Topics In..
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Chemical Instrumentation
fwfure
So. Oronga, N. J. 07079
Edited by GAUN W. EWINO, Seton Holl Univmity,
are no Cmwgrsinim a p t i n to int,mdtm nhrruratins nnd reduction 01 enern.. T h r FS-720 i* shown in Figure. I7 and'iu, and n m i s t * of avcrnl modules, M follows.
The mlirka are intended lo rra l h m d c r a ofmm JOURNAL bu rallino allenlion lo nnu dn*lomnenta in ilu I h m-.. desian.. m arnilabilifv "of. rhmiral labmalory inalrumenlalia, m by prcamling uaejul inaighla and exnlanaliona of tonira that are of nraclical i m w l o n c c lo I h w who uae. m h h ihr unr oj, &&rn inalrumm&m and indtrumenra~lerhniquca. 7% cdilm intS-il)O modulnr interferomrtcr i* designed fnr w e i l l the l+.Xi) ~ r n rwion - ~ n ~ for ~ drwdutintw of I to I r . T h r I'S-720 rmploya ofiaxis pnrnholoicl reflcrling optilr t h n n t ~ h out., thus maximizing thr PIIPTKY Ihrollghnut the rnnge of ihr inrtrumwt. There
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Model FS-720 speemm4.r
The FS724 modnle mntaina the following item*. : 12r.W hiplh-prepsure mrrrllry Inmp water-rmlrcl. S w r r c aperture: vnrinhlc iu the fnllowing ~ C P : 3-, Tr. nnd Ilkmm diameter. Odlimntor: f : I..? s ~ t r f n wnlmninized OK-axis par& oloicl. Chopper: aynrhronow motor pdydriven st I5 llr. Rcnm.plittcr: rthylene terephthal~tr. I3cnm.sphtter nww!t: the mwt ehirimt nv.nilnhlcon the mnrket affnnling n,ry repln,~ement of h n m r p l i t t ~ rwilhot~lthe ncrrwity lor re. n l i w i n ~ . Thehcnmsplitter mount is made of rpotprouncl s t ~ i n l ~xst w l . F i x 4 mirror: 3 in.4inmetcr stwfnw nluminizrd plsnr mirror inrorpornting lhc I(I1C vnnlilwer ndjurtmrnt principle. Fired mirror motlnl: hrld is positinn over 0rinw: rcmnvnhl~for other instrumcntnl nmfi~lsationr,nrrnnmmeutr, nnd nwwnnriw. i n i n : Imwnapliltw modtllc. 8 in. ~ l w n i n w nd o y CIIIW. The FS-721 module mntnlnn a lowvnltngesynrhronow nmtar nnd multispeed I [ C ~ ~ I I I D Xo w l l o ~ I M I U W mirror path dillerrnee r p d r of from 0.5 r 'wr to ,500 r w r . The p ~ t hclificrcnre i* *I0 mt. The moving mirror is i..; rm in diameter. The mirrnr motion is n~ositoredthrough the use of a \lnirE grnting. The JloirE f r i s w prodtl~wlby the ~y*lemare tad in n mnnner ?cimilnr tn the lnser fringe referenring dwrrilx=d earlier. The FS-722 mmple. rondenwr, and detwtor module. house aurfnce slwninired ofi-nxis pnrnhchirl nncl plnnc mirrors wed In form nn i m n ~ of c t.heaottrce in the renter of the ar-wry morlulp, nn elcrtroformd mpper light pipc urrvl to inrrcnv the cffirirrwy of the syrtem, and n ( M n y detector fitted with R ilimnond r i d o w . The "rnmpling nren" is n 5' ', in. rulw and will house IO-rm En* rclls, liquid cell., and mlid snmplr hrtlrlrrs. The w t m e is imngnl in the wntcr irf the rnndulc to nllnr the b n t nrrnngenwnt for positioning the snmplc and nrrrwries. T h r F r 2 M elertronin module mluists 01 n lork-it) lype amplifier, n dipitizcr, nnd (Canlimmd a page A.%5O)
Volume 47, Number 5, May 1970
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Figure 23.
LR-100 spectrometer
I n the very far-infrared region the plasticfilm hertmsplitters become inefficient. Energy is wasted because the films transmit poorly and multiple interference effect,^ impair spectral quality. The lamellar grating, however, uses reflecting surfaces to ~ r o d u c einterference effects. Haw this
Figure 19.
