__-----
--__-_1
BUCKING ~
CONTROL
~
FILTERING UNIT
?---, I VOLTAGE
I
I
DIVIDER
1 I
i Fib
Figure 2.
I
Schematic diagram of one of
4
identical channels of the in-
terface
Figure 1. Block diagram of the combined GC-MS-APS-Data System showing location of the interface
the 6-ng and f1.59% for the 300-ng sample, whereas the corresponding data system results were f3.44% and f1.13%. The interfaced data system has also been tested under continuous operating conditions in three pharmacokinetic studies, each involving the sequential assay of approximately 50 plasma samples and standards for the N-acetylated metabolite of procainamide ( 3 ) .Under these conditions, the automated system provided marked advantages over manual techniques with regard to the time required for data analysis and the wide dynamic range that obviated the need to repeat sample injections when the recorder was not properly attenuated to display the height of the mass fragmentographic peaks. Mass fragmentography can be thought of in practical terms as a gas chromatographic technique in which the mass spectrometer serves as a sensitive, ion-specific detector. For this reason, it is likely that mass fragmentography often will be introduced for routine quantitative analysis in laboratories already processing a large number of samples by gas chromatography. Many of these laboratories will already be equipped with a general purpose laboratory data system capable of time-shared, on-line analysis of data
from several gas chromatographs; and, for some, the expense of acquiring both a GC-MS unit and a second data system may be prohibitive. A less expensive alternative would be to connect the GC-MS to the existing data system using a multiple ion detector of the APS type and the relatively simple interface that we have described. Although the standard report format of our data system now presents the peak retention times and areas as the output from 4 different instruments, preliminary studies indicate that, with an 8K expansion of core memory, a BASIC program can be written to internally calculate and present retention time, area ratio, and concentration data in a single report. With this addition, the present system would provide fully automated data processing for mass fragmentography.
LITERATURE CITED ( 1 ) '2.-G. Hamrnar, B. Holmstedt, and R. Ryhage. Anal. Biochem., 25, 532
(1968). (2)J. M. Strong, and A. J. Atkinson, Jr., Anal. Chem., 44, 2287 (1972). (3)J. M. Strong, J. S. Dutcher, W.-K. Lee, and A. J. Atkinson, Jr., J. Pharmacokinet. Biopharm. (in press).
RECEIVEDfor review March 13, 1975. Accepted April 15, 1975. This project was supported by a Clinical Pharmacology Award from the Burroughs Wellcome Fund.
Potassium Bromide Disk Technique for Visible Spectra L. F. Power James Cook University of North Queensland, Post Office, James Cook University, Qld. 48 7 7, Australia
A. M. Tait U.S. Army Natick Laboratories, Physical Research Group, Natick, Mass. 0 1760
Allan et al. ( I ) devised a technique for the rapid determination of infrared spectra of water-free polymers using the KBr disk technique and suggested that the technique should have wide applicability in IR spectrometry. The technique involves the removal of water after the mixture of KBr and compound has been prepared, before consolidation into a disk. We have used their technique extensively for the infrared analysis of metal complexes from which bound or lattice water has been removed. Removal of bound water from a complex ion or molecule involving a transition metal will either produce a change in geometry about the metal atom, or allow the introduction
of an otherwise uncoordinated ion into the coordination sphere. Either of these possibilities will produce some change in the visible spectrum, whereas the removal of lattice water does not necessarily affect the nature of the absorbing species. The techniques normally used to study the visible spectra of transition metal complexes in the solid state involve specular reflectance from the powdered sample or transmission through a mull of the compound in mineral oil on filter paper or between salt plates. These techniques involve difficulties in maintaining anhydrous the compound from which bound or lattice water has been removed, even when prepared within a dry box. The disks ANALYTICAL CHEMISTRY, VOL. 47, NO. 9, AUGUST 1975
1721
