Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn I HC THI NGUYN TRNG I HC S PHM

NG QUC TRUNG XC NH ASEN TRONG CH XANH THI NGUYN BNG PHNG PHP PH HP TH NGUYN T LUN VN THC S KHOA HC HA HC Thi Nguyn Nm 2011 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn I HC THI NGUYN TRNG I HC S PHM

NG QUC TRUNG XC NH ASEN TRONG CH XANH THI NGUYN BNG PHNG PHP PH HP TH NGUYN T Chuyn ngnh: Ha phn tch M s: 60.44.29 LUN VN THC S KHOA HC HA HC NGI HNG DN KHOA HC PGS. TSNGUYN NG C Thi Nguyn Nm 2011 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn Li cam oan Tixincamoanylcngtrnhnghincu caring ti. Cc sliu,kt qunutronglun vn l trung thc. Nhng kt lun ca lun vn cha cng b trong bt k cng trnh no khc. TC GI LUN VN

Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn LI CM N EmxinchnthnhcmnthygioPGS.TSNguynngc trc tip giao cho em ti, tn tnh hng dn v to mi iu kin cho em honthnhlunvn.EmxinchnthnhcmnthygioPGS.TSNguyn Xun Trung, PGS.TS Nguyn Duy Lng tham gia ng gp gip trong qu trnh hon thnh bn lun vn. Em xin chn thnh cm n cc thy c gio Khoa Ho hc, Khoa Sau i hc HSPTN, cc thy c gio, cc cn b nhn vin phng th nghim Khoa HohcHKHHTN,PhngHaphn tchihc KHTN ihcQucgiaHNi,Banlnho,cccchanh(ch)khoaXt nghim Trung tm y t dphngtnh ThiNguyn gip toiukin cho em hon thnh bn lun vn ny. Thi Nguyn, ngy 10 thng 8 nm 2011 Hc vin Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 1 MC LC M U ............................................................................................................................ 1 Chng 1 ............................................................................................................................ 2 TNG QUAN .................................................................................................................... 2 1.1. Gii thiu chung v cy ch ................................................................... 2 1.1.1. c im v thnh phn ................................................................... 2 1.1.2. Cng dng ca cy ch..................................................................... 2 1.2. Gii thiu v nguyn t Asen ................................................................. 3 1.2.1.V tr, cu hnh electron v trng thi t nhin ................................. 3 1.2.2.Tnh cht vt l, tnh cht ho hc ..................................................... 4 1.2.3. Hp cht ca asen v tnh cht ca chng ....................................... 6 1.2.4. Cc phn ng c trng ca hp cht asen ...................................... 8 1.3. S nhin Asen v c tnh ca n ....................................................... 9 1.3.1. Ngun gc s nhim Asen ............................................................ 9 1.3.2. nhim asen trn th gii ............................................................. 10 1.3.3. nhim asen Vit Nam .............................................................. 12 1.3.4. c tnh ca asen ........................................................................... 13 1.4. Phng php in phn ........................................................................ 15 1.5. Cc phng php xc nh Asen .......................................................... 15 1.5.1. Cc phng php khi lng ......................................................... 16 1.5.2. Cc phng php phn tch th tch ............................................... 18 1.5.3.Cc phng php o quang ............................................................. 19 1.5.4. Cc phng php in ho ............................................................. 20 1.5.5. Phng php phn tch quang ph ................................................. 