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Basic Analytical
Tools
Dr. Kathlia A. De Castro-Cruz
Analytical Chemistry 1
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Basic Analytical Tools
What is Analytical Chemistry?
! It is what analytical chemist do
" Analytical chemists work to improve the abilityof all chemists to make meaningful
measurements.
! Often described as the area of chemistryresponsible for characterizing the compositionof matter, both qualitatively (what is present)and quantitatively (how much is present) misleading definition
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Basic Analytical Tools
What is Analytical Chemistry?
! The craft of analytical chemistry is not inperforming a routine analysis on a routinesample (chemical analysis), but in improving
established methods, extending existingmethods to new types of samples, anddeveloping new methods for measuringchemical phenomena
!
The science of inventing and applying theconcepts, principles, and strategies formeasuring the characteristics of chemicalsystems and species
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What is Analytical Chemistry?
! Typical problems on which analytical chemistswork include
" qualitative analyses (what is present?),
" quantitative analyses (how much is present?),
" characterization analyses (what are the
materials chemical and physical properties?),
"
and fundamental analyses (how does thismethod work and how can it be improved?)
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Classification of Analysis
! Based on goal of analysis
" Qualitative analysis an analysis carriedout to determine only the identity of a pure
analyte, the identity of an analyte in amatrix, or the identity of several or allcomponents of a mixture
"Quantitative analysis the analysis of amaterial for how much of one or morecomponents is present
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Classification of Analysis
! Based on nature of method used
" Physical property analysis involves no
chemical reactions and at times relatively
simple devices (although possiblycomputerized) to facilitate the measurement.Physical properties are especially useful for
identification, but may also be useful for
quantitative analysis in cases where the valueof a property, such as specific gravity orrefractive index, varies with the quantity of an
analyte in a mixture.
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Classification of Analysis
! Based on nature of method used
" Wet chemical analysis - involves chemical
reactions or classical reaction stoichiometry,
but no electronic instrumentation beyond aweighing device
" Instrumental analysis can also involve
chemical reactions, but it always involves
modern sophisticated electronicinstrumentation. Instrumental analysistechniques are high-tech techniques, oftenutilizing complex hardware and software
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Calculateand report
the results(5)
ObtainSample
(1) Preparethe sample
(2)
Workthe data
(4)
Carry out
the analysisMethod
(3)
General Analytical
Strategy
Analytical Strategy
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Calculateand report
the results(5)
ObtainSample
(1)Prepare
the sample
(2)
Workthe data
(4)
Carry out
the analysisMethod
(3)
General Analytical
Strategy
Analytical Strategy
The sample mustbe representative
of the bulk
system; its
integrity must be
maintained; andthe chain of
custody must be
documented.
A portion of the sampleis prepared for the
analysis by weighing it
(or measuring its
volume) and carrying
out certain physicaland/or chemical
processes, such asdrying, dissolving, etc.
Obtain weight or volume data on the prepared samplePrepare reference standards of the analyte or substances
with which the analyte will react.
Standardize solutions or calibrate equipment
Obtain the required data for the sample
A final calculation may benecessary to obtain the
desired results.
This requirescalculations and/
or the plotting of a
calibration curve
from which the
desired resultscan be derived.
Statistics are
usually involved
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Sampling
! The process of obtaining samples for analyses
" Samples must possess all the characteristicsof the entire bulk system with respect to theanalyte and the analyte concentration in thesystem (representative sample)
! Plays a crucial role in the quality and success
of an analysis
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Sampling
! Samples maybe
" Bulk sample
"
Primary sample" Secondary sample
" Sub sample
"
Laboratory sample
" Test sample
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Sampling Solid
! Sample preparations
" Particle size reduction
#Maybe crushing, milling, grinding orpulverizing
" Sample homogenization and division
" Solid-liquid extraction
" Total dissolution
# May use acids
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Sampling Solid
!
