto, K.; Fuwa, K. Anal. Chem. 1984, 56, 1758-1760. (23) Imaeda, K.; Ohsawa, K. Bunseki Kagaku 1974, 28, 239-244. (24) Boumans, P. W. J. M.; de Boer, F. J.; Witmer, A. W.; Bosveld, M. Specfrochim. Acta, Part B 1978, 338, 535-544. (25) Furuta, N.; Otsuki, A. Anal. Chem. 1983, 55, 2407-2413. (26) Nojiri, Y.; Kawai, T.; Otsuki, A.; Fuwa, K. Wafer Res. 1985, 79, 503-509. (27) Minagawa, K.; Takizawa, Y.; Kifune, I. Anal. Chim. Acta 1980, 775, 103-1 10. (28) Olafsson, J. Limnol. Oceanogr. 1980, 25, 779-788. (29) Yamamoto, J.; Kaneda, Y.; Hikasa, Y. Int. J. Environ. Anal. Chem. 1983, 76,1-16.
RECEIVED for review August 8, 1985. Accepted October 7, 1985.
X-ray Diffraction Spectrometry for Analysis of Lamellar Ion Exchangers of the a- and y-Zirconium Phosphate Type Ricardo Llavona, Marta Sulrez, Jose R. Garcia, and Julio Rodriguez* Departamento de Quimica Inorgcinica, Facultad de Qutmica, Uniuersidad de Ouiedo, CICaluo Sotelo sln, Ouiedo, Spain
X-ray dlffraction in the quantltative analysis of crystalllne solld phases was used. The evolution of y-tltanium phosphate in the H+/M+ (M = Na, K) ion exchange and the best condltions for the quantitative determination to be carried out are reported. The areas of each phase with dlfferent ionic composltlon were obtained. The use, in materials of the a-and y-zirconium phosphate type, of a linear relationship between intensity and concentration for mixtures of phases with different counterlon contents is proposed.
The ion-exchange properties of lamellar inorganic materials have been widely studied (1, 2). a-Zirconium bis(monohydrogen orthophosphate) monohydrate (a-ZrP) and its isomorphic titanium compound (3,4) belong to this group. Both have an interlayer distance of 7.6 8,, which restricts their
capacity for exchanging ions with a large diameter. In both compounds, the dihydrated form shows a different structure (5-8) known as the y variety (5) with a basal spacing quite higher than that of the cy form (12.2 8, for y-ZrP and 11.6 8, for T-TiP), which allows large ions to diffuse through it. Thus, in acidic media, cy-TiP retains Li+ and Na+ while K+ is only retained at pH >7 and with a high degree of hydrolysis (9-14). However, y T i P possesses a larger affinity for K+ than for Na+ ions reaching in acidic media 50 and 25%, respectively, of its exchange capacity ( 7 , 1 5 ) . Control of the degree of saturation of ion-exchange materials must be reproducible and should be done quickly and accurately and with small amounts of sample. In an earlier paper (16)a nonconventional method of calibration for mixtures of materials with the same chemical composition and isomorphic structure was described. The solution was possible by assuming a linear relationship between the intensity of a re-
0003-2700/86/0358-0547$01.50/0 @ 1986 American Chemical Society
548
ANALYTICAL CHEMISTRY, VOL. 58, NO. 3, MARCH 1986
(002)
rn
-a
0.3 0.2 0.1
"'1
T = 40.0
OC
0.8
0.710.6
0.5
5 0 % Na'
0.4 0.3
I
10.5 10.0
0.2 0.1
95
I
I
I
9.0
8.5
8.0
1
l
I
1
1
j
I
10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 Angle, 2 0
Figure 2. X-ray patterns of samples with 0.0 < XM< 0.5 conversion treated at 200 'C: (a) M = Na, (b) M = K.
deg/min, chart speed = 2 cm/min). Ion Exchange Studies. The exchanger was equilibratedwith (MCI + HC1) or (MCl+ MOH) solutions at 25.0,40.0, and 55.0 "C (*O.l), following the procedure described by Clearfield et al. (20). The equilibration time was 48 h. The solid was present in the solution in an approximate ratio of 250 mL:l g. 0.3 0.2 0.1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
XM Figure 1. Exchange isotherms H+/M+ in y-Tip: (a) M = Na, (b) M = K.
