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Figure 2. Total ion current curve for a sample of 3-(l-naphthyl)5-(o-hydroxyphenyl)-1,2,4-triazolecontaining 3,5-bis(1 -naphthyl)-
B
1,2,4-triazole peak a t 287, which is the molecular weight of the compound to be synthesized. The second, smaller, and rather sharp peak is due to a component with a molecular peak a t 321. The only reasonable compound which might be formed in the reaction and which has the molecular weight 321 is 3,5-bis( l-naphthyl)-1,2,4-triazole. Another application of the temperature programmed direct insertion probe is controlled pyrolysis. No simple inexpensive apparatus has been available commercially. An analytical application which is under study in our laboratory is the controlled pyrolysis of some sparingly soluble amine salts. Figure 3 shows the total ion current curves recorded when a mixture of 12-tungstophosphates of pyridine and 2,4,6-trimethylpyridine (A) and a mixture of 12tungstophosphates of quinoline and isoquinoline (B) were pyrolyzed. Some degree of separation could be attained in both cases. The recorded mass spectra showed t h a t the compounds emerging first were pyridine and quinoline, respectively. Complete analytical separation of components in the mass spectrometer solid inlet probe is seldom possible. However, a t least in the case of binary mixtures, the mo-
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Figure 3. Controlled pyrolysis of mixtures of 12-tungstophosphates of pyridine and 2,4,6-trimethylpyridine ( A ) and quinoline
and isoquinoline (5).Arrows show the points where mass spectra were recorded
lecular peaks of individual components can often be easily identified, even in the case of incomplete resolution, by inspecting the mass spectra run a t different moments of the sample evaporation. Incompletely resolved mixtures of three or more components form a more difficult problem. If an on-line computer is available, the spectra run during the sample evaporation may be analyzed using computer programs based on principal component analysis (3). Received for review August 27, 1973. Accepted November 26, 1973. (3) N. Ohta, Anal. Chem., 45, 553 (1973)
Mass Spectrometer Inlet Device for Highly Air-Sensitive Liquids and Solids R. S. Tse and S. C. Wong Department of Chemistry. University of Hong Kong. Hong Kong
Dunn and Hooper ( I ) suggested a method of incorporating a syringe injection inlet into a mass spectrometer which had originally not been so equipped. We have constructed a similar inlet into our analytical mass spectrometer (a Perkin-Elmer-Hitachi RMS-4) and found it very useful. However, in most analytical mass spectrometers, neither the injection or other liquid inlet, nor the usual direct inlet probe for solids, is suitable for handling highly hygroscopic and otherwise air-sensitive liquid and solid samples, because the samples in a syringe, in the usual liquid sample bulb, or in the direct inlet probe, must come into contact with air before being admitted to the mass spectrometer. The following is a description of an inlet device for such compounds t h a t has been successfully and widely used in our laboratory. This device allows the samples to be admitted to the mass spectrometer without contact with air.
TO ORIGIWL M S LI0U.D INLET
I. I
a31GIN4L EWIPMNT GL4SS S A W 2 WLB AND TEFLON GASKET
ACE GLASS ADAPIW
NYLON
U\
VITON O-RING/
n’GLAss
RM
U -5504-
Figure 1. Mass spectrometer inlet device for air-sensitive liquids ( 1 ) W G Dunn and J
B
Hooper. Anal Chem., 45, 216 (1973)
and solids A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 7, JUNE 1974
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CONSTRUCTION AND OPERATION An original equipment liquid sample bulb was glassblown, in a n L-shaped manner, to a n Ace Glass adaptor (Ace Glass Inc., Vineland, N.J., 07940, Cat. No. 5027). One end of a glass rod, which would fit snugly through the adaptor, was shaped into a small ring. The other end was made into a T-handle. The ring end of the piece was then passed through t h e adaptor, so t h a t the ring was roughly concentric with the original sample bulb. This device, shown in Figure 1, is small enough to fit into the liquid inlet oven. In operation, a n air-sensitive sample is sealed into a thin capillary tube (of the size of a melting point tube) in a vacuum system or a dry box in which the particular sample is normally prepared a n d handled. The sealed tube is then placed in the device a n d through the ring a t the end of the glass rod. The whole device is then fitted into the mass spectrometer liquid inlet system. After evacuating the air in the device, t h e sealed sample tube is
broken by turning the T-handle, a n d the sample is allowed to vaporize. The mass spectrum is then taken in the usual manner.
