檢測器基本原理

General

OverviewofDetectorSystemsDanielaCavagninoDetectors

classificationUniversalThey

respond

to

everything

eluting

fromthecolumnTCDPDD(FID)SelectiveThey

may

be

element

selective,structure/functional

group

selectiveorselective

to

other

propertiesFID(very

broad

selectivity)ECDPIDPDDSpecificTheyaresoselective

to

distinguish

particular

structuresorelementsNPDFPDConcentration

vsMassdependent

responseCommonconc.dependent:TCDPIDPDDECDCommonmassdependent:FIDNPDFPDNon-Destructive

vs

DestructiveCommonnon-destructive:TCDPIDPDDECDCommondestructive:FIDNPDFPDDetectors

classificationDetectorResponseCharacteristicsSensitivityDetectorefficiency

to

convertthesampleinan

electrical

signalNoiseShortterm:highfrequency

baseline

fluctuationLongterm:low

frequency

baseline

perturbationDynamic

RangeRangeofsample

concentration

for

whichthedetectorcanprovideadetectable

signal

variation

with

analyte

amountSelectivityTheratioofthedetectorsensitivitiesofagiven

compoundoverapotentially

interfering

compoundMinimumDetectabilityAmountofsampleinwhichthepeakheightis3timesthenoiseheight(S/N=3)DetectorResponseCharacteristics

SensitivityandMinimumDetectabilityFIDsensitivity:S===coulomb/g=FPDsensitivity

for

sulfur:S=*=uV/(gS/s)2MDA===g/secRF(Response

Factor)=MDA==gS/secpeakareasample

weightA*secgpeakareaSamount

PW?

Samount3NSA*gA*secpeakarea

amount3NSpeakheightmassraten-1?

DynamicandLinear

Range

Dynamic

range:overwhich

an

incremental

changeinthe

amountofcompoundsinthe

detectorvolumeproducesa

measurable

incremental

changeinthedetectorsignal

Linear

range:overwhich

theresponse

deviation

is

less

than5%DetectorResponseCharacteristicsFlameIonizationDetector

Universal

response

IonizationdetectionMassdetector

DestructiveFlameIonizationDetectorHydrogenismixedwithgasstreamatbottomofjetandairoroxygenissuppliedaxiallyaroundthejetHydrogenflameburnsatthetip,whichalsofunctionsascathodeanditiselectricallyinsulatedfromthebodyCollectorelectrodeisabovetheburnertipFlame

IonizationDetectorPrincipleofoperationCombustionof

organic

compoundsina

oxidizing

flameCH+OCHO++e-Electric

field

between

thejetandthecollector

electrodeVoltage-300VCollectionofthe

ions

generated

into

theflameCurrent

pAAgood

combustion

step

istheprevailing

factor

to

getthebestperformancesFlameIonizationDetector

Itrespondstoallorganiccompoundsexceptforformicacid

Responseisgreatestwithhydrocarbonsanddecreaseswithsubstitution

SensitivityhighduetolownoiselevelNoresponsetowater,permanentgases,andinorganic

compoundssimplifiestheresolutionofcomponentsinanalysisofaqueousextractsandinairpollutionstudies

Suitable

forfastandultrafastGCapplications

Flame

IonizationDetectorTechnical

Specifications

Operatingtemperaturelimit 450°Cwith

ceramicjet

Linear

range

better

than106

Minimumdetectable

amount 3x10-12

gC/sInputrange 0to10-6AInputattenuation 4steps(100-101-

102-

103)

Electrode

polarization

voltage -300VTimeconstant 6ms@63.2%

Acquisitionrate upto300HzFlame

IonizationDetectorStandardOperatingProcedure(SOP)C12C14C16AreaCounts>4000000C12=6877493C14=6790762C16=6988181Flame

IonizationDetectorMDLCalculation(C12)C12C14C16V=1.6uL@20ng/uLMassC12=32ng%C=84.7%MassC=27.1ngC12A=6877493(0.1uV*s)MDL=3N/S

S=Area(uV*s)/mass

MDL=48(uV)*27.1(ngC)/687749.3(uV*s)=0.00189ngC/s=1.89pgC/sNoise16uVElectronCaptureDetectorSelectiveresponseNon-destructiveIonizationdetectorprincipleConcentration-dependentdetectorRadioactivesource63Ni(10mCiactivity)Displaced

coaxial-cylinder

geometryPrinciplesofdetectionElectronCaptureDetector---e-e-+++-MMMABAB_+*+N2

+N2++e-*+Ar

+Ar++e-+Ar*Ar*+CH4

Ar+e-+CH4+dissociative-capture

mechanismAB+e- A·+B-nondissociative

mechanismAB+e- AB-sidereactionsC+e- C-N2++e- neutralsAB-+N2+

neutralsElectronCaptureDetectorPulsed

voltage[e-]V500TTime(s)w=0.11sPULSEvoltageDCvoltage

ElectronCaptureDetectorConstant

current

methodI=Ke-]f+-Iff=constI=constConstant

current

methodModulationofPulseFrequencyion

current=electrons

concentrationxpulse

frequencywithnosample

freq.=f°with

electronegative

sample

freq.=fssignaloutput=fs

-f°=sample

concentrationElectronCaptureDetectorElectronCaptureDetectorRadioactivesource: Nickel63–370MBq(10mCi)Cellvolume 450LOperatingtemperaturelimit: 400°CMinimumdetectableamount: 10

fgoflindaneLineardynamicrange: 104(argon/methane)