Total Dissolution
Name Formula Description Example Uses
Water H2O clear, colorless liquid with lowvapor pressure, highly polar
Dissolving polarand ionic
compoundsHydrochloric
acidHCl Commercially available
concentrated solution is 38% (12
M) HCl; evolves pungent fumesand must be handled in fume
hood
Dissolving somemetals and metal
ores
Sulfuric acid H2SO4 Commercially availableconcentrated solution is 96% (18
M) H2SO4; a dense, syrupy liquid;reacts on contact with skin and
clothing; evolves much heatwhen mixed with water
Organic samples,such as for
Kjeldahl analysis;also oxides of Al
and Ti
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Sampling Solid
!
Total Dissolution
Name Formula Description Example Uses
Nitric acid HNO3 Commercially availableconcentrated solution is 70%
(16 M) HNO3; reacts withclothing and skin (turns skin
yellow); evolves thick brownand white fumes when in
contact with most metals
Dissolving noblemetals (e.g.,
copper and silver)and also some
organic samples
Hydrofluoric
acid
HF Commercially available
concentrated acid is 50% (26M) HF; must be stored inplastic containers, since it
attacks glass; very damagingto skin
Dissolving silica-
based materialsand stainless steel
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Sampling Solid
!
Total Dissolution
Name Formula Description Example Uses
Perchloric acid HClO4 Commerciallyavailable
concentratedsolution is 72% (12
M) HClO4
Dissolving difficultorganic samples and
stable metal alloys
Aqua regia A mixture ofconcentrated HNO3
and HCl in the ratio
of 1:3 HNO3:HCl
Dissolving highlyunreactive metals,
such as gold
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Sampling Solid
! Sample preparations
" Fusion
#dissolving of a sample using a molteninorganic salt, generally called a flux, as thesolvent.
# This flux dissolves the sample and, upon
cooling, results in a solid mass that is then
soluble in a liquid reagent.
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Sampling Liquids and Extracts
! Extraction from Liquid solutions
" Maybe liquid-liquid, solid phase or purgeand trap
! Dilution and Concentration
! Derivatization
"To preserve the sample that are unstable
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Reagents for Sample Preparation
!
A reagent is a substance used in a chemicalreaction in an analytical laboratory because of itsspecific applicability to a given system orprocedure.
" Primary standard: A specially manufactured
analytical reagent of exceptional purity forstandardizing solutions and preparing referencestandards.
" ACS certified: A reagent that meets or exceeds thespecifications of purity put forth by the AmericanChemical Society. The certificate of analysis is on
the label.
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Reagents for Sample Preparation
" Certified reagent: A reagent that meets the
standards of purity established by themanufacturer. The certificate of analysis is onthe label.
" USP/NF: Reagents that meet the purityrequirements of the U.S. Pharmacopeia (USP)and the National Formulary (NF). Generally of
interest to the pharmaceutical profession,these specifications may not be adequate forreagent use.
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Reagents for Sample Preparation
" Spectro grade or spectranalyzed: Solvents ofsuitable purity for use in spectrophotometricprocedures. A certificate of analysis is on thelabel.
" High-performance liquid chromatography(HPLC) grade: Solvents of suitable purity foruse in liquid chromatography procedures.
"Practical: Chemicals of sufficiently high qualityto be suitable for use in some syntheses.
Organic chemicals of practical grade maycontain small amounts of intermediates,isomers, or homologs.
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Reagents for Sample Preparation
" Technical: Chemicals of reasonable purity forapplications that have no official standard forpurity.
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Interferences
! Substance that affects the analytical signal orthe background
! Foreign species that either attenuate the signalfrom the analyte or produce a signal that isindistinguishable from that of the analyte
! Also known as interferent
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Interferences
!
Method of eliminating interferences in chemicalanalysis
Method Basis of Method
Masking Immobilization of interferent as anonreactive complex
Mechanical Separation
Precipitation
and filtration
Difference in solubility of compounds
formedDistillation Difference in volatility of compounds
Extraction Difference in solubility in twoimmiscible liquids
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Interferences
!
Method of eliminating interferences in chemicalanalysis
Method Basis of Method
Ion exchange difference in stability of reactantswith an ion-exchange resin
Chromatography Difference in rate of movement of asolute through a stationary phase
Electrophoresis Difference in migration rate in anelectrical field
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Interferences Elimination
!
Masking
" Addition of reagent to the solution of thesample to immobilize or chemically bind, the
interferent as a complex that no longercontributes to or attenuates the signal fromthe analyte
# Masking agent a reagent that chemically binds
an interferent as a complex & prevents it fromcausing errors in an analysis
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Interferences Elimination
!