21 1.6. Phng php x l mu phn tch xc nh Asen ................................ 24 1.6.1. Phng php x l t (bng axit c oxi ho mnh) .................... 24 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 2 1.6.2. Phng php x l kh .................................................................. 25 Chng 2 .......................................................................................................................... 26 I TNG V PHNG PHP NGHIN CU....................................... 26 2.1. i tng v mc tiu nghin cu ....................................................... 26 2.1.1. i tng v mc tiu .................................................................... 26 2.1.2. Cc ni dung nghin cu ................................................................ 26 2.2. Gii thiu v phng php ph hp th nguyn t .............................. 27 2.2.1. Nguyn tc ca phng php AAS ................................................ 27 2.2.2. H trang b ca php o AAS ........................................................ 28 2.3. Gii thiu v phng php x l t mu ........................................... 31 2.3.1. Nguyn tc v bn cht .................................................................. 31 2.3.2. C ch phn hu ............................................................................. 32 2.4. Ha cht v dng c ............................................................................. 32 2.4.1: Ha cht.......................................................................................... 32 2.4.2: Dng c .......................................................................................... 33 Chng 3 .......................................................................................................................... 34 KT QU V THO LUN ................................................................................... 34 3.1. Kho st cc iu kin o ph GF-AAS ca Asen ............................... 34 3.1.1. Kho st chn vch o ................................................................... 34 3.1.2. Kho st chn khe o ca my ph hp th nguyn t.................. 35 3.1.3. Kho st cng dng n catot rng ......................................... 35 3.2. Kho st cc iu kin nguyn t ho mu .......................................... 36 3.2.1. Nhit sy kh mu ..................................................................... 37 3.2.2. Kho st nhit tro ho luyn mu .............................................. 37 3.2.3. Kho st nhit nguyn t ho mu ............................................ 38 3.2.4.Cc iu kin khc .......................................................................... 39 3.3.Kho st cc yu t nh hng n php o GF - AAS ........................ 39 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 3 3.3.1.Kho st nh hng ca nng axit v loi axit .......................... 39 3.3.2 Kho st nh hng ca cht ci bin nn (cht ci bin ha hc)40 3.3.3. Kho st thnh phn mu ............................................................... 42 3.3.4. Kho st nh hng ca cc cation v anion ................................. 43 3.5 Phng php ng chun i vi php o GF AAS ........................ 48 3.5.1 Kho st khong tuyn tnh ............................................................. 48 3.7.2. Xy dng ng chun .................................................................. 49 3.4.2. nh gi sai s, gii hn pht hin, gii hn nh lng v lp li ca php o .......................................................................................... 52 3.4.3. Tm tt cc iu kin o ph ca Asen ......................................... 