103(nitrogen)Operationmode: constantcurrentpulse-modulatedmodeReferencecurrent: 0to3nA(0.1nAsteps)Pulseamplitude: 5to50Vneg.Pulse

width: 0.1s(argon/methane),

0.5s,1s(nitrogen)Technical

SpecificationsElectronCapture

DetectorMolecular

features

governingtheresponseofECD

Low

response

for

alcohols,amines,phenols,aromaticsandvinyl

type

fluorinated

hydrocarbonsHighresponse

for

halocarbon

compounds,nitroaromatics,and

conjugated

compounds

containing

two

groups

which

individually

arenot

stronglyelectronattracting

but

becomesowhen

connected

by

specific

bridges

Response

towardsthehalogens

decreasesintheorderI>Br>Cl>FElectronCapture

DetectorMolecular

features

governingtheresponseofECDMultiplesubstitution

with

simpleelectronattracting

groupsor

atoms

may

increasethemolecular

absorption

by

an

amount

much

greater

than

expectedofasimpleadditiveeffectTheabsorption

conferred

byasimple

electrophoric

group

is

also

sensitivetothepositioninthemoleculeSomeinorganic

compoundsareelectronabsorbers,as

carbon

disulfide,ozoneandtheoxidesofnitrogenElectronCapture

DetectorRelativesensitivityEthaneBenzene 1ButanolAcetoneChlorobutane 1-102Chlorobenzene1,2-dichlorobenzeneAntracene 102-104ChloroformNitrobenzene 104-105CarbontetrachlorideDinitrophenolDiethyloxalate 105-106DihydropyridineInfluenceofdetectortemperatureDetectionlimit(x10-9g)CCl4 0.010.010.01CHCl31.00.10.05CH2Cl21000408CH2ClCH2Cl1000201

80°C227°C350°CElectronCapture

DetectorRelativeresponseofhalocarbonsCF3CF2CF3 1.0CF3Cl 3.3CF2=CFCl 100CF3CF2Cl 170CF2=CCl2 670CF2Cl2 3x104CHCl3 3.3x104CHCl=CCl2 6.7x104CF3Br 8.7x104CF2ClCFCl2 1.6x105CF3CHClBr 4.0x105CF3CF2CF2I 6.0x105CF2BrCF2Br 7.7x105CFCl3 1.2x106g-LINDANEMDA=10fgwithS/N=3ALDRIN(15pg)HEPTACHLOR(10pg)g-LINDANE(10pg)x2x64ECDperformanceMinimumDetectable

AmountBestconditions

forECDsensitivity

ECDsensitivity

is

affected

bythefollowing

factors:

Reference

current

Thehigher

isthereference

current,thegreater

isthesignal

response

but

alsothebaseline

noise.TheS/Nrationeeds

to

be

determined

for

sensitivity

evaluation

Ionizinggas(makeup)

TheECDisaconcentration-dependentdetector.Thelower

isthemakeup

flowrate(upto15-20mL/min),thehigher

istheresponse.

Argon/methane

asmakeupgasallows

tooperateatlower

frequencies

while

using

higher

reference

current

setting

Detectortemperature

Forsomecompoundsthesensitivity

will

increase

withthecelltemperature

(dissociativemechanismofreaction)ECDperformanceLinearityBestconditions

forECDlinearity

ECDlinearity

is

very

dependant

upon

several

factors:

ECDconditions

Pulse

Voltage:lowest

is

better(upto15V)according

totheoutputfreq.

Basefrequency:must

be

around1KHz

Reference

Current:itcanbe

reduced

to0.7-0.8nAif

necessary

Ionizinggas(makeup)–Argon/methane:assurethewidest

linearity

range

Nitrogen:should

be

usedunderclean

conditions

with0.5usofPulse

Width

Inboth

casestheflowratecanbe

increased

to40-45mL/min

for

maintainingalowbasefrequency

Carriergas–Hydrogen:linear

rangeupto

about100pg

Helium:sligthly

better

than

hydrogen

Nitrogen:linear

range

shiftedupto

about200pgThecompletesystemincludingthegassupply

linesandgases

have

to

be

very

clean

to

achievealowbasefrequencyElectronCaptureDetectorStandardOperatingProcedureSOPLindaneAldrinNoise73uV(10VFS)S/N>4000Lindane=4820Aldrin=4431ElectronCaptureDetectorLindaneAldrinNoise73uV(10VFS)V=1.6uL@30pg/uLMassLindane=48pgLindaneA=6122928(0.1uV*s)MDL=3N/S

