Post on 03-Jan-2017
Qualitative analysis: Identifying the components of a sample
Quantitative analysis: Measuring the amounts or concentrations of analytes in a sample
The three measurement terms of “analysis”, “determination”, and “characterization”have different meanings.
Analysis = Qualitative and quantitative characteristics of chemical analytes
Determination = Quantitative measurements of specific analytes
Characterization = Experimental description of properties of materials
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
Steps in an Analysis
Define the Problem Select a Method Obtain a Representative Sample
Prepare the Sample for AnalysisPerform Any Necessary
Chemical SeparationsPerform theMeasurement
Data Processingand Report
1. Define the Problem
Factors:
• What is the problem--what needs to be found? Qualitative and/orquantitative?
• What will the information be used for? Who will use it?
• When will it be needed?
• How accurate and precise does it have to be?• How accurate and precise does it have to be?
• What is the budget?
• The analyst (the problem solver) should consult with the client to plana useful and efficient analysis, including how to obtain a usefulsample.
2. Select a Method
Factors:
• Sample type
• Size of sample
• Sample preparation needed
• Concentration and range (sensitivity needed)
• Selectivity needed (interferences)• Selectivity needed (interferences)
• Accuracy/precision needed
• Tools/instruments available
• Expertise/experience
• Cost
• Speed
• Does it need to be automated?
• Are methods available in the chemical literature?
• Are standard methods available?
3. Obtain a Representative Sample
Factors:
• Sample type/homogeneity/size• Heterogeneity of sample composition increases from the fairly
homogeneous gas and liquid samples to solid samples that must be groundup prior to dissolution.
• Analysis of grains from crops (rice, wheat, etc.) requires dehusking to yieldmeaningful data.meaningful data.
• Milling and blending are usually parts of the sample preparation procedures.
• Sampling statistics/errors• The quality of analytical data must support the measurement objectives and
hence the sampling procedures have to satisfy statistical requirements ofthe analysis.
• The number of samples or sample size, the frequency and time of sampling,and the location of sampling have to be consistent with the analyticalobjectives.
4. Prepare the Sample for Analysis
Factors:
• Solid, liquid, or gas?
• Dissolve?
• Ash or digest?
• Chemical separation or masking of interferences needed?
• Need to concentrate the analyte?• Need to concentrate the analyte?
• Need to change (derivatize) the analyte for detection?
• Need to adjust solution conditions (pH, add reagents)?
5. Perform Any Necessary Chemical Separations
Factors:
• Distillation
• Precipitation
• Solvent extraction
• Solid phase extraction
• Chromatography (may be done as part of the measurement step as inthe hyphenated techniques of GC-MS or LC-MS)
• Electrophoresis (may be done as part of the measurement step as inCE-MS and microfluidics)
6. Perform the Measurement
Factors:
• Calibration• Instruments must be properly calibrated according to analytical protocols; for
instance, the wavelength scale of a spectrometer has to be verified with a standard;all sample preparation equipment from the balances to sample extraction devicesmust also be checked or calibarated
• Validation/controls/blanks• Validation/controls/blanks• Suitable matrix blanks, trip blanks, lab control standards must be analyzed to
support the sample measurements.
• Replicates• Appropriate number of replicates meeting the analytical statistical confidence is
necessary.
7. Data Processing and Report
• Conversion of raw instrumental signals into meaningful results ofchemical identification and determination
• Interpretation of data by correlating chemical parameters of analytes (formulamass, functional groups, etc.) with observed signals (energies of spectral peaks ,retention times of chromatographic peaks, etc.)
• Calibration plot of standards at various concentrations is used to determinequantitative results of sample constituents.
• Statistical analysis of quantitative results (reliability)• Accuracy – Results for standard reference materials (SRMs) from National Institute
Standards and Technology
• Precision – Relative standard of deviation or coefficient of variation
• Blanks, correlation coefficients of calibration plots, spike recovery, detectionlimits, and etc.
• Relating qualitative and quantitative results to the objectives ofanalyses (i.e. how C-14 results are used to determine the age of anarchaeological artifact or whether an art piece is authentic).
