LI CM N Ti xin gi li cm n chn thnh v su sc ti thy Chu Xun Anh, ngi rt tn tnh hng dn gip ti trong sut thi gian thc hin lun vn ny. Ti xin chn thnh cm n cc thy, c trong Khoa Ha hc - i hc Khoa hc T nhin gip ti trong qu trnh hc tp v nghin cu. ng thi ti cng xin gi li cm n ti cc bn b, ng nghip ng vin v to mi iu kin gip ti hon thnh tt lun vn. H Ni, ngy thng 12 nm 2009

HC VIN

Tng Th Vn Anh

MC LCM U......................................................................................................................1 Chng 1. TNG QUAN.............................................................................................3 1.1. C TNH PHN TCH CA MANGAN .........................................................3

1.1.1. 1.1.2. 1.1.3. 1.1.4. 1.1.5. 1.1.6.

Mangan kim loi (mc oxi ha 0)...................................3 Hp cht ca Mn(II)........................................................4 Hp cht ca Mn(III).......................................................5 Hp cht ca Mn(IV), Mn(V)...........................................5 Hp cht ca Mn(VI).......................................................6 Hp cht ca Mn( VII).....................................................6

1.2. PHNG PHP PH HP TH NGUYN T................................................7 1.3. PHNG PHP TRC QUANG V NG HC XC TC.........................8

1.3.1. Phng php trc quang................................................8 1.3.2. Phng php ng hc xc tc....................................14Chng 2. THC NGHIM.......................................................................................19 2.1. NI DUNG V PHNG PHP NGHIN CU............................................19 2.2. HA CHT V THIT B.................................................................................20

2.2.1. Ha cht.......................................................................20 2.2.2. Thit b.........................................................................222.3. QUY TRNH XC NH....................................................................................22

2.3.1. Cch tin hnh kho st cc iu kin th nghim 25oC v 80oC.........................................................................22 2.3.2. Quy trnh xc nh nh hng cc ion l......................23 2.3.3. Quy trnh xc nh mu gi..........................................24 2.3.4. Quy trnh phn tch mu thc t..................................242.4. X L S LIU THNG K............................................................................25

Sai s tng i (ER) .............................................................25 Tng quan tuyn tnh...........................................................25 Sai s h thng.......................................................................26Chng 3. KT QU V THO LUN.................................................................27

3.1. KHO ST CC IU KIN TH NGHIM...................................................27

3.1.1. Th nghim s b..........................................................27 3.1.2. Th t cho cc cht vo bnh phn ng.......................30 3.1.3. nh hng ca pH .......................................................31 3.1.4. nh hng ca nhit v thi gian phn ng...........35 3.1.5. nh hng ca nng KIO4.......................................39 3.1.6. nh hng ca nng cht hot ho xc tc phen...............................................................................................40 3.1.7. nh hng ca nng RhB........................................42 3.1.8. nh hng ca nng cht xc tc Mn2+................433.2. NH HNG CA MT S ION L ...........................................................50

3.2.1. nh hng ca Fe(III)...................................................51 3.2.2. nh hng ca cc ion khc .......................................523.3. XC NH MANGAN TRONG MU GI .....................................................54 3.4. XC NH MANGAN TRONG MU THC T ...........................................55 KT LUN.................................................................................................................59 TI LIU THAM KHO...........................................................................................61

M U Mangan (Mn) c trong t nhin rt nhiu v l nguyn t ng vai tr quan trng trong nhiu lnh vc khoa hc v i sng nh trong cng nghip sn xut thp v hp kim, trong ho hc, trong y hc... V vy, n s pht tn mt phn vo kh quyn, a quyn, sinh quyn. Trong c th ngi, Mangan ng vai tr quan trng trong s to thnh xng v m, nh hng n s to thnh hocmon tuyn yn, vitamin B1 v vitamin C. Hm lng cho php i vi ngi trng thnh khong 2 5 mg mi ngy (c cung cp t thc phm, nc ung) nn nu thiu ht Mn s lm gim qu trnh ng mu v tng lng Cholestorol, nh hng n s chuyn giao thng tin di truyn. V s chuyn ha Mn bt thng c th gy ra bnh tiu ng, bnh bo ph... i vi cc loi cy trng, hm lng Mangan v cc nguyn t vi lng khc cho php chn c cc loi ht ging, c nng sut cao, chu su bnh v iu kin thi tit khc nghit. Trong nc, Mangan v mt s nguyn t vi lng khc quy nh s pht trin ca vi sinh vt. V vy cn c vo hm lng Mangan c th x l v khai thc c hiu qu ngun nc s dng phc v nng nghip, i sng v bo v mi trng. Do hm lng Mn trong nc nh nn kim sot hm lng Mn i hi cc phng php phn tch phi c chn lc v chnh xc cao. Nhng phng php von ampe ha tan, phng php kch hot notron, phng php ICP-MS (quang ph cao tn plasma khi ph), phng php AES (quang ph pht x nguyn t) v rng ri hn l phng php AAS (quang ph hp th nguyn t) c s dng xc nh lng vt Mn. Cc

phng php ny i hi thit b t tin, tn thi gian phn tch, trnh tay ngh cao v thng c trang b cho nhng phng th nghim ln. khc phc c nhng nhc im trn, phng php o quang phn t (spectrophotometry) c u tin xem xt. c bit, phng php o quang ng hc xc tc l mt nhnh quan trng s c quan tm n v thi gian phn tch t, thit b r tin, thuc th d tm m t c nhy v chn lc thch hp. Trong lun vn ny, chng ti s nghin cu cc iu kin o quang ng hc xc tc xc nh lng vt Mn. C s ca phng php l Mn(II) lm cht xc tc cho qu trnh oxi ha Rhodamin B bng KIO4 trong mi trng axit yu. Phng php ny c ng dng xc nh Mn(II) trong nc b mt v kt qu s c so snh vi kt qu ca phng php AAS.

