GPC From PeakSimple Data Acquisition

Transcription

1 GPC From PakSmpl Data Acquston Introducton Th follong s an outln of ho PakSmpl data acquston softar/hardar can b usd to acqur and analyz (n conjuncton th an approprat spradsht) gl prmaton chromatography data. At ths tm, to dffrnt vrson of PakSmpl softar r rqurd for succssful analyss. Vrson 2.08 as usd to collct th data and obtan rsult tabls for narro polymr standard chromatograms, hl vrson 2.09 as usd to obtan th pak slc nformaton for broad unknon polymrs. That s, usng 2.09, th voltag dffrnc btn th dtctor output and th subsquntly dran basln as obtand for ach data pont and savd as an ASCII fl, hch as thn mportd nto Excl for n-dpth GPC analyss. Ultmatly, t ould b prfrrd to us only on vrson of PakSmpl. Hovr, 2.09 (th latst vrson) as not stabl hl acqurng data. Th program ould crash aftr approxmatly 5 mnuts. Furthrmor, th tm dsplay n th uppr rght hand cornr dd not appar to ork and rtnton ndos r not vsbl on th scrn although a componnt fl as actv. Thus, 2.09 as usd only for obtanng slc nformaton th non-actv channls. To llustrat ho PakSmpl can b usd for GPC analyss, I hav ncludd 3 narro polystyrn standard chromatograms (4 standards pr chromatogram) and to broad unknon polymr chromatograms. Chromatograms r obtand usng a Watrs 510 pump (U6K njctor), an thyl actat mobl phas (1 ml/mn), a srs of Ultrastyrogl columns (Watrs 10 6, 10 4 and 500 Å) and Watrs 2410 rfractv ndx dtctor. All polymrs r pr-dssolvd n thyl actat and chromatograms r collctd at 1 Hz. Polystyrn standard concntratons r 0.1 % / or lss (50 µl njcton volum) hl broad unknon polymrs r approxmatly 1 % / (75 µl njcton volum). Also ncludd ar componnt fls, contanng th standard dntts and xpctd rtnton ndos, an vnt fl for ntgraton, and to ASCII data fls contanng slc nformaton for th broad unknon polymrs, and an Excl fl th n-dpth GPC analyss.

2 Obtanng a Calbraton Curv Polydsprs polymrs n soluton ar fractonatd accordng to sz or hydrodynamc volum durng GPC, hch s also knon as sz xcluson chromatography. olcular ght s rlatd to th hydrodynamc volum. In GPC a dlut polymr soluton s njctd nto a solvnt stram hch thn flos through a srs of columns packd th porous gl bads. Smallr molculs pass through and around th bads hl largr molculs ar xcludd from all but th largst pors. Thus fractonaton occurs th th largst molculs lutng frst. Th molcular ght of an lutng polymr molcul vars xponntally th lutng volum, th lattr of hch s proportonal to tm undr constant flo rat condtons. To obtan molcular ght data and convrt th GPC chromatogram nto a molcular ght dstrbuton, th rlaton btn molcular ght and luton tm s obtand from a srs of polymr standards of knon molcular ght. Th calbraton curv s thus obtand from a plot of th logarthm of molcular ght vrsus tm. Gvn that GPC s a comparson of hydrodynamc volums, unknon molcular ght dtrmnatons ll b rlatv to th calbraton standards. For a good ntroductory rfrnc to polymr scnc, s R. J. Young and P. A. Lovll, Introducton to Polymrs. Usng PakSmpl 2.08, th rsult tabl for ach of th thr polystyrn standard chromatograms as copd usng DDE nto Excl. Th natural logarthm of molcular ght vrsus tm as plottd and a bst ft analytcal approxmaton to th curv as obtand from a thrd ordr polynomal, P t ). Ths s th calbraton curv rlatng molcular ght to luton tm. ( Obtanng olcular Wght Avrags Th most common and convnnt ay to charactrz a dstrbuton of molcular ghts makng up a polymr sampl s usng molcular ght avrags such as, numbr avrag molcular ght ( n ), and ght avrag molcular ght ( ), as shon n th follong fgur for a typcal polymr chromatogram. n s dfnd as a sum of products of th molcular ght of ach fracton multpld by ts mol fracton. That s: X n = hr X s th mol fracton of molculs of molcular ght mass. Th ght avrag molar mass s