Model FS-820 spedromeAr
ouneh. A 12-bit AID converter is ~ triggered hg the hloin' grnting p d . at111 n.;.,rinted ~lwtrouim. 'rhc Addo puwh remrrlx the inttrfrrugrnm 01. psprr t,ipe in 12-hit binary code. The FS-820 is shown schematically in Figure 19. The instrument basically consi& of the source and interferometer modules of the FS-720. However, a s t e p ping drive is used in place of the Moir6 drive, and polyethylene lenses as the condensing optios. The instrument is for use principally in the range 10-200 em-' with resolutions of up to 0.2 cm-I. Although the frequency range is limited to 10-200 cm-I by the polyethylene lenses and quartz-windowed det,ector, the range can be increased to 400 cm-1 by substituting a FS-722 module and diamond-windowed detector for the normal condensing optics and detector. The FS-820 will usually consist of the following modules. The FS-821 drive module contains the stepping motor snd micrometer drive. A lapped in.-diameter piston carries the moving mirror through x total distance of 5 em. The mirror is 7.5 ern in diameter. The FS-822 modde contains s n f:1.2 polyethylene lens fitted to the exit port of the interferometer. The cell compartment a
plates, as shown in the upper part of Figure 21. Each beam will travel the same distance after being reflected and will he in phase with the other. However, if one of the plates is moved with respect. to the other, then the paths differ and interference effects similar to those described edielier occur. A set of such plates constitut,es s. lamellar grating. The LR-100 lamellar grating spectromto the FS-200 module, and contains a eter is shown in Figures 22 and 23. The lock-in amplifier, a 12-hit A/D converter LR-100 is of modular construction and naes triggered by the stepping motor drive modules similar to those designed for the FS-720. The lamellar grating located in the LR-101 module is comprised of two sets of parallel intermeshing metal plates whoso front surfaces have been lapped accurately flat. The plates are mount,ed so that these faces can he kept parallel to each other within a, few seconds of arc. The total ares, of the grating is 8 cm X 8 om. The movable set of plates is positioned by a stepping motor operating in conjunction with a micrometer drive. The standard lsmellar grat,ing supplied /L with the instrument has a "grst,ing Figure 21. Interference by lomellorgrating eansbant'' of 0.95 cm, and allows interferograms of up to +.5 cm optical path difference to be scanned. Thin unit is intercircuit, and an Addo punch. TheFS-MC1 changeable, however, and other litmellar electronics me used to operate the stepping drive in 2.5-, ii-, lo-, 20-, 40-, and 80-lr grating assemblies can he supplied to order giving either a. maximum of 10 cm optical intervals with stop time adjustable from pat,h difference in one direction for higher 0.5334 sec. resohtt,ion, or a. "grating constant" of 0.64 The third instrument, the LR-100, differs from the others in that a com~Ietelv - . cm for an increased operating range to reflective "beamsplitter," a lamellar graG -100 em-'. The radiat,ion reflected by t,he lamellar ing, is used rather than the 50%-transgrat,inp is deflected by the off-axis p a r mitting, 50%-reflecting ones described holir mirror, to a transfer mirror positioned earlier. The reason for this choice becomes apparent in examining Figure 20. directly beneat,h t,he source apert,ure.
FREQUENCY (cm') Figure 20. Low-wavenumber energy comparison, between the FSJZO spectrometer employing 5 0 - and 1 0 0 - p melinex beomspiitlerr, and the LR-100 iomellar-grating spectrometer (groting mnrlonlO.95 cml.
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-". "...".Figure 22.
Schematic diagram LR.100
(Continued on page A362)
This transfer mirror directs all tho radiant energy toward the sample chamber, via two off-axis parabolic mirrors. The light source is a 125-W high-pressure mercury vapor lamp, water-cooled and fitted with a thermal cut-out safety switch. Source radiation passing through a 1-cm aperture is chopped a t 15 Hz. The radiation is collimated by a surface sluminiaed off-axis parabolic mirror. Lamellar-grating drive module (LR102): settings of the movahle lamellargrating plates are effected hy a stepping motor triggered by the control unit FSMCl. The motor is coupled to a micrameter drive consisting of a cylinder and s. nonrotating lapped piston to which the grating plates me attached. Sample, condenser, and detector module (LR-103): the sample and condenser chamber is approximately a 15-cm cube. The incoming light beam is imaged in the center of the chamber in order to permit the best possible positioning of specimens and accessories. The image sise is approximately 12 mm. The top plate of the chamber has a large glass ohservstian window, and the module is provided with an externally adjustable rotating wheel which seeommodates either five filters or five solid samples. This feature permits filters or samples to he changed without releasine the vacuum. The detector is an irnpnwe 1 ( h 1 . 1 ~ cdl ( U r i r a m having a :i-mm u r u 5-rnm iliunwter q u r r , wndrm, and a. vacuum nozzle. The FS-MCI control for the stepping motor snd the electronics are like those used for the FS-820. The three spectrometers produce interferograms. The paper tape thus serves as interface to a digital computer used toper-
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Figure 24. Spectro of water vapor. upper trace; single-beom rpeetrum of water vapor. Lowor trace; ratiood spectrum of water vopor. Both s ~ e c t r awore recorded with the FS-720: data riduction war molog, carried out wilh thd FTC-100 system.