Chng 1. TNG QUAN T nhim v t ra trn, chng ti ch xem xt mt s vn sau: - c tnh phn tch ca Mn - Phng php ph hp th nguyn t xc nh Mn. - Tnh hnh phn tch lng vt Mn bng phng php o quang c bit l phng php ng hc xc tc.1.1. C TNH PHN TCH CA MANGAN

Mangan l nguyn t kim loi chuyn tip ng v tr th 25 thuc phn nhm VIIB trong bng h thng tun hon. Cu hnh electron nguyn t l 1 s2 2s2 2p6 3s2 3p6 3d5 4s2. v lp 3d ny cha bo ha nn c mc nng lng cao. Nu mt i in t lp ngoi cng, n c th to c nhng hp cht c trng thi oxi ho t 2 n 7. 1.1.1. Mangan kim loi (mc oxi ha 0) c trng ca Mangan kim loi l tnh kh mnh. nhit cao, nht l khi dng bt, Mangan d tc dng vi cc phi kim. V d, tc dng vi O2 to ra Mn3O4, vi Cl2 to ra MnCl2 v tc dng vi S to ra MnS Mangan bn vi nc, k c khi un nng v ch c phn ng chm khi dng bt mn: Mn + 2H2O Mn(OH)2 + H2 Mangan tan d dng trong cc dung dch axit v to thnh mui Mn(II).

1.1.2. Hp cht ca Mn(II) S phi tr c trng ca Mn(II) l 6 ng vi dng lai ho sp3d2 vi s phn b lin kt 8 mt. Cc hp cht Mn(II) u c tnh thun t v u c 5 electron c thn. Hp cht oxit ca Mn(II) l MnO, c tnh bazo, tan d dng trong axit to thnh mui Mn(II) trong d tan nht l MnCl2, MnSO4, Mn(NO3)2. Cc mui Mn(II) trong mi trng kim d to thnh Mn(OH) 2 vi tch s tan l 7.10-15. Mn2+ + 2H2O + 2NH3 Mn(OH)2 + 2NH4+ Khi NH4+ d v un nng dung dch s c phn ng Mn(OH)2 + 2NH4+ Mn2+ + 2NH3 + 2H2O p dng phn ng ny c th tch v xc nh ring tng kim loi trong hp kim cha Mn, Fe, Ba. Mu c phn hy bng HCl, sau dng dung dch H2SO4 long kt ta Ba dng BaSO4, thm NH4Cl vo dung dch v cho t t dung dch NH3 n khi metyl da cam chuyn mu th Fe(III) kt ta dng Fe(OH)3. Nc lc ch cha Mn(II). [20] Lng Mn(II) trong dung dch cha Fe(III), Cr(III), Mn(II) c tch bng bt ZnO d. Ban u dng H2SO4 phn hy mu, sau dng dung dch NH3 trung ha lng axit d. Cho d bt ZnO vo bnh, Fe(III) v Cr(III) s i vo kt ta nn Mn(II) nm trong nc lc: ZnO + H2O Zn2+ + 2OH Cr3+ + 3OH- Cr(OH)3 Fe3+ + 3OH- Fe(OH)3 [7]

Mn(II) l cht oxi ha yu, phi dng phng php in phn hoc cht kh mnh nh Al mi c th chuyn Mn(II) v Mn(0). Mn(II) th hin tnh kh mnh. Trong mi trng kim, Mn(II) tc dng vi cc cht oxi ha nh (O2, Cl2, H2O2,...) to thnh MnO2. Mn2+ - 2e + 2H2O MnO2 + 4H+ C th tch Mn(II) ra khi cc kim loi kim th v magie bng thioaxetamit hoc tch khi st bng KClO3 (chuyn Mn(II) v MnO2) [10] Trong mi trng axit, Mn(II) b oxi ha bng cc cht oxi ha mnh nh PbO2, NaBiO3, KIO4, (NH4)2S2O8 to thnh MnO4-. Mn(II) c th kt hp vi cc cht v c (nh cyanua) v cc cht hu c (nh etilendiamin, oxalat, EDTA) to thnh cc phc bn. 1.1.3. Hp cht ca Mn(III) Hp cht ca Mn(III) l hp cht t bn v c tnh oxi ha kh. Mn(III) oxit c cng thc phn t Mn2O3. Mn2O3 khi tc dng vi axit long to ra MnO2 v mui Mn(II). Nhng khi tc dng vi axit c to thnh mui ca Mn(III) . a s cc mui Mn(III) bn nht trong mi trng kim, khng bn trong dung dch nc, d b phn hy thnh mui Mn(II) v MnO2. Mui Mn(III) d kt hp vi cc anion ca axit to thnh phc cht bn nh K3(Mn(CN)6), K3(Mn(C2O4)3.3H2O, K(Mn(EDTA).3H2O 1.1.4. Hp cht ca Mn(IV), Mn(V) Oxit ca Mn(IV) l MnO2. y l hp cht bn nht ca Mn. Khi un nng, MnO2 tan trong axit v kim nh mt oxit lng tnh.

