Element Ti Nb Sb Ta
Added
Table 111. Precision and Accuracy at 1 pprn Concentration, ppm Found Found Blank (corrected)
1
2.0
1
1.1
1 1
1.o 1.4
1.6 1.1 0.9 1.1
0.4 0.0 0.1
0.3
Analysis time, beginning with the solution of hydrolyzed UF6, is approximately 5 hours. In summary, spark source mass spectrometry has been used to determine 31 metallic elements and the isotope 233U in UF6 with a detection limit of 1 ppm or less, an average relative standard deviation of *33 %, and an analysis time of 5 hours. Although the method might be categorized as semi-quantitative, its precision is considered adequate for the purpose, and its relative inclusiveness, simplicity, speed,
Re1 std dev, 7Z
Re1 error,
+56
60 10
+13 ir 56 i64
- 10 10
and sensitivity make it attractive for determining metallicelement impurities in UFb. RECEIVED for review December 3, 1971. Accepted March 16, 1972. Presented at Fourteenth Conference on Analytical Chemistry in Nuclear Technology, Gatlinburg, Tenn., October 1970. Work performed at the Oak Ridge Gaseous Diffusion plant operated by Union Carbide Corporation for the U. S. Atomic Energy Commission.
Exact Mass Measurement Accuracy from CEC 21-llOB Mass Spectrometer and Commercial Data System DS-30 R. S. Gohlke G . P. Happ,] D. P. Maier, and D. W. Stewart Research Laboratories, Eastman Kodak Company, Rochester, N . Y . 14650 A DOUBLE FOCUSING, high-resolution mass spectrometer (Consolidated Electrodynamics Corp., Model 21-1 lOB), designed for electrical and photoplate recording, has been interfaced with a commercially available data acquisition and processing system (DS-30, AEI Scientific Apparatus, Elmsford, N.Y. 10523). An in-depth discussion of the parameters that must be considered in the use of small computers to process high-resolution mass spectral data has been presented (I). Our initial work was done in 1970 using AEI’s DS-20, a less versatile program which gave entirely comparable mass measuring accuracy. In our case, the DS-30 system utilizes a PDP-8/1 computer (Digital Equipment Corp., Maynard, Mass. 01754) (4096word memory) with high-speed paper-tape punch and reader, two 32 K disks, an ADC-1 analog-to-digital converter, and an ASR33 Teletype unit. If additional storage capacity is required, an RF-08 disk (256 K words) may be used. The mass spectrometer-computer interface is supplied by AEI and consists of an adjustable RC-clock (1-12.5 kHz), signal biasing and threshold controls, and requires an input signal in the range of 0 to approximately - 10 V. Operating programs and data are stored on the disks and called into core at the appropriate time by a specialized disk monitor system, SERF (SERial File Disk Monitor). SERF and DS-30, of which it is a part, were written by Applied Data Research, Princeton, N.J. The ASR33 keyboard provides the operator with program control. Data output can be
obtained on the Teletype or high-speed paper-tape punch. (Data output can also be obtained on a line printer or on a magnetic-tape unit, but these facilities are not a part of our system.) Basically, DS-30 samples and digitizes the analog signal from the mass spectrometer at a rate determined by the adjustable clock (typically 7 kHz); rejects values less than the preset threshold; and, in real time, computes the area and time centroid of each ion signal comprising the mass spectrum. In practice, we scan the mass range of 900 to 50 in approximately 90 seconds. Subsequent to data acquisition, the program calculates exact ionic masses by comparison of the stored time centroids with those derived from the known masses of a perfluorocarbon reference material run in admixture with the unknown sample. Although any reference material, fluorinated or not, can be used, we normally choose high-boiling perfluorokerosene, supplied by Pierce Chemical Co., Rockford, Ill. In DS20, only PFK could be used. The conversion of time centroids to exact mass (which requires 5-10 seconds) can be delayed indefinitely to permit the uninterrupted acquisition of multiple scans on the same sample. Approximately 20 spectra can be stored on 64 K disks and over 100 can be accommodated if the RF-08 (256 K) disk is used. A description of the numerous operating subroutines and data output formats available within DS-30 is available elsewhere (2). In addition to a 0- to - 10-V signal, DS-30 requires that the mass spectrometer be capable of providing an exponential
Present address, P. 0. Box 28033, San Diego, Calif. 92128. (1) R. T. Klimowski, R. Venkataraghavan, F. W. McLafferty, and E. B. Delany, Org. Mass. Spectrom., 4,17 (1971). 1484
ANALYTICAL CHEMISTRY, VOL. 44, NO. 8 , JULY 1972
(2) P. Powers and M. J. Wallington, paper F3 presented at the
Nineteenth Annual Conference on Mass Spectrometry and Allied Topics, Atlanta, Ga., May 2-7, 1971.