prepared by the method of Allan et al. remain anhydrous for some weeks even when exposed to the atmosphere, and hence the technique offers an opportunity to observe both the infrared and visible spectra of the hydrated and anhydrous compounds, and to distinguish between bound and lattice water, which distinction cannot always be made on the basis of infrared evidence alone. Transition metal complexes containing such coordinated ions as nitrate, perchlorate, and sulfate groups may exchange with bromide ion from the KBr on grinding. This is usually apparent from change in color on grinding, and may be readily checked by comparison of the infrared spectrum of the disk with that of a mull of the compound. This exchange can sometimes be useful for the preparation and spectral analysis of bromide compounds which cannot be prepared by other methods, as discussed later,
Table I. KBr Disk Visible Absorption Spectral Dataa Absorption max, nm
454, 520sh 454, 520sh 730, 1030 545, 570, 650 600sh, 900sh 580, 900sh 620br 665 780 560sh, 632 470, 525, 660 490br 670, 990, lOOOsh
EXPERIMENTAL
454 740, 990 570sh, 790sh 600, 950sh 630, 900sh 620 630 62 5
Preparation of KBr Disks of Anhydrous Compounds. AR KBr was finely ground and stored a t 100 O C under vacuum over phosphorous pentoxide in a drying pistol. T h e complexes (approximately 1 mg for Cu(1) or tetrahedral cobalt(II), 2 mg for copper(I1) a n d 2-3 mg for nickel(I1) or octahedral cobalt(I1) complexes) and KBr, to a total weight of 150 f 0.5 mg, were ground in a vibration mill for hour. T h e compounds were dehydrated by t h e method of Allan e t al. Disks, 13 m m in diameter, were pressed 5 times for 2 min each time under vacuum (0.05 mm), a t 5 tons per l’h-in. diameter ram, with t h e die rotated between pressings. T h e compounds were dehydrated as follows. T h e KBrisample mixture, as prepared above is placed within a horizontal glass tube, one end of which fits snugly into t h e orifice of a pellet die. Binding with thin polyfluorocarbon tape is a convenient method of ensuring the desired fit. T h e tube and pellet die are heated under an infrared lamp while a slow stream of nitrogen, dried by successive passage through sulfuric acid and phosphoric oxide, sweeps through t h e horizontal tube containing t h e sample a n d escapes t o t h e atmosphere via the cavity in t h e pellet die. After drying for usually three to six hours, t h e pellet die and tube are placed in a vertical position t o allow t h e mixture t o slide into t h e cavity of t h e pellet die. T h e glass tube is immediately replaced by t h e pellet plunger which has previously been heated in an oven. T h e disks are then prepared as described above. T h e infrared spectra were recorded on a Perkin Elmer 337 grating spectrophotometer. T h e visible spectra were recorded with Cary 15 and Beckman DU spectrophotometers using specially designed disk holders.
DISCUSSION We have been examining transition metal complexes of the ligands 8-amino-2-methylquinoline (maq) and N-(2methyl-8-quinolyl)-6-methylpyridine-2-aldimine (mqp) and had available to us complexes of 4,4’-6,6’-tetramethyl2,2’-bipyridine (tmb). Attempts to record the reflectance or mull on filter paper spectra of the hydrated complexes which had been dehydrated had been frustrated by the hygroscopic nature of some of the dehydrated complexes. I t was therefore decided to prepare KBr disks of the complexes using the method of Allan et al. The resulting spectral data for a series of complexes of tmb ( 2 - 5 ) , maq and mqp (6-10) with divalent cobalt, nickel, and copper and monovalent copper in KBr disks are shown in Table I. The infrared spectrum of each disk was examined to ascertain if any exchange had occurred with the KBr on grinding and heating. For the complexes containing no water, and for the undehydrated hydrates, the KBr disk spectra are in good agreement with the previously published reflectance spectra although small shifts in band positions do occur. The resolution of bands for copper(I), copper(II), and cobalt(I1) complexes is as good as, if not better than, reflectance or solution spectra, specifically with respect to the resolution of shoulders. The resolution of bands in the spectra of the nickel complexes examined is not as good, especially in the 800-1250 nm region where the 1722
ANALYTICAL CHEMISTRY, VOL. 47, NO. 9, AUGUST 1975
64 1 700, lOOOsh
670, 990, 1000sh 800br 770br Ni(maq)Cl, 2 H 2 0 Ni(maq)Cl, Ni(maq)Br, 7/2H,O Ni(maq)Br,
660, 1000 710. 900sh 640sh, 95Ush 700. 900sh
P) Cu(tmb)S04 Cu(tmb)SO, 3H,O Cu(tmb)2(C104), * H20 Co(tmb), (NO,)(ClO,) Co(trnb)(NO,), H20 Co(maq)SO, * 5H,O
443, 550sh, 830br, 1000sh 550sh, 870br, 1000sh 44Ush, 700 568sh, 593, 654 568sh, 593, 654 560, 590, 640
(A) Anhydrous compounds undergoing no exchange with KBr. (B) Hydrated compounds containing water of crystallization only. Spectra of dehydrated compounds are identical with those of the hydrated compounds. (C) Hydrated compounds containing some coordinated water, and their dehydration compounds. (D)Compounds undergoing exchange with KBr. sh = shoulder; br = broad.