Cc mui ca Mn(IV) rt km bn trong nc v dung dch axit, d phn hy thnh Mn(II). MnO2 va c tnh oxi ho, va c tnh kh. Tnh oxi ha: MnO2 trong mi trng axit to thnh mui Mn(II) MnO2 + 4HCl MnCl2 + Cl2 + 2H2O Tnh kh: MnO2 trong mi trng kim mnh to thnh hp cht ca Mn(V). 2MnO2 + 6KOHc K3MnO4 + K3[Mn(OH)6] Cc tetra halogenua ca Mn(IV) km bn trong nc, d kt hp vi halogenua kim loi kim to nn nhng phc cht c mu vng v bn hn nh: M[MnX5] v M2[MnX6] (trong M = K, Rb, NH4 v X = F, Cl). 1.1.5. Hp cht ca Mn(VI) Mn(VI) khng tn ti dng oxit MnO3 m ch thy trong ion MnO42-. Mn(VI) ch bn trong dung dch kim mnh, trong dung dch trung tnh hoc kim yu d b thy phn: 3MnO42- + 2H2O 2MnO4- + MnO2 + 4OHMui manganat ny l cht oxi ho mnh, phn ng vi nhiu cht kh trong dung dch tng t nh permanganat. Nhng vi cht oxi ho mnh hn th n li th hin tnh kh. Tuy nhin iu ny rt t xy ra: 2K2MnO4 + Cl2 2KMnO4 + 2KCl Ion MnO42- theo thuyt trng tinh th c xem l phc cht ca kim loi chuyn tip. 1.1.6. Hp cht ca Mn( VII) Mn(VII) khng tn ti dng oxit Mn2O7 m ch thy trong ion MnO 4-. Mui MnO4- u d tan trong nc.

KMnO4 l cht oxi ha mnh, c th oxi ha nhiu cht hu c hoc v c. Ty thuc axit ca mi trng m MnO 4- s b kh n Mn(II), Mn(IV) hoc Mn(VI). Trong mi trng axit mnh: MnO4- + 5e + 8H+ Mn2+ + 4H2O.E0 = 1,51 V Trong mi trng axit yu, bazo yu hoc trung tnh: MnO4- + 3e + 2H2O MnO2 + 4OH-.E0 = 1,23 V Trong mi trng kim: MnO4- + 1e MnO42- (xanh l cy) E0 = 0,56 V Ion MnO4- theo thuyt trng tinh th c xem l phc cht ca kim loi chuyn tip.1.2. PHNG PHP PH HP TH NGUYN T

Mangan c nhiu vch ph c trng nhng thng s dng ba vch c bc sng sau: 1=279,5 nm, 2 =279,8 nm v 3=280,1 nm. [4] C th xc nh Mangan bng phng php quang ph hp th nguyn t (AAS) vi k thut ngn la v k thut khng ngn la. chuyn nguyn t cn phn tch v dng nguyn t, phng php ngn la s dng hn hp axetilen v khng kh, phng php khng ngn la s dng dng in cao tn. [5] Gii hn ca cc phng php ny c trnh by trong bng 1 theo cc tiu chun th gii nh EPA (Hip hi bo v mi trng M), APHA (Hip hi bo v sc khe cng ng M). Bng 1. Mt s tiu chun xc nh Mn theo phng php AASTiu chun EPA 243.1 EPA 243.2 APHA 3500-Mn Phng php AAS vi k thut ngn la AAS vi k thut khng ngn la AAS vi k thut khng ngn la Khong xc nh Mn 0,1 3 mg/l 1 30 g/l 1 30 g/l

Nh bng trn, gii hn xc nh ca Mn theo phng php khng ngn la nh hn nhiu so vi phng php ngn la. xc nh Mn trong cc mu mu, huyt thanh hay ch, thc phm bng phng php AAS, u phi x l mu, chit bng dung mi. Vic xc nh lng vt Mn trong ch c Choary nghin cu bng ph hp th ngn la (khng kh axetilen l hn hp chy) = 253,7nm. Mu c x l bng cch sy kh 80 oC ri chit bng dung mi, x l cn b vi HCl v chit thm vi ln na, sau un nng vi hn hp H 2SO4 v HNO3 [19]. Furono xc nh Mn trong huyt thanh v mu bng phng php ph hp th nguyn t 1=279,5 nm. Mu c x l bng CH3COONH4 iu chnh n pH = 8 ri chit bng benzylxan togenat trong MIBK. Gii hn xc nh l 0,45 1,90 g/g [23].1.3. PHNG PHP TRC QUANG V NG HC XC TC

