Axit ascorbic (cn c gi l vitamin C) c tm thy nhiu nht trong tri cy v l cht dinh dng rt cn thit cho s sng ca sinh vt. lnh vc ha sinh, n l cht chng oxi ha, tham gia vo cc qu trnh tng hp enzim, tng sc khng, phc hi sc khe, c bit ngn nga bnh scurvy ngi. Axit ascorbic cn c dng lm cht bo qun thc phm v lm hng v cho mt s loi nc ung. Lng vitamin C c trong nhiu loi tri cy: trong 100g t c 1900mg, trong u , du, cam, chanh c t 40-60mg.Thng tin tng qut :

- Tn theo IUPAC: 2-oxo-L-threo-hexono-1,4- lactone-2,3-enediol

- Tn thng thng: axit ascorbic, vitamin C

- Cng thc phn t:C6H8C6

- Cng thc cu to:

- Khi lng phn t: 176,13 g/mol

- C dng: bt mu trng n vng nht (khan)

- Nhit nng chy: 193oC (phn hy)

- Kh nng ha tan trong nc: cao

Tnh cht

D trong CTCT khng c nhm COOH nhng vitamin C vn c tnh axit. N c tnh cht ha hc tng t cc axit thng thng, c kh nng b oxi ha v b phn hy thnh CO2v nc 193oC.

Lch s tm ra

- Vo th k 15, 16, trong cuc pht kin a l ca cc nc chu u, nhng nh thm him lun thy thy th ca h phi cht v cn bnh k l vi triu chng mt mi, au khp, chy mu nu, l bnh Scurvy (hay Scorbut).

- Mi n nm 1774, James Lind, bc s hng hi qu tc Anh, pht hin n tri cy s phng trnh c bnh scurvy. ng cho rng nhng ngi thy th i bin ch tip xc nhng mn n kh, mn, t n tri cy dn n cn bnh trn. Kinh nghim ca Lind cu sng rt nhiu thy th trong nhng chuyn hnh trnh bng ng bin sau ny.- Ngi nghin cu k v vitamin C l Albert Szent-Gyrgyi (1893-1986) gc Hungary v ng c trao gii Nobel y hc nm 1937 v cng lao trn. Cng vo nm , gii Nobel ha hc c trao cho Walter Norman Haworth, ngi Anh, tng hp thnh cng vitamin C. Tuy nhin, quy trnh tng hp vitamin C li c tn l Tadeus Reichstein, ngi cng tng hp thnh cng vitamin C cng lc vi Haworth (2 ngi tm ra cch tng hp hon ton c lp). iu ny s lm cho gi thnh vitamin C r hn rt nhiu, v trc y vitamin ny c chit ra t tri cy bng phng php kh phc tp.

Hin nay, vitamin C khng cn l vi mi ngi. T tri cy cho n nc ung, t vin thuc cho n ko ngm, u c s hin din ca n.

