Rapid Scanning Spectroscopy: Prelude to a New Era in Analytical Spectroscopy Robert E. Santini, M i c h a e l J. Milano, and Harry L. Pardue Department of Chemistry Purdue University Lafayette lnd 47907
FuturP d e i ~ e l o p m t ~ r iin ts ra P id qca ntiing s p e c tros cop? uill d(1pPnd h m c i l j upon recent a d c a n c e s En analog a n d d i,r:L t a 1 P 1e c tro n ics c o nip u t er t c c h t z o 1og?,, a I! d o p t o - e 1e c tronic st.jterns. Atnorig t h e s e o p t o - c k o t r o n i c s_t s l e m s arc inl:ludc,d the. itidicon t u b e . solid htate crrra\ tic>tector, acousto-optic filter, a n d elt3ctrcculli controlled refru c' t i n g 1f.mcJrits (1
e n z y m e -substrate cornplese> ( 1 j , mixed complexes in ligand-exctiange reactions ( 2 1 .a n d products of'electrcichemical CY) or t'lash photo1 experiments. A n entire issu was devoted t o t h e i na t r u n t e nt a t ion. in clutiing a comprehensi\e review of instrumental developments and ap1)lications reported prior t o 1968 (61. One ot t h e most striking feature+ ul t h e literature on this topic is t h a t i t involves a series of specialized instrutenis applied t o equally speirohlem>. 'l'heie have been virtually no example> in which RSS i t i B t ru men t a t ion has he en use ti 1'1ir such routine applicationb a > multielemerit analyses or ior developmerit a1 n o r k o n arialytical procedurez or even rrital studies of s l o ~re:^ terns at eqiiilit~riuni.I t 1 proliable t h a t nicist of t h e c o n ~ r n i i t i methods involving ariali,ticcal spectroscopy c a n profit from time -res o l \ - ~ tspectra l generated with a minim i r m of effort. '['here i h signif'ic.ant overlap iiet\vet.n t h e pertorrnance re. quirerrirrits of t h e convcritional re-
A
Dispersed Dispersing element
Source
I
Sample
x Spectrum
Detector Read out
Cell
I
Slit
0
Sample Source Cell
Figure 1.
TWO basic
A Scanr ed spectrum
B
Dispersing element
Dispersed
A~~~~
Spectrum
Retector
i
Read out
approaches to dispersion s c a n n i r i y s p e c t r o m e t e r s array
$atector
ANALYTICAL CHEMISTHY
VOL
45
NO
11
'3tPTFMBEtI 1973
915 A
log a n d digital electronics. computer technology. a n d optci-electronic terns. Among these opto-electronic systems are included t h e vidicon tube. solid state array detector. acousto-optic filter ( 7 ) .a n d electrically controlled refracting elements. However, t h e reader should not lose sight of t h e fact t h a t most of t h e hasic concepts will have h a d their birth in t h e KSS studies spanning t h e last two decades. \\-e have tu.o major goals in preparing this report. One of these velop a perspective o f t h e tiif general approaches ivhich have been dei-elol)ed for KSS a n d t o present representative examples of each of' these approache>.T h e other is t o project de\-elopmentr [vhich can be expected i n t h e near future as well as 1on g-r a n ge d eve 1op tn e n t s which w i 1I lie necessary t o achieve near optimal performmice. Space requirements have forcrtl us t o pay maximum a t tc9ntion t o thost>examples Ivhich are judged t o have been most usef'ul in t h e recent past or u h i c h show maxim u m I)rclmise tor t h e t'uture. Neverthelehs. some designs u h i c h are viewed t o be impractical in their present forms are given brief coverage with t h e prospect t h a t they may whet t h e appetite of one or more readers who m a y appl\- new or different technologies which could velopment of viable .
I I E I E L O Y I ~ LI HIGH SPEED
-_
LIOLII) CHROMATOGRAPHY
cations Ivhich we have chosen
1 cli.spcJr.i,cin a n d n7uitipics spectrometers. Xlost common instruments employ the dihpersion mode in which a prism ur grating separateh t h e spectrum ir.to narrow Iiands of' energy (resolution e l e m e n t s ~which caii be monitored independently. Spectrometeri; operating in t h e multi plex mode [Fourier 1 8 )a n d H a d a m ard 1911 utilize a sinxle detector t o monitor the total hearn Lvhich is modulated in a mariner i o t h a t t h e intensity for each resolution element caii be extracted trom t h e com1)osiit signal hy u>e of mathematical methods. E a c h of these major categories can be hubdivided i n t o at iealt two signifi ca n t 1y d i ff'ere n 1 huh g rou 1) s . F i y r e 1 represents t h e t\vo hubgrou~isof'the dispersion met h i i d . In one apprciach (Figure AI. the disperser1 hpectrutn n i,xit slit antl onto a single tletectoi~.t hc inslantaneou.. renponse ( i f whic.11 is tlcpcndent ul)cin t h e intensity of' :: hc, band of energy tieing passed h y t h e s l i t . I n th'e other approach (Figure IH I . t h e tiihperseti spectrum f'alls on a n arra? tlrtector. antl t h e array is interrogated electronically to generat e spectral infcirmation. These t,,vci apprciaches are labeled the .\cnr2nc>dspvctriin7 and arm>' d c t c c t o r n-iethods. Figure 2 presents hirnplii'ietl rc>l)resentations of t h e t w o multiplex m e t h ods. Figure 2.4 ri!pre>enth a Fourier transform spectrometer ( I T Si 1 8 ) . T h e primary b e a m i h split into two secondary beam-. which df'ter t i ~ i t i g reflected from a pair of mirrors are
G e n e r a l Considerations
Yl ( 1st scan 11i n g s pe c t rom e t ers can be grouped under one of ttl-vci major
Source
__ d , -
Mirror
// 1
Split beams
Consider Waters' library of liquid c t i rorn at ograph y information your remurce for s,olving separations problems. We'ke got factual, concise, and helpful monographs on a wide variety of topics. They are yours for the a'jking. Send foi- our complete Applications Index today ( I f your separa-tions problem is more pressing, give us a call and w e ' l l d o our best t o help you.)