(Continued on page AS64)
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Chemical lnstru~ttenfation ~
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form the da1.s reduction. An alternate approach involves the use of t,he FTC-100 Fourier Trnnfiform computer. While an interferogram is produced, the analog informai.ion is processed by an A/D converter and stored serially in one of two ferrit,e core mat,rix memories as binary words of 12 bib. Two sections of 1024word capacity memory me svailable to enable x rai,io of t.wo spectra to be obtained bvsimultaneous transformation. A ~ a r a l -
stored. A single-beam spertritm and the corresponding ratioed spectrum produced by the FS-720 using the FTC-100 analog data reduction system are shown in Figure 24. Ratiaed spectra recorded with the LR-100 spectrometer are shown in Figures 25 and 26. , . . , ,. ,
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FREQUENCY (cm) Figure 26. Trmsmisrian spectrum of a 2-mm powdered dim of Cals. The spectrum war me-. rvred with the LR-l 0 0 spectrometer, transformed with the FTC-100 elestmnics, ond i s a ratiocd spsctrum. The recording time was 20 min for each spectrum l & l - c m optical p ~ t h difference).
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FREQUENCY (cm9 Figure 25. Pure mtdionol spectrum of N p . The spectrum was meowred with the LR-100 spectrometer, tranrformed with the FTC. 1 0 0 electmnics, and is a ratioed'speclrum. It war recorded under conditions of 1 -meter optical path and .bout 10-cm Hg pressure. The recording lime war 1 hour for eoch interferogmm I+5-cm optical path difference).
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lel 12-bit input facility is fitted for paper tape or other already digit,ised data. (The paper-t,ape output of t,ho spectrometer can be retained, so that more extensive processing of data by a large digital computer is possible.) Compntution consists of cycling the stored informut,ion, passing the digitized data. through a. D/A converter, and then pa3sing the unslog output (the stored interferogram) through a scanning- wave analvzer. The outnut of the wnvo analyzer is a spectrum and is recorded by an X-Y plotter. The program provides for either section of the memory to be transformed and displayed
~ t r o m e t e r s ,nnd p r o d o r e n digitized i n t ~ r l e r o ~ n mT . h e lnttcr i* punrhrd on t n p for p r n r w h g in nn ofi-line mrnputer, or i* p n q d t o thc FTC-300 row rr~emory; ( D ) the 1~I)P-BlK)dnta prorm4nq w i t w n lains the lrl~ir.w n t m l , memory circuitry, r a v e nnnlyrer, nnd the flat-lwd pntcntiomctrir rewnlcr w n l to pmclwe mwcnt i m d spwtrn 011 prrprintnl charts. T h e FTC-ROO sy.;tcm i.; mnrr sophistirntwi nntl nwrrc rtmpler thnn the rnrlier FTC-IIW) system, Imt is nlw n hylrirl system. T h e d i ~ i t i z ~i nl t w f e r ~ g r ~ risn stornl in n ?Ilk-bit. memory. \Vhen ?omplrtc, the diaitirrd intrrfcromnnl ir mnv r r t d b y n I ) :\ ronvcrtcr and the n o r nnnlog signnl is prormwd hy n r a v e
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Figun 29. Polorized n R . r I h ipwtrum of o KC1 0s single crystal m a w - d at mom temperahn,. ~ i t h% beom r ~ ~ t r irNtor r porott.~ Icontiwwr liml ond p.rpsndialor ( b d e n line) to on axis of rrystol symmetry. An FS-720 sp.rtromst.r r o s vmd in ronjunnion with the FS-7RF rstlectwxe oUMhm.nl ond 4.p wire gtid polarize". (Cmlimml m pngr A:3.58)
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Chemical Instrumentation analyzer. As with the FTC-100, both background and sample interferograms can be stored, reduced individually or simultmeously, to produce singlebeam or ratioed spectra. The ratioed spectra. are
accurate t o within &17, when t,he baekground intensity ha? dropped to 3%. Plotting times vary from 8 to G4 min. Prices: due to the modulm nature of the instruments, many combinxt,ions me possible. The FS-720 is $7,550, wit,hout the electronics. For complete s@ms, FS-720 FTC-300 sy&m is $38,550; the FTC-300 FS-MCI syst,emis FS-820 $35,650. The LIL-100is ahout $11,000.