3 dfnd as a sum of th products of th molcular ght of ach fracton multpld by ts ght fracton,. That s: =. Addtonally, t can b shon that th numbr avrag molcular ght, n trms of ght fracton, s qual to: n = ( ). Th 1 rato n s knon as th polydsprsty or polydsprsty ndx (PDI). Th PDI s oftn usd as a masur of th bradth of th molcular ght dstrbuton. Polymrs that ar monodsprs (.. all chans hav th sam molcular ght) ould hav a PDI of 1. A typcal polydsprs polymr molcular ght dstrbuton shong th approxmat locatons of n and. Usng PakSmpl 2.09, polymrs p and p r ntgratd (usng th GPC vnt fl) and th rsults savd n ASCII fls. Th ASCII fls r mportd nto Excl and th corrspondng sampl tms r addd as a thrd column of data startng at tm qual to zro. Only slc and tm data corrspondng to th major pak of ntrst r rtand (columns A,B and J,K rspctvly). For ach tm slc, a corrspondng molcular ght,, as calculatd usng th analytcal quaton fttd to th calbraton curv (columns C and L, rspctvly). Not that xtrapolaton of a f mnuts outsd of th last standard (W = 1,000,000) s usually not a problm. Furthrmor, th rfractv ndx rspons of th dtctor s proportonal to th ght concntraton of lutng polymr, ndpndnt of molcular ght. Thus, th ght fracton,, of polymr n any slc s qual to th dtctor voltag rspons or hght (basln subtractd) dvdd by th sum of dtctor voltag rsponss for ach polymr

4 luton slc (.. = hght hght, columns D and rspctvly). as obtand by multplyng and and summng th approprat columns (s bottom of columns E and N) 1 n as obtand by dvdng ach by and summng th approprat columns (s bottom of columns F and O). Thus, th molcular ght avrags for th to polymrs r obtand and ar summarzd n th follong tabl. Polymr olcular Wght Avrags P P , ,000 69,500 99,300 n PDI Obtanng Normalzd olcular Wght Dstrbutons As mntond th polydsprsty ndx (PDI) s oftn usd as a masur of th bradth of th molar mass dstrbuton. Hovr t s a oftn a poor substtut hn compard to a graphcal rprsntaton of th complt molcular ght dstrbuton curv, spcally hn comparng polymr dstrbutons. To a frst approxmaton, th ra chromatogram (a graph of dtctor rspons, f ( t ), vrsus luton tm, t ) s a graphcal rprsntaton of th dstrbuton. Hovr, th chromatogram hght s njcton concntraton dpndnt, makng comparsons dffcult, and t s oftn non-lnar th ln( ), as vdncd by a thrd ordr calbraton curv. A normalzd molcular ght dstrbuton functon s gvn by ( ) = d d ln( ). Convrson of f ( t ) vrsus t to a normalzd molcular ght dstrbuton plot (.. ( ) vrsus or ln( ) ), s obtand by consdrng that th ght fracton, d, of polymr hch luts btn t and t + dt s gvn by: d = f ( t )dt f ( t )dt 0 hr th ntgral n th dnomnator s smply th ara undr th chromatogram. Thus, an analytcal approxmaton of d at th th slc s, th ght fracton of polymr

5 A normalzd analytcal approxmaton to th dstrbuton functon, ), s thus obtand from: ( ) = d ln( ). Gvn that dcrass as t ncrass, th sam ght fracton, d, of polymr that xsts btn t to t ( + dt also xsts btn ln( ) d ln( ). d ln( ) as obtand by valuatng th frst drvatv of th analytcal quaton fttd to th calbraton curv, d P( t ) dt and multplyng by th tm ntrval (.. th 1 Hz samplng frquncy ~ d t ). 2 ) 1 2 ( ( )) as valuatd pont by pont (columns H and Q) and plottd aganst molcular ght to gv a normalzd dstrbuton that s njcton concntraton and calbraton curv ndpndnt, as sn n th Excl fl.