Trong he FIA mfiu phan tfch dugc chuyen lú van bam mfiu deii vdng pluin ling, Uic dung vdi thude Ihii* de tao ra san phfim nhat dinh cd the phiil hien vii dinh lugng nhd mgl delecta thfch hgp. J. M. Burguera va cong su da sií dung phuang phcip DHXT-DC de xac djnh idt trong nude lieụ Theo phuang phiip nay, Í trong nude lieu dugc oxi hda thanh I2 bdi K2Cr207, rdi I2 dugc mang bdi mgl đng nitrogen. Phuang phiip nay diing detecia hda phat quang vdi chat pluit quang lii dung dich cobalt (II); GHPH la lOpgl/L [55], [75], [76], [100].
Tiic gia [100] da xiic dinh lugng vet idt trong sua bfing phuang piuip DHXT-DC. Theo đ mfiu siia dugc phan hiiy bfing phuang pluip v6 ca hda irong
moi Irudng kiem (KOH + ZnS04) d 600"C , sau 66 dua mau da xu If viio he FIA
ba kenh. su dung phiin ling chi Ihi lii KSCN-NaN02 vii detecia UV-VIS, phuong phap uiiy cd do lap Uii cao (94,5-100,7%), GHPH la 0,99|.igl7L vdi du lech chuan
tuang đi la 5%.
O Viet Niim, Chu Xuan Anh va cong su da iip dung phuang pluip DHXT- DC de Xiic dinh idt trong nude bien va mudi an; he phiin ling chi thj [Cé^^- As^^], he FIA ba kenh, delecta UV-VIS [2].
1.5.2.2. Phuong phiip DHXT khong su dung phan ling chi Ihi [Cc'**- As^"^] Ti^í sau khi Sandell Ẹ B va Kolhoff Ị M nghien ciiu phuang phiip dinh lugng idl. hfing ciich dua Viio hieu ling xiic Uic ciia idt len he pluin ting [Cé"- As^"*] ( 1937), cho den niiy, ngudi ta da nghien ciiu them nhieu phan liiig chi Ihi kluic thiiy the cho he [Ce"*"^- As"^^] de xiic dinh lugng vel idt [51].
TiCii biing 1.7, liel ke idm lai mgl sd cong Irinh ngliien cLiu xac dinh lugng vet idl bang phuong phap DHXT khong sii" dung he [Cc"^"^- As^^].
1,6. Phuoiig phap ke hoiich hda thuc nghiem [31], [37], [47], [95]
Trong thuc nghiem Hda hgc phan tfch, de lieii hiinh thn dieu kien tdi uu cho mot ihi nghiem cd nhieu yeu id anh hudng len ket qua pluin tfch, ngudi ta thudng Sli dung phuong phap dan bieii, tuy nhien piiuang phap nay thudng mac phai mgl sd nhugc diem, chang hiin nhu khong diinh gia dugc anh hudng luang lid cila Ciic ycu td len kel qua thf nghiem, hofic khong the biel dugc miic do anh hudng cuii Umg yeu td. VI the, de khfic phuc nhúng nhugc diem niiy, can phai lieii hanh ciic thf nghiem theo phuang phap ke hoiich hda lliuc nghiem. Ciie phuang iin . tim dieu kien tdi uu theo phuang phiip ke hoiich Iida thuc nghiem hiio gdm: phuang phiip mien gan diing, phuang phiip miing don hinh, phuang pluip mat muc lieu (res]-)onse surface), phuang phiip dudng đc nhat (the steepest ascent palh); trong đ phuong phiip mat muc lieu va dúdng đc nhiít la thudng dugc sii dung nhidu trong Hda phan tfch de thay the cho phuang phiip dan bieiị
* Phuang phap khao sat mat muc tieu: ngudi ta lien hiinh nhung ihii luc
toiin hgc de tim cue tri ciia ham muc lieu can khao sat. Ham muc lieu dugc bieu di6n bfing mgl phuang trinh hdi qui diing da thiic:
y = bo + Zb.Xi + bijXiXj + SbiiX;^ ( 1 . 1 4 )
Phuong trinh hdi qui bac hai mo la mot mat muc lieu trong khong giiin n chieu, cd Idi lom tuang ling vdi cac giii tri cue tri ciia ham muc lieụ Liíy diio ham rieng theo liing yeu td ciia ham muc lieu de lim cue tri va cac gia tri cue tri tim dugc se la dieu kien thuc nghiem tdi uu nhfim tdi uu hda thuc nghiem.