The sample size dictates what measurement techniques can be used.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
Classification of Analytical MethodsClassical methods
• Gravimetry
• Titrimetry
Instrumental methodsInstrumental methods
• Electroanalytical
• Spectroscopy
• Chromatography
• Radioisotopic measurements
Different methods provide a range of precision, sensitivity, selectivity,and speed capabilities.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
Types of Instrumental Methods
Configuration of Instrumentation
Instrument or Process
Control Diagnostics DataProcessing
Raw data
Processed data(Information)
Machine-level commands
Analyst
User InterfaceExplanation(Knowledge)
User-levelcommands
IntegratedComputers
Intelligent System
OutputDevice
(Information)High-levelcommands
Components of a Typical Instrument
Analytical
Electricalor
mechanicalinput
Meteror
Scale
Signalgenerator
Inputtransducer
ordetector
Analyticalsignal
Signalprocessor
inputsignal
12.301
Outputsignal Recorder
Digitalunit
Some Examples of Instrument Components
Selecting an Analytical Method
1. What accuracy and precision are required?
2. How much sample is available?
3. What is the concentration range of the analyte?
4. What components of the sample will cause
Defining the problem:
4. What components of the sample will causeinterference?
5. What are the physical and chemical properties ofthe sample matrix?
6. How many samples are to be analyzed?
Validation involvesdetermining:
•selectivity
•linearity
•accuracy
•precision
•sensitivity
•range
•limit of detection
General process for evaluation/validation of methodology
•limit of quantitation
•ruggedness/robustness
Standard referencematerials (SRMs) best fordetermining accuracy.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
Other Characteristics to BeConsidered in Choosing a Method
1. Speed of analysis
2. Ease of use and automation
3. Cost and availability of instrument3. Cost and availability of instrument
4. Per-sample cost (consumables and reagents)
5. Training and learning curve
6. Software features and compatibility withdatabases and data processing programs
COMPONENTS OF A QUALITY CONTROL
PROGRAM
QualityControl
Suitable andwell
maintainedfacilities
Maintainedand well
calibratedequipment
GMP
Welltrained
personnel
GLP Control GMP
CompleteDocumentat
ion
EvaluationSamples
GLP
SOP
IMPORTANT PROCEDURES IN QUALITY CONTROL
Measured parameter Procedure
Accuracy Analysis of reference materials or samplesof know concentration
Precision Analysis of replicate samples
Extraction efficiency Analysis of matrix spikes
Contamination Analysis of blanks
Steps in the analyticalprocess
Contamination sources
Sample collection Equipment, Sample handling steps such as compositing, orfiltering, Sample preserving additives, Sample containers,Ambient contamination
Sample transport and storage Sample containers, Cross contamination from ear reagents orother samples
POTENTIAL SOURCES OF SAMPLE CONTAMINATION
Sample preparation Sample handling, Dilutions, Glassware, Ambientcontamination
Sample analysis Instrument memory effects or carry-over, Reagents, Syringes,Glassware, Apparatus
Blank type Purpose Process
System or Instrument blank Establishes the baseline of an analyticalinstrument, in the absence of sample
Determine the background signal withno sample present
Solvent or Calibration blank To measure the amount of the analytical signalwhich arises from the dilution solvent. The zerosolution in the calibration series.