61 Fountain Street, Framingham, Mass.
CIRCLE 241 ON READER SERVICE CARD
A N A L Y T I C A L CHEMISTRY, VOL
/
Sample
Source
Computer
Detector
II Mirror 2
\
Dispersion
~
Sample
\
1
,
'
Dispersing element Recom bination
Mask
-
4
\
\ Corner mirrors
/
Detector Figure 2. Two basic a p p r o a c h e s to multiplex scanning spectrometers
7 A Fourler B Hadamard 916 A
Recombined beams
dp
t
Computer
WATERS ASSOCIATES
Beam splitter
45
NO
11
SEPTEMBER 1973
i
The 1L 433 does the work of two ordinary h 4 spectrophotometers --It analyzes two elements simultaneously. Reads out both concentrations at once. Thislatest addition to IL’s line of AA instruments can actuall) cut your analysis time in half. Lihe all our PIA units, the IL 453 Atomic Absorption/Emission Spectrophotometer is a doublebeam system, with an 0.33 m Ebert grating monochromator in one channel. Unlike the others, the 453 has another monochromator (0.16 m) in the second channel. \-hen aspirating a sample, the absorption or emission of two preselected elements is anal) zed simultaneously, and the concentration of each is disp1a)ed on a separate digital readout. For extreme]) precise measurement, the second element can be used as an internal standard. Physical variables such as viscosity or nebulization rate are compensated for and precision improved by a factor of 2 or 3. Accuracj ? The 453 is the only i2h with true doublebeam background correction at your working wavelength. Safety? Gas supply failure or flashbacks are safely handled by IL’s field-tested automatic control system. b-rite for literature.
U
h InstrumentationlaboratoryInc. 113 HartwellAvenue/Lexmgtm, Massachusetts 02173 CIRCLE 117 ON READER SERVICE CARD
L/C buyer’s tip: Don’t pay $5,000 for the cabinet A Model 1440 high pressure liquid chromatograph can give you separations and operating convenience identical to practically any $9,000 fancy cabinet competitor ISCO constant flow 2,000 psi gradient or metering pumps have absolutely pulseless vibrattonfree single stroke piston construction. You don’t have to settle for a gas pressure system (with you supplying the gas), or septum injection The 6 port sample injection vahe permits rapid and reproducible sample introduction Stainless steel columns have nonclogging supports and fittings with no dead volume or mixing Thedual beam, high sensitivity UV photometer has eight absorbance ranges from 0 01A to 2 OA full scale, and ins t a n t wavelength selection of 254nm or 280nm The whole chromatograph as pictured-pump, column (unpacked) photometer,lOcm recorder, and sample inject ion valve, costs under $4,200 Many additional features and options are available, all described in our current catalog. Send for your copy now
BOX 5347
LINCOLN, NEBRASKA 68505
CIRCLE 1 1 8 ON READER SERVICE CARD
CIRCLE 34 ON READER SERVICE CARD
918 A
ANALYTICAL CHEMISTRY, VOL. 45, NO. 11, SEPTEMBER 1973
recombined a n d monitored by a single detector. One mirror is stationary, whereas the other (Mirror 2) moves. T h e differences in t h e distances traveled by t h e two beams, d z - d l , determines whether constructive or destructive interference occurs at each of the different wavelengths contained in the incident beam. In the simplest case, Mirror 2 is moved a t a constant velocity, a n d the interference pattern which is generated by the detector can be transformed mathematically t o yield intensity vs. wavelength information, which is the desired result of a scanning experiment. Figure 2B represents a Hadamard transform spectrometer (HTS) (9). T h e energy from the source is dispersed so t h a t each resolution element can be passed through a set of multislit masks consisting of transparent and opaque slots. T h e beam is then recombined (“de-dispersed”) so t h a t t h e total intensity passing the masks for a number of different mask patterns is measured. Measurement of R different intensities passing R different mask patterns provides sufficient information t o resolve R different resolution elements. T h e conceptual representations in Figures 1 and 2 can be used t o compare some of t h e merits of the different approaches. One important parameter is t h e average time each resolution element is monitored by its detector. It is assumed t h a t each device produces a spectrum resolved into R resolution elements in a scan period t. In situations involving scanned spectrum devices and nonintegrating array detectors, the average time each resolution element is monitored is t / R In situations involving integrating array detectors or either of t h e multiplex methods, each resolution element is monitored for t h e total time t. By assuming Poisson statistics, t h e signal S for a resolution element is proportional to the observation time; t h e random noise signal N is proportional to t h e square root of t h e observation time (10). I t follows t h a t t h e signal-to-noise ratios, SIN, for t h e two situations described above are proportional to ( t / R ) l and t1 *, respectively. Thus, for a given detector in which t h e noise is independent of t h e signal level, t h e multiplex and integrating array detector approaches have a n advantage in SIN proportional to the square root of the n u m ber of resolution elements. This improvement in SIN is obtained a t t h e expense of time resolution. In other words a n observation made on a transient species a t a particular resolution element would be averaged over only t / R time units by any of the nonintegrating devices b u t would be spread
Gmves conple:e ce:ails and s p e c i f i c a t i o r s on nLndreds of k i g h p e r f o r m a n c e , b u d g et - c c n s c i o I;s i n s t rsJ m e -1:s ‘or research a n d industrial aop1ica:ions. Here are pist a few exainp!es NEW H i g h p e r f o r m a n c e strip c h a r t r e c o r d e r . . su:it:hselectec n p l t r a r g e s from 10 mV to 10 V full scale 10 chart speeds . a c c u r a c y w,:Clin l o % comolete remote ccn:rcl capability .switchaole input f , l t e r i i g . . e a s y paaer l c a d i n g aisposable nylon-:ip p e n Only 5365. NEW 110 M H z f r e q u e n c y c o u n t e r ..5Hz - 110 M l i z g u a r a n t e e d , 2 Hz - 130 M H z t y p r c a l . 15 mV m p u t sersitiv,’y guarar:eed 3-10 mV t y p 8 c a l . . i r p ~ senijit c c n t r o l . au:oranging w l h ‘our automa;icaily s e anges. 1 h l H z time base w/l part in lO5/r70 7 - d i g i t LED reacout 5325%. D u a l t r a c e o s c i l l o s c o p e . D C - I 5 MHz bandwidth \VI 24 -set risetime . 50 r r V i c m sensitivity . 200 nsmx tc 0.5 s e c i c m sweep rates. triggered sweep . X - Y caxbility $595*. , ,
For your free copy, mail coupon or use reader service number.
