Table I.
Cation Fe f a
c u +a Mn+P Mn+: co z
4
Analysis of a Sample of Nickel Oxide (NBS, SRM No. 671)
Amount present, %
Av. amount found, %
Rel.
[email protected] dev.,\%
0.39 0.20 0.13 0.13 0.31
0.37 0.19 0.134 0.138 0.316
7.1 6.8 39.5 3.8
No. det. 8 8 6 8 8
4.1
Rel. error, % -5.7 -5.0 $3.0 +5.8 -1.9
Method of analysis Ppt'd with phosphate labeled with Pa* Ppt'd with phosphate labeled with Paz Ppt'd with phosphate labeled with Pa2 Adsorption of Cow on man aneae dioxide Exchange of Fe69 with Co*($Fe(CN),,]
For a single determination.
The cobalt was precipitated on the paper by reacting it with a saturated solution of potassium ferrocyanide. The papers were then washed with water, with 0.1N hydrochloric acid, and then with water again. The papers were equilibrated with Fe59 solution to allow exchange with the ferrocyanide, washed with water, dried, and counted with a NaI(T1) scintillation well counter. Standard curves were prepared for each element by plotting counts per minute us. micrograms. The experimental points were fitted to a straight line by least squares analysis. Blanks were subtracted fpom all data for each element. Washing of the papers wm a very important factor in minimizing the blank. The method of vvashing was standardized to give the highest precision. The paper was washed by gentle shaking with 5 ml. of water for 10 minutes. After the first wwh the paper was removed from the beaker with forceps coated with Teflon allowing the water to drain off the paper, then the paper was placed in a second beaker containing 5 ml. of water. The procedure was repeated for a third time.
RESULTS AND DISCUSSION
Table I lists the results obtained along with data on the precision and accuracy of the method. The amounts analyzed were 3.9 pg. of iron, 2.0 pg. of copper, 3.1 pg. of cobalt, and 1.3 pg. of manganese. The limit of detection is 0.1 pg. for iron, 0.02 pg. for cobalt, and 0.01 pg. for manganese. The data show quite satisfactory precision except the labeled manganese phosphate precipitate. Efforts are under way to improve this precision. NBS Standard Reference Material No. 671 was certified by the use of gravimetric and spectrochemical techniques. No precision or accuracy is given on the certificate, but assuming that the recommended value is close to the true amount present, an estimate of the accuracy is given in Table I. The main advantage of the paper chromatographic method is that it permits the analysis of a number of elements in the same sample. The radiometric methods which are used to de-
termine the separated elements have a greater sensitivity than most other methods of quantitative analysis which have been applied to chromatographic separation on paper or thin layer plates. Additional studies are in progress to extend the use of these radiometric procedures on chromatographs to other elements. LITERATURE CITED
(1) Van Erkelens, P. C., Anal. Chim. Acta 25, 570-578 (1961) (2) Van Erkelens, P. C., Nature 172, 357-8 (1953'1. (3) Welford, G. A., Chiotes, E. L., Morse, R. E., ANAL.CHEM.36, 2350 (1964).
A. R. LANDGREBE T. E. GILLS J. R. DEVOE
Radiochemical Analysis Section Analytical Chemistry Division Institute for Materials Research National Bureau of Standards Gaithersburg, Md. 20760
Semiquantitative Estimation of Nitrogen in Ammonium Faujasite by Differential Thermal Analysis SIR: The use of differential thermal analysis as a tool in the analysis of minerals and inorganic compounds (8) and solid catalysts (5) is well known, and a review of significant developments in the thermal analysis field has recently been published by Murphy (6). Thermal analysis techniques have also been employed in the characterization of synthetic zeolites (8,Q). In the course of studies on the properties of zeolites, we have observed an association between the presence of exotherms near 4O0-55O0C. in the DTA pattern (run in oxygen atmosphere) of ammonium Y faujasite and the loss of zeolitic ammonium groups. Further examination revealed that the intensity of this DT.4 exotherm was proportional to the amount of zeolitic nitrogen (in the range of 0.2-5'%). Thus, a semiquantitative method of estimating zeolitic ammonia is afforded. 1266
ANALYTICAL CHEMISTRY
(5 ml./min. a t one atmosphere) of dry O2 established. The reactor was An R. L. Stone Difthen heated to the appropriate temferential Thermal Analyzer, Model perature and the catalyst calcined DS-19 was used for DTA analyses for 3 hours. The reactor was then (10' C./min., 0 . 2 mv. full scale, sealed off and transferred to a dry 150 mesh Vycor reference). A Conbox, where zeolite samples were placed solidated Electrodynamics Corp. in dry vials for Kjeldahl nitrogen deModel 21-103 mass spectrometer optermination and DTA analysis; cataerated a t 70 e.v. was used for gas lyst samples for infrared analysis were analyses. ,A Perkin-Elmer 421 specprepared in the dry box by mulling with trophotometer was used for infrared Fluorolube S (Hooker Electrochemical analyses. Co.). This procedure was repeated Reagents. The crystalline ammofor NH4Y samples calcined at temperanium Y faujasite (NH4Y) was pretures of 200-500' C. pared from a synthetic sodium Y Similarly, effluent gas studies were aluminosilicate by repeated ion exeffected by calcining zeolite samples change with warm 10% aqueous (7.44 grams, 17.0 ml.) in dry O2 or NH,C1 solution. Its unit cell composition was (NH4)as.9.(Na)6.1.(A102)51,He (1.2 ml./min.) for 3 hours at 550" C., and collecting the total effluent (SiOz)141. (HzO)Z. gas over 10% aqueous HzSOain a conProcedure. Zeolite (4 grams, 5 ml. ventional gas collection apparatus. mesh) was placed Tn an elecAfter vigorous shaking to complete trically-heated, tubular Vycor-glass the adsorption of XHa, the volume of reactor fitted with axial glass thermogas was recorded, and samples were couple well, and a continuous flow EXPERIMENTAL
Apparatus.
