NGHIEN CUtJ KHA NANG SU" DVNG PHlTONG PHAP CHlTNG CAT NHIET PHA RAN KET HgfP VOl KICH HOAT NOfTRON DE XAC DINH HG VA SE TRONG CAC MAU LU'ONG THlTC, THlTC PHAM
1 NGUYEN GIANG, NGUYEN THANH TAM, TRUONG THI PHl/ONG MAI,DO TAM NHAN, V 6 TRAN QUANG THAI Vi?n Nghien cuu Hgt nhdn (Dd Lgt).
Summary: A method was studied for the simultaneous determination of mercury and
• selenium in food and foodstuff by soil-phase heated distil and neutron activation analysis. After irradiation in Dalat Nuclear Research Reactor for 20 hours with a neutron flux of 2.1X10'^ n/cm^s. The samples were transferred into a ceramic heatproof boat. The boat was inserted into the quartz tube, which was packed with activated carbon ampul -1. The tube was placed in the tube furnace. Oxygen gas of about 0.4L/min was passed over the sample and the temperature of the furnace was heated at 400 C for 1 hour. Both mercury and selenium were evaporated from sample and completely collected in the ampul -1. After, the activated carbon in ampul -1 was quantitatively transferred into polyethylene vial for counting '^Se.
The activated carbon into polyethylene was quantitatively transferred into a ceramic heatproof boat, oxygen gas was replaced by nitrogen gas and the temperature of the furnace was heated at 400**C for 1 hour. In this process only mercury was separated , firom selenium and completely collected in the other ampul. The activated carbon in
this ampul was quantitatively transferred into polyethylene vial for counting •^"^Hg The activated carbon in the ampuls was quantitatively transferred into polyethylene vials for counting '^Se and ^"^Hg
Key words: Radiochemical Neutron Activation Analysis I. Gl6l THIEU
Phan tich kich boat notron (NAA) vdi su sir dung notron nhiet ciia 16 phan iing la mot trong nhung ky thuat phan tich hat nhan quan trong doi voi viec xac dinh cac nguyen to vet trong cac doi tugng moi trudng. Ky thuat nay cho phep phan tich dong thdi da nguyen to trong mau voi dp chinh xac va dp nhay cao. Cac gidi ban do cua NAA nam trong khoang ppm va trong mgt vai trudng hgp nam trong khoang ppb.
Nhieu ngu;^en to can phan tich nam trong nhiing vat lieu cd thanh phan phuc tap voi h ^ lugng chat nen Idn, khi chieu xa chiing bi gay nhilu, dan den viec xac dinh se khong chinh xac, hoSc khong the xac dinh dugc, nhit la khi ham lugng ciia nguyen to phan tich la vi lupng hoac vet. Vi du: khi phan tich mau diu khi, hoac cac loai mau dja chat hay mlu thuc pham CO thanh phan phuc tap... De cd the giai quylt bai toan nay ngudi ta da ket hgp cae phuong phap tach lam giau vdi NAA dl cd lap dugc ddng vi cin nghien cuu. Nhd vay, do nhay va do chinh xac ciia RNAA dugc nang cao.... Tuy nhien, d6i vdi mgt s6 loai mSu co ham lugng hgp chat huu co Ion khong nhiing rit kho xac dinh bing phucmg phap RNAA ma cac phuong phap khac nhu AAS, ICP -MS cung thuong gap kho khan trong khau boa tan mau.
Trong de cong ttinh nay, chiing toi sg nghien cuu dua ra phuong phap xii ly nhiet dk
366 Hgi nghi Khgg hgc vd Cdng nghe hgt nhdn todn quoc lin thiIX, Ninh Thudn 18-19/8/2011.
tach cac nguyen t6 Hg, Se va xac dinh bang NAA. Day ]h ky thuat tach dcm gian khong t6n hoa chfc, thai gian thuc hien qui trinh nhanh va nguy co nhilm xa dugc gitoi dSn mirc t6i thieu.
II. THLTC NGHIEM 1. Thidt bi
- Lo phan ling hat nhan: Lo phan ung hat nhan Da Lat co thong luijmg notron a kenh 7-1 la 2,5 X lO'^ n/cm^.giay va a mam quay la 2,0 x lo'^ n/cm^. giay khi cong suit 500kW.
- He ph5 k§ gamma da kenh vcri detector Ge sieu tinh khijt (HP-Ge), dg phan giai l,9KeV tai dinh 1173 keV va 1332 keV cua '°Co.
2. Hoa chat
- Cae dung dich chuSn cua Hg va Se dugc chuan bj tir dung djch chuan don san xuit tai cong ty Merck-Diic.
- Mau chuin Qu6c tS: six dung mau chu£hi quoc te Bovine liver - NIST - 1577b va Hay Powdered - IAEA V-10.
