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equation/H0 ":#2v :$v 

; van 9eemter plot for gas chromatography can seenbelow. "( # and $ are constants and v  is the linearvelocity( the carrier gas )ow rate. The " term isindependent of velocity and represents

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"omparison of the standard and sample retention timesallows qualitative analysis of the sample. "omparisonof the peak area of the standards with that of thesample allows quantitation of the analyte. The peakarea can be determined by measuring it directly on thechart recorder output with a planimeter( or by carefullycutting out the peak and weighing it on an analyticalbalance. "hromatographic integrators which calculatethe area automatically are also commonly used.If the relationship between standard solution amountand detector response is nonlinear( the peak areaversus amount data can be plotted to give a calibrationcurve. The amount of unknowns is then founddetermining their peak areas and reading thecorresponding amounts from the calibration curve. Ifthe relationship is linear( the data can be ,tted bylinear least squares to determine a response equation(or a conversion factor can be calculated for future use.;pparatus

= Gas chromatograph with thermal conductivity detector!T"9'.

= 9igital )ow meter and temperature monitors= "omputer data aquisition with peak+integration

software= 9igital balance

 Instrument 3ettings= "olumn/ ! x %21< 985= >low rate/ #- m?2min= Temp. setting/ @ o"= ;ttenuation/ as required

 5rocedure

% Aake % µ? in6ections of each of pure cyclohexane(

methylene chloride( and toluene. Aeasure retentiontimes of each. Aeasure the peak areas of each via the

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cyclohexane( methylene chloride and toluene using a

digital balance and a pipette. In6ect a % µ? sample of

the mixture. 5repare four di7erent mixtures !by weight' of toluene

and cyclohexane( using equal amounts of cyclohexanebut varying the amount of toluene !about .&/%( ./%( .

@/%( and %/% toluene to cyclohexane !w2w'.' In6ect % µ?

of each mixture.1 Cbtain a toluene unknown mixture from the Teaching

;ssistant. Aake % µ? in6ections to determine the

amount of toluene relative to cyclohexane.

 "alculations% "alculate the number of theoretical plates for

cyclohexane( methylene chloride( and toluene at #-m?2min )ow.

& 9etermine the detector response for toluene andmethylene chloride relative to cyclohexane as a ratio of peak areas.

9etermine the peak area ratio !toluene2cyclohexane'

for each standard mixture using either the automaticintegrator. 5lot the relative detector response curve.

1 9epending on the relationship between peak area andtoluene standard solution concentration( plot acalibration curve or determine a linear conversionfactor for converting peak area to concentration !w2w'in mg2g.

9etermine the concentration of toluene in the unknown

based on the calibration step.DeportDeport the concentration of the toluene unknown inmg2g( the two relative detector response values at #-m?2min )ow. Eour grade will be based F- on unknownconcentration and %- on the detector responsevalues.Deference

9. ". $arris Huantitative "hemical ;nalysis 1th 4d.( .$. >reeman and "ompany( 8ew Eork 1995 "hapters &&

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