4.2. Phng php quang ph hng ngoi

My quang ph

My quang ph hng ngoi dng ghi ph trong vng t 4000 cm-1 n 670 cm-1 (t 2,5 mm n 15 mm) hoc trong mt vi trng hp ti 200 cm-1 (50 mm). My quang ph chuyn i Fourier s dng bc x a sc v tnh ton ph theo di tn s t cc d liu gc bng chuyn i Fourier. Cc my quang ph vi h thng quang hc to bc x n sc trong vng o cng c th c s dng.

Thng thng ph c xem l hm s ca truyn quang T; T l t s ca cng bc x truyn qua v cng bc x ti.

hp th nh sng (A) l logarit thp phn ca nghch o truyn quang .


T = I/Io

Io = Cng nh sng ti

I = Cng nh sng truyn qua.

Chun b mu

ghi ph truyn quang hay ph hp thu, cht th c chun b theo mt trong cc phng php sau:

Cht lng

o ph ca mt cht lng di dng phim gia 2 tm phng trong sut i vi bc x hng ngoi hay trong cc o c b dy thch hp v cng trong sut i vi bc x hng ngoi.

 

Cc cht lng hay cht rn chun b di dng dung dch

Chun b dung dch th vi dung mi thch hp. Chn nng v b dy ca cc o thch hp c th ghi c mt ph tt. Ni chung, c th thu c kt qu tt vi nng t 1,0% ti 10% v b dy ca cc o t 0,5 mm ti 0,1 mm.

Cc cht rn

o ph ca cht rn c phn tn trong mt cht lng (bt nho) hay trong mt cht rn thch hp (a halid). Nu c quy nh trong chuyn lun ring, lm mt phim mng t khi cht rn nng chy gia hai tm phng trong sut vi bc x hng ngoi.

 

Bt nho

Nghin mt lng nh cht th vi mt lng ti thiu parafin lng hoc cht lng khc ph hp. Dng t 5 n 10 mg cht th l va to mt bt nho ph hp. p bt nho gia hai tm phng trong sut vi bc x hng ngoi.

Vin nn (a halid)

Tr khi c ch dn khc, nghin 1 - 2 mg cht th vi 300 - 400 mg bt mn kali bromid (IR) hoc kali clorid (IR) sy kh. Lng ny thng to mt vin nn c ng knh 13 mm v cho ph c cng ph hp. Nghin hn hp cn thn v ri u n trong mt khun thch hp. Nn khun c hn hp cht th ti p sut khong 800 MPa trong iu kin chn khng. Mt vi yu t c th to nn vin nn khng tt nh: Nghin khng k hay nghin qu k, m, cc tp cht trong mi trng phn tn. Vin nn khng t yu cu nu kim tra bng mt thy vin nn khng ng nht v khng trong sut hay truyn quang khong 2000 cm-1 (5 mm) nh hn 75% khi khng c bng hp thu c hiu vng ny v khng c b tr bn tia i chiu, tr khi c ch dn khc.

Cc cht kh

Ghi ph cc kh trong cc o trong sut vi bc x hng ngoi v c quang trnh 50 mm - 100 mm. i vi cc cht kh c h s hp th hng ngoi nh hoc c dng vt, ta dng cc cc o c h thng gng, to nn s phn x bn trong cc nhiu ln v do c th t quang trnh 1 mt hoc thm ch n 10 mt hoc hn na.

To chn khng trong cc o v np y kh n p sut yu cu nh mt nt xoay hoc mt van kim vi ng chuyn kh thch hp ni cc o vi bnh cha kh cn kho st. Nu cn iu chnh p lc trong cc o n p sut kh quyn, dng mt kh trong sut vi bc x hng ngai, th d kh nitrogen hay argon. trnh nh hng s hp th ca hi nc, carbon dioxyd hoc nhng kh khc c mt trong bu kh quyn, t mt cc o tng t nh cc o ng kh cn kho st bn tia i chiu. Cc o ny c ht chn khng hoc c np kh trong sut vi bc x hng ngoi.

