(13) M. J/ Cohen and M. F. Wernlund, Res./Dev., 26, 32 (1975). (14) R. W. Baughman and M. Meselson, Environ. Health Perspectlves, 5 , 27 (1973). (15) L. A. Shadoff and R. A. Hummel, 170th National Meeting, American Chemical Society, Chicago, Ill., Aug. 1975. (16) D. I. Carroll, I. Djidic. R. N. Stillwell, M. G. Horning, and E C. Horning, Anal. Chem., 46, 706 (1974).
(17) S. N. Lin, G. W. Griffin, E. C. Horning, and W. E. Wentwofth,J. Chern. mys., 60, 4994 (1974) and the references therein.
RECEIVEDfor review December 1,1975. Accepted March 25, 1976.
Isotope Dilution Assay of Boron- 10 Enriched Elemental Boron by Mass Spectrometry Rush 0. Inlow* and James M. Scarborough U S . Energy Research and Development Administration, New Brunswick Laboratory, P.O. Box 150, New Brunswick, N.J. 08903
Boron-IO enriched elemental boron is assayed for total boron by mass spectrometric Isotope dilution. Samples are fused wlth a sodium carbonate flux, dissolved in water, and spiked with National Bureau of Standards boric acid, whlch Is certified for boron content as well as isotoplc abundance. The mlxture is converted to sodium tetraborate and analyzed isotopically by thermionic emission of the Na2B02+ ion. The method is not biased wlth respect to titrlmetric assay. Replicate determinations have a relative standard devlation less than 0.1 %.
Elemental boron samples have been routinely assayed for boron at New Brunswick Laboratory by fusion with sodium carbonate and subsequent titration as a mannitol-boric acid complex with standard base ( 1 ) .This method is time-consuming, requiring at least two days, and suffers from the necessity for frequent blank determinations. Other methods of boron assay including pyrohydrolysis separatiop of boric acid followed by titration (I), spectrophotometric determination as the boric acid-diaminochrysazin complex (2),and gravimetric determination of boric acid with nitron ( 3 )do not offer greater precision or appreciable time savings. T h e relative standard deviation for replicate determinations by any of these methods is about 0.1%. Trace amounts of boron have been determined by isotope dilution using boron-10 enriched spiking material (4, 5 ) . Reported errors in t h e method are greater t h a n 10%. Boron used in nuclear technology is usually enriched in boron-10. Since complete analysis of this material requires a n isotopic abundance determination, assay for total boron by isotope dilution is readily available after one additional mass spectrometric measurement. National Bureau of Standards boric acid, Standard Reference Material (SRM) 951, being certified for boron content as well as isotopic abundance (6), is well suited for spiking boron-10 enriched samples. T h e high cost of SRM-952, enriched boric acid, makes its use for spiking normal boron samples less attractive.
EXPERIMENTAL Apparatus. Use only platinum, plastic, or quartz laboratory ware to avoid boron contamination from glass. Mass Spectrometer. A first-order directional-focusing mass spectrometer with a 60°-sector magnetic field and a radius of magnetic deflection of 6 in. is used. Reagents. All chemicals are analytical reagent grade. All solutions are stored in plastic containers. Sodium Hydroxide. To 100 g of freshly boiled water, add 17.4 g of NaOH pellets. Combining 35 g of this solution with 1g of boric acid yields a solution of sodium borate which has a boron concentration of 5 mg/g and a sodium/boron ratio of 2. Isotopic Standard. Weigh portions of SRM-951 and SRM-952 into
a small plastic vial by difference (nearest 0.02 mg) such that the resulting mixture is about 50 wt % boron-10. Add sodium hydroxide solution to the mixture as described above. I o n Exchange Column. Cut the bottom from a plastic 50-ml graduated cylinder and fit a Selas porcelain filter crucible (coarse) tightly into one end. Add thoroughly washed Dowex 50W-X8 (H+ form) to a settled depth of 10 cm. Procedure. Sample Treatment. Line a 30-ml platinum crucible with 1.5 g of sodium carbonate by heating over a Meker burner and swirling the clear melt onto the sides of the crucible. After the crucible cools, add 100 mg of boron (nearest 0.02 mg) and cover with 2.5 g of