XcnhvitaminCbngphngphpchunitVitaminC(acidascorbic)l1chtchngoxyhacnthitividinhdngcaconngi.ThiuvitaminCcthdnnbnhscurvy(scobat)ctrngkhinchoxngvrngkhngbnhthng.RtnhiutricyvrauquchavitaminC,nhngvicchbinmnnlmmtihmlngvitaminC,vvy,tricytiloicamqutvncungcachnglnguncungcpchyuacidascorbicchocth.1phngphpxcnhhmlngvitaminCtrongthcphmlsdngphngphpkhoxyha.Phnngkhoxyhatthnphngphpchunacid-bazbivchothmacidvoncqu,nhngmtsacidscntrsoxyhaacidascorbicbiit.Ittngikhngtantrongnc,nhngiunycthcithinbngcchphatrnitviiouavhnhthnhtriioua:I2+I-I3-TriiouaoxyhavitaminCtoaciddehydroascorbic:C6H8O6+I3-+H2O-->C6H6O6+3I-+2H+ChngnomvitaminCcnhindintrongdungdch,thtriiouacchuynthnhioniouartnhanhchng.Tuynhin,khittcvitaminCboxyha,thitvtriiouashindintrongdungdchvphnngvitinhbttonnmthnhpmuxanhen.Muxanhenlimdngchophnngchun.QuytrnhchunnythchhptrongvickimtrahmlngvitaminCtrongvinthucvitaminC,ncpqu,vtricyti,nglnhhoctricynggivrauqu.Phngphpchunc th thc hin ch s dng dung dch iot v khng dung iodate, nhng dung dch iodate n nh hn v cho kt qu chnh xc hnQui trnh xc nh vitamin CMc ch: Mc ch ca th nghim ny l xc nh hm lng vitamin C trong cc mu, v d nc p qu.Qui trnh thc hin:Chun b dung dch:Dung dch ch th 1% tinh bt:1. Cho 0,5 g tinh bt ha tan vo 50 ml nc ct nng gn si.2. Ha tan hon ton v dung dch ngui trc khi s dng (khng phi lc no cng l dung dch h tinh bt 1%, dung dch 0,5% cng tt)Dung dch iot:1. Ha tan 5 g KI v 0,268 g KIO3 trong 200ml nc ct.2. Thm 30ml acid sunfuric 3M.3. Cho dung dch ny vo ng ong 500 ml v pha long dung dch bng nc ct n vch nh mc 500ml.4. Ha tan dung dch ha tan5. Cho dung dch vo bcher 600ml.Ghi nhn trn becher l dung dch iotDung dch vitamin C chun:1. Ha tan 0,250 g vitamin C (acid ascorbic) trong 100 ml nc ct.2. Dng nc ct pha long thnh dung dch 250ml bng bnh nh mc. Ghi nhn trn bnh l dung dch vitamin C chun.Tiu chun ha cc dung dch:1. Thm 25,00 ml dung dch chun vitamin C vo erlen 125 ml.2. Thn 10 git dung dch h tinh bt 1%.3. Ra sch buret vi mt lng nh dung dch iot v sau chio dung dch iot vo buret. Ghi li vch th tch dung dch ban u trong buret.4. Chun d dung dch cho n im dng phn ng, khi bn thy du hiu mu xnh dng bn trong 20 giy khi bn lc u dung dch.5. Ghi nhn vch th tch dung dch iot trn buret.Lng iot dung cho chun chnh l th tch dung dch iot ban u tr i dung dch sau chn .6. Lm li th nghim chun t nht 2 ln.Cc kt qu chp nhn sai khc 0,1 ml. Nguyn l: nh lng vitamin C vi phng php Tinman da trn s oxy ha axit ascocbic vi 2-6 diclorophenol indophenol thnh axit dehydro ascocbic v 2 6 diclo phenol indophenol s chuyn thnh dn xut lco (lenco derive) khng mu. Phn ng ti thch mi trng pH: 3 4. Trong mi trng ny mt git 2-6 diclorophenol indophenol xanh tha s chuyn thnh mu hng.Nu trong thc phm c axit dehydro ascocbic, khi cn thit chun vitamin C ton phn cn th axit dehydro ascocbic bng H2S v chun vi thuc th tinman.Dng c, vt liu, thuc th:Ct sch khng ln stDung dch thy ngn II axetat: ha tan Hg(CH3COO)2vo trong mt t nc, yn mt m sau em lc v thm nc ct n va 100ml.Dung dch ch v natri axetatPb(CH3COO)2kt tinh khi lng 125g, CH3COONa kt tinh khi lng 500g, nc ct nh mc va 100ml.Dung dch axit metaphotphoric 2%Axit tricloaxetic 20%Dung dch HCl 1%Dung dch NaOH 10%Dung dch CuSO4Dung dch It 0.01N (dung dch iot 0.1N 10ml, dung dch KI 2.5N va 100ml)Dung dch axit ascocbic 0.1N (axit metaphotphonic 2% 100ml v dung dch CH3COONa 68.03% 17.8ml). Lc ha tan, xc nh h s hiu chnh bng dung dch iot 0.01N vi nc h tinh bt lm ch th mu.Dung dch axit ascocbic 0.001N (dung dch axit ascocbic 0.01N 10ml vi ung dch axit metaphotphoric + natri axetat theo t l va 100ml). Dung dch ny ch gi c 2 3 ngy.Dung dch 2 6 diclorophenol indophenol 0.001N (2 6 diclorophenol indophenols 0.268g, nc ct 2 ln khong 300ml). Ha tan nhit khong +500C, ngui, v thm nc ct hai ln va 1000ml. yn mt m sau lc qua giy lc gp. dung dch ny gi trong chai mu v trong t lnh, c th bo qun trong 4 tun, khi dng chun li bng dung dch axit ascocbic 0.001N.Tin hnh th nghim:Cn 5 10g thc phm ct nh vi dao khng r, cho ngay vo ci s vi mt t axit metaphotphoric 2%, mt t ct sch v nghin nh, thm dn 10ml HCl 1%, chuyn tt c vo ng ly tm 10 pht v gn dch chit vo bnh nh mc 100ml. Ra b 3 ln, mi ln vi 10ml axit metaphotphoric 2%, khuy u v ly tm, gn nc vo bnh nh mc. Cui cng cho thm dung dch axit metaphotphoric 2% va 100ml lc u.Ht ly 10ml dch chit, cho vo bnh chun v nh lng vi dung dch 2 6 diclorophenol indophenol 0.001N cho n mu vng nht bn vng.Song song vi nh lng chnh thc lm mt mu trng nh sau: ly 10ml dch chit cho vo bnh chun cho thm 1ml dung dch CuSO41%, un 10 pht cch thy ph hy ht vitamin C. ngui v chun bng dung dch 2 6 diclorophenol indophenol 0.001N.Tnh kt qu: hm lng axit ascocbic tnh bng mg trong 100g thc phm:

