(a)
Jewett contemporary styled
LABORATORY REFRIGERATORS & FREEZERS
î ί Mass (arnu)
(b)
î
I Mass (amu) Figure 10. Laser desorption mass spectra of polymers ( 79). (a) poly(benzylmethacrylate), positive; (b) poly(phenylmethacrylate), negative none a t all; frequently only (M + Na) + peaks are observed in t h e positive L D spectra of t h e s e c o m p o u n d s . Positive- a n d negative-ion L D spec t r a have been o b t a i n e d for six cobalamins including t h e cyano, hydroxy, d i methyl methylitaconate, methyl, and p e r e u t e r o m e t h y l derivatives, along with coenzyme B 1 2 . S p e c t r a of t h e hy droxy derivative are shown in Figure 9. Although t h e quasimolecular ions are sufficient t o distinguish between t h e derivatives, t h e r e is valuable infor m a t i o n t o be gained from t h e lower m a s s ranges as well. T h e series of p e a k s in t h e m/z 4 0 0 500 mass range of t h e positive-ion L D spectra corresponds t o fragments where t h e ribosyl p h o s p h a t e a n d t h e a m i d e s on t h e corrin ring have been cleaved. T h e axial ligand t h a t m a k e s each cobalamin u n i q u e is not cleaved if t h a t ligand is small. If t h e axial lig a n d s are large (as for coenzyme B ^ a n d t h e d i m e t h y l m e t h y l i t a c o n a t e de rivative) cleavage of t h e axial ligand j u s t beyond t h e Co—C b o n d occurs, leaving fragments in t h e 400-500 m a s s range similar t o m e t h y l cobalamin. Polymers Although laser pyrolysis m a s s spec t r o m e t r y is a n established t e c h n i q u e for polymer analysis, applications of laser desorption are m o r e recent. L D spectra of a variety of polymeric m a t e rials have shown t h a t fingerprint mass spectra can be o b t a i n e d (19). Poly mers containing only carbon, h y d r o gen, a n d oxygen are characterized by series of C n H m + / , _ peaks in their L D
mass spectra. F o r p o l y m e r s having t h e same b a c k b o n e s t r u c t u r e , d r a m a t i c changes in t h e m a s s s p e c t r a are ob served for different side chains. F o r example, a n a b u n d a n t ion m/z 91 was observed in t h e positive-ion L D m a s s s p e c t r u m of b e n z y l m e t h a c r y l a t e . P h e n y l m e t h a c r y l a t e , on t h e o t h e r h a n d , is characterized b y a n intense p h e n o x i d e anion p e a k (m/z 93) in t h e negative-ion L D m a s s s p e c t r u m . T h e s e are shown in Figure 10. E v e n for these simple polymers, analysis of L D spectra is based m o r e on c o m p a r i son with a s t a n d a r d t h a n on i n t e r p r e t a t i o n of t h e u n k n o w n s p e c t r u m alone. T h i s is also t r u e for m o r e complex polymers, such as S p u r r ' s m e d i u m , E p o n 812, Biomer, a n d A v c o t h a n e . T h e s e m a t e r i a l s all contain more t h a n one m o n o m e r . T h e s t r u c t u r e of Biom er itself is n o t known. I t is s o m e w h a t surprising t h a t useful information could be o b t a i n e d for these samples, b u t even such complex m a t e r i a l s give fingerprint L D m a s s spectra. I n our laboratory, L D s p e c t r a have been ob t a i n e d for a polyamide a n d for polydimethylsiloxane. T h e presence of n i t r o gen in t h e polyamide b a c k b o n e a n d of silicon in t h e siloxane s t r u c t u r e is r e flected b y t h e emission of nitrogena n d silicon-containing ions, respec tively. An interesting feature is seen in t h e negative-ion s p e c t r u m of poly(benzylm e t h a c r y l a t e ) . T h e s p e c t r u m consists of a series of p e a k s c o r r e s p o n d i n g t o Cn~ a n d CnH~, and t h e CnH~ peaks for η = even are nearly as intense as t h e C n ~ peaks, b u t n o t for η = o d d .
LAR 25B
5 Models to choose from 12 t o 5 5 c u . f t . capacity This new line of refrigerators and freezers is completely functional yet attractively con temporary in styling and finish. Exterior fronts are available in a choice of b l u e o r t a n qerine w i t h beige cabinet and illuminated interior. Both have stainless steel adjustable shelves interchangeable w i t h stainless steel drawers (optional extra). Thermal uniformity is maintained by automatic fan disconnect when door is open. The blower-coil cooling system has automatic defrost. The auto matic condensate evaporator eliminates the need for plumbing. Both refrigerators and freezers can be equipped with cylinder locks in door fasteners for safety.
LABORATORY REFRIGERATORS • white enamel interior* • uniform cabinet temperature (2° to 4 ° C) • quick temperature recovery • dual or single air circulation system
LABORATORY FREEZERS • stainless steel interior • uniform cabinet temperature of -18°C(0°F) • quick temperature recovery • dual or single air circulation sysiem All' refrigerator models are available w i t h glass doors. Pass-thru oper ation available for refrig erators and freezers. *Also available with stain less steel interior and ex J E W E T T terior finishes REFRIGERATOR
S L E T C H W O R T H ST. BUFFALD,N.V.14213
The Best of Both Worlds . . . individual Craftsmanship combined with Modern Technology CIRCLE 160 ON READER SERVICE CARD
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2, FEBRUARY 1982 · 295 A