3. Dieu che cac dong Vj ™'Hg, '^Sc, *'Br, ^'Cl, "As, '"Sb va "^Sb
Lay 1 OO^il dung dich chuan cua cac ion Hg, Se, Br, Cl, As va Sb co nong d6 1 mg/mL nho vao timg mieng giay loc; de kho tir nhien trong khong khi (rieng thuy ngan sau khi nlio I dung dich chuan can nho them vai giot dithizone/ aceton de trach sir bay hai cua thuy ngan trong khi say va chieu mau); cho vao tui PE; han kin. Cac mau tren dugc dua vao container nhom va chieu xa 20 gia tai vi tri m ^ quay cua Lo phan ling hgt nhan Da Lat vai cong suat 500kW. Sau idii de ngugi vai ngay lay mau ra cho vao cdc, them 5ml HCl (1:1) vao coc; dun nhe tren bep each cat cho den khi tan het. Chuyen dinh lugng dung dich trong coc vao binh dinh muc 1 OmL. Sau do diing nuac cat dinh muc tgi vach, lac deu.
4. Nhi^t do toi iru va tu-ng lo^i khi mang thich horp de tach Hg, Se
Dirng micropipet lay 50 ^L cac dung dich phong xg ^°^Hg va ^^Se co nSng do 10 Hg/ml va can khoang 0,5-1,0 g mlu thuc phim (thiic an tdng hgp) cho vao cac thuySn sil chiu : nhiet va dat vao ong thach anh, can khoang 1,0 g than boat tinh cho vao ampul -1 va lip da he thong nung mlu nhu hinh 1, dieu chinh t6c dg dong khi nita 0,4L/phut. Sau do, tien hanh nung mau trong 16 nung 6ng 6 nhi$t dg tir 100°C dSn 900°C voi thoi gian nung 1 gia; d6i voi khi oxy each tiSn hanh nhu khi nita. K^t qua dugc trinh bdy o bang 1.
5. Sy anh huong m§t so nguyen fo de bay hoi den qua trinh hap phu Hg va Se phu thuoc vao thM gian dgi
Dimg micropipet liy 50 nL d6ng vi phong xa nhu '^Br, '*C1, "As, '^^Sb, c6 n6ng dg 100 pg/mL va 50 n_L cac dung dich phong xg Hg va "Se co n6ng do 10 pg/ml va can khoang 0,5-1,0 g mlu thuc phim cho vao cac thuySn sii chiu nhiet khac nhau va dgt vao 6ng thgch aiih, can khoang 1,0 g than hogt tinh cho vao ampul hip phy -1 v4 lip dat h? thSng nuri^
mau, diSu chinh tdc do dong khi oxy 0,4 L/phiit. Tiln hanh nung mau trong 16 nung ong *"
nhiet do 900°C khoang 1 gio dS tach Hg va Se. Sau do than hoat tinh tir ampul -1 chuySn dinh lugng vao binh do va tien hanh do hoat do phong xa "Se tai dinh nSng lugng 264keV. Sau khi do xong, chuyjn dirJi lugng than boat tinh vao thuyen sCr chiu nhiet khac, khi oxy dugc thay bang khi nitg va tiln hanh nung mlu 6 400°C di tach H^ ra kh6i Se, thai gian nung 1 gia. Trong qua trinh nay thuy ngan dugc tach khoi selen va h^p phu vao mgt ampul hap phy khac, chuyen dinh lugng than hoat tinh trong ampul nay vao binh do va tiSn hanh do boat dOi
phong xa "•'Hg tai dinh nang lugng 279keV. Kit qua dugc trinh bay a bang 2. ,
S Hdi nghi Khoa hgc vd Cdng ngh? hgt nhdn todn qudc lan thu IX. Ninh Thudn 18-19/8/2011 367
; 6. Danh gia hieu suat hap phy
Dung micropipet Idy 50|il va 100 |j.l dung dich chuan cua cac ion Hg^^va Se^* co nfing dp O.Olmg/ml tdm len cac mieng giay lgc co duong kinh 0 = 1cm, dl kho tu nhien trong khong khi, sau do cho vao tiii PE; han kin. Cac chuan dugc chilu 20 gio. Sau khi dk ngugi khoang hai tuin, tiln hanh do ho^t dp phong xa cua ^"''Hg va '^Se; ghi dien tich dinh So voi thoi gian do la 60 phiit. Tien hanh tach Hg va Se nhu phan 1.5. Do boat dp phong xa ciia ^**^Hg
;; va ^^Se, ta thu dupe dien tich dinh S. Ket qua duge trinh bay d bang 3 i 7. Danh gia do chinh xac cua phirotig phap
i De kiem tra do chinh xae cua phuong phap phan tich, chiing toi dimg chuan Bovine Liver - NIST -1577b va Hay Powdered - IAEA - V 10 de xac dinh cac nguyen td Hg va Se. Ket qua duge trinh bay 6 bang 4
; 8. Quy trinh
Can khoang 0,2 - 0,5 gram cho vao tiii PE han kin; dimg micropipet hut 50|al dung
;• dich chuan Hg va Se co nong do 0,01mg/ml len mau giay Ipc co duong kinh O = 1cm, (rieng thiiy ngan sau khi nho dung dich chuan can nho them vai gigt dithizone/ aceton de trach su bay hoi cua thuy ngan trong khi sdy va chieu mau) de kho tu nhiSn trong khong khi. Mau chuan va mau phan tich dugc chieu dong thoi 20 gio, cong suat 500 KW tai vi trf mam quay I vcri thdng lugng 2.10 n/cm .giay tren Lo p h ^ umg hat nhan Da Lat.