Analytical instrument is run withdilution solvent only
Method blank To detect contamination from reagents, samplehandling, and the entire analytical process
A simulated sample containing noanalyte is taken through entireanalytical procedure
TYPES OF ANALYTICAL BLANKS FOR QUALITY CONTROL
analytical procedure
Matched-matrix blank To detect contamination from field handling,transportation, or storage
A synthetic sample which matches thebasic matrix of the sample is carried tothe field and is treated in the samefashion as the samples
Sampling media or tripblank
To detect contamination in sampling media suchas filters and sample adsorbent traps
Analyze samples of unused filters ortraps to detect contaminated batches
Equipment blank To determine contamination of equipment andassess the efficiency or equipment clean-upprocedures
Samples of final equipment cleaningrinses are analyzed for contaminants
Metals Regulatorylevel (mg/l)
Pesticides Regulatorylevel (mg/l)
Other organics Regulatorylevel (mg/l)
Arsenic 5 Chlordane 0.03 Benzene 0.07
Barium 100 2,4-D 1.4 Chloroform 0.07
Cadmium 1 Endrin 0.003 Cresol 10
Chromium 5 Lindane 0.06 1,4- 10.8
REGULATORY LEVELS OF TCLP CONTAMINANTS
Chromium 5 Lindane 0.06 1,4-Dichlorobenzene
10.8
Mercury 0.2 2,4,5-TP(Silvex)
0.14 Pentachlorophenol
3.6
Lead 5 Heptachlor 0.001 Trichloroethylene 0.07
Silver 5 Methoxychlor 1.4 TolueneVinyl chloride
14.40.05
Compound Regulatory concentration Averaging period
Ozone 0.12 ppm 1h
Carbon monoxide 35 ppm9 ppm
1h8h
Nitrogen dioxide 0.05 1 year
Sulfur dioxide 0.14 ppm 24h
REGULATORY LEVELS FOR AMBIENT AIR POLLUTANTS
Sulfur dioxide 0.14 ppm0.03 ppm
24h1 year
Particulate matter 150 µg/m3
50 µg/m3
25 µg/m3
24h1 year24h
Sulfates 25 µg/m3 24h
Vinyl chloride 0.01 ppm 24h
Lead 1.5 µg/m3 3 months
You can’t have accuracy without good precision.
But a precise result can have a determinate or systematic error.
Accuracy and precision
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
Figures of Merit for Precision of Analytical Methods
The precision becomes poorer at low concentrations.
(Also sometimes at high concentrations, as in spectrophotometric measurements–see spectrometric error, Fig. 16.27.)
Dependence of relative standard deviation on concentration©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
Random errors follow a Gaussian or normal distribution.
We are 95% certain that the true value falls within 2σ (infinite population),IF there is no systematic error.
Normal error curve (Gaussian Curve)©Gary Christian,Analytical Chemistry,6th Ed. (Wiley)
Bias
Bias = m - xi
where m => population mean
xi => measured concentration
Sensitivity
2 factors limiting sensitivity:
• slope of calibration curve
– steeper slope, greater sensitivity– steeper slope, greater sensitivity
• reproducibility of measurements
– equal slope, better reproducibility, greatersensitivity
Sensitivity
IUPAC defined calibration sensitivity
S = mc + Sbl
where S => measured signalwhere S => measured signal
c => concentration of the analyte
Sbl => instrumental signal for blank
m => slope of calibration line
ignores precision
Sensitivity
analytical sensitivity => g
g = m/ss
where ss =>standard deviation of the signals
advantages:
- relatively insensitive to amplification factors- relatively insensitive to amplification factors
- independent of units
disadvantage:
- standard deviation of signal can vary withconcentration
Detection Limit & Quantitation Limit
Instrumental detection limit refers to the minimumconcentration or weight of analyte that can bedetected at a known confidence level and isusually defined as being equivalent to 3 times theusually defined as being equivalent to 3 times thesignal background noise or the 3s-level.
Method or practical quantitation limit refers to thelevel at which reliable quantitative analysis canbe performed and is commonly defined at 9s to15s levels.
