Analytical methods and achievability

Transcription

1 ANNEX 4 Anlyticl methods nd chievbility A4.1 Anlyticl methods In volumetric titrtion, chemicls re nlysed by titrtion with stndrdized titrnt. The titrtion end-point is identified by the development of colour resulting from the rection with n indictor, by the chnge of electricl potentil or by the chnge of ph vlue. Colorimetric methods re bsed on mesuring the intensity of colour of coloured trget chemicl or rection product. The opticl bsorbnce is mesured using light of suitble wvelength. The concentrtion is determined by mens of clibrtion curve obtined using known concentrtions of the determinnt. The ultrviolet (UV) method is similr to this method except tht UV light is used. For ionic mterils, the ion concentrtion cn be mesured using n ion selective electrode. The mesured potentil is proportionl to the logrithm of the ion concentrtion. Some orgnic compounds bsorb UV light (wvelength nm) in proportion to their concentrtion. UV bsorption is useful for qulittive estimtion of orgnic substnces, becuse strong correltion my exist between UV bsorption nd orgnic crbon content. Atomic bsorption spectrometry (AAS) is used for the determintion of metls. It is bsed on the phenomenon tht the tom in the ground stte bsorbs the light of wvelengths tht re chrcteristic to ech element when light is pssed through the toms in the vpour stte. Becuse this bsorption of light depends on the concentrtion of toms in the vpour, the concentrtion of the trget element in the wter smple is determined from the mesured bsorbnce. The Beer-Lmbert lw describes the reltionship between concentrtion nd bsorbnce. In flme tomic bsorption spectrometry (FAAS), smple is spirted into flme nd tomized. A light bem from hollow cthode lmp of the sme element s the trget metl is rdited through the flme, nd the mount of bsorbed light is mesured by the detector. This method is much more sensitive thn other methods nd free from spectrl or rdition interference by co-existing elements. Pretretment is either unnecessry or strightforwrd. However, it is not suitble for simultneous nlysis of mny elements, becuse the light source is different for ech trget element. 476

2 ANNEX 4. ANALYTICAL METHODS AND ACHIEVABILITY Electrotherml tomic bsorption spectrometry (EAAS) is bsed on the sme principle s FAAS, but n electriclly heted tomizer or grphite furnce replces the stndrd burner hed for determintion of metls. In comprison with FAAS, EAAS gives higher sensitivities nd lower detection limits, nd smller smple volume is required. EAAS suffers from more interference through light scttering by co-existing elements nd requires longer nlysis time thn FAAS. The principle of inductively coupled plsm tomic emission spectrometry (ICP- AES) for determintion of metls is s follows. An ICP source consists of flowing strem of rgon gs ionized by n pplied rdio frequency. A smple erosol is generted in nebulizer nd spry chmber nd then crried into the plsm through n injector tube. A smple is heted nd excited in the high-temperture plsm. The high temperture of the plsm cuses the toms to become excited. On returning to the ground stte, the excited toms produce ionic emission spectr. A monochromtor is used to seprte specific wvelengths corresponding to different elements, nd detector mesures the intensity of rdition of ech wvelength. A significnt reduction in chemicl interference is chieved. In the cse of wter with low pollution, simultneous or sequentil nlysis is possible without specil pretretment to chieve low detection limits for mny elements. This, coupled with the extended dynmic rnge from three digits to five digits, mens tht multielement determintion of metls cn be chieved. ICP-AES hs similr sensitivity to FAAS or EAAS. In inductively coupled plsm mss spectrometry (ICP-MS), elements re tomized nd excited s in ICP-AES, then pssed to mss spectrometer. Once inside the mss spectrometer, the ions re ccelerted by high voltge nd pssed through series of ion optics, n electrosttic nlyser nd, finlly, mgnet. By vrying the strength of the mgnet, ions re seprted ccording to mss/chrge rtio nd pssed through slit into the detector, which records only very smll tomic mss rnge t given time. By vrying the mgnet nd electrosttic nlyser settings, the entire mss rnge cn be scnned within reltively short period of time. In the cse of wter with low pollution, simultneous or sequentil nlysis is possible without specil pretretment to chieve low detection limits for mny elements. This, coupled with the extended dynmic rnge from three digits to five digits, mens tht multielement determintion of metls cn be chieved. Chromtogrphy is seprtion method bsed on the ffinity difference between two phses, the sttionry nd mobile phses. A smple is injected into column, either pcked or coted with the sttionry phse, nd seprted by the mobile phse bsed on the difference in interction (distribution or dsorption) between compounds nd the sttionry phse. Compounds with low ffinity for the sttionry phse move more quickly through the column nd elute erlier. The compounds tht elute from the end of the column re determined by suitble detector. In ion chromtogrphy, n ion exchnger is used s the sttionry phse, nd the elunt for determintion of nions is typiclly dilute solution of sodium hydrogen crbonte nd sodium crbonte. Colorimetric, electrometric or titrimetric detectors cn be used for determining individul nions. In suppressed ion chromtogrphy, nions re converted to their highly conductive cid forms; in the crbonte bicrbonte 477

