and median relative error of 3.6% indicate that relative line intensities are being determined with accuracies very close to limitations imposed by emulsion variations and calibration techniques (1,7). The time required for data recording is of considerable interest. Table VI provides a brief comparison of the time required for the manual and the automated systems to read a typical photographic plate containing 300 lines. The first item listed, align photoplate and zero microphotometer, requires a few more minutes for the automated system in order to set the ancillary equipment. Line location is given the same time requirement although, with the automated system, the operator can consider subsequent line locations immediately after initiating a scan for a given line without having to read and record data in between lines. Scan time requirements are reduced considerably with the automated system. Of course, the biggest advantage is in the elimination of reading and recording time. The insertion of ancillary spectral information for the computer is different for the two systems. The automated system requires a code letter preceding mass-position reference data. The amount of information required with manual data recording will normally be much greater than the 100-s value given in the table because each line may have to be identified. The final item, resetting the linear motion encoder, requires approximately 3 min with the new system. Although the listed total time requirement will vary from plate to plate, the time advantage for the automated system of a factor of 3 to 4 is realized in practice.
CONCLUSIONS The system described here has been found to have distinct advantages over previously used manual techniques for recording microphotometer data. Precision of recording line transmittance minima is at least as good as carefully read strip chart recordings and will not include mental errors incurred in reading and logging large quantities of data. Background readings reflect averaged transmittance adjacent to spectral lines. Time requirements are decreased by a factor of 3 to 4. The recorded data contain mass information shown to be accurate to approximately five times the mass spectral resolution. These data are especially compatible with large computer techniques for interpretation of mass spectra. The cost of the system described here is moderate. Materials cost for the Ratio Circuit, Peak Detector, Peak DVM, Background DVM, Control Logic, and Control Panel circuits (see Figure 1)was
Table VI. Comparison of Time Requirements to Read 300 lines Manual Rate, s/line
Operation
Align photoplate and zero microphotometer Line location Scan Read and record data Special spectral information Reset position encoder
...
Total s
240
3 900 1 0 3000 1 0 3000
. . . 100 ... ...
Automated Rate, s/line
...
Total s
2.5
360 900 7 50
...
100 180
3
... ...
Total 7440 s 126 min
2290 s - 3 8 min
$1000 with $1000 additional labor costs. All other equipment was commercially available or on hand. Finally, the total operator time required to read a photoplate is comparable to some systems where an integrated computer is used to control the microphotometer and to record data automatically. This is due to the fact that the time required for eliminating false lines, locating mass-position reference points, and providing the additionally required operator contribution to limited small computer interpretive schemes will approach the total time required for the system described here. Details about the system are available from the authors.
ACKNOWLEDGMENT The authors gratefully acknowledge the help of Clarence Ness who operated the mass spectrograph. LITERATURE CITED R. A. Burdo, J. R. Roth, and G. H . Morrison, Anal. Chem., 46, 701 (1974). E. J. Millett, J. A. Morice, and J. B.Ciegg, lnt. J. Mass Spectrom. /on Phys., 13, l(1973). J. R. Woolston, Twenty-First Annual Conference on Mass Spectrometry and Allied Topics, San Francisco, Calif., 1973, p 514, Paper V 7. M. A. Frisch and W . Reuter, Anal. Chem., 45, 1889 (1973). C. A. Bailey et al., UCRL-70898 (1968). J. Franzen and K . D. Schuy, Fresenius'Z. Anal. Chem., 225, 295 (1967). K . D. Schuy and J . Franzen, Fresenius' 2.Anal. Chem., 225, 260 (1967).
RECEIVEDfor review January 23, 1976. Accepted May 13, 1976.
Tube Cracker for Opening Glass-Sealed Ampoules under Vacuum David J. DesMarais' and J. M. Hayes* Department of Chemistry, Indiana University, Bloomington, Ind. 4740 1
This report describes a device which can open glass-sealed vessels in a vacuum system or other confined atmosphere. The design permits the use of standard glass tubing for the sample vessel, thus permitting the vessel to be sturdy, inexpensive, and versatile. The present application involves the transfer of gas samples to a vacuum system in 10-cm segments of 6-mm Pyrex tubing which has been sealed at both ends. Figure 1is a schematic diagram depicting the construction of the sample tube cracker. The sealed end of a 6-mm quartz is shown inserted into the cracker or Pyrex sample tube (H) 1 Present address, Chemical Evolution Branch, Ames Research Center N239-9, National Aeronautics and Space Administration, Moffett Field, Calif. 94035.
and fastened by the Yd-in. Viton O-ring vacuum fitting of a Cajon Ultra Torr reducing union (G) (Cajon Company, 32550 Old South Miles Road, Cleveland, Ohio 44139). The commercially available fitting has been drilled out to permit a %-in. 0.d. tube to pass completely through the union. The 3/s-in. fitting of the Ultra Torr reducing union seals onto one end of a 2.5-in. long by %-in. diameter Cajon flexible stainless steel tube (C). The flexible tubing contains upper (D) and lower (F) cone-shaped stainless steel supports which cause the notched (E) sample tube to crack when the enclosed stainless steel tubing is flexed. The upper end of the flexible tubing is connected to the vacuum system (A) using a %-in. Cajon Ultra Torr union (B).