-- ----- -------I Heath/Schlbmberger Scientific Instruments Dept. 531-018 I Benton Harbor, Michigan 49022
1
1 Naie I TjtIE I Co T pa iy i 1 i s t t J!, c i I Address I C1ty -State I ‘Mail order price:;:
I
I I I
i
L-------
CIRCLE 116 ON READER SERVICE CARD
ZIP-
I I I I I I
_ _ _ _ _ _ _ _ _ _ _ _ _ _ -I FOB factory.
EK.325
A N A L Y T I C A L CHEMISTRY, VOL. 45, NO. 1 1 . SEPTEMBER 1973
919 A
over t time units b\ a n y i i t thr inte' grating instrument > , A b implemented t o d a t e . both 01 t h e multiplex method> and t h e more common hcanncd xpectrum methods involve mcchanic;il devices. This f'actor may limit t h e fa3teb.t which can be ohtained t j approaches. T h e mechanical tolerances on t h e mii\-ing mirror impoze se\.ere limitations o n t h e FTS method at wavelengths helow t h e near infrared region ( h ) ,l h e I T S met hod utilizes a high transmission. large aperture optical system Ivhich is particularly advantageous when dealing with low light-level measurements:. Finally. although all o f t h e approaches can henefit from computerization. t h e multiplex methods are i m p r a c t ic al without some co m p u t in g equipment t i l pert'orm t h e m a t h e m a t ical transf'ormatioris. These generalizations are useful i n estahlishinp a n overl-ien of t h e s e w r ai approaches. However. they do not emphasize characterixtics tvhich tlepend upon t h e comp(.inent; us optimize performance in t h e 3 spectral r lgioiis. These characteristics are discus3ed in more detail in t h r next section. 1
Rapid S c a n Instrumentation
Although rnost of t h e early IiSS instrumentation involved i>hi)tographic techniques. recent emphazis has shifted t !i 1I hi I t i)ele c t r ic trans ti 11 ce r\ ( 6'). a n d I he rc rnsinder oi't hi3 report i l restricted t o these device>..Tat)le I ziinimnrizrs performance characteristic> t r f a ti.ide range of rapid scan d e \-ice> which 1iiiL.e lieen reported recently. Selectee! cxarnples are d i a d i n some detail i n this zection. ugh Fourier a n d Haciamarti methods are included in t h e table for comparison purpo>es. these system3 are not rliscuhsed further in this report aince they were t h e topics of recent papers in this beri Scanned Spectrum chanicai Zk,\i,gm. A riumher (if K de>igns have been t,axeti upon mechanically scanned nionochromator~, The most ividely used tlesigr inccirporated a series 111'2-4corner mirrors mounted on a rotating d r u m to w a n t h e spectrum across the exit slit i 1 I I . T h e device achieves hitch scan rates u.ith ION d r u m velocity but requires exact matching ot t h e corner mirrors tor high ;)hcltometric accuracy. Am other device employ. a vihratirig mir]'or t o scar: the spectrum I : ~ I T . h e :in-
gular velocity ( i f the vibrating mirror i- cmtrolled by the frequency of a trian,gular Lvave which provides drive current. A beam splitter di\-ide>the energy from t h e exit slit into a s a m ple a n d reference beam. a n d logarithmic amplifiera generate a n output linear in absorbance. 'This instrument >cans t h e region ~ r o m'Ki)t o 700 nm ( o r any portion thereof) ivith scan rates between i~.01-10005ca T h e zero absorhI .
hetween :I80and 650 n m , a n d t h e a b sorbance range is 0.02-2.0 with spectral resolution o f 2 nm a t 1000 scans/ hec. T h e instrument was used t o s t u cl y t h e electrochemical rect u c t ion of'methyl vidigen at a n optically transparent electrode. T h e absorption spectrum ot'the free at dif'i'erent electroll presented in Figure 5 of the reference, Although t h e scan rate is relatively s l o ~ vhy RSS standards ( 2 Hzi. it would have been necessary t o have repeated t h e experiment many times with a single wavelength being monitored for each experiment to have ohtained these same d a t a with conventional instrumentation. I he next three examples are interesting in t h a t electrically tunable opr
7
Table I. Performance Characteristics of Rapid Scan Spectrometers Spectral range, nm Device classification
Overall"
Scan
Scan the, msec
Resolution, nm
Uncertainty, %T
Dynamic range
Integrating
Comments*
Ref.
Dispersion Methods SCANNED SPECTRUM Mechanical Rotating drum Vibrating mirror Electronic Electro-optic Fabray-Perot Flying spot Acousto-optic ARRAY DETECTORS Electron beam Image dissector Orthicon Vidicon Solid state Silicon diode Charge coupled Intensified devices Vidicon Silicon diode
Hadamard Fourier
250-1 4,500 220-700
220 370
1 1
N.A.C 2
1.3 1
30 102
No No
1,s
11 3, 29
400-2700
13 3 100 150
0.005 0.3 0.2 1
0.3 0.15
N.A. N.A.
2
No No No No
2
N.A. 0.2
N.A. N.A. N.A. N.A.
12 13 14 7, 15
400 300 400
0.1
1.5
17
1.2 0.1
N.A. N.A. 0.2
103
400-700 300-1 100
104
No Yes Yes
400-1 100 300-1 100
600 800
12 N.A.
N.A. N.A.
50,103 103
Yes Yes
3
350-800 300-800
100 500
N.A. N.A.
N.A. N.A.
Yes Yes
... ...
27
VIS-IR 300-30,000
13,000
N.A. N.A.
N.A. N.A.
Yes Yes
4 4
8
uv-VIS 300-700 550-700
330-1 000
N.A.
