Problem Set11 Solutions

Problem Set11 Solutions - CHAPTER 2 I PRINCIPLESO F C...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: CHAPTER 2 I PRINCIPLESO F C HROMATOGRAPHY A ND M ASS S PECTROMETRY 2 t-1. 2t-2. 2r-3. Eluenti s t he s olvent r g asg oing i nto a c olumn. E luatei s w hat c omeso ut. o Smallerp lateh eightg ives l essb and s preading:0 .1 m m. b If t he f low r ate i s t oo l ow, b andss pread y l ongitudinald iffusion. I f t he f low r ate t is t oo h igh, b andss pread ecausehe r ateo f m asst ransferb etweent he m obile b p i and s tationary hasess t oo s low t o k eepu p w ith t he r ate a t w hich t he m obile phasei s m oving. I n g eneral, herei s a n i ntermediatelow r ate a t w hich t he b est t f m i t tradeoffb etween heset wo b andb roadening echanismss o btained. 2r-4. (a) G asesd iffuse m uch f astert han l iquids. T hereforeg asesc an s preado ut a long the l engtho f a c olumn m uch f astert han c an l iquids. (b) B ecausel ongitudinald iffusion i s m uch f asteri n g as c hromatography han i n t m liquid c hromatography,he f low r ate i n g as c hromatography ust b e m uch t fastert o p reventb andsf rom b roadeningt oo m uch d uring t heir p assage throught he c olumn. 2t-5. c Silanization apsp olar h ydroxyl g roupsw ith l essp olar g roups. S trongh ydrogen bondingb etweenp olar s olutes nd t he h ydroxyl g roupsl eadst o t ailing. a Eliminatingt his h ydrogenb ondingr educes he t ailing. t 2t-6. g t For q ualitativea nalysis, he m asss pectrometer ivest he m asso f t he m olecular f ion a nd t he m olecularm asses f c haracteristicragmenti ons. F or q uantitative o t d c t analysis, he m asss pectrometer etector urrenti s p roportional o t he q uantityo f analytee luted. 2t-7. s a In s piking,o n a uthentic ampleo f a s uspected nalytei s a ddedt o a n u nknownt o p I seei f t he h eighto f t he c hromatography eak f or t he a nalytei ncreases. f a n ew peaka ppears,he a ddedc ompoundi s n ot i denticalt o t he a nalyte. I f t he a nalyte t peakg rows,t he a ddedc ompoundc ould b e t he s amea s t he a nalyte. I f t he s ame i resulti s o bserved n s everal ifferentc olumnsw ith d ifferentt ypeso f s tationary d phases,t i s l ikely t hat t he a ddeds amplei s i denticalt o t he a nalyte. W e d o n ot i expectt wo d ifferent c ompoundst o b e r etainedt o t he s amee xtento n s everal p t i b differents tationary hases, ecausehe r etentionm echanisms d ifferento n e ach p stationary hase. r 86 CHAPTER 2 I PRINCIPLESO F C HROMATOGRAPHY A ND M ASS S PECTROMETRY 2 t-1. 2t-2. 2r-3. Eluenti s t he s olvent r g asg oing i nto a c olumn. E luatei s w hat c omeso ut. o Smallerp lateh eightg ives l essb and s preading:0 .1 m m. b If t he f low r ate i s t oo l ow, b andss pread y l ongitudinald iffusion. I f t he f low r ate t is t oo h igh, b andss pread ecausehe r ateo f m asst ransferb etweent he m obile b p i and s tationary hasess t oo s low t o k eepu p w ith t he r ate a t w hich t he m obile phasei s m oving. I n g eneral, herei s a n i ntermediatelow r ate a t w hich t he b est t f m i t tradeoffb etween heset wo b andb roadening echanismss o btained. 