3 GUIDELINES FOR DRINKING-WATER QUALITY elunt, nions re converted to wekly conductive crbonic cid. The seprted cid forms re mesured by conductivity nd identified on the bsis of retention time s compred with their stndrds. High-performnce liquid chromtogrphy (HPLC) is n nlyticl technique using liquid mobile phse nd column contining liquid sttionry phse. Detection of the seprted compounds is chieved through the use of bsorbnce detectors for orgnic compounds nd through conductivity or electrochemicl detectors for metllic nd inorgnic compounds. Gs chromtogrphy (GC) permits the identifiction nd quntifiction of trce orgnic compounds. In GC, gs is used s the mobile phse, nd the sttionry phse is liquid tht is coted either on n inert grnulr solid or on the wlls of cpillry column. When the smple is injected into the column, the orgnic compounds re vporized nd moved through the column by the crrier gs t different rtes depending on differences in prtition coefficients between the mobile nd sttionry phses. The gs exiting the column is pssed to suitble detector. A vriety of detectors cn be used, including flme ioniztion (FID), electron cpture (ECD) nd nitrogen phosphorus. As seprtion bility is good in this method, mixtures of substnces with similr structure re systemticlly seprted, identified nd determined quntittively in single opertion. The gs chromtogrphy/mss spectrometry (GC-MS) method is bsed on the sme principle s the GC method, using mss spectrometer s the detector. As the gs emerges from the end of the GC column opening, it flows through cpillry column interfce into the MS. The smple then enters the ioniztion chmber, where collimted bem of electrons impcts the smple molecules, cusing ioniztion nd frgmenttion. The next component is mss nlyser, which uses mgnetic field to seprte the positively chrged prticles ccording to their mss. Severl types of seprting techniques exist; the most common re qudrupoles nd ion trps. After the ions re seprted ccording to their msses, they enter detector. The purge-nd-trp pcked column GC-MS method or purge-nd-trp pcked column GC method is pplicble to the determintion of vrious purgeble orgnic compounds tht re trnsferred from the queous to the vpour phse by bubbling purge gs through wter smple t mbient temperture. The vpour is trpped with cooled trp. The trp is heted nd bckflushed with the sme purge gs to desorb the compounds onto GC column. The principles of GC or GC-MS re s referred to bove. The principle of enzyme-linked immunosorbent ssy (ELISA) is s follows. The protein (ntibody) ginst the chemicl of interest (ntigen) is coted onto the solid mteril. The trget chemicl in the wter smple binds to the ntibody, nd second ntibody with n enzyme ttched is lso dded tht will ttch to the chemicl of interest. After wshing to remove ny of the free regents, chromogen is dded tht will give colour rection due to clevge by the enzyme tht is proportionl to the quntity of the chemicl of interest. The ELISA method cn be used to determine microcystin nd synthetic surfctnts. 478

4 ANNEX 4. ANALYTICAL METHODS AND ACHIEVABILITY A4.2 Anlyticl chievbility for chemicls for which guideline vlues hve been estblished Anlyticl chievbility for chemicls for which guideline vlues hve been estblished is given in Tbles A4.1 A4.6. Tble A4.1 Anlyticl chievbility for inorgnic chemicls for which guideline vlues hve been estblished, by source ctegory Field methods Lbortory methods Col Absor IC FAAS EAAS ICP ICP-MS Nturlly occurring chemicls Arsenic +++ # ++(H) + ++(H) +++ Brium Boron Chromium # Fluoride # Selenium # ++(H) ++ ++(H) +++ Urnium +++ Chemicls from industril sources nd humn dwellings Cdmium # Mercury +++ Chemicls from griculturl ctivities Nitrte/nitrite Chemicls used in wter tretment or mterils in contct with drinking-wter Antimony +++(H) ++(H) +++ Copper # Led # Nickel For definitions nd notes to Tble A4.1, see below Tble A