Detection Limit
minimum distinguishable analytical signal => Sm
Sm = Sbl + ksbl
where Sbl => mean blank signal
k => some multiple (normally 3)k => some multiple (normally 3)
sbl => absolute standard deviation of the blank
measure 20-30 blanks over extended period oftime to determine Sbl and sbl
detection limit => cm = (Sm - Sbl)/m
SNR=17
SNR= 5
SNR=2.8
100 ms, 50 um slit
10 ms, 50 um
10 ms, 20 um
Raman spectra of Calcium ascorbate
400 600 800 1000 1200 1400 1600 1800 2000
SNR=2.8
SNR < 2
10 ms, 20 um
10 ms, 10 um
Raman shift, cm-1
0.1 sec*
1.0 sec
Signal averaging improves S/N
400 600 800 1000 1200 1400 1600 1800 2000
Raman shift, cm-1
30 sec
* spectra were accumulated for period indicated
Linear Dynamic Range
LOL
Inst
rum
ent
resp
onse
Useful range
LOQInst
rum
ent
resp
onse
Concentration
LOQ => limit of quantitativemeasurement
LOL => limit of linearresponse
Selectivity
degree to which a method is free frominterference by other species contained inthe matrix
S = mAcA + mBcB + mCcC + SblS = mAcA + mBcB + mCcC + Sbl
where S => analytical signal
cA, cB, cC=> concentrations of A, B, and C,
mA, mB, cC => calibration sensitivities of A, B, and C,respectively, slope of calibration curve
Sbl => instrumental signal of blank
SelectivitykB,A = mB/mA and kC,A = mC/mA
where kB,A => selectivity coefficient forB with respect to A
k => selectivity coefficient forkC,A => selectivity coefficient forC with respect to A
yielding
S = mA(cA + kB,AcB + kC,AcC) + Sbl
The units ppm or ppb are used to express trace concentrations.
These are weigh or volume based, rather than mole based.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
m m
m
m m
This is a time plot for analysis of the same sample, assumed to have only
there is a 1 in 20 chance a value will exceed this only by chance.
This is a time plot for analysis of the same sample, assumed to have onlyrandom distribution, to check for errors in a method.
At 2s, there is a 1 in 20 chance a value will exceed this only by chance.At 2.5s, it is 1 in 100.
Typical quality control chart
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
Select a confidence level (95% is good) for the number of samples analyzed (N).
Confidence limit = x ± ts/√N.
It depends on the precision, s, and the confidence level you select.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
You compare the variances of two different methods to see if there is a
F = s12/s2
2
You compare the variances of two different methods to see if there is asignificant difference in the methods at a given confidence level.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
QCalc = outlier difference/range.
If QCalc > QTable, then reject the outlier as due to a systematic error.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
The median may be a better indicator of the true value than the mean for
And the range times a factor (K) may be a better measure of spread than the
The median may be a better indicator of the true value than the mean forsmall numbers of observations.
And the range times a factor (K) may be a better measure of spread than thestandard deviation (sr = RKR).
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
A least-squares plot gives the best straight line through experimental points.
Exel will do this for you.
Straight-line or Linear Regression Plot
©Gary Christian,Analytical Chemistry,6th Ed. (Wiley)
Purpose How Performed Usage Application Examples
Removal of interferences Interferences are allowed to passunretained through the cartridge withanalytes remained sorbed, or analytespass through the cartridge, withinterferences remaining on the cartridge
50% Removal of proteins from biological fluids,fats and lipids from food, ionic compoundsfrom aqueous samples and drugs of abusefrom urine, and extractions of dioxans fromwaste water.
Analyte Concentration Conditions are chose to achieve strongretention values (retentive stationaryphase/ weak mobile phase); elution in asmall volume of volatile organic solvent.
35 Trace enrichment of ppb of polynucleararomatics from water, trace pesticides inurine, caffeine from beverages, andtherapeutic drugs from plasma.
Phase exchange Analyte present in emulsion, suspension, 5 Exchange of aqueous solvent for
Main Purposes of Solid Phase Extraction
Phase exchange Analyte present in emulsion, suspension,or undesirable solvent is sorbed on SPEcartridge, dried, and eluted with desiredsolvent
5 Exchange of aqueous solvent fornonaqueous one with intermediate drynitrogen flush.
Solid-phase derivatization Specifically coated SPE phasesselectively derivatize analytes as theypass through the cartridge.
5 2,4-dinitrophenyl hydrazine-coatedcartridges that selectively derivatizecarbonyl-containing compounds; aminesand polyamines in air; organic acids inwater.
Sample storage andtransport
Vapor or liquid samples are collected atfactory or in field on an SPE cartridge ordisk and transported to laboratory.
