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<br />:1 • ^ -. ~,~al the c°A has sot the regulatory limits idi•
<br />_ .; aside i •.veak metal cyanide + CNATC (I)
<br />Curren! hYA ntetltoda for cyanide determination, while
<br />gelterally successful ill species differettl.ietion, are lengthy and
<br />lobar inteusiee. The <letecliun limits of these methods ere
<br />oirctt too high td provide useful information for typical en-
<br />detrlic concentratiuna. It is also well-known that these
<br />methods suffer Crom poor precision due in pall t0 a variety
<br />dt serious interferences (5). As A result of these shortcomings,
<br />A variety of altemativo mathod9 have reant.(y been developed.
<br />'These include calorimetric (5, 6), potentiometric (~, and
<br />ChromaWgraphic (8-l0) determinetinna T)te latter method,
<br />while providing the best speciation determination, lacks de-
<br />tection sensitivity. Roth the colorimelric end potentiometric
<br />methods, ]iko the tradilidna] procedures, continue to suffer
<br />from 6erlOUa 1ntErferEllCea nI lack 8 means Of BpeCmtlan da'
<br />termination.
<br />The goal of this work has been to produce a cyanide de-
<br />tection system that nut only has a limit of detection below
<br />the EPA water quality criterion of 5 ug/L Wtal cyanide (4)
<br />but is also able to differentiate cyenido epociee by elassiFica•
<br />lion, thereby providing a trotter representation of the potential
<br />toxicity of the sample. The use of a highly aeloctive reaction
<br />between cyanide sod silver metal ie employed to fulfill these
<br />stringent reyuicEments:
<br />4Ag + 8CN' + 2H10 + Oa -- 4Ag(CN12 k 40H' (2)
<br />The reaction in cry ? produces a soluble silver dicyano complex
<br />thae can be detected by standard atomic absorption apec-
<br />trnmotric (AAS) methods. Two factors that combine to make
<br />this silver AAS detection method splrealing ere (i) silver ie
<br />doe element that con he easily detected at extremely low
<br />concentrations by AAS xnd (ii) the cyanide resets rapidly with
<br />the normally inerl silver metal. The cotlplittg of this reaction
<br />with AAS detection was first used by G. Jungresia (11,12) u
<br />an indirect method for the c)'anide ion. While this procedure
<br />proved adequate Cor cyanide ion determination, emphasis has
<br />since shifted to the determination of total cyanide and all those
<br />species that make up this category. It has, therefore, been
<br />necessary to develop techniques and procedures that will allow
<br />this sensitive defection method W be used W epeeists and
<br />detect bath simple end complex cyanides.
<br />The results presented below demunatrate that. given the
<br />appropriate chemical conditions, the silver-cyanide tsACtion
<br />can be used for the quantitative deurmination of free cyanide
<br />cnntairted in an aqueous sample. Moreover, by employing
<br />photochemical ligand dieeocfation techniques, this same re-
<br />action can also be used to deWrmine WCaI cyanide concon•
<br />tratione. Finally, by coupling the above methods with es-
<br />tablished selective oxidation reaction chemistry, the quan•
<br />tltative determination of CNATCe may Ile obtained. These
<br />three determinations, thereby, provide a means of chereC-
<br />terizingcyanide samples through which the passible toxico•
<br />logical effects of rho salrtple are indicated. These techniques
<br />will also allow tits analysis td be performed in a manner that
<br />is safer and simpler than previously possible.
<br />EXPERIAIBNTAL 6ECTION
<br />Apparatus. `olucim:x were intred~:ced by using s Raisin
<br />InaCIanlGllt iRabbit ?,ludcll perlHi.altli pump. The phew cell
<br />(Figure '.) u~tm ~~uml n r~l c••:::.I L ., i ~n~ii~•s mercurg •anac lpmp
<br />tA1adel HJf7Ii B• ls5i ann ,,.,a ,,,,~: ~.r,..r by ~ I;I>ctn~ack r,'iscure
<br />(Modal lt-t7`:.' - .- _,.. : •r l~,.n, f,..._.::„., n
<br />xrl,.io ~ .. ,. _..... _. .