Masking
Masking AgentMetals that can be
masked
Metals thatcould not be
masked
F- Al+3, Fe3+, Ti4+, Be4+
CN- Cd2+, Zn2+, Hg2+, Co2+,Cu+, Ag+, Ni2+, Pd2+,Pt2+, Fe2+, Fe3+
Mg2+, Ca2+,Mn2+, Pb2+
Triethanolamine Al3+
, Fe3+
, Mn2+
2,3-dimercapto-1-propanol
Bi3+, Cd2+, Cu2+, Hg2+,Pb2+
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Interferences Elimination
!
Demasking
" Releases metal ion from a masking agent
# Example: cyanide complexes can be
demasked using formaldehyde
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Interferences Elimination
!
Separation by Precipitation
" Requires large solubility differences betweenthe analyte and the possible interferences
"
Needs to consider factors affectingprecipitation such as coprecipitationphenomena
"Could be# Separations Based on Control of Acidity
# Sulfide Separations
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Interferences Elimination
!
Separation by Precipitation
" Could be
# Separations by other Inorganic precipitants
#
Separations by Organic Precipitants
# Separation of Species Present in Trace Amountsby Precipitation
#Separation by Electrolytic Precipitation
# Salt-induced precipitation of Proteins
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Interferences Elimination
!
Separation based on control acidity
" Separations based on pH control
" Three categories
# Those made in relatively concentrated solutionsof strong acids
# Those made in buffered solutions at intermediatepH values
# Those made in concentrated solutions of sodiumor potassium hydroxide
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Interferences Elimination
!
Separation based on control acidity
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Interferences Elimination
!
Sulfide Separations
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Interferences Elimination
!
Separation by other inorganic precipitants
" Phosphate, carbonate, and oxalate ions areoften employed as precipitants for cations
(nonselective)" Chloride and sulfate
# Highly selective
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Interferences Elimination
!
Separation by organic precipitants
" Dimethylglyoxime (has remarkable selectivityin forming precipitates)
"
8-hydroxyquinoline
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Interferences Elimination
!
Separation of Species Present in Trace Amountsby Precipitation
" Used in isolation species present in
microgram quantities" Collector
# Used to remove trace constituents from solution
#Example: Al2O3as collector of trace amounts oftitanium/CS for collection of traces of Zn and Pb
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Interferences Elimination
!
Separation by Electrolytic Precipitation
" The more easily reduced species, either thewanted or the unwanted component of the
sample is isolated as a separate phase
! Salt-induced Precipitation of Proteins
" Addition of high concentration of salt (salting
out)
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Interferences Elimination
!
Separation of species by distillation
" Distillation is widely used to separate volatileanalytes from nonvolatile interferents
"
Maybe
# Simple
# Fractional
# Steam
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Interferences Elimination
! Separation by extraction
" The extent to which solutes both inorganicand organic, distribute themselves between
two immiscible liquids is used to accomplishseparation
" Governed by Distribution Law
"
Frequently used in separating inorganicspecies
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Interferences Elimination
! Separation by extraction
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Interferences Elimination
! Separation by Ion Exchange
" A process by which ions held in porous,essentially insoluble solid are exchanged for
ions in a solution that is brought into contactwith the solid
" Used to eliminate ions that would otherwise
interfere with an analysis
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Numbers in Analytical Chemistry
!
Fundamental Units of Measurements
" Measurements usually consist of a unit and a
number expressing the quantity of that unit.
#SI units after theSystme InternationaldUnits are the internationally agreed on unitsfor measurements
# Standards of length, mass, and time are themeter (m), kilogram (kg), and second (s),
respectively. Temperature is measured inkelvins (K), amount of substance in moles(mol), and electric current in amperes (A).
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Numbers in Analytical Chemistry
!
Fundamental Units of Measurements
" Common prefixes used for exponential
notation
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Numbers in Analytical Chemistry
!
Significant Figures
" The digits in a measured quantity, including all
digits known exactly and one digit (the last)whose quantity is uncertain.