2r-4. (a) G asesd iffuse m uch f astert han l iquids. T hereforeg asesc an s preado ut a long the l engtho f a c olumn m uch f astert han c an l iquids. (b) B ecausel ongitudinald iffusion i s m uch f asteri n g as c hromatography han i n t m liquid c hromatography,he f low r ate i n g as c hromatography ust b e m uch t fastert o p reventb andsf rom b roadeningt oo m uch d uring t heir p assage throught he c olumn. 2t-5. c Silanization apsp olar h ydroxyl g roupsw ith l essp olar g roups. S trongh ydrogen bondingb etweenp olar s olutes nd t he h ydroxyl g roupsl eadst o t ailing. a Eliminatingt his h ydrogenb ondingr educes he t ailing. t 2t-6. g t For q ualitativea nalysis, he m asss pectrometer ivest he m asso f t he m olecular f ion a nd t he m olecularm asses f c haracteristicragmenti ons. F or q uantitative o t d c t analysis, he m asss pectrometer etector urrenti s p roportional o t he q uantityo f analytee luted. 2t-7. s a In s piking,o n a uthentic ampleo f a s uspected nalytei s a ddedt o a n u nknownt o p I seei f t he h eighto f t he c hromatography eak f or t he a nalytei ncreases. f a n ew peaka ppears,he a ddedc ompoundi s n ot i denticalt o t he a nalyte. I f t he a nalyte t peakg rows,t he a ddedc ompoundc ould b e t he s amea s t he a nalyte. I f t he s ame i resulti s o bserved n s everal ifferentc olumnsw ith d ifferentt ypeso f s tationary d phases,t i s l ikely t hat t he a ddeds amplei s i denticalt o t he a nalyte. W e d o n ot i expectt wo d ifferent c ompoundst o b e r etainedt o t he s amee xtento n s everal p t i b differents tationary hases, ecausehe r etentionm echanisms d ifferento n e ach p stationary hase. r 86 a nd Principles f C hromatography M assS pectrometry o 18 7 2 t-8. (a) W e n eedt o e xpress r a nd w 12in t he s ameu nits,s o t heir u nits w ill c ancel. / Let's c onvert/ r t o s econds: r 'I t/ 5 .5 5 i ( s - -+ - 5 .55769.8)2 : 4 .3sxl oap tates ( 8.7 * r iz s )2 (b) H - ( 158 m m)/(4.3sx 1 04p lates): 3 .6 t rtm 2t-9. (a) w yz:0.8 a m m f or e thyl a cetate nd2.6 m m f or t oluene. (b) t r: | 1 .3 m m f or e thyl a cetate nd36.2m m f or t oluene. T he n umbero f a l theoreticalplatesisN:5.554 l *r?z : l .l x 1 03f orethyl a cetateand.l x 103f or t oluene. ,r_rn Lr-rv' l argeoad : ( lurg..olurn r udirl 2 l r s malll oad \ smallc olumn adius/ 250m g ( turg..otu*n r uditi2 n^g:(@ = l argec olumn r adius : 3 .42c m 6 The l argec olumn s houldb e a pproximately .8 c m d iameterx 2 5 c m l ong. i The v olume f low r ate s houldb e i ncreasedn p roportiont o t he c ross-sectional T herefore he f low r ate f or t he 2 50-mg s amples hould b . ( #:A)'z t (3.4't m\2 c times a s g reata s t he f low r ate f or t he l Z-mg s ample: [ gJs , ", ( 0.8 m L/min) : area( .c r \. 17 m Llmin. 2l-ll. 5.ss _ 5 .55 13.81 in) 2 ( m 4 _ 3 8 x 1o a : ( a) w y2:0.172 m in = , ly' --:'5 P lates * iz Q .l7zmiin)2 x (b) H : p late eight: ( 30.0x 1 03m m)/(3.58 l Oap lates): 0 .838m m h (c) w(measured): 0 . 3 m1 1 in : wlw12( measured)( 0.31 min) / ( 0.172): 1 .81 I 2l-12. : ( a) w lp ( heptane) 0 .126m in; w yz (Ca H+ F ): 0 . 1 l9m in 5 .55 ( m 4 - 5 . 5 5 1 4 . 5 6 in )2 : 7. 41x l 0a p latesor h eptane f ,\:---:^, * t iz Q .126m in)2 : * p m H: p lateheigh t 3 0 . 