Table I. Mass Measurement Accuracy for DS-30, 21-llOB System (ppm)
True value mle Perfluorotributyl amine 613.9647 575.9619 501 .9711 463.9143 425.9775 263.9811 175.9935
1
2
3
4
5
6
7
8
9
10
Av error
Std dev of error
2.7 -3.2 2.7 2.3 -2.8 -2.2 -1.7
1.9 4.3 4.9 1.0 -0.7 0.0 0.5
2.9 -12.1 -2.9 -2.1 1.1 -1.1 6.8
10.7 5.3 -0.5 -1.2 -1.6 3.0 9.6
4.3 -2.7 -2.9 -5.3 -2.3 0.7 7.3
5.8 -5.2 -2.5 -2.3 -5.3 5.6
8.4 -2.2 2.5 3.4 0.9 -3.0 0.0
13.5 -1.5 -7.3 -7.5 -3.7 4.1 -11.9
-11.4 2.4 1.3 2.1 2.3 3.4 10.2
-10.4 -4.5 0.5 -4.7 -4.6 -1.1 6.2
2.8 -1.9 -0.2 -1.4 -1.3 -0.1 3.2
8.1 5.1 3.5 3.1 2.2 3.0 6.1
-0.7 -5.7 -4.6 -3.8 0.8 2.2 0.8 -0.4 -4.1 1 .o -1.0 1.2 4.5 5.5 4.9 1.6 -3.3 -11.7 3.8
-0.3 -0.3 -2.3 -2.7 -3.0 3.0 1.3 2.6 4.6 -1.5 1.5 -1.9 2.6 -8.3 -5.6 -5.8 -7.6 8.5 3.9
-4.1 -3.8 -5.0 -3.4 0.4 3.9 3.5 2.6 -1.0 -0.5 2.1 0.0 -1.3 -1.3 2.1 -1.6 0.0 8.5 4.0
-4.1 4.5 2.3 3.8 0.4 -0.8 -1.3 2.2 2.0 0.5 -3.1 2.5 5.2 1.3 -2.1 5.8 0.0 5.3 4.1
-2.6 2.6 0.0 -0.3 2.1 1.3 -0.8 -2.2 -3.6 -3.1 -3.1 3.8 2.6 -2.0 -3.5 1.6 4.2 2.1 3.1
3.0 -1.5 -5.3 -5.4 2.1 0.8 1.3 0.4 4.1 2.1 -1.5 5.1 4.5 1.3 1.4 3.3 4.2 6.3 3.7
-0.3 -2.2 -0.7 -3.8 -3.0 -1.7 0.4 0.8 1 .o 3.1 5.3 5.8 5.2 -2.0 2.1 -6.6 -5.0 8.5 3.9
0.7 5.7 -1.9 -6.2 7.4 -1.7 3.1 2.2 1.0 1 .o -1.0 3.2 1.3 6.2 0.7 -1.6 5.0 10.6 5.7
3.4 -1.5 4.2 -0.7 3.0 3.0 5.3 2.6 2.0 5.2 2.1 -3.8 1.3 -6.2 -2.1 -0.8 -7.6 1 .o 4.5
3.0 -3.4 0.7 -3.4 4.3 -0.4 3.5 2.6 6.2 4.2 3.1 10.9 -2.6 -4.8 0.7 -3.3 -0.8 0.0 4.5
-0.2 -0.5 -1.2 -2.6 1.4 0.9 1.7 1.3 1.2 1.2 0.4 2.7 2.3 -1.0 -0.1 -0.7 -1.1 3.9
2.8 3.7 3.2 2.9 3.1 2.1 2.1 1.6 3.4 2.5 2.8 4.2 2.7 4.8 3.1 3.9 4.7 6.5
-0.1
Hexachlorobutadiene 263.8042 261.8072 259.8101 257.81 30 228.8354 226.8384 224.8413 222.8442 191.8695 189.8724 181.8754 154.9036 152.9065 142.9036 140.9065 119.9347 117.9377 93.9377 RMS error
FROM
ELECTRON MULTIPLIER 3.3K
IK
IOK
TO COMPUTER OR RECORDER
P45ALU .02 ,0068 ,002
+
q7K
T
l 1
TI
T
l o
Figure 1. Additions to 21-llOB magnet power supply to provide go-second, high-tolow-mass exponential scan
SI,SPDT 1 = Normal operation; 2 = Exponential scan, high mass to low. RI, 120-Kohm, wire wound 1%. CI, 270 pF/25 V (see text). K403, opens when scan is initiated and closes to recharge CI during magnet reset time, is a part of automatic cycling circuit, not shown. Parts enclosed by dotted line are added to 21-llOB schematic R-143290 (magnet sector)
scan (to keep ion-peak widths approximately constant) from high to low mass. This type of scan was not available on our 21-1 10B mass spectrometer. Also, the output amplifier normally supplied provided a signal of incorrect polarity and possessed frequency response insufficient to be usable with the computer system. The required high-to-low-mass exponential scan was obtained by adding a switch-selectable RC network to the normal 21-1lOB magnet power supply as shown in Figure 1. It is also desirable to rewire the existing relays of the magnet
power supply to provide optional continuous cycling of the magnet over the mass range to be used to improve stability. Details are available from the authors. The network consisted of a 120 Kohm wire-bound 1 resistor and a 270-pF capacitance, made up of four 50-pF and two 35-pF/25 V polycarbonate capacitors in parallel. Although the decay characteristic of this network, as sensed and amplified by the 21llOB magnet regulator, is probably far from ideal, it does provide a sufficiently exponential scan to permit the reliable use of DS-30 over the mass range 90Ck70. The unreliability ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
1485
Figure 2. Amplifier interface between mass spectrometer and computer Resistors are %-W carbon. Capacitor values are microfarads. SI, SPDT gain switch. 1 = X1, 2 = X50. Sz,SPDT mode switch. 1 = normal, 2 = bilinear (gain XSO, 0 to -6 V; gain X2, -6 V to -10 V). P25AU, P45ALU are supplied by Philbrick/ Nexus, Dedham, Mass. 02026