Trong :0.088mg = s mg axit ascocbic tng ng vi 1ml dung dch 2 6 diclorophenol indophenol 0.001N.N = s ml 2 6 diclorophenol indophenol 0.001N dng nh lng mu dch chit.n = s ml 2 6 diclorophenol indophenol 0.001N dng nh lng mu trng.P = s gam thc phm cn chit xut axit ascocbic.

2 Vitamin B2 ( Riboflavin)Tn gi khc: Riboflavin, riboflavine, vitamin B2, lactoflavin, ovoflavin

Tn IUPAC: 7,8-dimethyl- 10-((2R,3R,4S)- 2,3,4,5- tetrahydroxypentyl) benzo[g]pteridine- 2,4 (3H,10H)- dione

Cng thc phn t: C17H20N4O6 Khi lng phn t: 376.36 g/molNhit nng chy: 290 C2.2.2.1 c tnh l cc tinh th mu vng da cam, ha tan tt trong nc v ru, khng ha tan trong cc dung mi ca cht bo. Tinh th kh bn vi nhit v dung dch axit.Vitamin B2 gi vai tr xc nh trong cc phn ng ca mt s enzyme cn thit cho qu trnh h hp (tham gia vo thnh phn ca cc enzyme vn chuyn hydro).2.2.2.4. Phng php phn tchPhn tch nh tnh Phn ng khRiboflavin tn ti dng oxi ha v dng kh. dng kh c tn l locoflavin khng mu d b oxi ha thnh riboflavin.Nguyn liu v ha cht: Dung dch riboflavin 0,015% (gi trong ti), HCl c, km kim loi.Cch lm: Cho vo ng nghim 1ml dung dch riboflavin, thm 10 git HCl m c v mt t bt km, lc nh v quan st hin tng (kh hidro bay ra, mu chuyn dn t vng sang xanh lc, sau thnh mu hng v cui cng mt mu. Sau mt lc b mt dung dch li c mu vng). Phn ng vi AgNO3Trong mi trng trung tnh hay axit yu (pH = 6,5 7,2), riboflavin phn ng vi AgNO3 to thnh hp cht mu hng hay .Nguyn liu v ha cht: Riboflavin 0,015% (gi trong ti), AgNO3 0,1% (bo qun trong l nu)Cch lm: cho vo ng nghim 1ml dung dch riboflavin, thm 0,5ml AgNO3, quan st s xut hin mu hng hoc (cng mu ph thuc vo lng riboflavin trong dung dch).Phn tch nh lngPhng php hunh quang Nguyn tc Trong ng cc, riboflavin (latoflavin, vitamin G, vitamin B2) l cht c mu vng xanh l cy c ha tan trong nc c ch nh bng phng php phn tch hunh quang. Riboflavin c nhiu trong t bo ng vt v thc vt. N bn trong mui khong v phn ln cc tc nhn oxi ha, nhng li khng bn trong dung dch kim. N rt nhy cm vi tia kh kin v t ngoi nn cc thao tc c thc hin trong nh sng du hoc trong cc dng c th nghim thy tinh c quang ha thp.Hnh /138Trong cc t bo sng, riboflavin thng kt hp vi axit photphoric hoc c vi axit photphoric v axit adenylic (FMN hoc FAD). C hai u c th kt hp mt s protein c th hnh thnh cc enzym oxi ha. Trong mt s sn phm (sa), riboflavin tn ti di dng t do c th thm tch cng nh dng coenzym.Trong phn ln cc quy trnh tch riboflavin, cn thit phi x l cc sn phm t nhin vi axit hoc enzym thu c gi tr ti a. Bc x l ny gii phng riboflavin khi phc cht protein v gip cho vic tch chit d dng hn.Riboflavin c tch chit t ng cc v phn tch bng my quang ph hunh quang qut t ghi (scanning spectrophoto fluorimeter). Dng my quang ph hunh quang qut c iu khin iu chnh s pht hunh quang ca riboflavin khi c mt nhng cht gy cn tr, nhng cht ny theo l thuyt c nh hng n cht chun v mu th nghim. Do cng ca s pht hunh quang t l vi nng ca riboflavin trong dung dch long v nng ny c o da vo s chnh lch gia hunh quang trc v sau khi kh natri tiosulfit (Na2S2O4). Tin hnh1. Quy trnh th nghim tch chit1. Cn 6,0 gam ng cc (d tnh l cha 5 10 g riboflavin0, nghin bng ci s.1. vo bnh nn 100ml v thm 50ml dung dch HCl 0,1M. Lc bnh tm t ht ng cc. Sau y np bnh bng giy nhm (tt nht l giy bc) trnh riboflavin b phn hy bi nh sng. t trong ni cch thy ang un si khong 1 gi, c 5 pht li lc mt ln. Kim tra mc nc mi ln lc bnh, khng nc cn.1. Lm ngui bnh n nhit phng v cho vo cc 100ml. Dng my o pH chnh n 6,0 (bng dung dch NaOH 0,5M). (* note: Cho NaOH vo t t trnh nhng ch c pH cao s dn n mt riboflavin.1. Ngay lp tc thm HCl 1M gim pH n 4,5. Li tm bng ng li tm thy tinh 100ml 2000v/pht (rpm) trong 10 pht.1. Pha long dch lc n 250ml vi nc ct trong bnh nh mc.1. Qu trnh axit ha v oxi ha ca dch chit1. Ly 2 ng nghim, cho vo mi ng 10ml dch chit v 1ml nc. Trn u bng my trn.1. Ly 2 ng nghim khc, cho vo mi ng 10ml dch chit v 1ml dung dch chun riboflavin (0,5g/ml) v trn u.1. Cho 1ml axit axetic c vo c 4 ng nghim v 2 pht.1. Cho thm 0,5ml dung dch KMnO4 3% vo mi ng, trn u v 2 pht.1. Cho 0,5ml H2O2 3% vo mi ng v trn u. Mu s bin mt trong vng 10 giy. 1. o hunh quang ca dch chit1. o hunh quang ca riboflavin, bc sng pht x v bc sng kch thch phi c xc nh bng my o quang ph qut.1. Xc nh cc i ca bc sng pht x v bc sng kch thch ca dung dch chun riboflavin (nng 1 g/ml riboflavin). Gi tr cc i cho kch thch nn c gi tr l 450nm. Gi tr cc i cho bc x l 530nm.