Na2C03. Cap the crucible with a platinum cover. Heat gently for 10 min and then at full blast over a Meker burner for 30 min. Place the cooled crucible and cover in a 400-ml tall form quartz beaker and add 75 ml of water. When the fusion cake has dissolved, remove the crucible and cover with thorough rinsing. If the sample is to be spiked, add sufficient SRM-951 (nearest 0.02 mg) such that the boron in solution will be about 50 wt % boron-10. Stir for l h. Add 7-8 cm from the ion-exchange resin column to the beaker, cover, and stir rapidly for 10 min. Let the resin settle and decant the supernatant onto the ion-exchange column. When all the solution has passed through the column, rinse the resin into the column and wash with three 25-ml portions of water, allowing the column to drain completely between washings. Evaporate the eluate to dryness over a steam bath, weigh the boric acid in the beaker, and add sodium hydroxide solution as described above. Mass Spectrometry (7). To a 2-ml portion of the sodium borate solution, add 1drop of glycerol. Load about 5 pg of sodium tetraborate on a rhenium filament. Outgas the sample until a pressure of 5 X Torr is reached. Set the ion intensity for a minimum ion current of 3 X A for the major isotope. Record the ratio of m / e 89 (Na211B02+)and 88(Naz1OBO2+).Apply a correction factor for 1 7 0 by subtracting 0.00075 from the mean ratio.
RESULTS AND DISCUSSION T h e boron assay of t h e sample, Bo, is calculated from Equation 1,
E, =
W,B,(loB, - "E,) W,(loBm
- 'OB,)
x 100%
where W , = weight of spiking material used (g), W, = weight of sample used (mg), B , = concentration of boron in spiking material (mg/g), l0B, = lOB in spiking material (wt %), l0Bm = lOB in sample plus spike mixture (wt %), and l0Bo= loB i n sample (wt %). When SRM-951 is used as a spiking material, B , is 174.86 mg/g and lOB, is 18.362%. Air buoyancy corrections are applied t o t h e weights of boric acid (f0.71 mg/g) and boron (+0.37 mg/g for the @-rhombohedralform). A correction t o lOB, is made by using t h e isotopic standard described in t h e Experimental section as an internal standard. A correction t o l0Bo is made using SRM-952 as an internal standard. These standards allow correction for spectrometer bias and boron contamination of reagents and should be checked at regular inANALYTICAL CHEMISTRY, VOL. 48,
NO. 9,
AUGUST 1976
* 1357
Table I. Boron Assay Results No. of Assay by Sample determina- isotope No. tions dilution, % 1 2 3
4
6 3 2 2
99.35 97.26 97.23 97.50
Relative standard deviation, %
Assay by titrimetry,
0.05 0.10 0.08 0.05
99.38 97.36 97.20 97.50
%
tervals, especially when a new bottle of reagent is used. For this work the correction factor applied t o the mass 89/88 ratio for 10Bmis 0.9994 and t h a t for l0Bois 1.0005.T h e boron used was more than 90% enriched in boron-10. Boron assay results for four samples are shown in Table I. In each case, there is good agreement between the assay found by the isotope dilution technique and an independently determined chemical titration assay. The largest relative standard deviation found is 0.10%. Standard deviation for duplicate mass spectrometric determinations is 0.003% for l0B, and
lo&. This corresponds to errors in the total boron assay of 0.005%and 0.01%, respectively. A weighing error or loss during fusion of 0.02 mg of boron corresponds t o 0.02% error in t h e boron assay.
ACKNOWLEDGMENT We thank V. E. Connolly and E. L. Callis for performing the mass spectrometric analyses.
LITERATURE CITED (1) A. R. Eberle, M. W. Lerner, and L. J. Pinto, Anal. Chem., 36, 1282 (1964). (2) A. R. Eberle and M. W. Lerner, Anal. Chem., 37, 1568 (1965). (3) C. A. Lucchesi and D. D. DeFord, Ana/. Chem., 29, 1169 (1957). (4) A. A. Nemodruk and Z. K. Karolova, "Analytical Chemistry of Boron", E. Seijffers, Ed., Sivan Press, Jerusalem, 1965, p 97. (5) J. C. Landry et al., Mitt. Geb. Lebensmittelunters.Hyg., 65, 65 (1974). (6) E. J. Catanzaro et al., "Boric Acid; Isotopic, and Assay Standard Reference Materials", Nat. Bur. Stand. (US.). Spec. Pub., 260-17, Feb. 1970. (7) M. W. Lerner, "The Analysis of Elemental Boron", USAEC Div. of Tech. Information, TID-25190, Nov. 1970.