5 Soil gas analysis; trace organics in water.
Parameter Sonication Soxhlet
(traditional)
Soxhlet
(modern)
SFE ASE (ESE) Microwave-Assisted(closed
container)
Microwave-Assisted (open
container)
Sample size, g 20-50 10-20 10-20 5-10 5-15 2-5 2-10
Solventvolume, ml
100-300 200-500 50-100 10-20* 10-15 30 20-30
Temperature,°C
Ambient-40 40-100 40-100 50-150 50-200 100-200 Ambient
Pressure Atmospheric Atmospheric Atmospheric 2000-4000 psi 1500-2000 psi 1500-2000 psi Atmospheric
Comparison of Extraction Methods for Sample Preparation of Solids
Time, hr 0.5-1.0 12-24 1-4 0.5-1.0 0.2-0.3 0.2-0.3 0.1-0.2
Degree ofAutomation**
0 0 ++ +++ +++ ++ ++
Number ofSamples***
High 1 6 44 24 12 12
Cost§ Low Very low Moderate High High Moderate Moderate
* When organic modifier is used to effect polarity
** For the most complete commercial instrument;0= no automation, += some automation, ++= mostly automated, ++= fully automated
*** Maximum number that can be handled in commercial instruments
§ Very low = < $1000, Low= $10,000, Moderate= $10,000-20,000, High= > $20,000
Method of Sample Principles of Technique Comments
Accelerated(enhanced) solventextraction (ASE orESE)
Sample is placed in a sealed containerand heated to above its boiling point,causing pressure in vessel to rise;extracted sample is automaticallyremoved and transferred to vial forfurther treatment
Greatly increased speed of liquid-solid extraction process and isautomated. Vessel must withstand high pressure; extracted samplein diluted form requires further concentration; safety provisions arerequired.
Automated Soxhletextraction
A combination of hot solvent leachingand Soxhlet extraction; sample inthimble is first immersed in boilingsolvent then thimble is raised forSoxhlet extraction with solvent
Manual and automated versions are available; uses less solvent thantraditional Soxhlet and solvent is recovered for possible reuse.Extraction time is decreased due to two-step process.
Modern Extraction Methods for Solid Samples
Soxhlet extraction with solventrefluxing.
Supercritical fluidextraction (SFE)
Sample is placed in flow-throughcontainer and supercritical fluid (suchas CO2) is passed through sample; afterdepressurization, extracted analyte iscollected in solvent or trapped onadsorbent, followed by desorption byrinsing with solvent.
Automated and manual versions are available; to affect "polarity"of supercritical fluid, density can be varied and solvent modifiersadded. Collected sample is usually concentrated and pure becauseCO2 is removed after extraction; matrix has an effect on extractionprocess.
Microwave-assistedextraction (MASE)
Sample is placed in an open or closedcontainer and heated by microwaveenergy, causing extraction of analyte.
Extraction solvent can range from microwave-absorbing (MA) ornon-microwave-absorbing (NMA); in MA case, sample is placed inhigh-pressure, non-microwave-absorbing container and heated wellabove its boiling point. Also in MA case, the sample and solventcan be refluxed at atmospheric pressure, analogous to solid-liquidextraction, in NMA case, container can be open, with no pressurerise, safety provisions are required.
Method of Sample Principles of Technique Comments
Accelerated(enhanced) solventextraction (ASE orESE)
Sample is placed in a sealed containerand heated to above its boiling point,causing pressure in vessel to rise;extracted sample is automaticallyremoved and transferred to vial forfurther treatment
Greatly increased speed of liquid-solid extraction process and isautomated. Vessel must withstand high pressure; extracted samplein diluted form requires further concentration; safety provisions arerequired.
Automated Soxhletextraction
A combination of hot solvent leachingand Soxhlet extraction; sample inthimble is first immersed in boilingsolvent then thimble is raised forSoxhlet extraction with solventrefluxing.
Manual and automated versions are available; uses less solvent thantraditional Soxhlet and solvent is recovered for possible reuse.Extraction time is decreased due to two-step process.
Modern Extraction Methods for Solid Samples
refluxing.
Supercritical fluidextraction (SFE)
Sample is placed in flow-throughcontainer and supercritical fluid (suchas CO2) is passed through sample; afterdepressurization, extracted analyte iscollected in solvent or trapped onadsorbent, followed by desorption byrinsing with solvent.
