260
280
300
Tindim ted I O C I Figure 2. Melting thermogram of adamantane (25 mg) in a sealed cell at a scan speed o f 8 OC/min
I
1
LITERATURE CITED
-0
aJ c
E. M. Barrall and J. F. Johnson in "Techniques and Methods of Polymer Evaluation", Volume 2, Thermal Characterization Techniques, Marcel Dekker, New York, N.Y., 1970, Chapter 1, p 1. Perkin-Elmer, Norwalk, Conn., Instructions Volatile Sample, Sealer Accessory 219-0061, documentation No. 990-9338, December 1966. , , Perkln-Elmer, Norwalk, Conn , Instructions Large Volume Capsules (LVC) 319-0218, documentation No. 993-9115, July 1975. (4) F. E. Freeberg and T . G. Alleman, Anal. Chern., 38, 1806 (1966). (5) W. Knappe, G. Nachtrab, and G. Weber, Aflgew. Makromol. Chem., 18, 169 (1971). (6) H. Alberti and F. Frungel, Blech, 9, 678 (1961).
[3
.-u
-0
C .I-
with a sealed aluminum volatile sample pan (2) by measuring the melting peak temperature of 3.81 mg of tin as a function of the scan speed. The results, shown in Figure 3, indicate that the thermal lag of the welded cell is in between that of a sealed aluminum volatile sample pan and the Freeberg and Alleman design ( 4 ) . An interesting feature of our sealed cell is that it can be used in a greater temperature range since heat effects due to glass transition or fusion of the sealing material are absent. Furthermore, the broadening of the melting peaks was considerably less than in the case of the Teflon sealed cell. The welded cells could withstand higher pressures and were found to be particularly suitable for thermal studies in which the system is to be subjected to repeated heating and cooling cycles. The Teflon gasket turned out to leak under similar conditions. Preliminary measurements using nickel transistor caps instead of the cell of Figure 1also yielded favorable results. The resistance-welding technique is very simple, requires seconds, and can be applied to several metals and alloys so that the method of encapsulation described above can be employed in the study of the thermal behavior of many volatile systems.
520
RECEIVEDfor review October 7, 1976. Accepted November 1, 1976.
500 I 20
LO
Scan s p e e d (OC/,,,
I
Figure 3. Melting peak temperature of 3.81 mg tin in various cells as a function of the scan speed (0) Freeberg and Alleman design (brass; 1115.83 mg). ( 0 )Aluminum volatile sample pan sealed by cold-welding (28.88 mg). (0)Stainless steel cell sealed by resistance-welding (320.98 mg)
trodes. The welding pressure was lo00 kg/cm2 and the welding energy was 0.2 kJ. Calorimetric measurements were carried out using a Perkin-Elmer DSC model 1B.
RESULTS AND DISCUSSION At first it was established that resistance-welding of a cell filled with water did not cause any detectable change in mass. Furthermore, heating of this cell up to a temperature of 300 O C where the vapor pressure of water is 80 atm also did not lead to any weight loss. A melting thermogram of adamantane, that sublimes very readily, displays only a melting peak, and changes in the baseline due to sublimation or deformation of the sample pan could not be discerned (Figure 2). The thermal lag of the new sealed cell was compared with that of the cell designed by Freeberg and Alleman as well as
CORRECTIONS Theoretical and Experimental Characterization of Field-Flow Fractionation
In Figure 7 of this article by J. Calvin Giddings, Frank J. Yang, and Marcus N. Myers, Anal. Chem., 48, 1126 (1976), the exponents should be -8, -7, and -6 on each axis, replacing -9, -8, and -7, respectively. Calculator Program Yielding Confidence Limits for Least Squares Straight Line Regression Analysis
In Table I of this article by W. J. Blaedel and D. G. Iverson, Anal. Chem., 48,2027 (1976),the term in brackets in the expression of the confidence limit for parameter A should be raised to the power 1/2. In the legend to Table I, the definition of C should be B 2 - t2(sy2/Sx,),and (X2/df)o.osshould be a power series in ( N - 2) instead of in 1/(N - 2). The data point (700,4374) in the example (Table 11) should read (700,4347).
ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977
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