1.3.1. Phng php trc quang Phng php trc quang da vo o mu ca hp cht Mn. C th xc nh Mn dng Mn(II) v dng Mn(VII). S oxi ha cc hp cht ca Mn thnh MnO4- bng cc thuc th nh bismutat, periodat, persunfat v o hp th ca MnO 4- bc sng 528nm c coi l phng php tiu chun trong mt khong thi gian di. Ti Vit Nam cng s dng phng php ny nh tiu chun TCVN 4578 1988. Mangan cc mc oxy ha khc nhau (ch yu dng Mn(II)) c th xc nh theo phng php ny bng cch oxy ha thnh Mn(VII) bng cc cht oxy ha mnh nh (NH4)2S2O8 (Ag+ lm xc tc), NaBiO3, KIO4, trong mi trng HNO3, H2SO4). Lng ln cc cht hu c, ion c mu, Cl- cn tr php xc

nh. nh hng ca Cl- c loi tr bng cch kt ta vi AgNO 3 hoc bay hi vi H2SO4 c. nh hng ca Fe3+ c loi tr bng cch to phc vi H3PO4 v dung dch o quang tin hnh hai ln loi tr nh hng ca nhng ion mu khc [2]. Phng php ny thch hp phn tch Mn hm lng mg/l. Theo ti liu tham kho [16], nhy ca php o c c trng bi gi tr ( hp th mol, n v l l.mol -1.cm-1). Nu < 2.104 th phng php c nhy km, = 2-6.104 - phng php c nhy trung bnh v > 6.104 cho phng php c nhy cao. tng nhy ca phng php ngi ta s dng cc phng php trc quang vi thuc th hu c to mu. t c kt qu chnh xc v lp li tt, phc ca cc thuc th hu c vi cc kim loi phi m bo cc yu cu nh: - C hp th mol cao, cho nhy cao. - C tng phn tt, cho chn lc cao [16] Theo bi bo tng hp v cc phng php trc quang xc nh Mangan ca cc tc gi Barry Chriswell, Guy Rauchle v Mark Pascoe [16], c nhiu nh nghin cu tm ra cc cht hu c t c nhy v chn lc cao. t c mong mun ny cn phi chn hn hp dung mi ph hp, a vo cc cht che khc nhau ty tng mi trng, thay i nhm chc trong thuc th hu c bng nhm th, a thm nhng cht hot ng b mt thay i tan hoc s dng h lin hp 2 (3, 4) thnh phn. Cc cht hu c ny c chia thnh cc nhm nh: nhm azo, nhm oxim, nhm triphenylmetan, xanten v antraquinon,... [16].

* Nhm azo: l nhm thuc th c s dng rng ri nht trong phn tch so mu. Thuc th azo c s dng rng ri nht l nhm PAN. chn lc ca phng php c th ci thin bng cch iu chnh pH v che cc cht nh hng. tng nhy ca php phn tch, c th chit phc Mn PAN vo cloroform. Thm cc cht hot ng b mt vo n nh phc. Bng 2 ch ra mt s thuc th azo hay c s dng xc nh Mangan. Bng 2. Nhm thuc th azo to phc mu vi ManganThuc th Ch thch Chit trong cloroform pH = 9,2, = 4,8.104 l.mol-1.cm-1, max = 562nm

1-(2'-pyridinazo)-2-naphton (PAN)

Thm Triton X-100 lm cht hot ng b mt n nh phc ca PAN, = 4,4.104 l.mol-1.cm-1 = 7,8.104 l.mol-1.cm-1, max = 500nm, trong mi trng m borat pH = 10, khong tuyn tnh l 0,1 1,1mg/l = 4,2.104 l.mol-1.cm-1, trong mi trng m borat pH = 8,8, khong tuyn tnh l 0,04 1,4g/l Chit trong cloroform, =3,8.104l.mol-1.cm1 , khong tuyn tnh l 0,1 1,3mg/l = 1,06.105 l.mol-1.cm-1

4-(2'-pyridinazo)resorcinol (PAR)

4-(2'-thiazolylazo)resorcinol (TAR)

1-(2'-thiazolylazo)-2-naphton (TAN) 2-(5'-brom-2'-pyridinazo)-5dimetylaminophenon

* Nhm oxim: nhm oxim cng c ng dng rng ri trong thuc th phn tch. Trong cc phng php dng thuc th oxim, phng php formandoxim hay c s dng hn c v cng c coi l phng php tiu chun xc nh Mn nh tiu chun ca Hip hi nghin cu v th nghim vt liu M ASTM D2330-82 v tiu chun Vit Nam TCVN 6002-1995,

hm lng phn tch c mg/l. Phng php ny hay c s dng hn phng php permanganat do c nhy hn ( = 1,12.104 l.mol-1.cm-1, max = 562nm) v tiu tn thi gian t hn. Ngoi ra cn c mt s thuc th khc thuc nhm oxim cng c s dng xc nh Mn(II) (bng 3). Bng 3. Nhm thuc th oxim to phc mu vi ManganThuc th Salicylaldoxim Ch thch Chit trong n-butanol C mt H2O2 Xc nh ng thi Fe v Mn 3,5-diclo-2-hydroxyaxetophenone oxim 5-clo-2,4-hydroxypropiophenone oxim Diphenylsuccinimide monoxim Biacetyl oxim thiosemicacbazon Biacetylmonoxim phenylthiosemicacbazon Khong tuyn tnh 1 6mg/l p dng trn 14mg/l DL 0,1mg/l Trong dung dch nc hoc chit vi ru amyl. Khong phn tch l 2 -12mg/l To phc vi Mn(III)/Mn(IV), khong phn tch l 0-3g/l

Formandoxim

* Nhm porphin: Nhm thuc th ny cho nhy cao v chn lc vi cc ion kim loi do c tnh cht chn lc v cu hnh. * Nhm triphenylmetan, xanten v antraquinon Nhm thuc th ny c trnh by trong bng 4.