" reflection of a measurements uncertainty
" Itis equal to the number of digits in themeasurement, with the exception that a zero
(0) used to fix the location of a decimal point isnot considered significant.
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Numbers in Analytical Chemistry
!
Rules in Significant Figures
" For measurements using logarithms, such as
pH, the number of significant figures is equalto the number of digits to the right of the
decimal, including all zeros. Digits to the left ofthe decimal are not included as significant
figures since they only indicate the power of 10.
# Example: pH = 2.45 (has 2SF)
" Exact numbers, such as the stoichiometriccoefficients in a chemical formula or reaction,and unit conversion factors, have an infinitenumber of significant figures.
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Numbers in Analytical Chemistry
!
Rules in Significant Figures
" Mathematical operations involving additionand subtraction are carried out to the lastdigit that is significant for all numbersincluded in the calculation.
# Example: the sum of 135.621, 0.33, and 21.2163
is 157.17
"
When multiplying and dividing, the generalrule is that the answer contains the samenumber of significant figures as that number in
the calculation having the fewest significantfigures.
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Numbers in Analytical Chemistry
!
Units of expressing concentration
" Concentration is a general measurementunit stating the amount of solute present ina known amount of solution
" Molarity - The number of moles of solute per
liter of solution (M)
" Formality The number of moles of solute,
regardless of chemical form, per liter ofsolution (F)
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Numbers in Analytical Chemistry
!
Units of expressing concentration
" Normality The number of equivalents of
solute per liter of solution (N).
#The number of equivalents, n, is based on areaction unit, which is that part of a chemicalspecies involved in a reaction
$ n forsalt = charge
$ nfor acid = no of replaceable H
$ nfor base = no of replaceable IH
$ nfor redox = no of electrons involved
# Relationship between Molarity and Normalityis: N = nx M
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Numbers in Analytical Chemistry
!
Units of expressing concentration
" Molality The number of moles of solute per
kilogram of solvent (m).
"
Weight percent Grams of solute per 100 g ofsolution (% w/w).
" Volume percent Milliliters of solute per 100mL of solution (% v/v).
"
Weight-to-volume percent Grams of soluteper 100 mL of solution (% w/v).
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Numbers in Analytical Chemistry
!
Units of expressing concentration
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Numbers in Analytical Chemistry
!
Sample Problems
" Calculate the formula mass of CaSO4. Whatis the molarity of CaSO4in a solutioncontaining 1.2 g CaSO
4in a volume of 50
mL? How many grams of CaSO4are in 50mL of 0.086M CaSO4?
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Answers: 136.14 g/mol0.18 M, 0.59 g
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Numbers in Analytical Chemistry
!
Sample Problems
" Calculate the molarity and molality of 49.0wt% HF. Density of HF = 1.30 g/mL
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Answers: 31.8 M, 48.0 m
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Numbers in Analytical Chemistry
!
Sample Problems
" Normal alkanes are hydrocarbons with theformula CnH2n+2. Plants selectivelysynthesize alkanes with an odd number ofcarbons. The concentration of C29H60 insummer rain water collected is Hannove,Germany is 34 ppb. Find the molarity ofC29H60and express the answer using prefix.How many ppm of C29H60are in 23!MC29H60?
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Answers: 83 nM, 9.4 ppm
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Numbers in Analytical Chemistry
!
Sample Problems
" The molarity of concentrated HClpurchased for laboratory used isapproximately 12.1M How many millilitersof this reagent should be diluted to prepare1.00oL of 0.100M HCl solution.
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Answers: 8.26 mL
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Numbers in Analytical Chemistry
!
Sample Problems
" In a gravimetric analysis, we need enoughproduct to weigh accurately. Each tableprovide ~15 mg iron. How many tabletsshould we analyze to provide 0.25 g ofFe2O3product?
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Answers: 12 Tablets
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Errors in Analytical Measurements
!
Classification of errors
" Systematic errors (determinate errors)
generally arise from determinate or identifiablesources causing measured values to differ from
a true or accepted value. These errors can beavoided and the magnitude could be measured.
# Operational and personal errors these aredue to factors for which the individual analysts
is responsible and are not connected with themethod or procedure
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Errors in Analytical Measurements
!
