outer mantle of the bomb was made of pure copper (99.9%), and for the determination of copper we used a stainless steel mantle. In determining sodium and potassium, all handling must be done with gloves. Marking or numbering was done with a green felt pen. In case of doubt, first test to see if the marking remains after the treatment.
We think that the above-mentioned method of dissolution can be adapted to other types of analysis, provided no reaction gases emerge from the samples to be dissolved. Received for review August 16, 1973. Accepted October 19, 1973.
Simple Temperature Programmer for a Mass Spectrometer Direct Insertion Probe Jouko J. Kankare
Department of Chemistry, University of Turku, 20500 Turku 50, Finland A standard procedure for recording mass spectra of relatively involatile solids is to insert them directly into the ion chamber of the mass spectrometer using a specially designed solids inlet probe. Temperature of the sample is raised either by using the ion chamber heater or a separate heater of the solids inlet probe. Heating rate is either manually controlled or “ballistic”--i.e., controlled only by the rate of heat transfer from the environment. Majer et al. (1, 2 ) have shown that certain isomers have sufficiently different evaporation rates so that their separation is possible in the mass spectrometer solids inlet. They used the ballistic heating method. In some cases, they mentioned that the temperature of the ion chamber was rather critical in order to achieve satisfactory separation. It can be anticipated that if a smooth temperature control were available, more reproducible results might be obtained. The Perkin-Elmer double-focusing midresolution mass spectrometer Model 270 has a simple manual temperature control for the solids inlet system. Temperature is adjusted by controlling the voltage over the heater spool by a simple transistor circuit and a potentiometer whose knob is on the front panel of the instrument. This knob must be turned very slowly in the beginning of the heating process in order to avoid a sudden rise in the pressure of the ion chamber. Every user of this instrument also knows the “ghost peaks” in the total ion current which arise when the potentiometer is not turned sufficiently smoothly. With this particular instrument, there is, however, a very simple method for overcoming these difficulties. The instrument is a combined GC-MS, and the gas chromatograph has a temperature programmed oven heater controller. The temperature ramp is produced by a potentiometer driven by a stepper motor. It is rather easy to connect an additional potentiometer mechanically to the shaft of the gear-box. This potentiometer delivers the reference voltage to the control circuit of the solid inlet heater. There are now, in principle, two methods for producing a smooth temperature rise in the solids inlet system. One is a complete control system similar to that used in the GC oven heater control. Another possibility is to use the original circuit. The first method involves a complicated circuitry, but the temperature rise obtained is strictly linear. Fortunately, this linearity is not required in most applications, and in this work the latter method was employed. In the original circuit, the control potentiometer was nonlinear, but in this work, a linear precision 10-turn potentiometer was used. The heater voltage delivered by the circuit is proportional to the deviation of the potentiometer slider from (1) J. R . Majer and M . J. A. Reade, Chern. Cornrnun., 1970, 58. (2) J. R. Majer and R. Perry, J. Chern. SOC. A , 1970, 822. 966
A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 7, J U N E 1974
di#r,n b y ”‘DQ“’rnl,
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Figure 1. Temperature programmer for the solids inlet heater. The added circuit is enclosed by dotted line
the starting point unless some kind of nonlinearizing method is employed. Because the heating power is proportional to the square of voltage, it is desirable to have a voltage which is proportional to the square root of the deviation of the slider. This can be approximated to some degree of accuracy by connecting two resistors between the slider and both ends of the potentiometer. The values of the resistors shown in Figure 1 have been calculated so that below one-fourth of the total length of the potentiometer, the electrical power delivered to the solid sample is very nearly a linear function of dial position. The total resistance of the resistor circuit is not constant and thus the voltage over the potentiometer must be held constant using a zener diode. As previously mentioned, the different evaporation rates of some isomers have been employed for their analytical separation in the direct insertion probe of a mass spectrometer. It is clear that the method is not restricted to the analysis of isomer mixtures, and, indeed, it seems that it is highly useful, e.g., in evaluating the purity of synthetic products. A real example of this application is shown in Figure 2. 1-Naphthonitrile was allowed to react with salicoyl hydrazide p-toluenesulfonate in order to synthesize 3-(l-naphthyl)-5-(o-hydroxyphenyl)-1,2,4-triazole. The product was crystallized several times from benzenepetroleum ether, but the rather wide melting range showed that it was impure. In order to analyze this persistent impurity, a 10% solution in chloroform was made from the product. Five microliters of this solution was injected into a solids inlet sample capillary, the solvent was evaporated, and the tube was transferred into the direct insertion probe. The temperature of the probe was raised a t the rate of 5 centigrades per minute (GC panel setting). Total ion current was continuously monitored on a strip chart recorder and mass spectra were recorded a t peak current values. The spectra showed that the first peak in Figure 2 corresponded to a component with a molecular
A
- I ,oc
100
rnin
min
io
5
15
,
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300 20
10
L
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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 that 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-
0
.oc min
100
,
200
300
20
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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 that 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
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VITON O-RING/
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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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