RECEIVEDfor review March 23, 1976. Accepted April 29, 1976.
Computer Acquisition and Processing of Metastable Ion Scans in a Double Focusing Mass Spectrometer Lubomir Baczynskyj,* D. J. Duchamp, J. F. Zieserl, M. D. Kenny, and J. B. Aldrich Research Laboratories, The Upjohn Company, Kalamazoo, Mich. 4900 1
A computerized method for automatically acquiring metastable ion data in a double focusing mass spectrometer with reversed geometry is described. Programs have been developed allowing accelerating voltage and electrostatic sector scans. The data acquisition and data reduction are performed in real-time. Time for processing the data of a complete scan is 15-20 s. The accuracy of mass determinations is Increased for weaker metastable peaks and large gains in conveniences are achieved.
For many years, the study of metastable ions had been confined mainly to physical chemistry. In recent years, however, the usefulness of metastable ions in the analysis of mass spectra of organic molecules has been clearly demonstrated ( I ) . Rapid progress in this field has been achieved due to t h e pioneering work of Beynon, McLafferty, and others. T h e recent progress in instrumentation has made it possible for many laboratories, whose principal interest lies in the area of organic mass spectrometry, to become involved in this field. Recently we acquired a double focusing mass spectrometer with reversed geometry, the Varian MAT CH5 DF. T h e particular feature of this geometry is the arrangement of the analyzing sectors. The ion source is followed by the magnetic sector which is followed by the electrostatic sector analyzer and terminated by the detector. The advantages of such an arrangement have been discussed in the literature (2-4). T o detect metastable ions, two types of experiments can be performed. The accelerating voltage can be scanned (for the CH5 DF, from 1 to 3 kV or from 2 t o 3 kV) while maintaining t h e magnetic and electrostatic sectors constant ( 5 ) .Such scans yield information about the precursors of a given fragment ion. Scanning of the electrostatic sector (ESA), at constant magnetic field and accelerating voltage, gives rise t o a spectrum 1358
ANALYTICAL CHEMISTRY, VOL. 48, NO. 9, AUGUST 1976
of metastable peaks, which correlates a given ion with its daughter ions. This last technique has been called DAD1 ( 4 ) (direct analysis of daughter ions) or MIKES ( 2 ) (mass-analyzed ion kinetic energy spectrometry). Using the manual mode, we recently studied the fragmentations of some prostaglandin molecules by both defocusing techniques (6). Although the information obtained from these experiments was very useful, the process of obtaining such results was tedious. T o increase the accuracy of the measurements, four determinations of the tops of each metastable peak were made. Considering, that in general there are several metastable peaks in each ESA scan of a given ion, the acquisition of these d a t a manually was very time-consuming. Another disadvantage of this manual procedure on our mass spectrometer is that, in the decoupled mode, the accelerating voltage or the ESA voltage can slowly drift during t h e measurements. Such measurements can last from a few minutes to an hour per scan depending on the number of peaks measured. This small drift can lead to a decrease in accuracy. Furthermore, the electron multiplier is normally operated a t high gains because of t h e low intensity of some metastable peaks. This introduces noise on top of the peaks and makes the determinations more difficult. The shape of t h e metastable peaks is normally Gaussian; however, i t is well known that not all metastable peaks have a Gaussian profile ( I ) . For "flat" or "dish" top metastable peaks, it is important to determine the center rather than the high point of the metastable peak. For the above reasons, we decided t o computerize the scanning and processing of metastable ion data. Appropriate programs were written t o allow rapid scanning of the ESA or the accelerating voltage, acquiring the data automatically, and processing and presenting the final results in an appropriate format. This project became part of a larger programming effort in which three mass spectrometers may scan simultaneously in different modes. Data are acquired in real time and
