PLASMA DESORPTION MASS SPECTROMETRY : THE STABILITY OF MOLECULAR IONS
L. SILLY, R. J. COTTER
1989
Le Journal de Physique Colloques
A b s t r a c t -The peak widths and r e l a t i v e i n t e n s i t i e s o f t h e s i n g l y -and m u l t i p l y -c h a r g e d m o l e c u l a r i o n s appearing i n plasma d e s o r p t i o n mass s p e c t r a a r e used as a probe f o r t h e s t a b i l i t y o f m o l e c u l a r ions. Two peptides, lysozyme and l a c t a l b u m i n , which have s i m i l a r m o l e c u l a r weights and t e r t i a r y s t r u c t u r e s , b u t d i f f e r e n t p r i m a r y s t r u c t u r e
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... and i s o e l e c t r i c p o i n t s , were prepared i n s o l u t i o n s o f d i f f e r e n t pH, b e f o r e a d s o r p t i o n t o n i t r o c e l l u l o s e f o i l s . The peak widths o f t h e r e s u l t a n t molecular i o n s i g n a l s were minimized near t h e i r r e s p e c t i v e i s o e l e c t r i c p o i n t s , which i s c o n s i s t e n t w i t h r e p o r t s on t h e s t a b i l i t y o f t h e i r t e r t i a r y s t r u c t u r e s and/or enzymatic a c t i v i t i e s near t h e i s o e l e c t r i c p o i n t . S i m i l a r s t u d i e s were c a r r i e d o u t w i t h t h e a d d i t i o n o f g l u t a t h i o n e , a m a t r i x which has e f f e c t s on PDMS spectra s i m i l a r t o t h a t o f t h e n i t r o c e l l u l o s e surface. 1 -INTRODUCTION During t h e l a s t several years, a number o f new mass s p e c t r a l i o n i z a t i o n techniques have been developed, which employ h i g h l y e n e r g e t i c photon and p a r t i c l e beams. These i n c l u d e : l a s e r d e s o r p t i o n / I / , secondary i o n mass spectrometry 121, f a s t atom bombardment /3/ and plasma d e s o r p t i o n mass spectrometry 141. These techniques a r e o f c o n s i d e r a b l e i n t e r e s t t o biochemists, because ( d e s p i t e t h e h i g h p r i m a r y e n e r g i e s ) t h e y have enabled t h e d e s o r p t i o n o f i n t a c t m o l e c u l a r i o n s o f complex biomolecul es and t h e i r subsequent mass a n a l y s i s by mass spectrometry. I n a d d i t i o n , t h e absence o f s u b s t a n t i a l and i n f o r m a t i v e gas phase f r a g m e n t a t i o n o f molecules above 5000 d a l t o n s suggests t h a t such i o n s a r e formed w i t h unusual s t a b i l i t y and w i t h v e r y 1 i t t l e i n t e r n a l energy. I n t h e p a r t i c l e techniques, p r i m a r y i o n s have been used i n b o t h t h e k i l o v o l t and megavolt region. The l a t t e r were f i r s t employed f o r b i o m o l e c u l a r a n a l y s i s b y Macfarlane and Torgerson 141, who recorded t h e i r mass s p e c t r a u s i n g a t i m e -o f -f l i g h t analyzer. While t h e major coherent i o n s i g n a l f o r l a r g e peptides i s observed as t h e m o l e c u l a r i o n peak, consi-derable f r a g m e n t a t i o n does occur i n t h e a c c e l e r a t i n g and d r i f t r e g i o n s o f t h e t i m e -o f -f l i g h t analyzer, b u t c o n t r i b u t e s p r i m a r i l y t o t h e i n c o h e r e n t b a s e l i n e and t h e peak w i d t h /5-8/, and i s l a r g e l y due t o t h e l o s s o f small p e r i p h e r a l groups /5,9,10/. Article published online by EDP Sciences and available at http://dx.
doi:10.1051/jphyscol:1989207
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