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Flgure 1. Schematic diagram of the sample tube cracker (A) %-in. 0.d. tube leading to vacuum system. (B)%-in. Cajon Ultra Torr union, No. SS-6-UT-A-6. (C) %-in. 0.d. Cajon flexible tubing, No. 321-6-X-1. (D)Upper stainless steel cone. (E) Notch in glass tube. (F) Lower stainless steel cone. (G) 3/8-in. to Y4-in. Cajon Ultra Torr reducing union, No. SS-6-UT-A-6-4. (H) 6-mm or ’i4-h. 0.d. Pyrex or quartz sample tube
The procedure for using the sample tube cracker is relatively simple and straightforward. During the operation, the upper Cajon union (B),upper cone (D), and the flexible tubing ( C ) remain attached to the vacuum system (A). The lower union (G) and lower cone (F) are removed to facilitate proper insertion of the 6-mm sample tube. A 6-mm sample tube to be opened is notched about 1-cm from its sealed end using a file. Having first checked that the cone (F) is firmly seated in the reducing union (G), the operator pushes the 6-mm tube into the yd-in. fitting of the anion until the sealed end emerges from the top, tapered end of the cone (F) and the filed notch is aligned with the top edge of the cone. It is helpful also to align the notch rotationally with a mark scribed on an exterior surface of the reducing union. In this way, when the cracker is assembled and evacuated, the operator still knows which “side” of the tube has been scored. The lh-in. vacuum fitting of the reducing union is then tightened onto the aligned sample tube and the 3/s-in.fitting is slipped onto the flexible tubing (C) and tightened such that the sample tube notch is facing away from the operator. The operator then evacuates the cracker and prepares the vacuum system to accept the
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sample. The sample tube is cracked open by flexing the lower end of the flexible tubing towards the operator. After the transfer of the sample is completed, the reducing union and lower cone are removed to accept the next sample tube. The 3h-in. O-ring fitting is loosened only partly such that, when removed from the flexible tubing, the O-ring “catches” on the bottom exterior rim of the lower cone and withdraws it from the flexible tubing. The expended sample tube and its cracked-off top are discarded and a new tube is notched and inserted as described above. As a routine precaution, the two O-rings of the reducing union should be cleaned periodically to remove small glass chips which can accumulate. Such cleaning prolongs the lifetimes of the O-rings and ensures that the vacuum fittings will always seal properly. All parts of the device are commercially available except the cones (D and F), which must be machined locally from stainless steel or some other suitable material. In general, details of the construction of these cones are unimportant, and can be judged adequately from Figure 1.Note, however, that cone F must be able to slide out of the flexible tubing without binding, and that the bottom exterior rim of this cone should have an outside diameter exceeding that of the flexible tubing by a great enough amount that the O-ring will “catch” the cone and extract it from the flexible tubing during disassembly. The sample tube cracker system offers numerous advantages over conventional glass breakseals, principally because it permits the use of 6-mm or y,-in. sample tubes. A 10- or 15-cm section of 6-mm tubing is much more compact, durable, and leak-free than a breakseal tube, which contains a fragile glass partition which must be broken using a magnetic slug. Because the breakseal must be hand made by someone with appreciable skill, it is considerably more expensive than a simple tube. Tube crackers are easier to use than breakseals because operators often experience difficulty in fracturing the breakseal glass partitions with the magnetic slugs. If 10- or 12-cm sealed sections of 6-mm tubing can be used to collect condensible gas samples from a vacuum system, the operator can attach about 100 cm of 6-mm tubing to the system to serve as a sample collection area. T o collect a sample, the gas is cryogenically trapped at the lower sealed end of the tube, the lower 15 cm of tubing are sealed off under vacuum and removed using a torch, and a subsequent sample can be collected using the next 15 cm of remaining 6-mm tubing. In this fashion, about six samples can be collected in rapid succession before a new length of 6-mm tubing must be attached to the vacuum system. Sample tube crackers built for opening 3/8-in. diameter sample tubes have performed successfully. Also, 6-mm or %-in. tubing can be glassblown to a larger vessel, thus furnishing an easy-to-open glass seal for gas samples or other hard-to-handle substances which must be stored in larger volumes.
RECEIVEDfor review February 17, 1976. Accepted May 12, 1976.
ANALYTICAL CHEMISTRY, VOL. 48, NO. 11, SEPTEMBER 1976