5 GUIDELINES FOR DRINKING-WATER QUALITY Tble A4.2 Anlyticl chievbility for orgnic chemicls from industril sources nd humn dwellings for which guideline vlues hve been estblished GC-ECD GC-FID GC-FPD GC-TID GC-MS PT-GC-MS HPLC HPLC-FD HPLC-UVPAD EAAS IC-FD Benzene Crbon tetrchloride ,2-Dichlorobenzene ,4-Dichlorobenzene ,2-Dichloroethne ,2-Dichloroethene Dichloromethne Di(2-ethylhexyl)phthlte ++ 1,4-Dioxne +++ Edetic cid +++ Ethylbenzene Hexchlorobutdiene Nitrilotricetic cid Pentchlorophenol Styrene Tetrchloroethene Toluene Trichloroethene Xylenes For definitions nd notes to Tble A4.2, see below Tble A

6 ANNEX 4. ANALYTICAL METHODS AND ACHIEVABILITY Tble A4.3 Anlyticl chievbility for orgnic chemicls from griculturl ctivities for which guideline vlues hve been estblished,b GC- ECD GC-FID GC-FPD GC-TID GC-MS PT-GC-MS HPLC HPLC-FD HPLC- UVPAD EAAS IC-FD Alchlor Aldicrb +++ Aldrin nd dieldrin Atrzine nd its chloros-trizine metbolites Crbofurn Chlordne Chlorotoluron Cynzine ,4-D ,4-DB ,2-Dibromo-3-chloropropne ,2-Dibromoethne ,2-Dichloropropne ,3-Dichloropropene Dichlorprop Dimethote +++ Endrin Fenoprop Hydroxytrzine Isoproturon Lindne MCPA

7 GUIDELINES FOR DRINKING-WATER QUALITY Tble A4.3 (continued) GC- ECD GC-FID GC-FPD GC-TID GC-MS PT-GC-MS HPLC HPLC-FD HPLC- UVPAD EAAS IC-FD Mecoprop Methoxychlor +++ Metolchlor Molinte Pendimethlin +++ Simzine ,4,5-T Terbuthylzine Triflurlin For definitions nd notes to Tble A4.3, see below Tble A4.6. b LC-MS is lso pplicble for mny of these griculturl chemicls. Tble A4.4 Anlyticl chievbility for chemicls used in wter tretment or from mterils in contct with wter for which guideline vlues hve been estblished GC-ECD GC-FID GC-FPD GC-TID GC-MS PT-GC-MS HPLC HPLC-FD HPLC-UVPAD EAAS IC Disinfectnts Monochlormine +++ Chlorine +++ Sodium dichloroisocynurte Disinfection by-products Bromte ++ Bromodichloromethne Bromoform Chlorte

8 ANNEX 4. ANALYTICAL METHODS AND ACHIEVABILITY Tble A4.4 (continued) GC-ECD GC-FID GC-FPD GC-TID GC-MS PT-GC-MS HPLC HPLC-FD HPLC-UVPAD EAAS IC Chlorite +++ Chloroform Dibromocetonitrile Dibromochloromethne Dichlorocetic cid Dichlorocetonitrile Monochlorocetic cid N-Nitrosodimethylmine +++ Trichlorocetic cid ,4,6-Trichlorophenol Trihlomethnes b Orgnic contminnts from tretment chemicls Acrylmide + + Epichlorohydrin Orgnic contminnts from pipes nd fittings Benzo[]pyrene Vinyl chloride For definitions nd notes to Tble A4.4, see below Tble A4.6. b See lso individul trihlomethnes. Tble A4.5 Anlyticl chievbility for pesticides used in wter for public helth purposes for which guideline vlues hve been estblished GC-EC GC-FID GC-FPD GC-TID GC-MS PT-GC-MS HPLC HPLC-FD HPLC-UVPAD EAAS IC/FD Chlorpyrifos DDT (nd metbolites) For definitions nd notes to Tble A4.5, see below Tble A