Bng 4. Nhm thuc th triphenylmetan, xanten v antraquinon to phc mu vi ManganThuc th Triphenylmetan o-hydroxyhydroquinonphtalein Metylthymol xanh Antraquinon Phc antrapurprin (1,2,7-trihydroxy-3- Khong phn tch 1-7mg/l metylamin-antraquinon-N,N-diaxetic axit) Phc alizarin Xanten Rhodamin 6G Chit trong benzen vi ion lin kt phc ca Mn(II) v 5,7-diclo-84 hydroxyquinolin, = 7.10 l.mol-1.cm-1 c chit vi EtOAc, = 1,05.105 l.mol-1.cm-1 To phc vi CTAB, = 8.104 l.mol1 .cm-1 Chit vi CHCl3, = 5,5.103 l.mol-1.cm1

Ni dung

c xc nh nh l phc 3 thnh phn vi zephiramin Vi cht hot ng b mt cetylpyridin bromua v CTAB lm tng nhy

Khong phn tch 1-10mg/l

Tetraiodflorescein Phenyl fluorin N-Butyl xanthate

T nhng nm 1990 tr li y, phng php trc quang vn tip tc c pht trin v c nghin cu tm ra nhng thuc th c nhy v chn lc cao hn. Nm 1998, M.Kamburova tm ra thuc th neotetrazolium clorua. Thuc th ny phn ng vi MnO4- to thnh phc c max =260nm v c chit vo 1,2 dicloetan. nhy ca phc ny t = 9,1.105 l.mol-1.cm-1.

Phng php ny c th phn tch Mn vi s c mt ca lng ln cc cation v anion. c p dng trong phn tch t v thp. [29] W.Wankler v F.Buhl vo nm 2003 dng phc hn tp c 4 thnh phn xc nh Mn tng n nh ca dung dch cng nh nhy. H ny gm c Mn(II) to phc vi 9-phenyl-2, 3, 7-trihydroxyl-6-fluoron trong s c mt ca cetylpiridin clorua v Triton X-100. nhy ca phc ny l = 1,77.105 l.mol-1.cm-1. Gii hn pht hin ca phng php 4ng/ml. Tuy nhin, phng php ny b nh hng bi nhiu ion l. [39] Nm 2006, A.Abdel v Shafi p dng hiu ng lin hp s dng thuc th tris(2,2'bipyridin)Osmi(II) ([Os(bpy)3]2+) xc nh Mn. Ion phc ny kt hp vi MnO4- to thnh cp ion lin hp c trng thi nng lng v th oxi ha kh thp. Trong phn t lin hp ny s c s chuyn dch electron t Os2+ sang MnO4-, a Mn7+ ln trng thi kch thch. Tc gi tm ra c rng, t l mol Mn7+ phn ng vi [Os(bpy)3]2+ l 1:5 ngha l Os2+ chuyn ln Os3+, Mn7+ xung Mn2+. Cp ion phc lin hp ny c hp th quang cc i ti cc bc sng 290nm, 315nm v 480nm. Phng php ny c nhy rt cao v khng b nh hng nhiu bi cc cation v anion (gii hn pht hin khi o bc sng 290nm l 0,72ng/ml). [15] tng nhy v chn lc, phng php chit trc quang cng c s dng rng ri. Theo B.Rezaei, mu c ph bng HNO3 v H2SO4, thm KIO4 vo v ph mu cho n mu hng chuyn Mn(II) thnh Mn(VII). Mn(VII) phn ng vi benzyltriphenylphotphoclorua (BPPC) to thnh phc v chit vo dung mi hu c (cloroform). S dng phng php ANN (mng noron nhn to) m rng khong tuyn tnh ca Mangan [18]. Mn(VII) c th to phc vi metylen xanh (phc ny c max =245nm) v c chit vo 1,2-dicloetan.

1.3.2. Phng php ng hc xc tc a) Nguyn tc Phng php ny c nhy v chn lc cao, thng dng phn tch vi lng m khng cn phi tch loi cc nguyn t cn hoc lm giu. Phng php s dng h phn ng ch th oxi ha cht mu hu c trong mi trng kim hoc axit. Mn(II) s xc tc lm tng tc phn ng oxi ha lm cht hu c b gim mu. Theo di s gim mu t l vi nng xc tc Mn(II). b) Cc phn ng ch th thng dng xc nh Mn(II) Trong dung dch, Mangan trng thi Mn2+ c kh nng xc tc cho nhiu phn ng gia KIO4 hoc H2O2 vi cc cht hu c hoc v c. Theo bi bo tng hp v cc phng php trc quang xc nh Mangan ca cc tc gi Barry Chriswell, Guy Rauchle v Mark Pascoe, t nhng nm 1990 tr v trc, phng php ng hc xc tc xc nh Mn rt pht trin. c rt nhiu nh nghin cu tm ra cc cht hu c c mu (cht ch th) khc nhau vi mc ch nng cao nhy v kh nng chn lc ca phng php (bng 5 v 6).