0
T
,
I
PO0
I
1
400
1
1
600
TEMP,,
1
1
800
l
1000
OC.
f
Figure 1. Comparison of DTA profiles in 0 2 and N2 atmosphere for uncalcined NH4Y zeolite
sp
I
1400'
removed for mass spectrometric analyses. Precautions were taken to prevent air contamination at all stages.
20 40 60 80 100 REL. HT. OF D. 1. A. EXOTHERM NEAR 400°C.. mm.
Figure 2. Correlation between wt. % nitrogen and height of DTA peak near 400" C. in NHlY zeolites calcined in 0 2 at different temperatures
RESULTS AND DISCUSSION
D T A Analysis of Uncalcined NH4Y.
Figure 1 shows a comparison of DTA profiles recorded in oxygen and nitrogen atmospheres for previously uncalcined NH4Y. Both curves show broad endotherms near 200-300' c. corresponding to desorption of physically adsorbed water, sharp exotherms near 980" C., presumably associated with lattice reorganization and weak endotherms near 750" C. Most prominent, however, in the thermogram recorded in oxygen are two intense exotherms near 400' and 550" C. Similar exotherms, but of much weaker intensity, are present in the thermogram of the sample run in nitrogen atmosphere. Correlations of D T A Exotherms with Loss of Zeolitic Nitrogen. As shown in Figure 2, when weight per cent zeolitic nitrogen (Kjeldahl) is plotted against the height of the exotherm near 400' C., for a series of NH4Y samples calcined a t various temperatures in oxygen, a nearly linear, empirical relationship is observed. The heights of the exotherms (DTA analyses run in oxygen atmosphere) are referred to the average base lines in the region 700-900" C. Thus, these exotherms are absent in zeolite samples where calcination (500" C.) has removed all nitrogen. They are present however, in samples calcined a t 450' C. containing 0.15y0 nitrogen (2.82% of calculated maximum based on sodium-free AIOz-units), the infrared spectra of which do not show a detectable H-N-H deformation band (7) near 1410-1425 cm.-' That is, the DTA method appears to be slightly more sensitive than infrared in detecting small amounts of zeolitic ammonium groups. While the appearance of two exotherms associated with the loss of zeolitic ammonium groups may correspond to sites of different energy, it is possible that other lattice-associated processes could contribute to the overall thermochemistry of these transformations.
.4nalogously, an exotherm near 608°C. in the DTA profile of the ammonium feldspar buddingtonite (4) has been associated with ammonia loss; we have also observed an exotherm near 580" C. in the differential thermogram of uncalcined ammonium mordenite. Role of Intracrystalline Oxidation in D T A Interpretation. Table I shows an analysis of the effluent gas collected during the calcination in oxygen of NH4Y in a continuous-flow reactor a t 550" C. From the large amounts of nitrogen gas present, it is apparent that oxidative decomposition of 44% of the zeolitic ammonium groups has occurred. Such an intracrystalline oxidation is not without precedent, since Barrer has reported a reaction conforming to the stoichiometry 4 Zeolite-ONh4 302 + 4 Zeolite-OH 2N2 6H20 for the thermal decomposition in oxygen of the ammonium forms of mordenite and chabazite (1). Thus, while recognizing the limitations inherent in comparisons of data obtained in the DTA instrument with that
+
+
+
Table 1. Analysis of Effluent Gas Collected during Calcination of NHdY Zeolite in Oxygen at 550" C.
Carrier
Control (He)
0.01199 38.6
0,01175 Trace
44.2
-
02-
Total moles of gas collected Mole-% Nze yo Theoretical zeolite nitrogen as Nzb yoNitrpgen remaining in zeolite after calcination e
0.01
0.83
No oxides of nitrogen present. Based on Na-Free AlO2-units.
from a gross reactor system, we feel that the existence of an intracrystalline oxidation in the DTA sample run in oxygen atmosphere can reasonably explain the differences observed in the DT.4 profiles in Figure 1. Similarly, Ellis has reported an exotherm from oxidation of ammonia released during the DTA analysis of ammonia-treated bentonite (3). ACKNOWLEDGMENT
We thank J. B. Milliken for running the differential thermal analyses and J. L. Montgomery and staff for performing the mass spectrometric analyses. LITERATURE CITED
(1) Barrer, R. M., Nature 164, 112
(1949).
(4) Erd, R. C., White, D. E., Fahey, J. J., Lee, D. E., Am. Mineral. 49, 831 (1964). (5) Keeley, W. M., "Application of DTA to the Evaluation and Testing of Catalysts," Proc. 1st Toronto Symposium o n Thermal Analysis, 131-40 (1965). (6) Murphy, C. B., ANAL. CHEW.38, 443R (1966). (7) Rabo, J. A., Pickert, P. E., Stamires, D. N., Boyle, J. E., in "Proceedings of the Second International Congress on Catalysis," Vol. 11, p. 2055, Editions Technip, Paris, 1961. (8) Smothers, W. J., Chang, Y . , "Differential Thermal Analysis: Theory and Practice," Chemical Publishing Co., NPWYnrh 1958 -----, ----. (9) Toth, K., Flora, T., Acta Chim. Acad. Scz. Hung. 45, 87 (1965). P. B. VENUTO E. L. Wu J. CATTANACH Applied Research and Development Division Mobile Oil Corp. Paulsboro, N. J. VOL. 30, NO. 9, AUGUST 1966
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