flection characteristic of a definite crystalline phase and its concentration in the mixture by considering the mass absorption coefficients of the mixture components to be the same. The application of this assumption to a different system should give more information about the general validity of the method. The present paper reports the quantitative determination of the concentration of solid phases on samples of y-TiP unsaturated in Na+ and K+ by measuring the intensity of the X-ray diffraction lines characteristic of the interlayer spacing. The experimental conditions under which this determination can be best carried out are also discussed. For the sake of brevity, the various ionic forms are simply indicated by their counterions (under a bar) and water content, while their interlayer distances are reported in parentheses.
RESULTS The conversion degree of y-TiP was obtained by chemical analysis (Figure 1). In acidic media, the substitution increased with the amount of metallic chloride added, conversions of 25% in the Hf/Naf system and 50% in the H+/K+ being reached. In alkaline media, saturation was reached and partial decomposition of the exchanger took place thereby forming soluble phosphates and amorphous titanium oxides, which remained into the solid fraction. In both systems, the process occurred with formation of intermediate phases with conversions of 25 and 50%. In samples of intermediate composition, only two crystalline phases coexisted. Some of the exchanged solids were stabilized at room temperature either in air or over P205. Other were heated at 80 or 200 "C. The water content and the interlayer distance of each crystalline phase with different ionic composition under the reported conditions are shown in Table I. The behavior of the 25% Na and K phases against dehydration is peculiar (15, 21) and can be summarized as follows: 2Hl.5M0.5*H20
2
m
5
-< 200
"
O C
HM
The splitting of the H1,5M0,5 phase is a slow process at 80 However, a t 200 'C this splitting is rapidly achieved. The choice of adequate treatment conditions in order to determine the relative intensities of the reflections corresponding to each crystalline phase present was made on the basis of the following points: (a) Every phase with a different ionic composition must have an unique hydration degree. (b) The selected reflection must differ a t least in 0.5' from the nearest one. (c) The solids must remain stable against hydration-dehydration during their manipulation. (d) When hydration processes are likely to occur, the more drastic drying conditions compatible with the existence of the phase must be chosen. In the conversion range of 0.0 < X M< 0.5 (M = Na, K) the measurements were performed after heat treatment of the OC.
EXPERIMENTAL SECTION Reagents. All chemicals used were of reagent grade. The NaOH and KOH solutions were standardized with HC1, which had previously been standardized against Na2C03. The y T i P was obtained by using 16.5 M H3P04and reflux times of 10 days, as previously described (17). Analytical Procedures. The analysis of the concentration of phosphorus and titanium in the solids was carried out gravimetrically (18). The released phosphate groups were measured spectrophotometrically (19), using a Perkin-Elmer Model 200 spectrophotometer. The Na and K ions in solution were determined by atomic absorption spectrometry, using a Perkin-Elmer model 371 spectrometer. The diffractometer used was a Philips Model PV 1050/23 (A = 1.5418 A, 28 scan rate 0.125-0.250
p20s
-
~
ANALYTICAL CHEMISTRY, VOL. 58, NO. 3, MARCH 1986
549
Table I. Water Content and Interlayer Distance of the Ht/M+ (M = Na, K) Substitution Phases Depending upon the Treatment Conditions
air
80
p2°5
200 "C
OC
nHzO
d, 8,
nHzO
d, 8,
nHzO
d, 8,
nHzO
d, 8,
HH
2
11.6
0
9.1
0
9.1 9.1
0
9.1 9.1
HLSNao.5
1
11.0
0
10.1
0
HNa
3 2
13.2 12.6
1
11.1
2
12.8
-
0
10.1
10.1
-
NaNa
1
11.5
1
11.0
0
10.1
0
10.1
0
10.1
1
11.5
1
11.5
0
10.6
0
10.8
0
10.8
10.8
H1.SKO.S HK
-
KK
HNa
9.1
9.1
-
(002)
0
0
10.8
(2-3)
14.2
-a (002)
10.8
1
13.0
0
12.2
0
10.8
0
10.8
0
12.2
0
12.2
-b
m
A
(002) NTa.Hz0
0
(002) iT/T.(2-3)H20
1
50PK'
68% N