4 2.5
1
60 N.A. N.A. 13 Multiplex Methods
lo3 103
2.5cm-' 20crn-'
N.A.
10
...
...
... 3
... 5
20 19
...
21, 22, 23
...
16, 26 18
28
9
a Overall range represents the total spectral range which can be covered by the instrument, whereas scan range represents the range covered in
the scan time quoted in the next column. Comments: 1, Several different defectors are required to cover the spectral range. 2. An existing optical system can be adapted to this mode of operation. 3. Application of this device in a practical spectrometer has not yet been reported. 4. A computer is required to transform the data into a useful spectrum. 5. Dynamic range estimated as the signal-to-noise ratio. N . A . , not available.
920 A
ANALYTICAL CHEMISTRY, VOL. 4 5 , NO
1 1 . SEPTEMBER 1973
phor t o correspond t o a Iieiim 01 energy ot'det'ined wavelength tlJcu3ed on t h e exit slit, Different phosphor* were used to cover the range f'rom :jOO t o 660 n m tvith repetition rates u p t o 10 kHz a n d a photometric error ot' 1-27; T.T h e obviou+ lirnit'ition> l i t 1 hi'tern are t h e Imv intcnsit! o[ r h c source and the limi!etl -pectral riiiiges of available phosphor-. .4 cou.itci-optic~FiItw I n r e w n t r p ports it tvas demon+rrated t!iut t h e w a w 1en gt h i or maxim urn t rank ni is sion o t certain tiic,hroic materia!+ such a- LiNhOs. sapphire. anti q u a r ? I iz dependent upon the frequency i i i I' standing acoustic \r-ave tvhich is ailplied t o the crystal ! 7,1 . i ) . Frir exampie. the transmission peak ( i t l,iXi)03 c a n tie varied between 400 anti 700 n m hy sLveeping the acoust ic trequenCJ- trom 990 to 428 AIHz. T h e peak transmih>ion ef'tic.iency is a h i u ? 20% \\it11 a n optical ljandjiass (11 0 . 2 nrn. I his tie\.ice reprekeiitb another example of an electrically cwiitroileti highs pe eti rno II(ic hr ( 1m i i t ( 1i' :\ 1t ti 11i!11 n ( ) practical instrument Iiased oii t h i s tiel ice ha:, been reported. thc, I)otenrial t o r rurther tievelopmeti: i - t.t.ident Array Detector Devices. T h e overall concept of a n array detecror spectrometer is presei1tt.c Since the detector i.7 the characteribt ic.3 oi xtrument. it is clesira types of array t1etecti)rs h e tliwu-hed in some detail. .4rra? L)c>tt>ctiir('iinrtrc t i Figure ;iX present3 ii ccinceI)tuni re[)rebentation ot a n array dett,ctor which can he vieLveti a + a collcction ( i t tlikCrete sensor:: arranged either i n a (inedimenhional I linrar 1 array i i i r~ ilet ec-
Interrogation Pulses
//
\
Seauencer
... s1 s2
S"
__
Figure 3. Simplified representation
of array detectors
()
A Mbltie emen* array detector B Equivalent circuit for integrating array detector C i n t e r r o g a t i o i format for vidicon tuDe D interrogation format for ole-dimensional diode array E interrogation format for two-dimensional charge coupled oevice
tical elements augment t h e conventional nionochromator. f*.'/cjctrri-cipticMatPriais. Lf-hen an electric tield is properly applied t o a n electrci-optic material huch a s 1 , i N l i O ~ t. h e p a t h of radiant energy passeti by the material is shifted by a n amount proportional t o t h e a p plied field. This property c a n he used t o -can a dispersed spectrum across I 121.'I'>-liical results reported involved a 13-nm scan in the visible region in 3 psec a n d a :30O-nm scan ( a t 2.7 pni I in 8 mhec. with 8-mbec repetition rate. Inhufficient d a t a were preqentecl t o permit a n evaluation o f t h e photometric accuracy of t h e device. ['rincipal advantage3 of t h e device include taster scan rates t h a n for mec h ii n i c '1 1 ii n alo gs . applicability a t longer Lvavelengths t h a n other no n m e c h a ni c a1 device s . a n d e le c t ron ic control of scan variables (such as range. speed. a n d repetition ratel. Limit at ions include t h e relatively hiirh-voltage drop across t h e element anti t h e low transmission of t h e crystals. E.'nhr~,-E-'crot Etnion. A recent example of a very high-speed RSS device utilizes a Fabry-Perot interf'erometer i 1 ; ) ) . .A piezoelectric element modulates t h e spacing between t h e interferometer plates. a n d a conventional photomultiplier is used a s t h e detector element. T h e primary a d vantage> o f t h e device are its high
922 A
ANALYTICAL CHEMISTRY, V O L
resolution anti scan speed. a n d its major limitation is t h e narrow range covered by each scan. T h e performance characteristics of any particular device depend upon the optical system in lvhich it is installed. Fi? ins?S p o t S o u r c c ~ .In another instrument. a n electron beam generates a moving light source on a phosphor T h e optical arrangement screen I 14). must permit each spot on t h e phos-
100
Is
I
I
50-
0
I 450
I I 510 47 5 Wavelength (nm)
Figure 4 . Rapid scan spectrum of holmium oxide glass 45. N O
1
I
11
SEPTEMBER 1973
Scan time
I 550
4 msec