DISCUSSION The Ace Glass adaptor is superior to other adaptors for this device because of its glass-Viton-Nylon material of construction, because of its light weight, and because of its small size. The sample comes into contact only with glass, Teflon (both in the original equipment), and Viton. The limitations of this device are the temperature of the oven enclosing the original liquid inlet system and the heat resistance of Teflon, Viton, and Nylon. In our case, t h e temperature limit is about 200 "C, well above the requirements of most samples. A similar device can probably be made for most analytical mass spectrometers. Received for review November 30, 1973. Accepted March 4, 1974.
Reference Electrodes for Nonaqueous and Corrosive Media Nils S. Moe Department of General and Organic Chemistry, University of Copenhagen, The H. C. Orsted Institute. OK-2700 Copenhagen, Denmark
The usefulness of ordinary commercial aqueous reference electrodes in nonaqueous and corrosive media has its limitations. The aqueous calomel electrode clogs in nonaqueous solvents, because of precipitation of potassium chloride, and in a solvent such as trifluoroacetic acid, the porous plug of some reference electrodes has been found to dissolve completely within a few seconds. This report describes how to prepare reference electrodes t h a t have proved to be resistant, reliable, and cheap. The electrode is constructed in the following way: The end of a piece of borosilicate glass tubing is heated in a hot flame until the bore is constricted to about 1 m m . A soft glass rod is drawn in a relatively cool flame to a diameter of less than 1 mm. The end of the thin glass rod is heated in the cool flame until a bead of about 2-mm diameter forms. The glass rod is inserted in the tube, so that the bead stops a t the constriction, with the rod extending from t h e tube: (Figure 1A). The glass rod is drawn off in the flame, so that 1-2 cm extends through the constriction. The extending end of the glass rod is heated in a cool flame, until the bead which now forms touches the constriction, and then some: (Figure 1, B and C. ) After cooling, the electrode body, constructed as above, is filled with the desired solvent, and a nitrogen pressure of about 2 a t m is applied. The solvent leaks through the cracks formed between the borosilicate glass and the soft glass during the cooling. If the applied pressure causes just the tip of the electrode body to be moistened by the solvent, the electrode body is retained. Note: Electrode bodies found too leaky with a nonhydrogen-bonding solvent may be well suited for hydrogen-bonding solvents! A solution of silver nitrate in the desired solvent is poured into the electrode body, and a silver wire is inserted. If a sealed system is desired, the silver wire may be 968
ANALYTICAL CHEMISTRY, VOL. 46, NO. 7, JUNE 1974
A
0
C
Figure 1 ( A ) . Borosilicate glass tubing with constricted end, showing soft glass bead inside the tubing, and the protuding soft glass rod drawn off at proper distance. ( B ) Bead formed by heating the drawn-off end of the soft glass rod. (C) Electrode body finished
fused t o a platinum wire, and this may be put through a fused glass seal. With modern electronics, wide variations in electrode resistance are acceptable. It should be noted, however, t h a t reference electrodes with high resistances are a p t to pick u p noise, whereas electrodes of very low resistances may cause oscillations when placed in the feedback circuit of some potentiostats. A resistance of about 100 kQ has been found to be very satisfactory. The reference electrode described here has also been tried as a second order electrode. It was found that the narrow cracks were filled by precipitated silver chloride, thereby greatly changing the electrode resistance. When stored with t h e electrode tip immersed in a solution identical t o the filling solution, this reference electrode has been found very stable, without measurable changes in potential after several months of use. Received for review October 29, 1973. Accepted January 14, 1974.