De tap trung khao sat cac mien cue tri cua ham muc lieu, ngudi la phai dua ham muc lieu bac hai ve diing chfnh tfic:
/ = 1 / = 1
Neu n = 2 ta dugc: Y- Y, = B, jX,^ + B22X2I Khi đ: Bn, B22 tim dugc nhd dinh thiíc:
0,5b,2 b , , - B
= 0 (1.15)
0,5bi2 0,5b22
Trong đ
Y,: gia tri ciia ham muc tieu d gdc tga do mdi Y: gia tri ciia ham muc lieu
X|...X„: cac bieii chufin, la ham tuyen Ifnh ciia cac yeu td x,, X2-'-K
B|,, B22..-B,,: he sd ciia phuang trinh hdi qui diing chfnh tfic Dieu kien de xet tinh diing ciia viec lim cac gia tri B nhu sau:
/ = ! ;=l
Khiio sat y nghla hinh hgc ciia ham muc lieu dang chhih tfic se biel diem cue tri la cue diii hay cue lieu
* Phuang phap dúdng đc nhat (cdn ggi la phuang phap Box- Wilson-
dudng đc nhat :1a dúdng chuyen dich theo vecta gradient y(x), vecta nay bieu thi su bicii thien nhanh nhitt ve phfa cue tri y(x) lii ham muc lieu bieu thi cho diii
lugng do). Theo phuang phap nay, cac thf nghiem dugc lien hiinh bfing ciich thay đi tilt ca cac yeu td anh hudng theo iCrng khoang bien thien xiic dinh theo hudng lien dfin vc phfa cue Irị Tun dieu kien tdi uu theo phuang phap dudng đc nhai la
lim cac khoang bien thien mdi Xp X^ luang ling vdi cac ycu id Xj, Xj ti Ic vdi nhau
theo mot ti sd nhat dinh de chuyen dich đng thdi cac dieu kien thf nghiem ve phfa cue trj. Cac khoang bien thien mdi nay dugc xay dung tren ca sd phuang trinh hdi qui mo ta diing thf nghiem dang lieii hanh. Sa đ tdng quiit phuang phap dudng đc nhat dugc bieu di6n tren hinh 1.5
y^ i yi ^ k , , • • • ' . . - • • ' • 1 • • ' i 1
Hinh 1.5. So 66 bieu diSn thuc nghiem tim dieu kien tdi uu theo phuang
phiip dudng đc nhat
Phuang trinh hdi qui bieu thi cho ham muc lieu cd dang tdng quiit nhu sau:
y = ZbiX.+ZbjjXiXj + Ibij^Xj Xj x,, +,... Zbij x^^ + (1.16)
Trong đ: y: ham muc tieu bieu thi dai lugng do
x: cac yeu td anh hudng {x•^, Xj, x^.)
b; he sd hdi qui mo la anh hudng ciia cac yeu td (bj, bj, b^^...) Bac da thiíc cang cao thi mo hinh met la ham muc tieu cang chfnh xac va ngugc liiị Vi the, de nang cao do chfnh xac ciia ham muc lieu, chiing tdi chgn mo hinh hda bac haị
Theo phuang phap dudng đc nhat, trinh tu lien hanh thf nghiem Iheo ciic budc sau:
"= xay dung ma Iran thuc nghiem. Trong ma Iran thuc nghiem, ngudi ta diing Ciic gia tri ma hda cho cac yeu td anh hudng, va chi chgn hai miic de lam
thuc nghiem: miic cao +1 va miic tháp -1 vdi khoang bien thien ban dau X dugc
chgn sao clio dii Idn đi vdi khoang bien đi ciia mo hinh de vugt quii sai sd binh phuang irung binh ft nhitt la 3 hoac 4 Ifin. Diil x,, X2, X3,..., x„ la cac kf hieu chi gia
tri thuc 66 tieii hanh thf nghiem; miic ca sd de lien hanh thf nghiem luang ling vdi
cac yeu id nay la Qj, Q2, Q3v.-, Qn» bang dieu kien thf nghiem ciia cac yeu id dugc trinh biiy n h u d bang 1.4.