tors or in a tn.o-dimensional array of rn x n detectors. T y p i c , d values of rn a n d n range u p t o 500 with u p t o 2-51).OOOdetector elements arranged on 1-mil centers. T h e silicon target vidicon. silicon diode array. a n d charge coupled device ( C C DI represent t h e most promising array detectors for t h e near fut u v . Figure :iB represents a simplif i e d equivalent circuit of t h e active suri'ace for these detectmors. E a c h detertiir element is represented a s a series ccimhination of a capacitor a n d a photosensitive resi5,tor. At t h e beginning of an ohservation cycle ( e n d of thv previous cycle). a n interrogation 1)ul.e cherges t h e capacitor t o a predetermined voltage level. \\-hen t h e pulbe is removed. t h e capacitor discharges at a rate determined hy t h e series resistance. w:hich decreases with increasing light intensity. T h e next interrogation pulse restores t h e charge lost trom t h e capacitor. a n d a n amiilifier responds t o t h e charging current. I\ hich is proportional t o t h e integrated light intensicy hetween interrogation p u k e s . :Sincij t h e response mechanisms are t hanie t o r these three detectors. dittereiices in characteristic< will d e p e n d uiioii t h e manner in which t h e (let ector elements are interrogated. _1 he . ,ampling modes tor t h e three detectors are represented in Figures :;C E tor +imulated detectors in \vhic,h in anti I? are hoth equal to .i. l ' h e vidicon I Figure :iC I r?mploys an e I t c t r i11 i hea m \v h i c h c a n he de i'lect ed rapidly anti in almost an!; dpsiretl pat t e r n t o supply chargirig current t o any element on t h e t w o - c imensional ?. arr:i!-, I he one-dimensioiial diode ;irra? einiiliiy> solid stare styitches nI-~ic,ha r e turned on one' a t a time t o sujilily charging curren't t o t h e diodes. T h e ('($1) I Figure :E I i:, designed so th;it charge packet> are shifted serially thri)ugh t h e storage a w a s of t h e ral tiett,ctor elements i n a pattern permits each t o be sampled hy tht- ami)lit'ier. Both t h e diode arrays anti the CCII's utilize s q u e n t i a l a d dr(,s,Giii< t h a t every element must lie interriigated during c?ach cycle. l e a d i n g ti, a m a x i m u m irepetition rate eq la1 t o t h e >ampling fremquency ( u s u all\. 1 10 1 1 H z i divided by t h e n u m t drtt3ct:ir element,. t 128 t o 2.5 x h i d
Sc~ver:iIt actors will comhine t o determinc, \\ hich tle\ices a r tu1 tor genera-liurpose R ni c, tit at 11)n . Fact ors such , a n d .ervice 1:t'etime 5%-ill tii\or t h e .cilitl s t a t e d e ~ i c e sOther . !uc,tiirs Guch a s \-ersatility. resolution. an:l cju;intitative reliability merit a d ditional rliscuasion in t t r i n s of lvhat i a de:>iredof' KSS i n s t r u m ~ ~ i i t a t i o n . .I'he a r r a \ detector device!: ot'fer t h e
1
I
I
I
100-
-
cu c y DTA*-
\ m c
e s n
Mixed complex1 30-
prorct
Q
10-
I
I
I
500
550
620
I 700
Wavelength (nrn)
Figure 5. Time-resolved spectrum of CuCyDTA-ethylene diamine reaction Scan time. 20 msec, repetition rate, 2 sec
potential ot pert'orming in ii single many measurement oprrations requiring ,s;rveral s t e l l s kiy use of conventional recording si)ectrol,hotome-ter-. Some of these measurements include enbemble averaging. dark current and 100% 7'settingb. multichannel operation. anti rapid repetitive m ( ini t or i n g I I t P 1t'c t e ti \vav el e n gt hi. Fizure :K illustrate> holr these i i ! ~ ticins can lie accomplished. I n this example. three rlrtecior elements arv sariipletl at each ixiint along t h e \valelength a s k . T h t o r i could he e s p i i s r c t h e s a m e h e a m . in hich caqe t h e a v eragr ol'the three iletcctor resp(inse> ci~ultll i e conip:itid. or they could t i e e x p o s d t o three rlitterent bample beama. Furthermore. each area in thi- f'igure coulti represent many detecror element- i t 1 a real system t o yield avc.mgc's ot t lit. three riiff'erent resiiiiiiwy. T h e h r i r i z r i n t ai I \vavelength axis sccin ci i u l ( ! inclurle all reio1uri:ii-r element. or could involve stepni>e inti.rrcigation of'selected eleme n t Clearly. t h e ideal bpectrcimeter n-ould permit electroiiic selection of the motir o! :iper;it ion. anti t h e ideal d ei e c t or \\-ou1d he a t \vi 1- d i r i i e 11si i111a 1 array ptJrmitti n g rantiom access t o all element . T h e vidicon a p prcia this ideal mobt closely. antl t h queiit ially atttlres.ed linear array allp r o a c h e s it leaht c,liisel?. '1'n.o-tiirnensional solid state array. \r.ith more flexible addrrs-ing schemes \vi11 he develciped. hut they n.ill require corr e ~ p o i n d i n g l ymiire complex a d dre + ing circuitry . T h e d i g i t a l nature ot'the addressing scheme in linear diode arrays and steli
y,
ANALYTICAL CHEMISTRY. VOl
CCD's. as opposed t o analog focusing a n d deflection of a n electron beam in a d i c o n . permits more precise control of t h e detector elements being addressed in t h e solid s t a t e devices. Accordingly. it is expected t h a t these cievices Kill hold a n edge in spectral resolution. At t h e present time. twoe.imerisional solid state arrays are not available with numbers of detector elements equivalent t o those of available i.idiconi. Quantitative reliability i i a more difficult parameter t c i e\.aluate u.ithout good experimental ciata. D a t a presented tielow demonstrate a dynamic range of 10" for a silicon target \-idicon t u h e . One mancfacturer of linear diode arrays quotes dynamic ranges 1 saturation signal + d a r k curr e n t ) of 30 a n d 100. depending upon t h e output circuitry ( 1 6 1 A . dynamic range of 1000 has tieen reported from a n independent s t u d y ( ; T i . Insufficient d a t a are available t o drarv any meaningful conclusions concerning t h e CCD: ho\vever. two points are in order. One is t h a t t h e charge transfers are not 100% et'ficient i 181. and t h e other is t h a t t h e charge packets will pick up additional charge from succesbile detector elements if light is permitted t o fall on t h e detector during t h e transfer process. This factor m a y be a prohihitive deterrent t o t h e use of these devices in RSS, Tn-o other types of array detectors Fvhich ha\-e been used ir.1 RSS inatrumentation are t h e image dissector a n d orthicon tubes. Because of t h e I o w S / ~ V-10) ( o f t h e orthicon ( I S ) . it probably will not play a n y significant role in future developments arid will 45.