Bng 5: Phng php ng hc xc tc phn tch Mangan s dng cht oxi ha KIO4TT Thuc th Phm vi 1 15 g/l 5 100 g/l 0,4 5 g/l nhy 0,2 g/l Nitrilotriaxetic axit (NTA) Che Fe v Al bng FTartrat, Nc t citrat, oxalat nhin v Fe (II) gy nh hng NTA Cht hot ha Ch thch i tng p dng Huyt thanh ngi

1 Leucomalachite Green 2 Malachite Green

3 Dianisidin

4 Fuchsin leuco base nhy 2 g/l 5 Thymol Blue 6 Acetylaceton 5 500 g/l 7 Sulphanilic axit 0.5 5 g/l

Nc t nhin 1,10phenanthroline (phen) Nc t nhin Ch v hp kim Al

8 N,N- Diethylanilin 10 80 g/l 9 Bromophenol Blue 0,6 40 g/l Phen

Bng 6: Phng php ng hc xc tc xc nh Mn s dng cht oxi ha H2O2TT Thuc th Phm vi Cht hot ha Ch thch i tng p dng

0,005 5 Phen v Natri xitrat g/l 2 o-Dianisidine + tiron 0,2- 1 ng/ml Phen 1 Luminol 3 Alizarin S 4 5-(2-Hydroxy-3sulpho-5chlorophenylazo) barbituric axit 5 Indigo Carmin 0,3 -56 g/l nhy 6 Etylendiamin g/l

0,3 16 Phen g/l 6 1-Amino-8-naphthol- nhy 0.5 Etylendiamin 3,6-disulphonic acid g/l 7 Eriochorome Blue Trn 1.6pg/l Black R 8 Pyrogallol Red nhy 18 2,2-bipyridyl pg/ml

Phn ng pH 9.8 Nc sch

Da vo hai bng trn, cc phn ng ch th vi cht oxi ha l H2O2 xy ra trong mi trng kim cn vi KIO4 xy ra trong mi trng axit yu. Khi c cc cht hot ha nh o-phenanthrolin (phen-), nitrilotriaxetic (NTA), etilendiamin, 2,2-bipyridyl, nhy ca phng php tng ln rt nhiu. T nm 1990 tr li y, phng php ng hc xc tc vn pht trin mnh. Cc cht oxi ha nh KIO4 v H2O2 vn tip tc c p dng. Ngoi ra cn s dng thm cc cht oxi ha khc nh O2 [33], KMnO4 [30]. t c nhy cao (gii hn pht hin thp), cc phn ng oxi ha thng tin hnh nhit cao (ln hn 50oC). Bozhanov v Alexandrov p dng phng php ng hc xc tc xc nh Mn trong tinh du hoa hng vi khong xc nh l 0,05 2,5 g/l. Phng php ny s dng h

phn ng oxi ha diphenylamin-4 azobenzen-4-sunfonic axit bng KIO4, cht hot ha l phen- v tin hnh 80oC. [36] Cc thuc th thuc nhm azo [25,26], axit sunfanilic [27] phn ng vi KIO4 nhit 55 70oC cho php xc nh Mn(II) vi nng nh hn 6g/l. Cc h phn ng ny u s dng cht hot ha o-phenanthrolin tng nhy. Qin Wei v cc cng s tm ra cht hu c dahlia violet c th xc nh Mn(II) trong mi trng huyn ph. Tc gi s dng cht hot ng b mt Tween-20 tng tan nhng vn t c nhy cao vi gii hn pht hin l 3,75.10-2 g/l. Phng php ny c p dng phn tch Mn trong thc phm [31]. Nm 1991, Gomez v cc cng s p dng h phn ng H2O2 v Tiron trong mi trng axit, cht hot ha l phen- xc nh Mn(II) nhit 25oC. Khong tuyn tnh ca phng php l 1 200 g/l. Phng php ny p dng cho phn tch nc, bia v ru [22]. H phn ng oxi ha Rhodamin B bng KIO 4 trong mi trng axit yu, vi cht hot ha l phen- xc nh Mn(II) trong l ch [32] v hp kim [40]. Vi h phn ng ny, gii hn pht hin Mn(II) rt nh, khong 0,02g/l. Vo nhng nm cui th k 20, u th k 21, nhiu phng php ng hc xc tc s dng k thut FIA nng cao nhy v chnh xc. Phng php ny cho php kim sot c lng thuc th v nhit , thi gian n nh c chnh xc. H ny d dng t ng ha v tc phn tch nhanh, 1 gi c th xc nh c 30 60 mu. S.Nakano v cc cng s p dng k thut FIA xc nh Mn(II)

xc tc cho phn ng oxi ha 2,2-azinobis(3-etylbenzothiazolin-6-sunfonic axit) bng KIO4. Phn ng ny c hot ha bng phen-. Phng php ny cho php xc nh Mn(II) trong nc sng, h vi khong xc nh l 0,05 1 g/l.[34] H phn ng oxi ha N,N-bis(2-hydroxy-3-sunfopropyl)tolidin bng KIO4 vi Mn(II) xc tc, cht hot ha l 2,2bipyridin cho php xc nh Mn(II) trong nc sng, h. Phng php ny s dng k thut FIA vi khong xc nh Mn(II) l 0,02 3 g/l. [35] Ling Su v cc cng s p dng phng php ng hc xc tc xc nh Mn(II) trong nc t nhin. Phng php ny s dng k thut FIA, thuc th hu c l 4,4-bis(dimetylamino)-diphenylmetan, cht oxi ha l KIO4, cht hot ha l NTA. Phng php cho gii hn pht hin l 0,073 g/l.[28] Nh vy, cho n ngy nay, phng php ng hc xc tc vn pht trin mnh. Cc nh nghin cu vn ang tip tc tm ra cc thuc th hu c cng nh p dng cc k thut hin i, tm c phng php c chn lc tt v nhy cao.

