4.4 Phng php quang ph nguyn t pht x v hp th

Cc phng php quang ph nguyn t pht x v hp th c s dng xc nh nng ca cc nguyn tố bng php o cng pht x hoc hp th nh sng bc sng c trng bi hi nguyn t ca nguyn t c ha hi t cht cn phn tch, v d, bng cch a mt dung dch ca cht phn tch vo ngn la.

Phng php quang ph pht x nguyn t

Phng php quang ph pht x nguyn t l phng php xc nh nng ca mt nguyn t trong mt cht bng cch o cng ca mt trong cc vch pht x ca hi nguyn t ca nguyn t c ha hi t cht . Vic xc nh nng nguyn t c tin hnh bc sng tng ng vi cc vch pht x ny.

Thit b

My quang ph pht x nguyn t bao gm cc b phn ch yu l b phn ho hi nguyn t ca cc nguyn t cn xc nh (ngn la, plasma, h quang in v.v...), b n sc ho v b phn pht hin. Nu b phn ho hi l ngn la, nc l dung mi c la chn pha dung dch th v dung dch chun. Tuy nhin, dung mi hu c cng c s dng nu m bo chc chn rng n khng nh hng n n nh ca ngn la.

Phng php tin hnh

Vn hnh my quang ph pht x nguyn t theo nh ch dn ca hng sn xut v cch t bc sng quy nh. a dung dch mu trng vo b phn ha hi nguyn t v hiu chnh tn hiu c c v "0". a dung dch chun c nht vo bung ha hi nguyn t v hiu chnh nhy ca my c tr gi c thch hp.

Vic nh lng c thc hin bng cch so snh cc dung dch th cha bit nng vi cc dung dch chun ca nguyn t cn xc nh bng phng php xc nh trc tip (phng php 1) hoc bng phng php thm chun (phng php 2).

S dng phng php 1, tr khi c ch dn khc.

Phng php 1: Phng php xc nh trc tip

Chun b dung dch cht th (dung dch th) nh c m t trong chuyn lun ring sao cho nng ca nguyn t cn xc nh nm trong khong nng ca cc dung dch chun. Chun b khng t hn ba dung dch chun ca nguyn t cn xc nh c nng nm trong khong ph thuc tuyn tnh gia nng v cng vch pht x ca nguyn t cn phn tch. Bt k thuc th no c dng trong vic chun b cc dung dch th u phi c thm vo cc dung dch chun v dung dch mu trng cng nng . a dung dch mu trng vo my, iu chnh tn hiu c c v "0". a ln lt dung dch th v tng dung dch chun vo my, t nht mi dung dch lm ba ln, ghi li kt qu c n nh. Ra my bng dung dch mu trng sau mi ln o cho n khi tn hiu tr v gi tr c ban u ca mu trng. T cng vch pht x c c ca cc dung dch chun, thit lp ng chun biu th s thay i cng vch pht x theo nng nguyn t cn xc nh v t ng chun ny xc nh nng nguyn t trong dung dch th.

Phng php 2: Phng php thm chun

Cho vo t nht ba bnh nh mc c dung tch nh nhau, cc th tch bng nhau ca dung dch cht em th (dung dch th) c chun b nh ch dn trong chuyn lun. Thm vo tt c cc bnh, tr mt bnh, cc th tch ln dn ca dung dch chun c nng bit ca nguyn t cn xc nh sao cho nng ca nguyn t ny trong cc bnh u nm trong khong tuyn tnh gia nng v cng pht x. Pha long cc dung dch c cha trong bnh n va th tch bng dung mi.

a dung dch mu trng vo my, iu chnh tn hiu c c v "0". a ln lt dung dch th v tng dung dch chun vo my, t nht mi dung dch lm ba ln, ghi li kt qu c n nh. Ra my bng dung dch mu trng sau mi ln o cho n khi tn hiu tr v gi tr c ban u ca mu trng. Tnh phng trnh hi quy ca ng thng chun bng cch dng phng php bnh phng ti thiu v xc nh t ng thng ny nng ca nguyn t cn xc nh trong dung dch th. Mt cch khc, v th biu din s lin quan gia gi tr c c v lng thm vo ca nguyn t cn xc nh. Ni cc im trn th v ko di v pha tri cho n khi n gp trc nng . Khong cch gia im ny v im giao nhau ca trc ta l nng ca nguyn t cn xc nh trong dung dch th.

Phng php quang ph hp th nguyn t

Phng php quang ph hp th nguyn t l phng php xc nh nng ca nguyn t trong mt cht bng cch o hp th bc x bi hi nguyn t t do ca nguyn t c ho hi t cht th. Vic nh lng c tin hnh bc sng ca mt trong nhng vch hp th ca nguyn t cn xc nh.