NO. 1 1 , SEPTEMBER 1973
923 A
the phosphate-free detergent makes cleaning easier in the Lab.
Simply a d d LIQUI-NOX to water . . . Wash a l l glassware, porcelain, plastic, rubber, metal instruments, a n d components i n the s o l u t i o n . . . t h e n rinse. All your critical cleaning p r o b l e m s are solved while you save time a n d money too! 0
For Ultrasonic w a s h e r s . . cleaning. 0
. Manual
B i o d e g r a d a b l e . . . For Biochemical laboratories... For tissue culture w o r k . . B l o o d a n d fat solvent
0
0
.
Dissolves completely i n hot or c o l d w a t e r . . . rinses-clean.. . mild to h a n d s . . . n o residue. 0
PHOSPHATEFREE.
LIQUI-NOX PRICE LIST 1 qt. Container $2.50 Case of 4x1 gal.* 26.00 Case of 1 2 x 1 qt. 22.00 15 gal. D r u m 80.00 1 gal. Container 8.00 55 gal. D r u m 255.00 * C o n t a i n s one i - o z Dispenser p u m p
NOTE: Prices Slightly Higher West of Rockies.
F o r FREE Samples, contact your l o c a l Laboratory S u p p l y Dealer, o r write to:
ALCONOX, INC.
215 Park Avenue South, Ne& York, N.Y. 10003 CIRCLE 9 ON READER SERVICE CARD
924 A
ANALYTICAL CHEMISTRY, V O L . 4 5 . NO. 1 1 . SEPTEMBER 1973
not be discussed further. In a n image dissector tube, electrons emitted trom specific areas of t h e photocathode can be selectively focused on a dynode structure. As such. t h e image dissector c a n be viewed a s a n array of photomultipliers. Three features of t h e image dissector t u b e which could tie attractive in some situations are its nonintegrating response. its high sensitivity !via internal electron multiplication). a n d its use of photoemissive surfaces which could make i t useful in t h e ultraviolet region. Characteristics of KSS instrumentation based upon t h e image dissector a n d vidicon tubes are summarized b e h . I m a g e D i s s e c t o r Ttchr,. \.ersions of the RSS instruments utilizing image dissector tubes have covered the spectral range from 3:10 t o 530 n m a n d from 600 to 1000 n m (201with a resolution of 1.5 n m a t scan rates UI) to 10 kHz ! X i ) .A maximum dynamic range of 1000 was reported. I t was suggested t h a t t h e useful spectral range could be extended t o t h e ultra\-iolet h y using dissector tube:: \vith 5-11or S-20photocathode surfaces. IYdicon Tube. Recent reports have described successtul application- of antimony sulfide 121J a n d silicon target (22, 2'1) tuhes tor KSS. T h e c w mulative characteristics riemonstrated by t h e report> are >urnmarized here. T h e hpectral range between 20!) a n d 1100 n m ia covered. a n d t h e scan range can be varied between 10 a n d 400 n m u i t h >can times ranging between 4 msec atid Zeveral seconds. Each scan produce> information trom u p to 1000 resolution elements. a n d spectral resolution t o about 0.1 n m is possible (2.11.One of t h e instruments utilize> a portion ot' t h e photosensitive surface tcir hackground compensation ( 2 2 1 ai-erage the response of' seL-eral detector elements at each resolution element, In our laboratorv a vidicon instrument was interfaced to a strippeti-tlow mixing system and a small c o m p u t e r . Figure 1 represents a typical -pett r u m of'a holmium oxide g1a-h filter. T h e nonlinear wavelength >vale i h a characteristic of t h e monochromator used. This background corrected spectrum compares favorably with a reference spectrum re p(ir t e tl p a r 1i e r ( 2 1I . .A linear transmittance >y>tem (LTS hlodel 1001 M. 'I'echnometrics. Purdue Research Park. \\.e>t I.aiayette. Ind. 47906) wa- uhed t o evaluate the linearity a n d dynamic range oi' t h e vidicon t u b e . Typical re>\iltq taken at 800 n m a n d at a >can sprc'ti ot msec exhihit standard deviwtion, of 0.2% ?'at 95% 7 ' a n d O.O(J68% T a t 0.01'7r T.respectively. .A lea-tsquares tit of lug response \.>, lcig in
tensity from 9,570 t o 0.01% Tyielded a g a m m a function of 0.998 f 0.005 (response a P . 9 9 8 ) .Linear least-squares fits of response vs. intensity yielded a slope of0.9921 f 0.0022 for four decades (0.01 ~ 9 5 % with a correlation coefficient of 0.99995. Figure 5 shows time-dependent spectral changes which occur when CuCyDTA2 reacts with ethylene diamine ( 2 ) .T h e spectrum of CuCyDTA*-- has a maximum a t 700 n m and does not pass through t,he isosbestic point. I'pon mixing, the absorption maximum shifts from 700 t o 720 n m . T h e gradual decrease i n absorbance a t i20 nm is accompanied by a n increase at -550n m . These observations are explained on the basis of mixed a s represented complex formation (2)% in reactions 1 and 2.
