JEWETT REFRIGERATOR - Analytical Chemistry (ACS Publications)

May 29, 2012 - JEWETT REFRIGERATOR. Anal. Chem. , 1982, 54 (2), pp 295A–295A. DOI: 10.1021/ac00239a837. Publication Date: February 1982...
3 downloads 0 Views 1MB Size
(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