1: Sau khi de nguoi khoang vai tuJin, mau dugc chuyen vao thuyen sii ehju nhiet dupe K dat trong ong thuy tinh thach anh, I5p ampul hap phu, dat ong thuy tinh vao 16 nung, dieu :: chinh toe dp dong khi oxy 0,4 L/phiit. Tien hanh tach Hg va Se nhu phan 1.5.
:i III. KET QUA VA BIEN LUAN
' Ket qua dupe trinh bay 6 bang 1 cho thay:
Ddi vai khi mang nita: 6 nhiet dp tren 400*'C, thuy ngdn bay hoi va hap phu khoang 90% va o nhiet do Ion hon SOO^C, selen bay hoi va hip phu >87%.
'^ Ddi voi khi mang oxy: 0 nhiet do 400*'C, thuy ngan bay hoi va hap phu khoang 78,5%
'•• va 6 nhiet dp >800°C, selen bay hoi va hdp phu >92%
i, Tir do dua ra kit luan nhu sau: Six dung khi mang nito dl tach Hg va sur dung khi
; mang oxy de tach Se.
TiJ cdc bang 2 cho thdy cac nguyen t6 Br, Cl, As va Sb, ddc biet ^^Br se anh huong , den qua trinh tach He va Se bdng ky thuat chimg cat nhiet pha rdn nlu thoi gian dgi khong du ' 16n. Vi cac ddng vj ^^Br (T1/2 =35,34 gio), ^^Cl (Tm = 37,3 phut), ''^As (Tm = 25,6 gio), '^^Sb
(Tl/2 = 2,8 ngay) co Ti/i (thoi gian ban ra) trung binh ngdn. Khi thoi gian du Ion cac dong vi nay
^phanra.Rieng'^''Sb(T|/2 = 60ngay)Eyi = 602 keV, E^z = 1691 keV [5] vatheo [6] 0 nhiet do 1: bay hoi cua Sb khoang 30%, hon nGa ham lugng Sb trong cac mdu luong thuc thuc phdm ii'thuong nho (I0'^-10"Vg) [1,2,3,4]. Do do '^"Sb se khong dnh huong . Vi vay, dh tach Hg va I'Se trong cac mau luong thuc, thuc phdm bdng ky thudt ndy can c6 thoi gian nguoi tren UOngay.
:; Hieu sudt tach trung binh cua Hg la 91,0 % va Se la 91,4% dupe trinh bdy 6 bang cho .thiy kha nang hdp phy than boat tinh d6i v6i Hg va Se cao.
a
^ Cac kit qua phdn tich mau chudn Bovine Liver - NIST -1577b va Hay Powdered - jlAEA - V 10, dupe trmh bay d bang 3 cho thdy: D6i vol Hg, dp diing cua kit qua phdn tich jidupc so voi gia trj thirc ciia mlu chudn Hay Powdered - V 10 la 86,6%; D6i voi Se, dp diing
cua kit qua phdn tich dugc so voi gia tri thvre cua mau ehuan qu6c tl Bovine Liver-1577b la
368 Hgi nghi Khga hgc vd Cdng nghe hgt nhdn todn qudc lan thi IX, Ninh Thudn 18-19/8/2011 90,4% va Hay Powdered - V 10 la I
va do chinh xac cao.
J,3%. Tir do cho thay phuong phap phan tich dgt dg nh?y Kit qua nhan dugc a bang 5 cho thay:
Ham lugng Hg trong cac mlu luong thuc, thuc pham a cac mau nghien ciiu dao dpng tir 9 - 223 ng/g. Mlu co ham lugng Se cao nhat la dSm bong beo (223ng/g) va mlu co ham lugng Hg thap nhat la gao nep cai (9 ng/g).
Ham lugng Se trong cac mlu luang thuc, thuc phim 6 cac mlu nghien ciiu dao dgng tir 132 - 869 ng/g. Mlu co ham lugng Se cao nhit la dam bong ga (869ng/g) va mau co ham lugng Se thip nhit la gao thorn Min (132 ng/g).