Thit b

My quang ph hp th nguyn t ch yu bao gm ngun bc x, b phn ha hi nguyn t ca nguyn t cn xc nh (ngn la, l graphit v.v...), b n sc ho v b phn pht hin.

Phng php a cc cht vo phn tch ph thuc vo k thut nguyn t ho mu. Nu nguyn t ha bng ngn la, cc cht s c ho hi v nc l dung mi c chn chun b cc dung dch chun v th, tuy nhin cc dung mi hu c cng c th c s dng nu m bo chc chn l dung mi khng nh hng n n nh ca ngn la. Nu nguyn t ho khng ngn la (s dng l graphit), cc cht a vo c th c ho tan trong nc hoc trong dung mi hu c.

Qu trnh ha hi nguyn t cng c th c to ra bn ngoi my quang ph, v d, phng php ha hi lnh cho thy ngn hoc mt s hydrid. i vi thy ngn, nguyn t c ha hi bng s kh ho hc v hi nguyn t c dn bng mt dng kh tr n mt cc o c t trong ng quang trc ca my. Cc hydrid c dn bng hn hp kh t hoc bng kh tr n mt cc o c t nng, ti y chng c nguyn t ha.

Phng php tin hnh

Vn hnh my quang ph hp th nguyn t theo cc ch dn ca hng sn xut my v cch t bc sng quy nh. a dung dch mu trng vo bung ha hi nguyn t v hiu chnh kt qu sao cho hp th c c trn my bng "0". a dung dch chun i chiu c nng ln nht vo my v hiu chnh nhy t c mt php c hp th thch hp.

Vic nh lng c thc hin bng cch so snh vi cc dung dch chun i chiu bit nng ca nguyn t cn xc nh bng phng php xc nh trc tip (phng php 1) hoc bng phng php thm chun (phng php 2).

S dng phng php 1 tr khi c ch dn khc.

Phng php 1: Phng php xc nh trc tip

Chun b dung dch cht th (dung dch th) nh c m t trong chuyn lun ring sao cho nng ca nguyn t cn xc nh nm trong khong nng ca cc dung dch chun. Chun b khng t hn ba dung dch chun ca nguyn t cn xc nh c nng nm trong khong tuyn tnh gia nng v hp th ca nguyn t cn phn tch. Bt k thuc th no c dng trong vic chun b cc dung dch th u phi c thm vo cc dung dch chun v dung dch mu trng cng nng . a dung dch mu trng vo my, iu chnh tn hiu c c v "0". a ln lt dung dch th v tng dung dch chun vo my, t nht mi dung dch lm ba ln, ghi li kt qu c n nh. Ra my bng dung dch mu trng sau mi ln o cho n khi tn hiu tr v gi tr c ban u ca mu trng. Nu s dng k thut nguyn t ho khng ngn la, l graphit phi c t li gia cc ln phn tch. T cng vch hp th c c ca cc dung dch chun, thit lp ng chun biu th s thay i cng vch hp th theo nng nguyn t cn xc nh v t ng chun ny xc nh nng nguyn t trong dung dch th.

Phng php 2: Phng php thm chun

Cho vo t nht ba bnh nh mc c dung tch nh nhau, cc th tch bng nhau ca dung dch cht em th (dung dch th) c chun b nh ch dn trong chuyn lun. Thm vo tt c cc bnh, tr mt bnh, cc th tch ln dn ca dung dch chun c nng bit ca nguyn t cn xc nh sao cho nng ca nguyn t cn xc nh trong cc bnh u nm trong khong tuyn tnh gia nng v cng hp th. Pha long cc dung dch c cha trong bnh n va th tch bng dung mi.

a dung dch mu trng vo my, iu chnh tn hiu c c v "0". a ln lt dung dch th v tng dung dch chun vo my, t nht mi dung dch ba ln, ghi li kt qu c n nh. Ra my bng dung dch mu trng sau mi ln o cho n khi tn hiu tr v gi tr c ban u ca mu trng. Nu s dng k thut nguyn t ha khng ngn la, l graphit phi c t li gia cc ln phn tch.

Tnh phng trnh hi quy ca ng thng chun bng cch dng phng php bnh phng ti thiu v xc nh t ng thng ny nng ca nguyn t cn xc nh trong dung dch th. Mt cch khc, v th biu din s lin quan gia gi tr c c v lng thm vo ca nguyn t cn xc nh. Ni cc im trn th v ko di v pha tri cho n khi n gp trc nng . Khong cch gia im ny v im giao nhau ca trc ta l nng ca nguyn t cn xc nh trong dung dch th.