54 3.5. Xc nh Asen trong ch xanh .............................................................. 54 3.5.1 a im thi gian ly mu v k hiu mu ................................... 54 3.5.2. Chun b mu phn tch .................................................................. 56 3.5.3. Kt qu phn tch cc mu ch xanh .............................................. 56 3.5.4: Kim tra qu trnh s l mu ......................................................... 57 KT LUN ..................................................................................................................... 61 TI LIU THAM KH0 ........................................................................................... 62 PH LC ......................................................................................................................... 65 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 4 DANH MC CC K HIU CH VIT TT AAS: Atomic Absorption Spectrometry ( Ph hp th nguyn t) Abs: Absorbance ( hp th) AES: Atomic Emission Spectrometry (Ph pht x nguyn t) ETA-AAS: Electro Thermal Atomization Atomic Absortion spectrometry(Ph hp th nguyn t khng ngn la) F-AAS: Flame- Atomic Absorption Spectrometry(Ph hp th nguyn t ngn la) GC-MS: Gas Chromatography Mas Spectroscopy(Sc k kh ghp khi ph)GF-AAS: Graphite Furnace- Atomic Absorption Spectrometry(Ph hp th nguyn t khng ngn la) HCL:Hollow Cathode Lamp (n catot rng) HG-AAS: Hyrie Generation- Atomic Absorption Spectrometry (Ph hp th nguyn t k thut Hidrua ha) HPLC: High Performance Liquid Chromatography(Sc k lng hiu nng cao) ICP-AES: Inductively Coupled Plasma Mass- Atomic Emission Spectrometry (Ph pht x nguyn t dng nng lng plasma cao tn cm ng) ICP-MS : Inductively Coupled Plasma Mass Spectrometry (Ph khi lng dng nng lng Plasma cao tn cm ng) LOD: Limit of detection (Gii hn xc nh) LOQ: Limit of quantitation (Gii hn nh lng) UNICEF: United Nations Children's Fund ( Qu nhi ng Lin hip quc) WHO: Wolrd Health Organization (T chc Y t th gii) Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 5 DANH MC CC BNG Bng 1.1: Cc thng s vt l ca Asen ........................................................... 5 Bng 1.2: Mt s thng s vt l ca cc hp cht ca Asen ........................... 6 Bng 1.3: Tnh hnh nhim asen ti mt s vng quc gia trn th gii ..... 11 Bng1.4: TiuchunVit Nam vhm lngAs trong nc (Tiuchun Vit Nam 2007) ................................................................................ 15 Bng 3.1: Kho st vch o ca Asen ............................................................. 34 Bng 3.2: S ph thuc ca hp th vo cng dng n .................... 36 Bng 3.3: Kt qu kho st nhit tro ho ca Asen ................................... 38 Bng 3.4: Kt qu kho st nhit nguyn t ho mu ............................... 39 Bng 3.5: nh hng ca nng axit v loi axit ....................................... 40 Bng 3.6. Kho st nh hng ca cht ci bin ha hc ............................... 41 Bng 3.7: Kho st nng Mg(NO3)2 .......................................................... 42 Bng 3.8: Kt qu kho st s b thnh phn mu ......................................... 43 Bng 3.9: nh hng ca kim loi kim n ph hp th ca Asen ............. 44 Bng 3.10: nh hng kim loi kim th n ph hp th ca Asen ............ 44 Bng 3.11: nh hng ca kim loi nhm III, IV n ph hp th ca Asen .. 44 Bng 3.12: nh hng ca nhm kim loi nng n ph hp th ca Asen ..... 45 Bng 3.13: nh hng ca nhm kim loi mu n ph hp th ca Asen .. 45 Bng 3.14: nh hng ca tng cation......................................................... 45 Bng 3.15: nh hng ca nhm anion n php o ph hp th ca Asen . 