L6 nung * Ampu| Aiypul
(Than hogt tinh) (Than boat tinh) Hmh 1. Md tinh tdch Hg vd Se bdng phuang phdp chung cdt nhiet pha rdn Bdng 1. Nhiet dg tdi uu di tdch Hg vd Se bdng phuong phdp chung cdt nhiet pha rdn
vdi khi mang nita vd oxy.
Stt 1 2 3 4 5 6 7 8 9
Nhiet do (C) 100 200 300 400 500 600 700 800 900 S(chuan)
Khi nito S(Hg)
2389 4121 6231 6612 6537 6578 6514 6527 6513 7281
S(Se)
-
181 210 231 1672 1753 2219 2359 2351 2792
Khi oxy S(Hg)
2107 3814 5612 5712 5634 5819 6533 6491 6437 7281
S(Se)
-
145 172 203 1521 1566 2289 2474 2468 2792 S: Dien tich ciia dinh nang lupng
Bang 2 Stt
1 2 3 4 5 6
Su dnh huong ciia cdc ding vi ''Br, '^CI, '^As, '"Sb len qud trinh hip phu Hg va Se phu thudc vdo thoi gian dai
Thoi gian doi (ngay) 3 5 7 10 15 20
S(Hg) 1079 1154 1260 1910 1887 1926
S(Se) 1329 1338 1449 1756 1727 1745
Hgi nghi Khga hgc vd Cdng nghe hgt nhdn tgdn qudc lin thi IX, Ninh Thudn 18-19/8/2011 369 Bdng 3. Kit aud khdo sdt hieu sudt tdch cua Hg vd Se
Hg So
14219 13737 11254 Hieu suat ta
S, 12771 12495 10372 ch trung binh
S,/So'100 89,8 91,0 92,2 91,0+1,2
Se So
5011 5517 5196
Sl 4578 4997 4787 Hieu suat tach trung binh
S,/So*100 91,4 90,6 92,1 91,4± 0,75 Bdng 4. So sdnh gid trf phdn tich vd gid tr
Nguyen to
Hg Se
Bovine Liver-1577b Gia tri dugc
cong n h ^ 0,003 0,73±0,06
Gia tri phan Tich
-
0,66 ± 0,05
thuc trong cdc mdu chudn tren V-10 Gia tri dugc cong
nhan 0,013 0,213 ± 0,018
Gia tri phan tich 0,015 ±0,002 0,188 ± 0,021
STT 1 2 4 5 6 7 8
Bdng 5. Hdm luang Hg trong cdc mdu luang thuc, thuc phdm (ng/g) Ten mau
Gao Tao Nguyen Gao Thom Min Nep Cai
Thiic an tong hop - 1 Thiic an tong hgp - 2 Dam bong thit heo Dam bong thit ga
Ham lugng Hg (X ± OT) 18±2 32 ± 4 9 ± 2 15 ± 2 22 ± 2 223 ± 29 125 ±11 ...
Ham lugng Se(X + SZ)) 201 ± 23 132 ±12 183 ±14 487 ±33 512±27 349 ±46 869 ±37
sS dli
L L > l
Wili>ilw«ii
2500 s « kenl,5000 Hmh. 1. S\t dnh hucmg ciia cdc ddng vi "'Br, ^Cl, ^^As, '"Sb len qud trinh hip phu Hg va Se
^oi T40 =i ngay
370 Hdi nghi Khgg hgc vd Cdng nghe hgt nhdn loan quic lin thi IX, Ninh Thudn 18-19/8/2011 sd atm
500 : 400 - 300 : 2O0 100 0
"^1 S e + H g
vdi Ta^ =10 ngay
TA! LIEU THAM KHAO
[1]. Sun Laiyan, Lufengying, Su Rongwei, Zhen Houxi (1991). Determination and evaluation of some trace elements in Chinese foodsuffs J. Radioanal. Nucl. Chem., Vol. 151, No. 2 p.p.277-285
[2]. Y. Muramatsu, M. Sumiya (1994). Report on an IAEA Co-ordination Research Programme. NAHRES-23. Vienna, p.p. 157-180.
P].N. Leelhaphunt, S. Chueinta, M. Puruiachaiya, W. Chueinta, S. Nouchpramool (1994).
Report on an IAEA Co-ordination Research Programme. NAHRES-23. Vienna, p.p.
215-287.
[4]. Nulcear techniques for toxic elements in foodstuffs. Report on an IAEA Co-odinated research Programma. NAHERES-23, IAEA, Vienna 1994.
[5]. E. Bujdoso, I.Feher and G. Kardos. Activation and decay tables of radioisotopes.
Budapest 1973 p.p 86-87
[6]. Textbook on advanced nuclear analytical techniques in environmental impact from industry (1995)
