Summary Analytical Chemistry 264

chemicalm easurements



analysis
chemical




importantterms
not
usuallyassessed


homogenoussample
itsconstituentpartsvisually indistinguishablefromoneanother
has
eatapwater

samplehas
heterogenous
itsconstituentpartsvisually distinguishable
egsand

is is
analyte thatwhich beingmeasured detected iethe inasampleofmatteraboutwhichchemicalinformationissought
components


cg whenmeasuring the concentration
ofacidafteratitrationtheacidistheanalyte
speciesrefers
tothechemicalofinterest
Interferenceoccurswhen
aspeciesanalyteincreasesdecreasestheresponsebytheanalyticalmethod makingitappearasifthereismorelessofaparticularanalyte
maskingallows aninterferingspeciestobetransformedintoaformthatwillnotbedetectedbytheanalyticalanalysis
Aliquotisaportionwithknownvolumemasstakenfroma largersampleie subsample

,SIunits
time s
length M
mass kg
electricconstant A Ampere


Temperature K
Amiofsubstance mol

luminousintensity od oanoe.la



prefixes




common
onesmustknow



ne ne
red
4000000 tells
blood 100 10 d blood
400000 red cells

ixiooe.pro



1,3010mgon
19 1000,19 100,04




8 101249

,chemical concentrations


saved millipedes
Asolutionisa homogenousmixture
ofsolutes
thesmallestquantity
mikorspeciesalways


how
concentration expresses s olute
m uch is a
containedwithin particular
ofsolution
volume




mm
L caresolution
mm
ite
iiii anion
asa
changes
of
function temperature stays w
c onstant temperature
change

involumeliquidsdependsontemp
molarity molalitywhensolutionconsists ofliquids



loose mono m
I m15,4 1000
100 0mm
mm
p mop

moles n
ideal
gases


Minor
nomotionsroms a pygym

percentc omposition



thepercentageofa component inamixturesolutioncanbeexpressedasa weight wt or volumev01 percent
theunitofmasses volumes doesnotmattersolongastheyarebothofthesameordereggramsonly mionly

we a of
mass solute V01 ofsolute
volume

oftotalsinmixture
mass volumeoftotalsinmixture




acid
109Nitric 1009solution




Kr and 0,825roll 0,825h Kr 1001air
p
PVART
in
L
0033mmol



Carl 0,033279 am
3,3310
100

, molarity molality



men
iii
3iwe 319He1009sin blagme
pay
Osohu.int
If
massme
mgmtroomienaog masssolvent 11909440,39749,79
31111909 440,39

nHa 12,01me
gf
Minqmol aims m1 5
10,1m



partspermillionbillion ppmppb

usedtoexpressconcentrations verydilutesolutions
of
109
ppm of
mass substance 10 ppb massof
substance

massof
s ample massof
s ample


1whendoing calculations with aqueous solutionsthathaveadensity mL
1,009 pom and IPPD
Ma
h ff
30
ppm somgolomon insolution
M and n 0101120
112 10mol
iM
f 4
gym
42.110
1,710am




1h and ppm masssubstanie 10
i m masssample

m
j ppm

morefractions



I ie numberofmolesofa substanceexpressedasafraction ofthetotalnumberofmoles inamixture

v
xi foridealgases Dalton'slawofpartialpressures

, ErrorAnalysis Bstatistics

statisticalt echniques usedtoevaluateerrorsoccurringinanalyticalc hemistry
are

random indeterminateerrors sustematicdeterminateerrors




fromuncontrollableuncontrolledvariablespresentduringmeasurements
arise arise ofanexperiment
fromaflawinequipment design
there
e rrors notbeeliminatedbut
can onlyreducedbyabetter these
errors be
can discovered
and in corrected
priniple
design
experimental
intheywillalwaysbe
present

the individualreadings
on sideotfhemean
tall either thetruevalue ieall
thereplicatemeasurementsdeviatefrom theresultsinaseriesare
toohighortoolow
e ither

is
precision affected randomerrors poor
large precision Accuracy
isaffected
random
errors arerevealedwhenreplicatemeasurementsofa errors
systematic
arerevealedwhentheerrorisreproducibleTheseerrorsmaybe
single are theyaffect
avantity made each decision

if itL
observation
i ndependentist
unpredictably



in
way caitiff ifeng.ptiiige
g whenopeningawindow
change airflow inthelab
affects theair pressurereading

Bias
constant Bias
proportional




Waystodetectsystematic

a
analyze knownsamplecertified material
reference
tocompareresults
measurethesame q u
uantity sing
a m
different ethod

Analyzeablanksampleie analyte nonzero
no results error
standard
reference yieldtrue
m aterials values forthemeasuredavantity
wastocorrect sustomaticerrors
calibrate checkinstruments


Precision reproducibility Accuracy

the
describes obtained
were
internalagreementb etweenresultsthat describeshowclose
a measuredvalueistothetrueacceptedvalue
inthesamewayienowclosethevalvesare to eachother estimated
by comparing
w srm
maybe improved
byrepeatingthemeasurements




Anideal procedureis BOTH precise allurate

limit
bycentral theorem
Gaussian Normal distribution propen


whenanexperimentisrepeatedmanytimesANDtheerrorsarepurelyrandom theresultswilltendtoclustersymmetricallyaboutthemeanvalue
repeating
the moretimes
experiment
theshapeofthe willresemble
measurements
anidealbellshapedcurve GaussianDistribution




shall
setofresults used toestimatethepropertiesofa hypotheticallargeset
sampledataset populationdata set
asmallersetofdatawhichis Alargesetofdatacontainingallpossibledatavalues
apartofa populationdataset
in subset