46 Bng3.16:nhhngcatngcationvanionnphpophhpth ca Asen ........................................................................................... 47 Bng 3.17: Kho st khong tuyn tnh ca Asen .......................................... 48 Bng 3.18: Xc nh ng chun ca Asen .................................................. 51 Bng 3.19: Kt qu sai s v lp li ca php o ...................................... 53 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 6 Bng 3.20: Tng kt cc iu kin o ph GF-AAS ca Asen ...................... 54 Bng 3.21: a im, thi gian ly mu v k hiu mu ................................ 55 Bng 3.22: Hm lng kim loi As tnh theo mg/kg ...................................... 56 Bng 3.23: Kt qu phn tch i vi cc mu lp ......................................... 58 Bng 3.24: Mu thm chun ........................................................................... 59 Bng 3.25: Kt qu phn tch mu thm chun .............................................. 59 Bng 3.26: Kt qu xc nh Asen bng hai phng php GF AAS v ICP - MS................................................................................................. 60 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 7 DANH MC CC HNH V TH Hnh 1.1: Vng tun hon ca Asen trong mi trng ..................................... 4 Hnh 1.2: Cc con ng xm nhp ca Asen vo c th ngi .................... 14 Hnh 2.1: n catot rng ................................................................................. 28 Hnh 2.2: n D2 ............................................................................................ 28 Hnh 2.3: S h thng my quang ph hp th nguyn t ........................ 30 Hnh 2.4: Cuvet Graphite ................................................................................ 30 Hnh 2.5: H l Graphite nguyn tho mu ................................................ 31 Hnh 2.6: H thng my quang ph hp th nguyn t AA-6300 .................. 31 Hnh 3.1: th kho st khong tuyn tnh ca Asen .................................. 49 Hnh 3.2: Ph hp th ca Asen ...................................................................... 50 Hnh 3.3: th v phng trnh ng chun ca Asen .............................. 51 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 1 M U Hinnaymitrngnngnghipniringangchunhhng nghim trng bi s gia tng ph thi. Phn ln ngun ph thi cha c x luvomitrngt,nc,lmchomitrngngycngb nhim.Phthicngnghip,phthisinhhot,phthiccmkhaithc khong sn, ho cht nng nghip tn d i vo nc, vo khng kh ri tch ttrongt,lmchotbthoiho,lmgimnngsut,chtlngsn phm, c bit l sn phm nng nghip sn xut trn khu vc t b nhim c th tr thnh c hi cho ngi s dng.ThiNguynlkhuvccnhiumkhongsnangkhaithc,cc khu cng nghip ng thi cng l vng sn xut ch c sn. t, nc sn xutnngnghipkhuvckhaithckhongsn,cngnghipthngb nhim trong c kim loi nng. Ch c th b nhim mt s kim loi nng t t,nc,vkhngkh.Vvy,cnphiquantmnghincuvkimtra khng ch cc cht c hi, c bit l cc kim loi nng nh hng trc tip n sc kho con ngi. [17] XcnhAsentrongchxanhThiNguyn bngphngphp ph hp th nguyn t l mt trong cc nghin cu phc v mc tiu ni trn. Nhim v c th l:1. Tm cc iu kin ti u cho php o Asen 2.KhostccyutnhhngnphpoxcnhAsen.Tm khong tuyn tnh, xy dng ng chun. nh gi sai s v lp li gii hn pht hin, gii hn nh lng ca php o Asen. 3. Vn dng phng php xc nh hm lng Asen trong mt s mu ch khu vc Thi Nguyn, v nu ra mt s kt lun ban u v Asen trong ch xanh mt s khu vc ca tnh Thi Nguyn. Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 2 Chng 1 TNG QUAN 1.1. Gii thiu chung v cy ch 1.1.1. c im v thnh phn Cy ch c tn khoa hc l Camellia Sinensis. Cy thng c trng ly l ti sc nc ung hoc ch bin theo nhng quy trnh nht nh thnh tr pha nc ung. Cy ch c mu xanh, cao 1- 6m, l mc so le, hnh tri xoan, di 4 - 10cm, rng 2 - 2,5cm, nhn gc, nhn t c mi nh, phin l lc non c lng mn, khi gi th dy, bng, mp kha rng ca rt u. Hoa to vi 5-6 cnh hoa mu trng, mc ring l nch l, c mi thm, nhiu nh. Qu nang thng c ba van, cha mt ht gn trn, i khi nhn nheo. NgungccychBcnvNamTrungQuc,ctruyn sangMianma,ThiLan,VitNam.Chctrngkhpnincta,tp trung nhiu Ph Th, H Giang, Thinguyn, Qung Nam- Nng cho ti c Lc, Lm ng. Cy a kh hu m, t chua v cn c che bng mt mc nht nh m bo hng thm. Thnhphnhohc:Tronglchctinhdu,ccdnxut polyphenolic(flavonoid,catechol,tanin)ccalcaloidcafein,theophyllin, theobromin, xanthin. Cn c cc vitamin C, B1, B2, B3 v cc men. Cy ch c s dng cnh l nu nc ung gi l ch ti. Ch hi bp v l non, v ri sao lm ch hng pha nc ung gi l tr. Hoc cho ch ln men sau phi sy kh lm ch mn hay ch thnh ch en. 1.1.2. Cng dng ca cy ch Ch c s dng hn 2000 nm trc Cng nguyn. Do c cafein v theophyllin, ch l mt cht kch thch no, tim v h hp. N tng cng sc lm vic tr c v ca c, lm tng h hp, tng cng v iu ho nhp Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 3 pcatim.Ncnglitiu,lmdtiuho.Scmtcaccdnxut polyphenolic lm cho tc dng ca ch hi hn v ko di hn cafein. Cc flavonol v polyphenol lm cho ch c tnh cht ca vitamin P. Tuy vy, nu sdngkodiviliucao,chcthgynhimcmntnh,biuhin bi s mt ng, s gy yu, mt cm gic ngon ming, c ri lon thn kinh. Tcdngcacych:Thanhnhit,giikht,tiucm,litiu,nh thn,lmchounocththi,damtm,khichngmt,btmn nht, v cm t l. Ch thng c dng trong cc trng hp: Tm thn mt mi, ng nhiu, au u, mt m, st kht nc, tiu tin khng li, ng c ru. Hoc nu nc ra vt bng, l lot s nhanh ra da v ln da non. 1.2. Gii thiu v nguyn t Asen 1.2.1. V tr, cu hnh electron v trng thi t nhin [5], [6], [8] Asen(As) l nguyn t th 33 trong bng h thng tun hon cc nguyn t ho hc. N thuc chu k 4, phn nhm chnh nhm VA. Cu hnh electron: 1s22s22p63s23p64s23d104p3 hay [Ar]3d104s24p3 vi cu hnhlpvelectroncstham gia ca cc obitan dnn trongcc hpcht As c th c s oxi ho +3, +5, -3. [14], [15] Asenchimkhong10-4%tngsnguynttrongvtritl nguyn t giu th 20 sau cc nguyn t khc. Trong v tri t, Asen nguyn cht l kim loi mu xm, nhng dng ny t tn ti trong t nhin. Ngi ta tm thy As tn ti dng hp cht vi mt hay mt s nguyn t khc nh Oxi,Clo,Luhunh,Asenkthpviccnguynttrntothnhcc hpchtasenvcnhcckhongvt,thinthch:Reagal(AsS), orpiment(As2S3),Arsenolite(As2O3),Arsenopyrite(FeAs2,FeAsS, AsSb)Hp cht ca Asen vi cacbon v hidro gi l hp cht asen hu c. Thng cc dng hp cht hu c ca asen t c hn hp cht asen v c. Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 4 TrongthuquynAsentntididngmuiasenathocasenic. Trongsinhquynasentntidngasenmetyldochuynhosinhhc. Nng asen trong nc t nhin t khi vt qu 10 g/l . Trong nc ma asen c t 0,04 - 0,1 g/l. Asenctrongkhquynldoqutrnhluynqung,snxutximng, sn xut nng lng. Trn mt t asen dng AsO33- hoc AsO43- l do bi cng nghip lng ng. Kh quyn (CH3)2As(O)OH Thu quyn (CH3)3As(CH3)2AsH V tri t HxAsO4(3-x)HxAsO3(3-CH3As(O)(OH)2 (CH3)2As(O)OH AsenatAsenicMetylamin Dimetylamin Vi khun khVi khun metyl ho Hnh 1.1.Vng tun hon ca Asen trong mi trng 1.2.2.Tnh cht vt l, tnh cht ho hc [9], [14],[15] Asen c mt vi dng th hnh, dng kim loi v dng khng kim loi. dng khng kim loi asen c to nn khi lm ngng t hi ca n. l chtrnmuvnggilAsenvng,cmngliphntgingPhtpho trng, ti cc mt ca mng li l phn t As4. So vi pht pho trng, asen vngkmbnhnnhiu,nhitthngditcdngcanhsngn chuyn nhanh thnh bt. Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 5 DngkimloiAsencmuxmvldngbnnht,dnghinnh thnh bt, dn in vdn nhit tt, hi asen c mi ti rt c. dng kim loi Asen c mt s thng s vt l bng 1. Bng 1.1. Cc thng s vt l ca Asen Khi lng nguyn t74,92 g Nhit nng chy817 0C (36 atm) Nhit si6100C (1 atm) T khi5,727 g/cm3 m in2,18 Nng lng ion ho (I1)947 kj/mol S ng v8 Asen l nguyn t va c tnh kim loi va c tnh phi kim. V l tnh n c tnh cht ging kim loi, cn ho tnh li ging cc phi kim. Khi un nng trong khng kh n chy to thnh As2O3 mu trng. 4As + 3O2 =2As2O3 dng bt nh As c th bc chy trong kh Clo to thnh triclorua 2As + 3Cl2 =2AsCl3 Khi un nng As tng tc vi Br, S, kim loi kim, kim th v mt s kim loi khc to nn asenua. 2As + 3M= M3As2(M = Mg, Ca, Cu) 2As+ M=MAs2(M = Zn, Ca, Fe) As +M = MAs (M = Al, Ga, In, La) KimloiAskhngphnngvinc,axitlongnhngtantrong HNO3 c, cng thu, kim, cht oxi ho in hnh. As + 3HCl + HNO3() = AsCl3 + NO|+ 2H2O As + 5HNO3 + 2H2O = 3H3AsO4 + 5 NO| 2As + 6NaOH = 2Na3AsO3 + 3H2 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 6 1.2.3. Hp cht ca asen v tnh cht ca chng Bng1.2. Mt s thng s vt l ca cc hp cht ca Asen Hp cht Khi lng nguyn t(g/mol) Trng thi Nhit si (0C) Nhit ng c(0C) Khi lng ring (g/cm3) Asin(AsH3)77,95kh-62,47-116,923,52 iasentrioxit (As2O3) 197,84 Tinh th rn 4613143,74 iasenpentaoxit (As2O5) 229,84Rn3154,32 Asen(III)clorua (AsCl3) 181,28Lng131,4-16,22,16 Asen(III)florua (AsF3) 131.92Lng57,8-5,942,73 Asen(V)florua (AsF5) 169,91Kh-52,8-79,87,71 Asen(III)bromua (AsBr3) 314,63 Tinh th rn 321313,4 Asen(III)iodua (AsI3) 455,63 Tinh th rn 41314,3 Asen(III)sulfua (As2S3) 246,04Rn7233103,43 Asen(V)sulfua (As2S5) 310,17Rn Asensulfua(As4S4) 427,92 Tinh th rn 5343213,5 1.2.3.1. Asin AsH3 l cht kh khng mu, c mi ti rt c, liu lng cht ngi l250ppm,AsH3lchtkhmnh,ncthbcchytrongkhngkhv kh c mui ca cc kim loi nh Cu2+, Ag+ n kim loi. AsH3 + 6AgNO3 + 3H2O = 6Ag + 6HNO3 + H3AsO3 Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 7 AsH3tcdngviHgCl2tmtrngiylctothnhhpchtcmu bin i tvng n nu: AsH2(HgCl), AsH(HgCl)2, As(HgCl)3, As2Hg3. Asin tng i bn phn hu nhit cao (15000C) to nn trn thnh bnh kt ta en lp lnh nh gng. 1.2.3.2. Asen(III) oxit trng thi rn As2O3 c mu trng, rt c, liu lng gy cht ngi l0,1g.As2O3tanttrongnc(khong2%250C)chodungdchctnh axit yu gi l axit Asen. 2 3 2 3 3As O+ 3H O 2H AsO + 3-3 32H AsO6H+ 2AsO Asen(III)oxitdtantrongdungdchkim,tothnhmuiasenitv hiroasenit. As2O3 + 6NaOH = 2Na3AsO3 + 3H2O As2O3 thhintnhkhkhitcdngviO3,H2O2,FeCl3,K2Cr2O7, HNO3 v n b oxi ho n AsO43- 3As2O3 + 4HNO3 + 7H2O = 6H3AsO4 + 4NO| Trong dung dch nc axit asen lun c cn bng. 2- 3- +2 3AsO + H O AsO+ 2 H Cho nn trong dung dch kim AsO33- chim u th, cn trong dung dch axit AsO2- chim u th. 1.2.3.3. Asen(V)oxit Asen(V)oxitlchtrndngkhivnhhnhgingnhthutinh, cutrccanchacbitrvngitagnchoncngthckinh nghim lAs2O5. As2O5 d tan trong nc to thnh axit asenic. As2O5 + 3H2O = 2H3AsO4 As(V)oxit c tnh oxi ho mnh n gii phng kh clo khi tng tc vi HCl. Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 8 1.2.3.4. Asen halogenua(AsX3) AsX3 l nhng hp cht cng ho tr, d tan trong cc dung mi hu c, trong nc v thu phn mnh. AsCl3 + 3H2O = As(OH)3 + 3 HCl AsX3 d dng kt hp vi halogenua kim loi (MX) to nn cc phc c cng thc chung l M(AsX4), M2(AsX5). 1.2.3.5. Asensunfua AsensunfuachaidngAs4S4vAs2S3udngbtmuvng,tan trong dung dch kim. As4S6 + 12NaOH = 2Na3AsO3 + 2Na3AsS3 + 6 H2O Tan trong sunfua kim loi hay amoni to thnh mui tio As4S6 + 6(NH4)2S = 4(NH4)3AsS3 ( amonitioasenit) TtcccmuiasensunfuautantrongaxitHNO3c,khngtan trong HCl c. 3As2S3 + 28HNO3 + 4H2O =6H3AsO4 + 9 H2SO4 + 28NO1.2.4. Cc phn ng c trng ca hp cht asen [8] Hp cht asen(III) [9] PhnngcaAsH3vibcdietyldithiocacbamatrtctrngvc dng nh lng Asen theo phng php trc quang. 