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CODERG
manufactured by CODERG (SociBtE de Conversions des *nergies, Clichy, France) is now marketed by Scientific Instrumentation, Inc. A block diagram of the MIR-2 is given in Figure 31. The Izyout of the o ~ t i c sis shown in Fiewe 32. and addit,ional sample space configurations are shown in Figure 33. The opbics are mounted in two chambers. A conventional Miehelsan interferometer with f :2 entrance aperture is used. The beamsplitter is polyethylene terephthalate, and various thicknesses ranging between 6 and
The MIR-2 far-infrared spectrometer
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Figure 30. RllC Fourier Tronrfoim electronics FTC-300. The fop module of two panels is the FS-300 electronics required for operotion of the interferometers, and produces a digitized interferogram on punch tape. The lower module is the FDP-300 d a t a procesing unit and producer canventionol spectra on preprinted chortr. The lowest panel with the A m t front con b e pulled out; o Rot-bed recorder it housed within.
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Figure 31.
Block diagromof MIR-2 for-infrared spectrometer
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(Continued on page A.960)
Chemical Instrumentation
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Figure
MIR.2 spectrometer
100 r are required for complete coverage of the spectral region. The light source
is a high-pressure water-cooled mercury vapor lamp, and t,he light-source unit can he readily removed so that a laser beam can be used for alignment purposes. The beam is modulated a t 12.5 HE,and a variable iris diaphragm controls the source aperture. The moving mirror is mounted on a high-precision slide bar. Motion is provided by a. stepping motor in steps, or a continuous motion controlled by Moire fringe-referencing is used. The beam emerging from the interferometer is parallel and enters a serond chamber
Figure 33.
Sample orear of MIR-2 rpedrometer
(Continued on pngr A%%?)
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Chemical lnshumentation
Figure
34. Spectra of voter vopom
where, depending on the sampling configuration (Fig. 33), the beam is reshaped. A Golay detector is used. The system can be evacuated to 10-'torr. The instrument covers the range 800-10 em-'. The maximum resolution is 0.1 cm-1 over a 75-cm-1 region in the singlebeam mode, or a 30-cm-' region in the douhle-beam mode. Scanning rates vary. ks shown in Figure 31, the MIR-2 can he used to produce digitized interferogram. These are punohed out on tape, which serves to interface with an off-line comouter. The mare interestine., svstem is the O I W ittrwporafittg a Vxria!. Ii20 i minicmq,utPr w d H T ~ k t m ~ s .;forage ix &play unit. As with the Digilab, Inc., FTS-14 system, the computer of the MIR-2 system totally controls the entire interferometer/ data handling and processing systems. However, the data reduction methods differ. With the FTS-14, the entire interferogrrtm produced by a scan is stored, and additional successive interferogrsms produced by multiple scanning are coherently added until the SIN ratio is acceptable. The entire interferogram is then transformed and the resulting spectrum is plotted out. With the MIR-2 system, computation is continuous. The scan is started and produces a segment of the interferogram. The computer quickly performs a 750-value transform, stores the data, and also displam the rudimentary spectrum on s. screen. This procedure is repetitive, and as the mirror continues to move and the computer continuously computes and adds data to those already ~
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(Continued a page AS64) A362 / Journol of Chemical Education
I n practice, the operator would insert the sample and, after a vacuum was established, would give the computer the required data about (a) single- or doublebeam operation; (b) the spectral range; (e) smallest separation between two points on the spectrum; (d) number of points, being 750 points maximum for doublebeam, or 1500 points maximum for singlebeam; (e) motor steps or motion; (f) appodising function (a choice of ten is available) for the transform. Operation thereafter is automatic. and the instrument
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spectra. recorded by the MIR-2 are shown in Figures 36 and 37. Prices: t,he MIR-2 equipped wit,h electronics and tape readout is $10,600. The data system incorporating the comuuter is $26,250. so that the commterieed
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Figure 37. Reflection spectrum of NoCl recorded with the MIR-2
Figwe 35. Spectrum of water recorded with MIR-2 for-infrared spectrometer; see Figure 34 and text.
stored. an incressinelv . . . refined soectrum nppmrs ,>I.the v i t , a i ~ ~wwm. e. 'l'hi* pro~ t\ w r taw w d t ~ r ei, lllo\~ratwl1.y ~ I ~ e i p ~ oi sIms,u III Fagurc : i l Lhrh trarr war displayed on the viewing screen and photographed. The time in minutes elapsed since the scan was started is shown beside each trace. When the spectrum has reached sn acceptable S/N value, determined by examining the spectrum displayed on the viewing screen, the spectrum is plot,ted out. For example, when the water spectrum had reached the quality indicated by the lowest trace in Figure 34 after a 4Trmin scan period, the plat,ter was activated and the spectrum of Figure 35 resulted.
RESOLUTION
("Fourier Transfo~m Spectrometers" will be concluded in
the nezt issue.) Figure 36. me MIR-2
Spectrum of Nz"OS recorded with
