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HUR TECHIVUL05IE5 INC
<br />
<br />u
<br />9
<br />li
<br />V
<br />ac
<br />Irretltallon Tlms (min.)
<br />+ Felll ®365nm
<br />+ F~II ~ 365nm
<br />-.. FFIII®2rvlnm
<br />r F~11~25anm
<br />Flpun 9. Photoconvar6bn 01 Iron cyanba COmplexe6 u61np the OzSTa
<br />uttravlolat Ilpht source.
<br />be measured na a function of the stability of the competing
<br />metal complex and of the contact time of the complex with
<br />the silver. Table III shows the results from these axporiments.
<br />Two trends era evident in these data Firefly, ae the formation
<br />constant of the metal c}'ettido complex increases, the ability
<br />of the ailvor to successfully compete for the cyanide ligand
<br />decreases. Secondly, as the flow rate decreases and the su-
<br />lution contact time with the filter ittcroasee, the percentage
<br />of bound ligmtds acquired by the silver also increases. Thasa
<br />results indicate that selective kinetic equilibrium can be
<br />utilized to aid in the categorical differotttiatiott of the various
<br />cyanide apeciea. By choosing a 2.6 mi./min [low rate, the free,
<br />molecular, and zinc cyanides can be selectively detected by
<br />the silver Clter, while leaving the remaining metal cyanide
<br />complexes essentially undetected. Since these three species
<br />are dissociated by conditions that ere prevalent in natural
<br />aquatic systems, they typically comprise the bulk of the free
<br />cyanide category.
<br />Determination o[ Total Cyanide. Currently mast
<br />Countries with Cyanide regulatory standards set limitations
<br />only on total cyanide concentrations. Whether such a limi-
<br />tation is well founded or not, it dues make the total cyanide
<br />determination of foremost importance to most investigations.
<br />Since Goulden (!3) showed in 1972 that eomplax metal
<br />cyanides can be phutudecompnsod by ultrnviolot light, many
<br />others (7, 8, 14, 15) have attempted to utilize photodecom-
<br />position in place of the etenrlard strong acid distillation in
<br />total cyanide dotormittation procedures.
<br />Pltotodecompositiun offers aevera] pnuihlo advantages over
<br />traditional strong acid distillation methods, e.g., reduced
<br />analysis times, improved accuracy and precision, safe end
<br />simplistic operation, and adaptability toward nuuttnation. The
<br />problem with phutodecumpneitio», ae pointed out by Puhlandt
<br />(3), has been the varied results reported by different inve6-
<br />tigotors. The inconsistencies found in tlta literature (8, 10,
<br />16) rvncerning the effectiveness of various photodecomposition
<br />systems are likely a result of the greatly differing experimental
<br />parameters used for these studies. Through testing, we have
<br />found that several ppratnetera play important rotas in the
<br />photoconversion of metal cyanide complexes to Free cyanide.
<br />Tho wavelength of sample irradiation is extremely important.
<br />Not only moat the light source be considered, but also the
<br />experimental gentnetry and construction of the photocell. In
<br />constructing our flow-through system, we had the choice to
<br />contpin the sample in narrow tubing made of either quartz
<br />or FLP'1'eilon. The FEP Teflon and quartz proved equally
<br />transparent througltottl the spectral raginna of int.ereet. The
<br />Teflon was, however, more economical and easily faltricatetl
<br />in W various cell geometries, making it the material of choice
<br />far use in the photocell. While using FEP tubing, various
<br />irreriiatiun sources were tested. The light sources varied by
<br />both itttertaity and spectral output. Lamps with high-energy
<br />entissinn such as the General Electric G25T3 (71m„ = 253.6
<br />TEL~~U~-79~-5533
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<br />Mau oa '?~%
<br />ANALYTICAL CHEM1~, VOL. 63, NO.