0 m1 7 . 4 1 1 04 lates: 0 .404 m ly' : 5 .55( 14.77 . min)2 : u ' )) x l0a p latesor C 6HaF2 f g (0.11 ^tF a nd Principles f C hromatography M assS pectrometry o 18 7 2 t-8. (a) W e n eedt o e xpress r a nd w 12in t he s ameu nits,s o t heir u nits w ill c ancel. / Let's c onvert/ r t o s econds: r 'I t/ 5 .5 5 i ( s - -+ - 5 .55769.8)2 : 4 .3sxl oap tates ( 8.7 * r iz s )2 (b) H - ( 158 m m)/(4.3sx 1 04p lates): 3 .6 t rtm 2t-9. (a) w yz:0.8 a m m f or e thyl a cetate nd2.6 m m f or t oluene. (b) t r: | 1 .3 m m f or e thyl a cetate nd36.2m m f or t oluene. T he n umbero f a l theoreticalplatesisN:5.554 l *r?z : l .l x 1 03f orethyl a cetateand.l x 103f or t oluene. ,r_rn Lr-rv' l argeoad : ( lurg..olurn r udirl 2 l r s malll oad \ smallc olumn adius/ 250m g ( turg..otu*n r uditi2 n^g:(@ = l argec olumn r adius : 3 .42c m 6 The l argec olumn s houldb e a pproximately .8 c m d iameterx 2 5 c m l ong. i The v olume f low r ate s houldb e i ncreasedn p roportiont o t he c ross-sectional T herefore he f low r ate f or t he 2 50-mg s amples hould b . ( #:A)'z t (3.4't m\2 c times a s g reata s t he f low r ate f or t he l Z-mg s ample: [ gJs , ", ( 0.8 m L/min) : area( .c r \. 17 m Llmin. 2l-ll. 5.ss _ 5 .55 13.81 in) 2 ( m 4 _ 3 8 x 1o a : ( a) w y2:0.172 m in = , ly' --:'5 P lates * iz Q .l7zmiin)2 x (b) H : p late eight: ( 30.0x 1 03m m)/(3.58 l Oap lates): 0 .838m m h (c) w(measured): 0 . 3 m1 1 in : wlw12( measured)( 0.31 min) / ( 0.172): 1 .81 I 2l-12. : ( a) w lp ( heptane) 0 .126m in; w yz (Ca H+ F ): 0 . 1 l9m in 5 .55 ( m 4 - 5 . 5 5 1 4 . 5 6 in )2 : 7. 41x l 0a p latesor h eptane f ,\:---:^, * t iz Q .126m in)2 : * p m H: p lateheigh t 3 0 . 0 m1 7 . 4 1 1 04 lates: 0 .404 m ly' : 5 .55( 14.77 . min)2 : u ' )) x l0a p latesor C 6HaF2 f g (0.11 ^tF r88 H - p late eight: 3 0.0m / 8 .55x 1 04 lates: 0 .351 m h p m : (b) w ( heptane) 0 .214 in; w ( C6HaF) : 0 .202min m Chapter l 2 : w ^v : * ro.T4+ o . z o 2 ) o . 2 o g m in : resorurion * ")1 1 a Lr'rr' : 1 {hf1e : r .or 2 , a/ L argel oad : ( turg. . oturn r uOiril (,^\ S mallload_ ( @ ' 12 1 .50 m c ,. 2.4 m e ( = r a d iu s : 0 . 5 5 7 c m ( .m l0^ 0;;: = d iameter: l .l I c m ( Lengths u nchangedt 3 2.6c m.) i a (b) S cale olumei n p roportiono m ass f a nalyte v t o : = v olum. ( ## \v,' S mall f low r ate mllmin. 2l-14. ,^l ( o.5ooL): o .o6e L m m c I O.SSZ m/ 2 f . ,^\ L arge low r ate _ ( l"rg. . "lur" r .Oirl _ f t .SO *_) z \ small c olumn r adius/ Puttingi n l argef low r ate: 1 .85m llmin g ivess mallf low r ate: 0 .256 5 0 c m o f c olumn w ith a d iametero f 0 .25 m m h asa v olume o f x P x l ength: zr(0.0125 m)zx 5 0 c m : 0.0245 c m3 : 0.0245 m L. A f low r ateo f 0 .0245 m '-is c coffespondso ( 0.0245 m l/s)(60 s /min) : 1 .47m llmin. t A\ : fl 2 l - 1 5 . ( a ) r " i _ r,ffi!q ) = L.rr 3 473 : , ( ) 0222 \ , . 72m M )r 3 A? \l ^ N4 F :0. l 68a ( b ) t s l : W : 0 . 8 4 7m M (c) Av ^ , l :I[ts i l = Lx - (l s) ( J4? s 42s: 0 ' 1 6 8 a t 04 43t n\, , M ] = : 6 ' 1 6 m M [x] IXf (d) T he o riginal c oncentration f [ X] w as t wice a s g reata s t he d iluted o concentration, o [ X] : 1 2.3m M. s 2l-16. F irst f ind t he r esponse actor f rom t he k nown m ixture: f Ag : , (D 4 .42 : - r J .sz ) : n [ tD, = n 6 t tst^L F lzn r g^t1 = F t 't4:q lq Then f ind t he c oncentration f C i n t he u nknown m ixture: o P rinciples f C hromatography M assS pectrometry o a nd r 89 t cl : 6 4.5a t rtglmL : 1 61 p glmL 3.33 -: tcl I . 