absorption appears as a broad band or ill-resolved shoulder on the more intense absorption a t longer wavelengths. Some of the hydrated complexes [Table I(B)] do not contain coordinated water. The lattice water in each case can be removed by heating the KBrisample mixture under a flow of nitrogen without a change in color of the complex occurring. The absence of water in the resultant disk is verified by the infrared spectrum, while the visible spectra of the anhydrous complexes are identical to those obtained for the respective disks without heat. On heating the complexes, Ni(maq)C1~.2H20and Ni(maq)Bry7/2H20 a t 140’ under vacuum over phosphorous pentoxide for four hours, the complexes change color from pale green to yellow and brown respectively (6). The weight loss and infrared spectra confirm that all water has been removed. The magnetic moments under nitrogen for the yellow and brown anhydrous forms are 3.30 and 3.51 WB, respectively, suggesting retention of octahedral configurations presumably by the formation of halo-bridges (6).
These anhydrous forms are insoluble in non-coordinating solvents and solution of them in methanol or in N,N-dimethylformamide gives the original pale green color. Reflectance spectra could not be obtained because of their extreme hygroscopic nature. The anhydrous forms can however be obtained in KBr disks by heating the mixture under an IR lamp for six hours under a flow of nitrogen and pressing the disk in a hot die. The infrared spectra of the disks confirm the absence of water and the visible spectra [Table I(C)] show bands of 710, 900sh nm for Ni(maq)Clz and at 700, 900sh nm for Ni(maq)Brz. These spectra argcharacteristic of octahedral compounds of nickel(I1) and differ from the spectra of the analogous hydrated complexes. Complexes containing nitrate, perchlorate, and sulfate groups may be subject to exchange with potassium bromide on grinding. Table I(D) shows the visible spectral data of the complexes examined which do undergo exchange as indicat,ed by a change in color on grinding and changes in the infrared. The copper(II)(tmb) complexes exchange to the analogous bromo complex, although a comparison of the spectra with the spectra of Cu(tmb)Br2 or Cu(tmb)nBrz ( 1 1 ) indicates that the exchange is not complete. The COT balt complexes Co(tmb)(N03)yHzO and Co(tmb)nNOr C104 are pink in color and octahedral ( 5 ) . On grinding in potassium bromide, the complexes turn bright blue, The visible spectra of the disks are very similar to that of the
blue tetrahedral Co(tmb)ClZ Table I(A) and suggest that in both cases the exchange product is the blue Co(tmb)Brz. The conversion of octahedral-tetrahedral cobalt in the solid is unusual, especially for Co(tmb)zN03C1O4 which must necessarily lose both a bidentate nitrato group and a molecule of tmb from the coordination sphere on grinding. This suggests that the bis complex is relatively unstable and this is supported by the failure to produce the bis complex Co(tmb)~(NO3), from solution ( 5 ) . The complex Co(tmb)Brz has not previously been prepared.