Trong : - hiu sut lng t, cng ti, hp th phn t, di ng dn. nng .Phng trnh ny ch ng vi nhng dung dch c nng thp. phng trnh trn, cng hunh quang t l thun vi cng ti p0 v nng c. hunh quang cng tng khi nng ca cht pht quang tng. thnh lp mi lin quan theo nh lut Lambert Beer, c mt ng chun cho riboflavin cha 0,5 1,0 2,0 v 4,0 g/ml.(* Note: trong khi o hunh quang phi cn thn trnh khng cho dung dch tip xc vi tia t ngoi qu lu nu khng s lm riboflavin b phn hy rt nhanh.1. o hunh quang ca dch chit khng cha riboflavin (kt qu A). Dng 3ml dung dch trong cuvett.1. Cho vo cuvett cha 3ml dch chit ny khong 5mg Na2S2O4 (pha trong nc), trn u v o ngay lp tc (kt qu C).1. o hunh quang ca dch chit c cha riboflavin thm vo (kt qu B). Tnh kt quTnh lng riboflavin c trong ng cc bng cng thc sau:

2.2.3.Vitamin B6Vitamin B6 c tch ra dng tinh khit vo nm 1938, u tin t nm men sau t cm go. Cu to ca vitamin B6 c xc nhn nm 1939 nh s tng hp ha hc, l cht piridoxin.Vitamin B6 cn tn ti cc dng nh piridoxal, piridoxamin

Chemical name: Pyridoxine Molecular formula: C8H11NO3; Molecular weight: 169.18 g/mole2.2.3.1.c tnhPirdoxin l tinh th khng mu, c v hi ng v ha tan tt trong nc, ru. C ba loi piridoxin, piridoxal v piridoxamin u bn khi un si trong dung dch acid hoc kim nhng khng bn khi c mt ca cc cht oxy ha. Chng b phn hy nhanh nu em chiu sng mi trng kim cng nh trung tnh, cn khi chiu sng dung dch acid (0.1 N HCl) th cc dng piridoxin v piridoxal bn hn so vi piridoxamin.

