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<br />TE~~HPdOLf]GIEO II`i~.. TEL ~ ~0~-~ 9~-56'~
<br />884 • ANALYTICAL CHEMISTRY, ~ 03, N0. 7, APRIL 1, 1991
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<br />Teblo i. AeDOndeace of the Silver Filter Itenction
<br />Efficiency on Flltar Pore Slxa, Sample Flow Rata, and
<br />Fillor Thloknesa
<br /> °/a enelyta
<br /> reacted with Ag
<br />Ilow rale,° S~µm 045-eta
<br />mL/min pore airs pore else
<br />4.94 GI BI
<br />3.R0 83 87
<br />3.02 88 93
<br />2.47 97 99
<br />1.75 101 (02
<br />1.23 101 100
<br />0.76 100 101
<br />Ag Nkr thickness
<br />(5•µm pore wise)
<br />96 rec, 46 rec, 46 rec,
<br />40 µm 80 µm 120µm
<br />61 66 67
<br />83 BB 88
<br />88 91 90
<br />91 58 B9
<br />101 99 101
<br />• Analyze ] mg/L CN-, pH = 12.
<br />timize tiro Aq epectrnmeter by directly aspirating silvor standard
<br />solutions and adjusting the wxvelettgth, xir•to-ecetylarre ratio, slit
<br />width, and burner position W obtain maximum signal. Check all
<br />samples for silver contont by direct comparison of signals from
<br />filtered (.0.46-µta) sample Solutions with silver standards, using
<br />distilled water as a blank. With the AA spectrometer optimized,
<br />place the Ag filter, photocell, and pump in-lino as Shown in Figure
<br />2. With rho pump rpte sat at 10 mL/min, rinse rho filter with
<br />pH . 12 protihered distilled water until a zero (no silver) baseline
<br />!s achieved. Next, hypeeaing the photucell,introduce aevergl
<br />cyanide atattdards at 2.b mL/mitt, while rinsing with blank so-
<br />luti~n inbetween samples, until repmducible signals era obtaDted.
<br />Always atop ihn pump when switching solutions to avoid intro•
<br />ducittg air huhbles into rho system. With the photocell still
<br />bypassed, intrnducr sample until s steady signal is obtained.
<br />Comparison of the eemple aignala with the signets obtaittod From
<br />the cyanide standards will yield the cyanido concentration n(the
<br />sample.
<br />Next, with aamplo continuing to ba pumped, place thn photocell
<br />in-lino. Pump until a steady baseline signal is obtained. Stop
<br />the sample flow and allow the sample to be irradiated for 31 min.
<br />Restart the pump end analyzo the irtadiated sample. Follow thin
<br />eamplo with an aliquot of cyanide standard of en aquivalont
<br />volume as the irradiated sample (the volumo of the photocell).
<br />Cvmpariaon of the sample signals with signals obtained from the
<br />cyanide standards detorminee the total cyanide concontretion,
<br />Determination of cyanido Nnt Amonable to Chlorlnetloo.
<br />Place 40 mL of the preserved sample to he analyzed in a lleaker
<br />on a magnetic stirrer and stir with a triflueroathylene (TFE)
<br />tooted stir bar. Ensure the pH is wall above f 2 by dissoh~ng Q2
<br />g of potassium hydroxide itt the eemple. Chlorinate the eemple
<br />by adding calcium hyptK•hlorite solution until potassium iodide
<br />starch paper shows an excess of chlorine. Maintain this excess
<br />of chlorine and pl{for 1 h. Keep solutions protected from light.
<br />I•;liminste residual chlorine by adding 60-mg ineremonta of as-
<br />corbic acid, testing with KI starch paper niter each addition, Allow
<br />solution to age at least 1 h, as cot xacorbic acid-KOH precipitate
<br />tnrms. Filter thiq precipitate from tiro solution, Add b mL of
<br />sodium hyirophosphite solution and mix well. Mal}ze the sample
<br />as above for total cyanide.
<br />RESULTS AND DISCU88ION
<br />Detormination of Frec Cynnida, rl'he ahility of the de-
<br />acribed silver AAS system to detect cyanide is direMly related
<br />to thr efficiency of rexctiOtt 2. Initially, free cyanide deter-
<br />minations relied an the reaction of cyanide with narrow gauge
<br />silvor wiro; however, this required lengthy contact times. The
<br />officienCy of toactiun 2 was greatly increased by providing a
<br />larger silver surface area to the cyanide. Passing the enelyta
<br />cyanide solution through a filter composed of pure silver
<br />introduces the cyanide to an enormous excess of silver. The
<br />percentage oC rho cyanide that reacts with the silver is a
<br />function of both the poro size of the filter and the flow rats
<br />U( the enelyta through the filter. Table I ehowa that filters
<br />with a amallet pore size provido rnvre complete reaction of
<br />the enelyta at higher f+.~. rates. However, at iluw rates of
<br />Mau 04 9~ 5~ 4 No .004 F.04
<br />•
<br />TeUle IL Free Cyanide Determine ion
<br />amt GN' added, mg/L amt CN- found; mgJL
<br />0.004 0.006 * 0.001
<br />0.01 G 0.015 4: 0.001
<br />0.050 0.051 3 0.001
<br />0.116 0.114 t 0.002
<br />0,230 ~ 0.230 t 0.017
<br />0.423 0.439 t O.Ol2
<br />0.830 0.818 t 0.028
<br />• n = 4 aamplca.