LITERATURE CITED (1) G. G. Allan. H. Chang, and K. V. Sarkanen, Cbem. Ind. (London), 699 (1967). (2) J. R. Hall, M. R. Litzow, and R. A. Plowman, Anal. Cbem., 35, 2124 (1963). (3) J. R. Hall, M. R. Litzow. and R. A. Plowman. Aust. J. Cbem., 18, 1339 (1965). (4) J. R. Hail. M. R. Litzow, and R. A. Plowman, Aust. J. Cbem., 18, 1331 (1965). (5) J. R. Hall, M. R . Litzow, and R. A. Plowman, Aust. J. Cbem., 19, 201 (1966). (6) M. R. Litzow, L. F. Power, and A. M. Tait. J. Cbem. SOC.A, 275 (1970). (7) M. R. Litzow, L. F. Power, and A. M. Tait, J. Cbem. SOC.A, 3226 (1970). (8) M. R. Litzow. L. F. Power, and A. M. Tait, Aust. J. Cbem., 23, 1375 (1970). (9) M. R. Litzow, L. F. Power, and A. M. Tait, J. Cbem. SOC.A, 2907 (1970). (10) J. King and L. F. Power, Aust. J. Cbem., 25, 1863 (1972). (1 1) M. R. Litzow, Ph.D. Thesis, University of Queensland, 1964.
RECEIVEDfor review December 2, 1974. Accepted April 21, 1975.
Simple, Inexpensive Monochromator Modification Permitting Dual-Channel Operation D. W. Brinkman and R. D. Sacks’ Department of Chemistry, University of Michigan, Ann Arbor, Mich. 48 104
As the need for lower and lower detection limits has increased in optical spectroscopy, methods for controlling external variables have proliferated. Mechanical or electronic chopping in conjunction with a phase-sensitive lock-in amplifier detection system has become a normal part of many spectroscopic instruments (1-3). When flame sample cells are used, even more sophisticated techniques, using two light sources, have been proposed ( 4 , 5 ) ,including one variation utilizing a vibrating quartz plate (6). However, there are conditions under which none of these methods is feasible. In many actual applications, only micro quantities of sample are available for analysis. This has led to the routine use of a number of flameless atomizer systems for atomic absorption and fluorescence in which the resultant signal is transient in nature. In other cases, the method itself involves a transient signal, such as exploding wire atomic emission ( 7 ) and exploding wire-excited atomic fluorescence (8). Here a simultaneous background correction is necessary. Some attempts a t background correction have been reported using optical multichannel analyzers (9) or a second, totally separate detection system for background monitoring (10). Both of these approaches suffer the obvious disadvantage of large expense and, in the case of the latter method, an increase in the overall complexity. The drying and ashing sample pretreatment recommended for carbon rod atomizers is another attempt a t side-stepping the background problems encountered in non-ideal samples ( 1 1 ) . The instrumental modification described here combines
an inexpensive monochromator with a simple addition to the exit slit assembly to obtain simultaneous line and background or line and reference line detection. Full slit width flexibility is retained, and separation of observation wavelengths is variable up to about 2 nm. The basic component is a quartz plate which is positioned just in front of the exit slit. The plate is placed so that it intercepts only the radiation from the focusing mirror of the monochromator going through the top half of the exit slit. By rotating the plate to some incidence angle CI# with respect to the surface normal, as shown in Figure 1, a different wavelength passes through the top half of the exit slit than through the bottom half. The wavelength separation Ah can be predicted knowing the linear reciprocal dispersion p of the monochromator, the thickness a of the quartz plate, and the incidence angle 4, along with the tabulated index of refraction for quartz in the wavelength region of interest. The wavelength separation Ah in nanometers is expressed as,
where cl is the linear displacement of the refracted and unrefracted rays of a given wavelength. This displacement, however, can be expressed as a function of line segment CD and the angle a between the emerging ray and the plate surface. [ A A ~ ,=
p CD sin
cy
=
p
CD cos 4
(2 )
However,
* Author to whom correspondence should be directed.
-
CD =
BD - BC
=
AD s i n 4 - AC sin e
ANALYTICAL CHEMISTRY, VOL. 47, NO. 9, AUGUST 1975
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