below m/e 70 can be tolerated since high-resolution data in that mass range are required rarely and manual peak-matching techniques are, of course, still usable. The original output amplifier of the mass spectrometer was replaced with that shown in Figure 2. It consists of a current amplifier (P25AU) and an inverting voltage amplifier (P45ALU) which provide the required 0- to - 10-V signal (3). In the X50 gain, bilinear mode, the output voltage is 50X the input voltage over the range of 0 to -6 V. From -6 to - 10 V, the amplifier gain is reduced to approximately 2X by the action of diode 1N629. This simple form of signal compression ( 4 ) permits the scanning of ion signals of low intensity without overloading the computer input when signals of high intensity occur. Quantitative peak-area data, also pro-
s. Lewis, Tennessee Eastman Company, Kingsport,Tenn., private communication, 1969. (4) C. N. Reilley, University of North Carolina, Chapel Hill, N.C., private communication,1970.
vided by DS-30, are distorted by this compression, but this has not been a serious disadvantage for applications in structure characterization. This system has been in use for over one year and is capable of providing the mass measuring accuracy shown in Table I. Ten consecutive scans of a sample consisting of 0.8 p1 of perfluorotributylamine and 0.2 p1 of hexachlorobutadiene mixed with 1 pl of high-boiling perfluorokerosene (the mass reference compound) were obtained. The following instrumental conditions were used: electron beam, 70 V, at 100 pA, 8 kV ion energy, electron multiplier 140 V/stage. The static resolution was adjusted to approximately 7,000. An all-glass inlet system at 175OC was used to contain the sample. The beam monitor indication was 2 X A throughout the scans. The average error of each of the scans lies between 3.1 and 5.7 ppm; the individual errors range between - 12.1 and +13.5 ppm. This compares favorably with the AEI specification of 5-ppm root-mean-square error for peaks in a given scan when DS-30 is used with the mass spectrometer for which it was designed (AEI MS-902). The ions presented in Table I were chosen to avoid the inclusion of unresolved doublets. In routine operation, where less care in instrument or peak-shape adjustment is exercised, the errors are approximately 20% greater than those shown. We have found that the mass accuracy remains constant when the 21-llOB is operated within the resolution range of 7,000 to 15,000 (10% valley). It is important to reduce the ripple on the electric sector voltage to the lowest possible value and to be certain that the output transistors of the magnet power supply are operating well within their suggested limits. Failure to observe these precautions results in reduced mass measuring accuracy.
(3) P. E. Morrisett and J.
RECEIVED for review January 19, 1972. Accepted March 29, 1972.
Determination of Mass Spectrometric Sensitivity Data for Hydroaromatic Compounds J. L. Shultz and A. G . Sharkey, Jr. Pittsburgh Energy Research Center, Bureau of Mines, US. Department of the Interior, Pittsburgh, Pa.
R. A. Brown Esso Research and Engineering Co., Linden, N.J. CURRENTINTEREST in utilizing coal to meet the projected energy requirements for the nation has stimulated interest in coal gasification and liquefaction processes. Products from coal hydrogenation have been studied at the Pittsburgh Energy Research Center since mid-1940. Other investigators have also contributed to the literature of coal-derived compounds, as indicated in the extensive bibliography published by Wiley and Anderson ( I ) . Many of these studies depend heavily upon low-voltage mass spectrometric analysis of products. In the low-voltage method only the sensitivity of the molecular ion is required for analysis of mixtures. Aczel et al. (1) J. L. Wiley and H. C. Anderson, US. Bur. Mines Bull., No. 485, (1950). 1486
ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
(2) and Kessler et al. (3) both report on use of the method for the analysis of hydroaromatics. Both methods are limited in application because of a lack of reference compounds, including hydroaromatic hydrocarbons. The work reported here indicates that the sensitivities of these hydroaromatic compounds can be predicted from the sensitivity of the corresponding aromatic ring compound. This observation is based on the behavior of 15 hydroaromatics listed in Table I. (2) Thomas Aczel, J. Q. Foster, and H. H. Karchmer, Reprints, 157th Nat'l Meet. Amer. Ckem. SOC.,Diu. Fuel Chem., 31, NO. 1, Minneapolis, Minn., April 1969, p 8. (3) T. Kessler, R. Raymond, and A. G. Sharkey, Jr., Fuel, 48, 179, (1969).