Ghi ph bng phn x ton phn suy gim

t mu th tip xc trc tip vi lng knh phn x ton phn suy gim

Ghi ph bng phn x nhiu ln

Khi c ch nh trong chuyn lun ring, chun b cht th theo cc phng php sau:

Dung dch

Ho tan cht th trong dung mi thch hp theo nhng iu kin c quy nh trong chuyn lun ring. Lm bay hi dung dch trn tm thalium bromo - iodid hoc tm phng khc ph hp.

Cht rn

t cht th trn tm thalium bromo - iodid hoc trn tm phng khc ph hp sao cho c s tip xc ng u.

nh tnh

nh tnh bng cc cht i chiu ho hc

Chun b cht th v cht i chiu theo cng mt quy trnh v ghi ph t
4000 cm-1 n 670 cm-1 (2,5 mm n 15 mm) trong nhng iu kin nh nhau. Cc tiu truyn quang (cc i hp th) trong ph ca cht th v cht i chiu phi tng ng v v tr v cng tng ng.

Khi ph ca cht th v ca cht i chiu dng rn c s khc nhau v v tr ca cc tiu truyn quang (cc i hp thu), phi x l cht th v cht i chiu theo cng mt cch sao cho chng kt tinh hay to thnh cng dng, hay tin hnh nh m t trong chuyn lun ring ri mi ghi ph.

nh tnh bng ph i chiu

Kim tra phn gii ca my

Ghi ph ca phim polystyren c b dy 0,04 mm. Hiu s x (hnh 4.2.) gia phn trm truyn quang cc i truyn quang A ti 2870 cm-1 (3,48 mm) v cc tiu truyn quang B ti 2851 cm-1 (3,51 mm) phi ln hn 18. Hiu s y gia phn trm truyn quang cc i truyn quang C ti 1589 cm-1 (6,29 mm) v cc tiu truyn quang D ti 1583 cm-1 (6,32 mm) phi ln hn 12.

 

 

 


Text Box:  truyn quang %
 

 

 


Kim tra thang s sng

C th kim tra thang s sng bng cch dng phim polystyren. Phim ny c cc cc tiu truyn quang (cc i hp th) cc s sng (tnh bng cm-1) nh bng 4.2.

 

Bng 4.2. Cc tiu truyn quang ca phim polystyren v cc gii hn cho php

 

3060,0 (1,5) cm-1

2849,5 (1,5) cm-1

1942,9 (1,5) cm-1

1601,2 (1,0) cm-1

1583,0 (1,0) cm-1

1154,5 (1,0) cm-1

1028,3 (1,0) cm-1

 

Phng php:

Chun b cht th theo ch dn i km vi ph i chiu. Tin hnh trong iu kin ging nh khi kim tra phn gii, ghi ph ca cht th v chng ln ph ln cc bng ca polystyren 2849,5 cm-1 (3,51 mm), 1601,2 cm-1 (6,25 mm) v 1028,3 cm-1 (9,72 mm). So snh ph cht th vi ph i chiu v vi cc bng ca polystyren nh ch dn trn. Dng cc v tr ca bng polystyren lm chun, v tr ca cc bng c gi tr trong ph ca cht th v ph i chiu phi tng ng trong khong 0,5% thang s sng. Cng tng i ca cc bng phi ph hp gia 2 ph.

 

 

Phng php quang ph cn hng ngoi

Phng php quang ph cn hng ngoi l k thut c bit hu ch nh tnh cc cht hu c. Mc d cc ph ch gii hn trong cc cng hng ca C - H, N - H, O - H v

S H, thng chng cho cc thng tin c gi tr. Tuy vy, cc ph ph thuc vo mt s thng s nh kch thc ht, tnh a hnh, vt dung mi, m ... m nhng thng s ny khng th lun c kim sot. V l do ny, khng th so snh trc tip ph ca cht th vi ph i chiu m cn x l d liu bng phng php ton hc c thm nh.