Chng 2. THC NGHIM2.1. NI DUNG V PHNG PHP NGHIN CU

Phng php nhy v kh chn lc xc nh Mn l ng hc xc tc. T phn tng quan trn cho thy, h ng hc xc tc s dng rt nhiu thuc th hu c lm cht ch th trong c Rhodamin B (RhB) c dng xc nh Mn trong ch [29] v trong hp kim [37]. Trong lun vn ny, chng ti la chn h RhB v KIO4 xc nh lng nh Mn(II). Trong qu trnh oxi ha ny, RhB mt mu. Nh kh nng xc tc ca Mn(II), tc phn ng tng ln v tc phn ng c hot ha bng o-phenanthrolin (phen-). Tc mt mu ca RhB l ch th cho tc oxi ha. Gi s phn ng oxi ha xy ra nh sau: RhB + KIO4 R' + KIO4' Khi c mt cht xc tc Mn2+ c cc phn ng : KIO4 + Mn2+ KIO4' + Mn* Mn* + RhB R' + Mn2+ trong R' dng oxi ha ca RhB KIO4' sn phm qu trnh kh KIO4; Mn* - trng thi xc tc ca Mn2+ (Mn3+ hoc Mn4+) to phc vi phen-. Gi s phn ng (3) xy ra nhanh nn tc gim mu ca RhB nhanh. Tc phn ng chung ca h ph thuc vo tc phn ng (2). Nh vy, tin hnh o quang dung dch RhB s tnh c nng ca Mn(II). Trn c s , chng ti s tin hnh cc bc sau: (2) (3) (1).

- Kho st c trng ph ca h phn ng ch th oxi ha RhB v KIO4. Kho st cc yu t nh hng n h phn ng nh: pH, thi gian v nhit phn ng, nng KIO4, nng phen-, nng RhB. - Kho st tc dng xc tc ca Mn(II): xc nh c gii hn nh lng, gii hn pht hin, lp li, sai s h thng. - Kho st cc yu t nh hng. nh gi c thu hi v cch khc phc. - ng dng phng php ny vo phn tch mu gi v nc b mt. Kt qu c so snh vi phng php AAS. - Cc kt qu c x l s liu thng k bng phn mm Minitab.2.2. HA CHT V THIT B

2.2.1. Ha cht Cc ha cht s dng u dng tinh khit phn tch (PA) v s dng nc ct hai ln. Dung dch chun gc Mn(II): 1000 mg/l (Merk). Dung dch Mn(II) 10mg/l: ly 1ml dung dch chun gc Mn(II) vo bnh nh mc 100ml, thm 0,15ml HNO3 c, nh mc n vch bng nc ct sao cho pH dung dch khong 2 3. T dung dch Mn(II) 10mg/l, pha ch dung dch Mn(II) lm vic hng ngy l 100 g/l c pH khong 2 - 3. Dung dch RhB gc 4.10-4 M: cn 0,0479g RhB (C28H31O3N2Cl), chuyn vo bnh nh mc c 250ml, ha tan v nh mc n vch bng nc ct .

Dung dch KIO4 gc 0,01M: cn 0,5750g KIO4, chuyn vo bnh nh mc c 250ml, ha tan v nh mc n vch bng nc ct . Dung dch phen- 0,01 M: cn 0,4950g phen- (C12H8N2), chuyn vo bnh nh mc c 250ml, ha tan v nh mc n vch bng nc ct. T dung dch phen- 0,01M, pha dung dch phen- hng ngy s dng c nng 2,5.10-4M. Dung dch m axetat: pha dung dch m t dung dch CH3COONa 0,5M (Ac-Na) v dung dch CH3COOH 0,5M (Ac). Dung dch m pH = 3,8: trn dung dch Ac-Na v dung dch Ac theo t l th tch 12 : 88. Dng my o pH kim tra li v iu chnh cho thch hp bng dung dch HCl long v NaOH long. c dung dch m vi pH khc nhau, iu chnh t dung dch m pH = 3,8 bng dung dch HCl long v NaOH long v kim tra bng my o pH. Cc dung dch ion nh hng n php phn tch nh Cu2+, Ni2+, Co2+, Fe3+, Zn2+, Cl-, PO43-, c pha ch c nng thch hp t dung dch chun gc 1000mg/l (Merk). Dung dch NH4SCN 2M: cn 15,202g NH4SCN, chuyn vo bnh nh mc c 100ml, ho tan v nh mc n vch bng nc ct. Dung dch cht che: dung dch NaF 0,5M (cn 2,10g NaF, chuyn vo bnh nh mc c 100ml, ha tan v nh mc n vch bng nc ct) v dung dch citrat 0,5M (cn 14,71g natri xitrat, chuyn vo bnh nh mc c 100ml, ha tan v nh mc n vch bng nc ct. iu chnh pH ca dung dch nm trong khong 3 4).

2.2.2. Thit b My UV-VIS 1601 (Shimazu - Nht) vi di o 190 1100nm. Cuvet thch anh dy 1,0cm. My quang ph hp th nguyn t AAS A800 (Perkin Elmer M). My o pH vi cp in cc kp (Thermo Orion - M). Ni iu nhit (Trung Quc). ng h hn gi.2.3. QUY TRNH XC NH