S=Area(uV*s)/mass

MDL=219(uV)*48(pg)/612292.8(uV*s)=0.0172pg/s=17fg

Lindane/sMDLCalculation(Lindane)ElectronCapture

DetectorMultiplesimultaneousdetectionFID,NPDorFPD

stackedonECDAirColumn

effluent+Hydrogen/MakeupHeated

source(Rb

ceramic

matrix)CollectingelectrodeNitrogen

PhosphorousDetector

Specific

response

vsNandP

organic

compounds

Ionization-typedetectorMassdetector

Destructive

Rb

ceramic

bead

as

thermionic

ionization

source

Sampledecomposition?Electronegativeproducts(e.g.NO2,CN,PO2)2+Hotsource?NegativeionsElectronegativespeciesNPD:detectionmechanismTID-2(BlackSource)Sample?Electronegativedecompositionproducts+Hotsource?NegativeionsElectronegativespecies2ENSmode:detectionmechanismTID-1(White

Source)NPDmode:newglass

beadCanreplaceTID-2source

Higher

response

for

Phosphorous

compounds

(…but

tailing

peakscanbe

observed)

Lower

operating

current:

extended

lifetime

Same

flow

rates

setting

as

TID-2Blos-Source(Glass

Bead)ThethermionicsourceelementisaconsumablecomponentthatmustbereplacedperiodicallyEasilyinterchangeablethermionicsourcesThermionicsourcelifetimeisstrictlydependentontheoperativeconditions.

Nitrogen

PhosphorousDetectorTechnical

Specifications

Operatingtemperaturelimit 450°C

Linear

range

better

than104

Minimumdetectable

amount 5x10-2

pgN/s 2x10-2

pgP/s

Selectivity N/C=105:1 P/C=2x105:1Inputrange 0to10-6AInputattenuation 4steps(100-101-

102-

103)

Heating

current

setting1.00to3.50Ain0.01step

Polarization

voltage

setting1.0to9.9Vin0.1stepNitrogen

PhosphorousDetectorNitrogen

PhosphorousDetectorStandardOperatingProcedureSOPAzobenzeneMethylparathionAreaCounts

>1500000(Azobenzene)

>3000000(Methylparathion)Azobenzene=1598004Methylparathion=4688635Nitrogen

PhosphorousDetectorAzobenzeneMethylparathionMDLCalculation(Azobenzene)V=1.6uL@1ng/uLMassAzobenzene=1.6ng

%N=15.3%

MassN=0.244ngazobenzeneA=1598004(0.1uV*s)MDL=3N/S

S=Area(uV*s)/mass

MDL=54(uV)*0.244(ngN)/159800.4(uV*s)=8.24E-5ngN/s=8.2E-2pgN/sNoise18uVFlamePhotometricDetector

specific

response

vsSorP

compounds

destructive

light-emissiondetectionmassdetector

single-flamedesign

dual

parallel

configurationFlame

PhotometricDetectorPrincipleofoperationSulphur

compoundsH2S+HHS+H2HS+HS+H2S+SS2*S+S+MS2*S2*S2+hQuadratic

response

for

sulfur

compounds!Phosphorous

compoundsPO+H+MHPO*+MPO+OH+H2

HPO*+H2OHPO*HPO+hFlame

PhotometricDetectorChemiluminescent

emission

spectraofsulfurandphosphorous

compoundsinhydrogen-rich

flameEmission

signalWavelength(nm)Wavelength(nm)Sulfur(S2*)Phosphorous(HPO*)Flame

PhotometricDetectorTheemissionofexcited

molecules

is

measured

against

someflamebackgroundby

meansofnarrow

bandpass

interference

optical

filters:S394nmP526nmSn610nmFlame

PhotometricDetectorNon-linear

responseinsulfur-selectivedetection

Intensityofthesulfur

emission:

I[S]nlog[S]1/nlogI

theexponential

factor

n

is

theoretically

equal

to2

it

is

dependent

upontheFPDoperating

conditions

it

is

strongly

compound

dependent

it

is

experimentally

determinedFlame

PhotometricDetectorQuenching

effectinsulfur-selectivedetection

collisional

quenchingofS2*byCO2,CH4,andother

combustion

products

reducesthesulfur

response

hydrocarbonsareparticularly

effectiveinquenchingthe

sulfur

responseincaseofcoelution

athighconcentrations,quenching

effect

may

be

observed,leading

toacurvatureofthecalibrationcurveFlame

PhotometricDetectorTheoptimumairflowrate

should

be

experimentally

determinedafter

correct

settingofthehydrogen

flowrate

Variationsintheair/hydrogenratiolead

to

deviations

fromthe

sulfur

quadratic

response

When

operatinginphosphorousmode,variationsintheair/hydrogen

ratiocanstrongly

affecttheresponse

for

certain

phosphorous

compounds

while

tiophosphatesareunaffectedThepositionofthecolumnendis

especially

critical,since

most

compounds

containing

sulfurandphosphorousarevery

activeThephotomultipliertubenoise

increases

with

increasingdetector

temperature

By

increasingtheH2/airratio,thenegativeresponseofHCdecreaseandalsotheScompounds

tailing

decreasesPractical

hintsFlame

PhotometricDetectorMaintainingandtroubleshooting

ifahighnoiseandstandingcurrent

is

observed,itcanbedueto:

-column

bleeding-opticalsystemn