<br />
<br />TeUle III. Kinetic Equili brium Eff c t: Stability and Timc
<br />Faetore on the 9llver Probe Resettc
<br /> 9o cyanide
<br /> Wnv r ted u, Ag(CNIp
<br />aGtbility 5 2.5 0.5
<br />enmpd toner mL/min mL(min mL/min
<br />CN- fit 97 102
<br />2niCN)j" 10'~ 48 96 100
<br />CrICN)s'" 10x' 2 B 1@
<br />Fe(CN)e' lOtr 0 0 0
<br />2.5 mLjmin end holow, the recovery
<br />identical, producing wmplete silver
<br />Unlike pore size, the thickness or the
<br />filf4Ca has little to no effect On teacti r
<br />in Tnblo I illustrate. The small, 0.4b- ~
<br />the advantage of near complato con
<br />Lhe snlUble dicyanosilver complex e
<br />7'hia advantage is, howevor, some 1
<br />bubble pressure of theso filters.
<br />function of poro size and filter Lflic i
<br />0.45-µm filters than the pressures pr
<br />Celtic or syringe pumps. As a result, a +
<br />to the filter catlnut be passed, ceusi
<br />blockage of rile system. Duo W this o
<br />it was found that the 5•µm filter (3 '
<br />at a Cinw rate of 2.5 mL/min, prov
<br />recovery, while allowing for simplified
<br />reaulte obtained with these conditivna
<br />nro shown in'1'eble Il. These resul
<br />responao Chia system providos, eve
<br />cyanido concentrations.
<br />8y using the Optimized silver filie
<br />carried ottt to investigate the charec
<br />While thin reaction ie often cited wits
<br />mechanism of the reaction, other redt
<br />farad ht aqueous syetome may also foci.
<br />reaction. IIy sl»kittg samples with cya
<br />rho solution with either nitrogen, air, ~
<br />that reaction 2 proceode equally well
<br />oration, However, saturation with n
<br />pressed Lhe reaction. This indicates 1
<br />reaction 2 in these samples; therofore,
<br />excluded from ambient airbxygen solo
<br />The ability of silver to competo fo
<br />bound in metal conrplezes is tmntkter it
<br />relptive to reaction 2. Whsle the dicy
<br />a large formation t•onstant, it is mttclt
<br />of the other metal cyanido complexes.
<br />of the silver to acquire cyanides already
<br />was investigated. The large excess of
<br />silver filler may provido a chemical e
<br />pable of producing Lhe dicyanoai]ver p
<br />different metal Cyanide cotnplexos W tt
<br />the ability of the silver W compete for
<br />both fdtcrs was noarly
<br />ryanide tromplexetian.
<br />tmber of stacked silvor
<br />efficionty, as the date
<br />n, pore size fdtora have
<br />•ai0n Of cyanide ion to
<br />n al higher flow rates.
<br />at uffaot by the high
<br />to bubble proesure, o
<br />mss, 19 greatCr fur the
<br />sided by typical peris•
<br />gas bubble introduced
<br />partial or even Wtal
<br />rmtinnal disadvantage,
<br />0µm thick), operated
<br />lad exccilent cyatride
<br />system operation. The
<br />tr freo cyanide samples
<br />t exemplify Che linear
<br />over a wide range of
<br />method, studies wore
<br />eriatics of reaction 2.
<br />oxygon as rho driving
<br />able chemical species
<br />late the silver-Cyanide
<br />ids pod then sparging
<br />r oxygen, it was famtd
<br />+ith air or o:ygen eatr
<br />6rogen eompletoly re-
<br />rat nxygea does drivo
<br />temples should not be
<br />ation prior to anal)reis.
<br />cyprtide ions already
<br />iportant characteristic
<br />mosilvcr complex has
<br />ass then that of many
<br />Therefore, the ahility
<br />Uound W other metals
<br />fiver provided by the
<br />virunment that is ca-
<br />duct. 13y introducing
<br />filter at various rates,
<br />e cyanide ligands cart
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