2.3.1. Cch tin hnh kho st cc iu kin th nghim 25oC v 80oC 2.3.1.1. Phn ng tin hnh 25oC Ly vo hai dy bnh nh mc 10ml c Dy 1: RhB 8.10-6M, m pH = 3,8 c nng m 0,15M; phen- 5.10 -5M, Mn(II) 5ng/ml; KIO4 6.10-4M. Dy 2 (ng nn): c cc cht nh dy trn nhng khng c Mn(II). Theo di tc phn ng t lc cho KIO4. Ngay khi thm KIO4, nh mc, lc u v nhanh chng a dung dch vo cuvet my trc quang v theo di ng h n giy th 30 ghi hp th quang ph thuc vo thi gian (A t) bc sng 550 nm, dung dch so snh l nc ct. Dung dch c o n giy th 120. T kt qu ny xc nh c gi tr tg = A/t, A = A30 A120, A30 hp th quang giy th 30, A120 - hp th quang giy th 120. Mn(II) c xc nh theo tg. 2.3.1.2. Phn ng tin hnh 80oC Nu khng c cht c ch: Cng hn hp pha 2 dy nh trn nhng c nng phen- 10-5M v Mn(II) 3ng/ml. Sau khi cho KIO4, a bnh vo ni

iu nhit, gi 80oC trong vng 8,5 pht. Ly ra lm ngui nhanh n nhit phng. Nu c cht c ch: ly vo ng nghim chu nhit dung tch 10ml, dung dch RhB 8.10-6M, phen- 10-5M, pH = 3,8; Mn(II) 3ng/ml; KIO4 6.104

M, thm nc ct sao cho th tch dung dch khong 9,5 ml. Gia nhit dung

dch hn hp 80oC trong thi gian 8,5 pht sau thm NH4SCN 0,02M. Lm ngui dung dch n nhit phng. Chuyn vo bnh nh mc dung tch 10ml, thm nc ct n vch v lc u. o hp th quang ca tng dung dch bc sng 550 nm, dung dch so snh l nc ct. T kt qu ny xc nh c gi tr A = Ann AcMn(II)

. Mn(II) c xc nh theo hp th quang A. 2.3.2. Quy trnh xc nh nh hng cc ion l Ly vo hai dy bnh nh mc 10ml c Dy 1: RhB 8.10-6M, m pH = 3,8 c nng m 0,15M; phen-

(5.10-5M 25oC v 10-5M 80oC), Mn(II) (5ng/ml 25oC v 3ng/ml 80oC); KIO4 6.10-4M, SCN- 0,02M. Dy 2: c cc cht nh dy 1 nhng thm cc ion cn tr. Tnh thi gian bt u t lc cho KIO4. Tin hnh nh quy trnh 2.3.1.1, sau o hp th quang ca dung dch c xc tc v dung dch c thm cc ion cn tr theo thi gian. T tnh c tgMn(II) v tgion. Tin hnh nh quy trnh 2.3.1.2, o c gim hp th quang ca dung dch c xc tc AMn(II) v dung dch c thm cc ion cn tr Aion so vi mu nn. T cc kt qu trn tnh c sai s tng i (%).

2.3.3. Quy trnh xc nh mu gi Ly vo dy bnh nh mc 10ml c RhB 8.10 -6M; m pH = 3,8 c nng m axetat 0,15M; phen-10-5M; F- 0,02M; Fe3+ 0,5.10-7M, Co2+ 2.10-7M, Ni2+ 10-6M, Zn2+ 2.10-6M , Cu2+ 6.10-6M, Pb2+ 2.10-6M, Cd2+ 5.10-6M, PO43- 104

M; Mn(II) 1ng/ml; KIO4 6.10-4M, SCN- 0,02M. Dy 2: c cc cht nh dy 1 nhng khng c Mn(II). Tin hnh nh quy trnh 2.3.1.2. Gi tr Mn(II) trong mu gi c xc

nh da vo gim hp th quang A. 2.3.4. Quy trnh phn tch mu thc t Quy trnh ly mu v bo qun mu: mu c ly vo y bnh PE dung tch 1 lt, thm 2ml HNO3 c vo bnh (lng mu trn ra nh hng khng ng k n kt qu phn tch) sao cho mu t gi tr pH = 1 - 2. Vn np bnh v lc u. Mu c chuyn n phng th nghim v phn tch ngay. Nu khng, phi bo qun mu nhit di 4oC (c th trong vng 1 thng). Quy trnh phn tch: Trung ha mu bng NaOH hoc HCl long sao cho t pH = 3 4. Lng mu ly phn tch sao cho trong 10 ml dung dch o c Mn(II) nm trong khong tuyn tnh ca php o. Ly vo dy bnh nh mc 10ml c: RhB 8.10-6M, m pH = 3,8 c nng m 0,15M; phen- 10-5M, F- 0,02M; mu cha Mn(II); KIO4 6.10-4M. Phn tch mu theo quy trnh trong mc 2.3.1.2. Xc nh c Mn(II) da vo gim hp th quang A. Phn tch Mn(II) theo phng php AAS: tin hnh quy trnh phn tch Mn(II) nh tiu chun EPA 243.1.

2.4. X L S LIU THNG K

Sai s tng i (ER) ER =EA xi hay ER % = . 100%

xi gi tr o c; - gi tr tht hay gi tr bit trc lch chun (S)

S=

(xN i =1

i

x

)

2

N 1

vi N l s th nghim. S bc t do trong trng hp ny l f =N-1. lch chun tng i (RSD) RSD(%)= .100 % Tng quan tuyn tnh Dng chun Student t =r. n2 (1 r 2 ) S x

vi r l h s tng quan Pearson, n l s th nghim , tchun tra bng P=0,95, s bc t do f=n-2. Nu ttinh > ttra bang th x v y c tng quan tuyn tnh. Nu tnh ton bng cc phn mm thng k, c th s dng gi tr P ( Pvalue) v so snh vi khng tin cy . Thng thng nu P value