ANAL-
INFRARED
~
+
hC'yDTX'- (-700 n m ) e n --t C'u(ClyD7'A)en'( i n t e r m e d i a t e 720 nni I ( 1 I
+
-+
en ~ u ( e n ) ~ (-550 '+ nm)
('u(('yDTA)m-
Cy DTA-
(2)
'These d a t a demonstrate the value of KSS in following intermediates in relatively slow reactions. Other d a t a demonstrate the utility a t stoppedflow speeds. Spectral changes resultir.g from t h e FelII1)-SCN - reaction (2-1)were recorded in t h e range from 420 t o 600 nm a t scan rates of 4 msec/ scan. Conditions were adjusted t o yirld pseudo first-order kinetics, and a 1)lot o f l n ( A , - A ) vs. time ( a t 460 This apparent first-order rate constant was used to calculate a secondorderrateconstant of'21%M--lsec--l, which is in good agreement with a value 01 214 M - 1 s e c - - Ireported previously (8.3i . -/,incar Ihodc]A r m ) . Applications of a linear diode array to flame emission an(-latomic absorption spectroscopy have heen reported ( % i . At the time o f t his writing. insufficient d a t a are available t o present a detailed discussion o f t he findings; however, t h a t report demonstrated t h a t this detector can be used successl'ully for quantitative spectroscopy. Im q q 6 , I n t ~n .sifiers. ;Claj or 1i m it a tions of the currently available array detectors are their low sensitivity in t h e visible region and virtual absence of useful response in t h e I-.Y. For example. a high-quality photomultiplier tube (RCA 31034) will have a sensitivity in t h e range of 108 pA/lm. Silicon diode devices have sensitivities in the range of lO3 t o 104 ptA/lm. Image intensit'iers can be used to increase the sensitivity a n d spectral range of' any of t h e array detectors. These and other t u b e configurations
faster and less expensive and less ex results than gas chromatography. Three different analyzers, any type of sampling system, a variety of readouts, and several special modifica-
The Wrlks Scientific MlRAN I " system of infrared anaiyzers offers analytical chemists an economical measuring package adaptable to a WJde variety of sampling situations. Wherever infrared absorption can be measured, a MlRAN I instrument provide outstanding results at low ers claim quantitative preciai or suDerior i o researchgrade spectrophotometers. And infrared usually produces better. faster,
ClENTIFIC W L K SSCORPORATION PO
'
6 0 X 449.5 NORWALK
C T 06856.203/a38-45~1
CIRCLE 242 ON READER SERVICE CARD
FOR MOISTURE MEASUREMENT OR SAMPLE PREPARATION
Llodel \ P
276
F 0 R Detroit
I
HARRY W. DlETERT CO.
I
I 9330 Roselawn, Detroit, MI 38204 I Send dpta!is on iornplete Moictiire T e l l e r
Includes two 1" or 2" deep pans, 5'%" dia.. nlus counterweight set, b r u s h a n d I I Name scoop-pan grip I CompanV --.. Price< o n other inodels furnished Yo 278-A takes 1 , 2 ' or 4" deep -----;I; l l td&\ pans 8 dia No 295-A Speed Oven __---___-----II CltY ~
-
I
--
- I
-
~
dries slurries and paste4
I
-~~__..
~ ..~ .
~~
line.
I
~
State
ZIP
I
L-----------------d
CIRCLE 56 ON READER SERVICE CARD
A N A L Y T I C A L CHEMISTRY, VOL
45
NO
11 SEPTEMBER 1973
925 A
ON-THE-SPOT METAL ANALYSIS -IN SECONDS
I
Metascop, a h a n d y - s i z e d m e t a l spectroscope, c a n be used anywhere w i t h i n reach of an electrical outlet for qualitative work a n d s e m i quantitative m e t a l analysis. Determ i n a t i o n s are m a d e in seconds a n d without s a m p l e preparation. It is ideal f o r t h e fast separation of f e r -rous from nonferrous metals or r a p i d identification of alloy steels. Metascop's c o m p a c t size a n d t h e portability of its carryingcase w i t h a b u i l t - i n power u n i t m a k e i t valuable f o r metal service centers, scrap yards, steel m i l l s , foundries, m a c h i n e shops, construction sites a n d refineries. To obtain prices a n d m o r e information, contact Shandon Southern Instruments, Inc., 5 1 5 Broad Street, Sewickley, Pennsylvania 1 5 1 4 3 (Pittsburgh District).
P I T T S B U R G H
L O N D O N
F R A N K F U R T
~~
CIRCLE 2 12 ON READER SERVICE CARD
if only hed hAd A FimonitoK The Thermolyne FlMONlTOR Level Module assures safe operation c laboratory apparatus. Write for free brochure and application manua *FIMONITOR I
6THEHMOLYNE \M Wlfh H\
a trade mar of Fisons Ltc
SYBWOh CORPORATION
2555 Kerper Blvd., Dubuaue, Iowa 52001 CIRCLE 216 ON READER SERVICE CARD
926 A
ANALYTICAL CHEMISTRY, V O L . 45, NO. 11, SEPTEMBER 1973
such as the secondary electron conduction (SEC), silicon intensifier t a r get (SIT),and electron bombardment silicon (EBS) tubes can yield sensitivities from lo4 pA/lm up through values which are competitive with photomultipliers. Combinations of intensifier sections with vidicon tubes (27)and solid state diode arrays (28) have been reported. Although this a p proach is promising, judgment must be reserked until quantitative d a t a are available.
Summary All spectroscopic measurements involve some trade-offs among spectral resolution, photometric accuracy, and measurement time. An ideal spectrometer would include the capability o f varying each of these measurement parameters over a relatively wide range. Conventional recording spectrophotometers which feature mechanical scan mechanisms have tended to emphasize spectral resolution and/or photometric accuracy a t the expense of scan speed. Custom-designed rapid scan instruments have emphasized scan speed a t the expense of other performance parameters. Consequently, each type of instrument is limited t o a particular experimental time scale. Some of'the electronically scanned systems described above offer the user sufficient degrees of freedom to optimize measurement parameters to his problem. For example. available d a t a for the vidicon spectrometer demonstrate t h a t this system is reliable for scan times from a few milliseconds to several minutes. However, neither array detectors nor t h e electronically controlled dispersion elements can match all of the performance parameters of photomultipliers or conventional monochromators. Conversely. array detectors and electronic dispersion elements have received only casual attention as quantitative devices. Currently. the technology of the array detectors is farther advanced than t h a t of'electronic dispersing elements, and we feel t h a t major advances will come most quickly through the use of array detectors. Detailed studies are needed to provide quantitative d a t a from which limitations of available devices can be evaluated. Areas which merit significant attention are sensitivity. dynamic range. spectral response. and addressing schemes. Xlanufacturers must be made aware o f t he limitations of existing devices and the need for versions optimized for scientific measurements. Technology exists now for major advances in instrumentation for measurements in the visible region. Array detector and dispersion elements can
probably be developed to provide comparable performance a t low light levels in other regions of the spect r u m . I t is our responsibility to see t h a t t h e technology is developed and t o apply it t o meaningful problems. In this presentation we have a t tempted t o present both a n overview of t h e total area as well a s a moderately detailed discussion of one type of application of t h e vidicon tube. We anticipate more detailed presentations of specific applications of the several devices in t h e near future.