.2.3.6. Phng php phn tch Phn tch nh tnh Phn ng vi FeCl3Di tc dng ca FeCl3, piridoxin s to thnh phc cht c mu c trng.Nguyn liu v ha cht: Dung dch piridoxin 1%, FeCl3 5%.Cch lm: cho vo ng nghim 1ml piridoxin 1%, thm 5 git FeCl3 lc u. Quan st s xut hin mu ca phc cht to thnh. .4. Vitamin BC (Vitamin B11/ Folic acid)Acid folic bao gm ba gc lin kt vi nhau l gc pterin, gc acid paraaminobenzoic v gc acid glutamic .

Chemical name: Folic acidMolecular formula: C19H19N7O6; Molecular weight: 441.40 g/mole2.2.4.1. c tnh Axit folic l tinh th hnh kim mu vng , n b phn gii nhanh ngoi nh sng nht l trong mi trng axit bn trong mi trng PH t 5 10 . Khi tn ti trong thc phm n bn hn khi dung dch tinh khit .Vitamin AXc nh vitamin A bng phng php so muNguyn tc:Vitamin A l mt alcohol cao cp cha no v thng kt hp axit bo (palmitic v stearic) to thnh este phc tp.V vy mun xc nh vitamin A phi x phng ha cc sn phm, ri xc nh vitamin A trong phn khng x phng ha.Vitamin A c tch khi dung dch khng x phng ha bng chloroform khan v n cho phn ng vi antimony (III) clorua to sn phm mu xanh v em so mu vi dung dch tiu cun.Dng c v ha chtCan phn tchBnh nn dung tch 250mlPhu chitng lm lnhni cch thy, cc thy tinh dung tch 250ml, gi ng nghimdung dch mu tiu chun dc chun b nh sau: cn 75 ng sunfat (CUSO4.5H20) V 3,5 g Coban nitrat Co(NO3)2 cho vo bnh nh mc dung tch 500ml, them nc n vch nc, lc k cho tan ht.Giy qu, natri sunfat khan: sy 100 C trong mt h.Cloroform (CHCL3): ra nc ct nm ln bng nc t l 2 nc:1 cloroform (CHCL3) trong phu chit ri lm kh bng natri sunfat khan sau chng ct thu dch tinh ch.Dung dch antimony (III) clorua (Sb Cl3) bo ha: SbCl3 c ra bng cch khuy trong clorua n khi nc ra khng mu, SbCl3 ra c trong bnh lm kh(c cha axit sunfuric c) qau 2 ngy, sau ha tan SbCl3 trong chloroform n bo ha.Ete etylic tinh khitKali hydroxit dung dch 20% trong ru etylic.Cch tin hnhCn 10g n 20 g mu cho vo bnh nng dung tch 250ml them 20ml dung dch kali hydroxit 20% trong ru etylic.y bnh bng nt bt c gn lm lnh v un hi lu trn ni cch thy nht 85-90 C trong 2 gi x phng ha.Dung dch x phng ha dduwwocj pha long bng 20ml nc ct ri chuyn vo phu chit,them vo phu chit 50ml t etylic v lcs k( trnh huyn ph cn chit dch lc ngui v lc mnh) chit phn khng x phng ha ra, tip tc lc v chit ly lp trn vo phu chit th 2.Ra dch chit bng nc ct trong 3-4 ln mi ln 20ml nc ct cho n khi nc ra c phn ng trung tnh (th bng giy qu).Lm kh nc chit ra bng 6 gam natrisunfat khan trong 30 pht.Chuyn c dung dch vo cc, sau un ui este trn ni cch thy.Ha tan cn khng x phng ha thu c bng chloroform (sau khi ui ht este) v chuyn vo bnh nh mc dung tch 250 ml, them cliroform cho n vch, lc nhCho vo ng nghim ( kh, sch, cng mu, cng kch thc nh ng nghim cha dung dch tiu chun) dung 0,2 ml dung dch trong bnh nh mc trn, them 1-3 git anhydric axetic, 2ml dung dch SbCl3 bo ha lc nhanh v khng qu 10 giy em o mu vi ng chun trong 20 giy.