Classification of errors
# Instrumental and reagent errors these arisefrom the faulty construction of balances, theuse of uncalibrated or improperly calibrated
weights, graduated glassware and otherinstruments
# Errors of method originate from incorrectsampling and from incompleteness of areaction
# Additive and proportional errors
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Errors in Analytical Measurements
!
Measurement of errors
" Accumulated errors - Errors are associatedwith every measurement made in an analyticalprocedure, and these will be aggregated in the
final calculated result. The overall error fordeterminate error maybe calculated using
either of the following expression:
# where only a linear combination of individual
measurements is required to compute theresult, the overall absolute determinate error,
ET, is given by:ET=E1 +E2+E3+.......
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Errors in Analytical Measurements
!
Measurement of errors
E1andE2etc., being the absolute determinateerrors in the individual measurements takingsign into account
#
where a multiplicative expression is requiredto compute the result, the overall relativedeterminate error,ETR, is given by
ETR=E1R+E2R+E3R+.....
E1RandE2Retc., being the relative determinateerrors in the individual measurements takingsign into account.
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Accuracy and Precision
!
Accuracy
" The closeness of an experimental measurement
or result to the true or accepted value.
"It is generally the more importantcharacteristic of quantitative data to beassessed, although consistency, as measured byprecision, is of particular concern in somecircumstances.
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Accuracy and Precision
!
Precision
" The closeness of agreement betweenreplicated measurements or resultsobtained under the same prescribedconditions.
" Can be assessed in several ways.
# Spread or range (i.e. the difference between
the highest and lowest value) is sometimes used
# Standard deviation of the data popularlyused.
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Accuracy and Precision
!
Precision
" Commonly divided into two categories:
# Repeatability - the precision obtained when
all measurements are made by the sameanalyst during a single period of laboratory
work, using the same solutions andequipment.
#
Reproducibility - the precision obtainedunder any other set of conditions, includingthat between analysts, or betweenlaboratory sessions for a single analyst.
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Accuracy and Precision
!
Precision vs Accuracy
" Commonly divided into two categories:
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Neither precisenor accurate
Precise but
not accurate
Accurate
and precise
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Statistics and Statistical Analysis
!
Mean, arithmetic mean or average
" obtained by dividing the sum of replicatemeasurements by the number ofmeasurements in the set:
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x =
xi
i=1
N
"
N
wherexirepresents individual values ofxmaking up a set ofN replicate measurements
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Statistics and Statistical Analysis
!
Median
" the middle result when replicate data are
arranged in order of size
!
Range" the difference between the largest and
smallest values in the data set.
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w = xl argest"xsmallest
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Statistics and Statistical Analysis
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Deviation, d
" determines how far the measured value
deviates from the mean.
! Estimated Standard deviation, s
" measure of the dispersion of data around the
mean
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d = x" xi
s =(d1
2+ d2
2+ d3
2+ ...
n "1
where n is the number of measurements and n-1 is thedegrees of freedom
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Statistics and Statistical Analysis
!
Standard Deviation, s" the smaller it is numerically, the more precise the
data (the more the measurements are bunchedaround the mean)
"
For an infinite number of measurements (wherethe mean is m), the standard deviation issymbolized as s (Greek letter sigma) and is knownas the population standard deviation. 30 ormore measurements approximate an infinitenumber of measurements.
kadecastro-cruz 68
"=
(xi# )2
i=1
N
$
N
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!
Relative Standard Deviation" Relates the standard deviation to the value of the
mean and represents a practical and popularexpression of data quality. It is calculated by
dividing the standard deviation by the mean andthen multiplying by 100 or 1000:
kadecastro-cruz 70
RSD =s
x
relative % standard deviation = RSD x 100relative parts per thousand standard deviation = RSD x 1000
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!
Normal DistributionCurve
" For an infinite dataset (in which the
symbols and !apply), a plot offrequency ofoccurrence vs. themeasurement value
yields a smooth bell-shaped curve.
kadecastro-cruz71
Deviation from mean
Frequency
ofocc
urrence
ofeach
devia
tion
sd = s2
sd = s1
s1> s2
m +
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Basic Analytical Tools
Statistics and Statistical Analysis
! Uncertainty - the range of possible values fora measurement
! Confidence Interval - the range of values
around an experimental result within whichthe true or accepted value is expected to lie
with a defined level of probability.