Bdng 1.4. Dieu kien thf nghiem ciia ciic yeu td anh hudng
Yeu to Muc goc (0) Khoang bien thien (Ạ)
Muc cao (+1) Mile thap (-1) X| Q, ^ , Q,+A, Q,-X, X, Q, K Q,+?i, Q2-^2 x„ Q„ K Qn + K QnA„ Ma Iran thuc nghiem đi hdi phai tuan theo ba dieu kien:
+ Tfnh chat chuan hda: tdng binh phuang ciic gi*i tri trong mot col bfing sd N
thf nghiem, nghla la: ^ Xjj = N; j = 0, 1 k 1=1
+ Tfnh chat true giao: ma Iran khong cd thi nghiem trCing nhau, liic la: N
^ X u j X u j = 0 ; u ^ i ; u,j = 0, 1,..., k 1-1
+ Tfnh đi xiing: sd miic cao va miic tháp trong mot cot bang nhau N
^ X i = 0 ; j = l , . . . , k ; j ^ O i=1
Trong đ Xjj la yeu td anh hudng d hang thii: i va cot thiíj; n la tdng sd thf nghiem; u la mot thf nghiem bat kị
bac hai lam xoiiỵ So thf ngliiem theo mo hinh bile hiii lam xoay dugc tfnh nhu sau:
N = 2""*' + 2.n + No; trong đ: 2""'': sd thf nghiem d ma Iran gdc 2.n: sd thf nghiem diem siio
N{,: sd Ihi nghiem d diem tam No > 1. D6 ma Iran bao dam tfnh iruc giao,
duii them tham sd cp, khi đ dieu kien true giao lii: can
N 2^~^ _ 2d
X (X^i - (p).(xfu - cp) = 0 ; trong do: cp = — - ^ va:
1=1 + 2n + N,
d — ± V V N . 2 ^ _ 2 ^ , d day q la sd thi nghiem nil ggn. Vi q va n la sd cho trudc, nen cd the tfnh sSn dugc d va cp theo bang 1.5
Bdng 1.5. Gia tri canli liiy don d va tham sd cp trong ma tain bac hai tam xoiiy
Mo hinh 2' 2' 2' 25-1 N 9 15 25 27 d 1,414 1,682 2,000 2,378 (p 2/3 = 0,6667 V 8 / 1 5 = 0 , 7 3 0 3 4 / 5 = 0 , 8 0 0 0 ( 4 V 3 ) / 9 = 0 , 7 6 8 9 * Liim ihi nghiem theo ma Iran
"' Xií If sd lieu thu dugc va tim phuang trinh hdi qui - Tim he sd phuang trinh hdi qui
- Danh gia tfnh cd y nghla ciia he sd hdi qui theo chuan Student (t)
Mot he sd hdi qui dugc xem la cd y nghla, nghla la cd đng gdp dang ke
Viio phúóng trinh hdi qui neu gia tri chuan Student: t„'r,h > tbiing (P^fo - No-l)
Diinh gia tfnh phCi hgp ciia phuang trinh hdi qui theo ehuiui Fisher (F)
OQ J\ - L „=] yV(, - 1 ^=1
Vdi: N(,: sd thf nghiem lap lai d miic gdc
YQ : gia tri trung binh d miic gdc
Kô - FQ : su sai khac giua gia tri thuc nghiem Ian thu k d miic gdc va gia tri trung binh d miic gdc
hiim muc lieu tfnh d thf nghiem Ihií u
N: tdng sd Ihi nghiem = T'^-\- 2,, + N,,
L: sd sd hiing cdn liii trong phuang liinii hdi qui sau khi da danh giii tfnh cd y nghla cua cac he sd hdi qui
N„: sd thf nghiem lap liii d muc gdc
Tu phixang trinh hdi qui tim dugc se chi ra ham muc lieu mo ui dung thf nghiem, neu: F,,-,,, < F^:,^^ (PJiia) tldng thai cd the su dung phuang irhih nay de
lam thf nghiem theo phuang phiip dudng đc nhat Trong đ Ft,an.(P,f|,f2). vdi P: do tin Ci)y thdng ke
f I = N - L = f thfch ling; f2 = n - 1 = f thf nghiem; n: sd yeu td anh hudng
'^ Dua vao ham muc lieu tim dugc de tim dieu kien tdi uu theo phuang
phiip dudng đc nhat
Ciic dieu kien mo lii quy hoach Ihuc nghiem ihco phuang pluip duang đc nhal dugc neu d bang 1.6
Bdng 1.6. Quy hoach thuc nghiem theo phuang phap dudng đc nhiít
Yen td Muc goc (0)
He so b, (tinh tu phuong Irinh hoi qui)
Khoang bien thien (X)
b,A,
X'= b,.XJ (b,AJ),„„
Lam tion X cho X*-,
Lam thf nghiem 1 theoẠ*| Lam thi nghiem 2 theo/V*, Lam till' nghiem 3 theol*, Lam till nghiem k theoA,*,
X| 0, 0, b, X, B|A, X\ X\ Q , + r , Q , + 2 r , Q,+3X*, Qi+k;V*, X, Q, b2 K. Kh x\ x\ Qp.+^*, Q2+2?^*2 Q2+3^*2 Q,+k^*, Xi 0. b. X, bvẠ-, x\ x\ Q.+X\ Q . + 2 r , Q.+3^*, Q,+kA\ Xn Q„ bn K b„A„ ^ • „ r„ Qn+>t*„ Qn+2r. Q„+3A*„ Qn+k^*n y y*i * y 2 y\ y\
Neu yi^ la gia tri thu dugc cue dai, khi đ dieu kien thuc nghiem de thu dugc y,, lii dieu kien tdi uu tim dugc [31]
1.7. TINH HINH NGHIEN CUU XAC DINH HAM LUONG IOT TRONCJ: N U 6 C TIEU, SLTA, T O C , MAU NGUC)I VA NUOC SINH HOAT.