<br />of fSn tyr-.. -
<br />sour~-~ _ .. ........
<br />and ,5='-.. ._.
<br />4i ,~. IY~ i.l `~ - -
<br />?.r:,:! uric.'+_ .___ ..•
<br />Flqure 1, H39X&775 pholdcetl.
<br />95
<br />3~ t r5
<br />Ip
<br />4BR
<br />(part
<br />Ppo
<br />.,Pm,e
<br />BvmPY aoNN PM1FbCtlI a0d, MFO,PIIPO
<br />FW7 Fop, SBCI,OmvIU
<br />Figure 2- 61ocx diagram oT the exparlmetnal design.
<br />merely 9 mL of sample. Other light ebutroa used iocludad a
<br />General Electric germicidal lamp (Madkl G25Tf1) end the same
<br />lamp with a 1.5-mm•tltiek tx,rusilicate fees sleeve. The entire
<br />system rose cooled by a 5•ln. fen mounts axially above the lamp
<br />and enclosed in s foil-lined light shield t at wan nominally 3o cm
<br />in diameter. The silver reaction chamber donsisted of a pure ailvu
<br />meml)rane filter (pore size 5 um, dipmetpr 13 mm) held in place
<br />by a 13-mm stainless steel Idler holder (1'~eti~ Corp., LivermorE,
<br />CA). The resulting solutions were anal)z fur their soluble silver
<br />concentration by using a Varian Ter;htronlatomic ebsorptioo (AA)
<br />spectrometer. The above components $re finally corrected in
<br />aeries pe Illustrated in Figure 2.
<br />Roagonta, All chemicals used wore oil the highest grade com-
<br />mercielly available. Standard cyenido eplutions were prepared
<br />from s 1 g of CN-/L ut potassium cyanidelstock aolutian, adjusted
<br />W Ali = 12 with potassium hydroxide ifor seta handling, and
<br />standardized with silver nitrate.
<br />Standard metal cyanide aolutiuna weYe prepared by dilution
<br />from their potassium spits, Stock solutbtts of potassium fetri-
<br />eyanide, KaFe(CN)B; potassium cobaltic~anido, K9Cu(CN)a; po-
<br />tassium chromic cyanide, KaCr(CN)s; p tasaium terrucyenitle.
<br />KrFe(CN)s•3Ha0; potassium ether cymid~, KAg(CN)y po4lesium
<br />thiotyanate, KSCN; and potassium zinc youido, Ka7.niCN)t, all
<br />Available from Pfolt2 And Raver, were di urea i» distilled water
<br />to p concentration of l0u mg/L cyanide, ~d held at pH ~ 12 by
<br />the addition of potassium hydrozide. Al] ere stored under light
<br />And hout~prntected conditions. Sodium ypophosphite solution
<br />wee prepared !ly dissolving 44 g of Np}i YOz•H;0 in loo mL of
<br />distilled rooter. Preparation of all othersolutiuns needed may
<br />be found in the Cyanide section A-D of Standard Methude (~).
<br />bus to the toxicity of cyanide, care shpuld be taken to avoid
<br />accidental ingestion of skin contact with pulutions. Acidi~catiun
<br />of cyanide solutions may Liberate acutely tunic NCN gas, As a
<br />safety precaution, all analytic procedures yin this work have been
<br />devoUiped using solmions of pH ~ 12 nr BI}~oae. Complete safety
<br />^•xoutinrs sGri First aid treatments art aptly described in
<br />3;ar.dard Methods (3).
<br />Yroeedures. Determinoricn nJ Tntr.! rod Frce C•.cnide. Td
<br />lU :nL n( i~iPiE^+ed (p}T ?1~~f IJgt Fit [u _ ' inltie serif plP add O.:
<br />_cciu:r. !,>d; n;jdr mid 5 mL „t'_U:;,..:, ~..: ptipLusphlte solution
<br />..~,ac mlE wail. Begin t4 set up the Byecem ny ^r~c op[imizing cha
<br />.,u.a;c ~bsurption spectrometer for t;~a dkt action of sdeer. Op•
<br />- „_ .Iii)4 P.O.~
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