6(C2H5)2NCSSAg + AsH3= 6Ag + 3(C2H5)2NCSSH + [(C2H5)2NCSS]3As AsCl3 tc dng vi H2S trong mi trng axit cho ta kt ta vng ti. 2H3AsO3 + 6HCl = 2AsCl3 + 6H2O 2AsCl3 + 3H2S = As2S3 ++ 6HCl As2S3tantrongHNO3cnng,tantrongdungdchkimmnhhoc sunfua ca kim loi kim. As2S3 + 3(NH4)2S = 2(NH4)3AsS3 As(III) tc dng vi AgNO3 cho kt ta vng ti Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 9 H3AsO3 + 3AgNO3 = Ag3AsO3 ++ 3HNO3 TrongmitrngpH=8,As(III)tcdngvilngI2,phnngny c dng xc nh AsO33-. AsO33- + I2 + H2O = AsO43- +2I- + 2H+ Hp cht ca As(V) Mui ca As(V) tc dng vi H2S trong mi trng H+ khi un nng s to kt ta As(V)sunfua. 2AsCl5 + 5H2S = 10HCl + As2S5 Tng t photphat, As(V) tc dng vi hn hp dung dch MgCl2, NH3 cho kt ta NH4MgAsO4 mu trng. H3AsO4 + MgCl2 + 3NH4OH=NH4MgAsO4 + + 2NH4Cl + 3 H2O Khi tc dng vi amoniphotphat trong mi trng HNO3, As (V) to kt ta tinh th mu vng tng t PO43-. H3AsO4 + 21HNO3 + 12(NH4)2MoO4 =(NH4)3[AsMo12O40]+ + 21NH4NO3+12H2O CnkhitcdngviAgNO3,As(V)tokttamunuAg3AsO4, trong mi trng axit da trn phn ng to vi I- ra I2 chun theo phng php Iot Thiosunfat c th nh lng As(V). AsO33- + I2 + H2O = AsO43- +2I- + 2H+ 1.3. S nhin Asen v c tnh ca n 1.3.1. Ngun gc s nhim Asen Asen l mt kim loi c th tn ti nhiu dng hp cht v c v hu c. Ngun nhim asen ch yu l do cc qu trnh t nhin ( phun tro ni la, hot ng maga, nhit dch, phong ho). Vn asen bt ngun t a cht trong cc trm tch cch y khong 20-80 nghn nm nh hng ti 50% lnh th Bangladesh. Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 10 Theo iu tra ca UNICEF, asen c trong tt c cc t , cc trm tch c hnh thnh t nghn nm trc ti Vit Nam. Asen t t tan vo cc mch nc gy nhim. Mt phn nc b nhim bi Asen l do tc ng ca con ngi ( t nhin liu, t rc, nu chy qung, luyn kim, khai thc v ch bin cc loi qungsunfua,asenua,snxutvsdngthuctrsuditc,phnho hc, thuc bo v thc vt, v kh ho hc) gy ra. LmtncnngnghipVitNamsdngmtlnglnthuctr suditc,phnhohc,thucbovthcvtcchaasenlmtngs phn tn As vo mi trng nc v trm tch. Hn na trong chin tranh k thcngsdngmtlnglnchtchichaAsenlmtngcng trm tch bi nguyn t ny. Vi s pht trin ca khoa hc k thut v nn cng nghip ho lm cho mi trng nhim ch yu l do ngun ph thi cha c x l hoc x l chatyucu.Phthicngnghip,phthisinhhot,hochtnng nghip tn d i vo trong nc, vo khng kh ri tch t trong t, lm cho t b thoi ho, lm gim cht lng sn phm. c bit l cc loi cy trng trn khu vc t b nhim c th tr thnh c hi cho ngi s dng. 1.3.2. nhim asen trn th gii [16] Tnhtrngnhimasentrnthgiiangcchiuhnggiatngrt nhanh. Nhiu ni, hm lng Asen trong t, nc, khng kh vt cao hn so vi gii hn quy nh ca cc t chc sc kho th gii. Bnh thng hm lngasentrongkhngkhchkhong1nvimg/m3,trongmitrng nc khong mt vi g/l v trong t khong 0,2 - 40 mg/kg. Nhng mt s vng trn th gii mc asen trong mi trng t nhin tng ng k. [8] nhimasencphthintrongncnhiunitrnthgiinh Achentina, M, Trung Quc, n , Bangladesh, Chile, Vit Nam, Rumani, Sha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn 11 Myanma vi nng t vi trm n 1000 g/l. mt s bang pha Ty ca nc M nh New Mexico, Arizona, Nevada, Nam Califonia, ngi dn phi s dng nc c nng > 50 g/l. Mt s nghin cu ti Thi Lan gn ychothy21%trongs83563gingkhoanchmlngasenvtqu 50 g/lv 5,2% vt qu 350 g/l , vi ngng cao nht l 2500 g/l . Bo co tng kt tnh hnh nhim c do asen ti Trung Quc nm 2004 cho thy, 8 tnh thuc Trung Quc lc a vi hn 2 triu ngi b thm nhim Asen t nc ging khoan vi hm lng Asen nm trong khong t 50-2000 g/l. Trong 10 nghn ngi c chun on l mc cc bnh c lin quan ti asen. SlngccimccoilngunncbnhimAsenhinnay vn gia tng. Bng 1.3. Tnh hnh nhim asen ti mt s vng quc gia trn th gii Tn Nc S dn chu nh hng (triu ngi) Khong nng As trong nc ( g/l) Achentina2100-1000 Bangladesh50