'New,
sensitive, automatic
Acknowledgment T h e authors are grateful t o J . LV. Amy for helpful discussions during t h e preparation of this manuscript.
References Y.Massey a n d G. H . Gibson. Fed. Proc.. 23. 18 119641 ( 2 ) J D C a r r R A Libbq. a n d D \$ M a r g e r u m . Inorg Chem 6, 1083 (196;) (31 J L$ Strojek, G A Gruker, a n d T Kuwana.Ana!. Chem., 11,481 (19691 14) .J. I. H. Patterson a n d S. P. Perone. ibid.. 41,1978(1972). (51 .4pp!.Opt.. i(1968). (6)G. C. Pimentel. ibid., 2155 (1968). ( 7 ) S.E. H a r r i s a n d R.\V. L$-allace, J . O p t . Soc. A m e r . . 59, 7-14 (1969). (8)>-1. I. D. Low. Anal. Chem., -11 (61, 97A(1969). ( 9 ) J . A . Decker, ,Jr., i b i d . , 11 (21, 127A (1972). (10) P.Fellpett, J . Ph?,s. R a d i u m . 19, 187 (1958). (1)
Silicagel Sintered Plctte Excellent sintered plate' I t i j strong chemically and physically. Th s is easy to handle, much wore USefJ1 than any ones ever known This is really reusable for dozens of time
Espec i al Iy
. .
This IS useful for ideritification of antibiotic agent by msans of bioautography. Furthermore, this is applicable for several kinds o f f m g i by means of a chromatogram. Separation is also good. This can be used withoutc,ires for diffusion o f Silicagel in Fil sub stances. This is also useful in radioautographical operatioris Sintered plate REPLATE.-26 2 6 X 7 6 X 1 5mm 100pca 1 pkg Sintered plate REPLATE-50 5 0 X 2 0 0 X 1. 5 m m 50pcs 1 pkg. Sintered plate PEPLATE-100 1 O O X 2OOX 1. 5mm 5Opcs 1 pkg. Descriptive pamphlet anc sample available. I
YAMATO SCIENTIFIC CO.,lTD. 9, 2-chome, Nihonbashi Honcho, Chuo-ku, Tokyo, Japan Cable Address : "YAMATO" TOKYO Telex : 0222-391 0 YAMATO J Tel. : TOKYO '279)0911
Chemiluminescence Principle. Compact, completely self contained. 0 Atmospheric pressure operation. Analysis by unattended operation. Rapid Response. Model 1200 Ranges 0 - 0.2 p.p.m., 0 - 0.5 p.p.m. 0 - 1.0 p,p.m., 0 - 2.0 p.p.m. Model 1400 0 - 100 p,p.m., 0 - 200 p.p.m. 0 - 500 p.p.m., 0 - 1000 p.p.m. 0
(11) H. .J. B a b r o v a n d R.S.Tourin. A p p l . O p t . . 7. 2171 119681. i121 E.
(1 (1
Grabowski. ibia (15) S. E. Harris,
..
i 1969) (161 Reticon Corp h l o u n t a i n View. C a l i f
.
( 1 7 ) Electronic Engineering Timen. p 1. >larch 26. 1973. (18)hI.F. Tompsett. LV. .J. B e r t r a m . D. A . Sealer, a n d C.H. Seguin. Electronics, 16-2, 162 119731. (191 S. A . .Johnson. \V. M.Fairbanks. ,Jr,% a n d A . .J. Schawlon. .4pp/.O p t . . 10, 2%9 (19711, (201 D. .J. B a k e r a n d '4.J . Steed. ibid., 2190 (1968). (211) R.E . Santini. SI. .J. M i l a n o . H. L. Pardue. a n d D. \V, M a r g e r u m . .4na!. C'hem.. 11,826 (1972). ( 2 2 ) F. \V. Karasek. R e , s . / D e c e / o p . .23, -17 (197"). (23) P. B u r k e . ibid.,2 4 , 2 4 (1973). ( 2 4 ) M. .J. M i l a n o . R.E.Santini, a n d H. L. Pardue. Anal. C'hem.. in preparation. (25) .J. F . Below. .Jr.. R.E.Connick. a n d C. P.Coppel. J . Amer. C'hem. Soc., 80, 2961 I 1958). (26) G . H o r l i c k a n d E. G . Coddington. Abstract 25. Pittsburgh Conference o n A n a l y t i c a l Chemistry a n d A p p l i e d Spectroscopy. 1978. ( 2 7 ) \V. D. hletz. Science. lis, 1448 119721, ( 2 8 ) E. A . Beaver a n d C. E . I l c I l w a i n ,
Series 1110 Chemiluminescence Principle. Covers full scale ranges from 0 1.0 p.p.m. to 0 - 10,000 p.p.m. (or to 1.O'/O 0 3 concentrations) Series 1100 Ranges 0 - .05 p,p.m. 0 - 1.0 p.p,m. 0 - .10 p,p.m. 0 - 5.0 p p m . 0 - .SI p.p.m. 0 - 10.0 p . p m Stable Calibration Sources.
Series 1000 Ozone Generators provide sustained, highly repeatable stream of ozonized air from 10 p.p.b. to 10 p.p,m. Series 1500 NO-NO2 Calibration Gas Source provides sustained, calibrated stable gas source, Dual NO and Nor wtputs. May be set from 0.2 p,p.m.to 1,000 p.p.m.
Send for brochures.
Rec. Sei. Instrum., 12, 1321 (1971). (29) T. K u w a n a . p r i v a t e communication, Portions of the work reported herein were s u p ported under AFOSR Grant S o . 71-1938
CIRCLE 239
ON READER SERVICE CARD
CIRCLE 154 ON READER SERVICE CARD
A N A L Y T I C A L CHEMISTRY, VOL. 45, NO. 11, SEPTEMBER 1973
927 A