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! Confidence Interval
" Known standard deviation:
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CL() = x z"
Nwhere z is a statistical factor relatedto the probability level required
ConfidenceLevel%
zConfidene Level, %
z
50 0.67 95.4 2.00
68 1.00 99 2.58
80 1.29 99.7 3.00
90 1.64 99.9 3.29
95 1.96
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! Confidence Interval
" Using estimated standard deviation:
kadecastro-cruz74
where t is a statistical factor related to the probability levelbut in addition determined by the number of degrees of
freedom for the set of data, i.e. one less than the number ofresults.
CL() = x tsN
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kadecastro-cruz 75
Degrees ofFreedom
Factor for Confidence Interval
80% 90% 95% 99% 99.9%
1 3.08 6.31 12.7 63.7 637
2 1.89 2.92 4.30 9.92 31.6
3 1.64 2.35 3.18 5.84 12.9
4 1.53 2.13 2.78 4.60 8.60
5 1.48 2.02 2.57 4.03 6.86
6 1.44 1.94 2.45 3.71 5.96
7 1.42 1.90 2.36 3.50 5.40
8 1.40 1.86 2.31 3.36 5.04
9 1.38 1.83 2.26 3.25 4.78
10 1.37 1.81 2.23 3.17 4.59
11 1.36 1.80 2.20 3.11 4.44
12 1.36 1.78 2.18 3.06 4.32
13 1.35 1.77 2.16 3.01 4.22
14 1.34 1.76 2.14 2.98 4.14
! 1.29 1.64 1.96 2.58 3.29
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! Standard deviation of computed results
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!
t Test
" This is used to compare one set ofmeasurements with another to decide whetheror not they are the same.
" Three cases:
# Case 1. Comparing a Measured Result with aKnown Value
kadecastro-cruz 77
tcalculated
=
x " known value
sn
If tcalculated> ttableat 95% confidence level, the two resultsare considered to be different.
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t Test
# Case 2. Comparing Replicate Measurements(Use to decide whether two sets of replicatemeasurements give the same or different
results )
$ For two sets of data consisting of n1 and n2measurements:
kadecastro-cruz 78
tcalculated =x1
" x2
spooled
n1n2
n1 +n2
spooled =s1
2(n
1 "1)+ s22(n
2 "1)
n1+n
2 " 2
If tcalculated
> ttable
at95% confidence
level, the two resultsare considered to be
different.
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t Test
# Case 2. Comparing Replicate Measurements
$ If the population for both series of
measurement is different:
kadecastro-cruz 79
tcalculated
=
x1
" x2
s1
2
n1
+
s2
2
n2
Degrees of freedom =
s1
2
n1
+s2
2
n2
"
#$
%
&'2
s1
2
n1
"
#$
%
&'2
n1+1
+
s2
2
n2
"
#$
%
&'2
n2+1
"
#
$
$$$
%
&
'
'''
(
)
*****
+
*
*
***
,
-
*****
.
*
*
***
/2
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t Test
# Case 3. Comparing Individual Differences (Iftwo different methods were used to makesingle measurements on several different
samples, are they different?)
kadecastro-cruz 80
tcalculated
=
d
sd
n
sd =
di" d( )
#
2
n "1
If tcalculated> ttableat 95% confidence level, the two results areconsidered to be different.
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Q Test
# Use to help decide whether to retain or discardquestionable datum.
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Qcalculated =gap
range
range is the total spread of the data
gap is the difference between the questionable point andthe nearest value
If Qcalculated> Qtable, the questionablepoint should be discarded
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Q Test
# Values of Q for rejecting data
kadecastro-cruz 83
Q (90% confidence)Number of
Observations0.76 4
0.64 5
0.56 6
0.51 7
0.47 8
0.44 9
0.41 10
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References
"
Kenkel, J. (2003). Analytical Chemistry forTechnicians, 3rded. CRC Press, US.
" Harvey, D. (2000). Modern AnalyticalChemistry, McGraw-Hill, US, 104-134.
" Harris, D. (2007). Quantitative ChemicalAnalysis, 8thed., Freeman, NY.