<br />120
<br />11a
<br />g too
<br />9p
<br />so
<br />r0
<br />8a
<br />~a
<br />~ 30
<br />to xo so ao
<br />Irretllatlon Tlme (m
<br />Pleura 4. Total cyenlde detection using the
<br />nm) provided rapid photuoonversion will
<br />only a Cew minutes of exposure. This M
<br />decrease in the free cyanide concpntrn
<br />all liberated free cyanide was eliminat
<br />botosilicate glass filter added to this sl
<br />emission output to a lower energy (~,
<br />produced on ovtirely different photon
<br />cyanide was slowly produced and, even
<br />sores, continued to produce an inereal
<br />concentration. 8y using another lower
<br />(am,r ~ 36G nm), but with a much rr
<br />(Philips H3D-KB, 175 W, eve total of
<br />Increasing photoconvorted free cyattidl
<br />again obtained. By use of the H39.1
<br />complete conversion of a variety of met
<br />was achieved after 33 min of exposure e
<br />4.
<br />$uch behpvior, aL least Cur the ferric
<br />Deen well explained and similar situotior
<br />cyanides (17). Tho high•energy irrediatil
<br />with photooxidation reactiuaa that pr
<br />agreee with our results, showing a doe
<br />centretiun with continued irradiation I
<br />Alternatively, irradiation at 366 nm has
<br />ligand d'ISeociatione that quantitatively p
<br />ions. The rate of phoWconvenion for t}
<br />ie a ftutction of both the stability consul
<br />maxima of the respective compounds.
<br />The roes these factom play in inffuer
<br />exemplified by two extreme exatnltlet
<br />ferric cyanide. As expected, the ext
<br />complex requires extended exposure ti
<br />percent of photoconversion (Figure 4).
<br />e very stable complex, but unlike cube
<br />sorption bend over the wavelengths nl
<br />it t0 decompose rapidly. I''erzuus an
<br />represent more typical complexes that
<br />stability constantx, are photnconverted
<br />to the extromea.
<br />In order W obtain photoconversion
<br />those presented above, rho electrochen
<br />the photnlysie ettvironmenl must he a
<br />tolyeifi environment contains a significal
<br />agent., irradiation oven at higher ens
<br />predominantly produce undesirehlo cyl
<br />cyanide ions. A 0.45 i\1 concenl.rat
<br />phosphite was found to effectively st
<br />oxidation. Such a aolution did not re
<br />present in the sample. This is imports.
<br />to be included in the defined total cy
<br />Through our experimentation, we h.
<br />fectivenese of n photodecumpositinn s;
<br />s IJo . ]I]a ~ . zs
<br />APRIL t, 1881 • E96
<br />+ F1111 CN
<br />w Fell GN
<br />-r CiCN
<br />CdN
<br />+ rgCN
<br />•~ rnCN
<br />-- a
<br />~~
<br />60
<br />Ilpltt sowce.
<br />a peek recovery after
<br />u followed by a slow
<br />ion, until eventually
<br />d (nee Figure 3). A
<br />Ina lamp shitted the
<br />„ ~ 365 nm). This
<br />action in which free
<br />after extended expo-
<br />t in the free cyanide
<br />nergy emission lamp
<br />xe powerful output
<br />:put 31 W), steadily
<br />concentrations were
<br />B lamp, essentially
<br />d cyanide complexes
<br />illu_gtrated in Figure
<br />ranide complex, has
<br />exist for Other metal
<br />I hoe been associated
<br />toes cyattate. This
<br />mso in cyanide con•
<br />lower wavelengths.
<br />een shown to induce
<br />xluce simple cyanide
<br />different oomplexes
<br />C and the absorption
<br />:ing recovery rate are
<br />cobalt cyanide and
<br />emely stable cobalt
<br />nee to ac)tieve a ]tigh
<br />ferric cyanide is also
<br />t, it has a strong ob•
<br />irradiation, allowing
<br />I chromium cyanide
<br />even with their high
<br />st rale6 Intermediate
<br />+coveriee as high es
<br />al characteristics of
<br />trolled. If the pho•
<br />amount of oxidizing
<br />y wavolongths will
<br />ate ions rather titan
<br />n of sodium hypo-
<br />presse any cyanide
<br />tee cyanete already
<br />since cyanete ie not
<br />tide determination.
<br />e found that the ef-
<br />tcm depends on the
<br />e Ie se ro
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