1434 ( 2.22 il 230p g125.00 L m 1)= ) : [C] i n o riginal u nknown 2l-17. ( a) T he s preadsheetnd g raphb elow s how t hat m inimum p lateh eight o ccursa t a a f low r ate o f 3 1.6 m Llmin. A B A + B /u+ C ul C I 2 3 4 5 van D eemter c alcu ati ons[ H : A (m m ): B( m m * m l- / m i n ) : Flow r ate ( u. m llmin) H (mm) 1.5 25 C( m m * m in/ m l ) : 2 5 l0 20 30 3l . 6 40 80 t20 r4 .050 6.625 4.250 3.250 3.083 6 8 9 l0 ll 0.025 3.081 3.125 3.81 3 4.708 l3 l4 15 + C 4 : $ A $ 4+ $ ,4$6/84 $ A $8* B 4 12 H(mm)= A +Blu+Cu A =1'50mm C=0.0250mm'minlm ge -c .9 E e6 g o o -3 3 1.6 | 10 20 44.7 + 50 60 I = 5 0.0m m'ml/min A 40 B = 2 5.0m m'ml/min 70 80 90 1 00 1 10 1 20 30 Flow r ate ( mL/min) (From c afculus,he m inimum o ccursw hen d Hldu: 0 . t dHldu: - Blu2 + C: uoptimum 0 = E :\e: 25.0 : 3 1.6m l/min 0.025 0 (b) I f t he r ateo f l ongitudinald iffusion i s i ncreased, e m ust r un t he c olumn w fasters o t hat t he b andsd o n ot s pread oo m uch. T he o ptimum f low r ate t shouldi ncrease nd t he o ptimum p lateh eightw ill b e l arger( worse)t han a with t he s lowerl ongitudinal iffusion. T he g rapha boves howst hat d oubling d 1 90 C hapterl 2 B i ncreaseshe o ptimum f low r atet o 4 4.7m llmin. t (c) I f t he r ateo f e quilibration etweenp hasess i ncreased, e c an r un t he b i w column f asterw ithout s preadinghe b andst oo m uch. T he o ptimum f low r ate t shouldi ncrease nd t he o ptimum p lateh eightw ill b e s maller( better)t han a with t he s lowere quilibration etweenp hases. b 2l-18. ( a) l {mm) : A +B/u+Cu = ( l.50mm)+ 25.0m m.mllmin + ( 0.025 m m.minlmL)(20.0 0 m llmin) 20.0 m Llmin = 3 .25 m m (b) H : L IN ( Z: c olumn l ength,.A/: n umbero f p lates) ly' : L IH : 2 .00 m /0.0032 5 m : 6 15 p lates 5 .5 5 2 (c) / v: I *2 wiz ) r tt2: tr 5 . 5 5: ( 8.00 in) m il 5 . 5 5: m 6 1 5 0 .760 in 2l-19- M olecular m ass i s a w eighteda veragem assb asedo n t he n atural a bundance f a ll o isotopes n t he m olecularf ormula. T o c omputem olecularm ass,w e s um t he i atomic m assesistedi n t he p eriodict able,w hich a re w eighteda verages f t he l o isotopeso f e ache lement. N ominal m assi s t he i ntegerm asso f t he s peciesw ith the m ost a bundant f e acho f t he i sotopesn t he f ormula. o i : CoHom olecularmass 6 x 1 2.010 + 6 x I . 0079 4 : 7 g.l I I g 7 CoHonominal ass:6x 1 2+6 x l :78 m 2l-20. A tomic m asso f c l : I (atomic m assx n aturala bundance) = ( 34.9685X0.757+ ( 36.9650X0.242 3 5.453 8 S) 9 2 ): Happily, v aluen r he eriod t he i p t ables a lso3 5.453. i 2 t- 21. C+H11N3S+:4 t2C:4x ll l H: l l x 1 .007 25= 8 3 l 4N:3 x 14.003 7 : 0 329: subtractI e lectron sum +48 ( exact) +l 1.086 75 0 +42.009 l 2 +31.972 7 0 5 - 0 .000 49 r3 3 . 0 6 6 1 8 ...
View Full Document

This note was uploaded on 04/06/2011 for the course CHEM 2011 taught by Professor Buhlman during the Spring '10 term at Minnesota.

Ask a homework question - tutors are online