Automated and manual versions are available; to affect "polarity"of supercritical fluid, density can be varied and solvent modifiersadded. Collected sample is usually concentrated and pure becauseCO2 is removed after extraction; matrix has an effect on extractionprocess.
Microwave-assistedextraction (MASE)
Sample is placed in an open or closedcontainer and heated by microwaveenergy, causing extraction of analyte.
Extraction solvent can range from microwave-absorbing (MA) ornon-microwave-absorbing (NMA); in MA case, sample is placed inhigh-pressure, non-microwave-absorbing container and heated wellabove its boiling point. Also in MA case, the sample and solventcan be refluxed at atmospheric pressure, analogous to solid-liquidextraction, in NMA case, container can be open, with no pressurerise, safety provisions are required.
Parameter Sonication Soxhlet
(traditional)
Soxhlet
(modern)
SFE ASE (ESE) Microwave-Assisted (closed
container)
Microwave-Assisted (open
container)
Sample size, g 20-50 10-20 10-20 5-10 5-15 2-5 2-10
Solventvolume, ml
100-300 200-500 50-100 10-20* 10-15 30 20-30
Temperature,°C
Ambient-40 40-100 40-100 50-150 50-200 100-200 Ambient
Pressure Atmospheric Atmospheric Atmospheric 2000-4000psi
1500-2000 psi 1500-2000 psi Atmospheric
Time, hr 0.5-1.0 12-24 1-4 0.5-1.0 0.2-0.3 0.2-0.3 0.1-0.2
Comparison of Extraction Methods
Time, hr 0.5-1.0 12-24 1-4 0.5-1.0 0.2-0.3 0.2-0.3 0.1-0.2
Degree ofAutomation**
0 0 ++ +++ +++ ++ ++
Number ofSamples***
High 1 6 44 24 12 12
Cost§ Low Very low Moderate High High Moderate Moderate
* When organic modifier is used to effect polarity
** For the most complete commercial instrument;0= no automation, += some automation, ++= mostly automated, ++= fully automated
*** Maximum number that can be handled in commercial instruments
§ Very low = < $1000, Low= $10,000, Moderate= $10,000-20,000, High= > $20,000
Sample
Solid Liquid
Organic
Extraction Methods for Various Types of Samples and Analytes
OrganicAnalytes
SupercriticalFluid
Extraction
AcceleratedSolvent
Extraction
SoxhletExtraction
UltrasonicExtraction
Metals
MicrowaveDigestion
AcidDigestion
OrganicAnalytes
Solid PhaseExtraction
Solid PhaseMicro-
extraction
Liquid/liquidExtraction
Dissolved Metals
Chelation/OrganicExtraction
Ion Exchange SolidPhase Extraction
Compound Absorbing solution Analytical method Range Interferences
Ammonia Dilute sulfuric acid React with phenol to form blueindenophenol, Colorimetricmeasurement
20-700micrometers/m3
LOD 0.2micrometers/ml insolution
Some metal ions(EDTA prevents someinterference)
Nitrogendioxide
Triethanol amine, o-methyl-phenol, sodiummetabisulfite
React with sulfanilamide and 8-anilino-1-naphthalenesulfonicacid- colorimetric measurement
20-700micrometers/m3
HNO2, N2O3
Sulfurdioxide
Sodiumtetrachloromercurate
React with formaldehyde andpararosaniline, Colorimetric
500 ml/m3 to 10micrometers/m3
None (note hightoxicity of abs. soln)
METHODS FOR ANALYSIS OF AIR POLLUTANTS BY IMPINGER METHODS
dioxide tetrachloromercurate pararosaniline, Colorimetricmeasurement
micrometers/m toxicity of abs. soln)
Phosgene 4-(4’-nitro-benzyl)pyridine indiethylphthalate
Colorimetric measurement Down to 40microliters/m3
Acid chlorides, highhumidity
Chlorine Methyl orange at pH3 Bleaching of the methyl orange ismeasured colorimetrically
Down to 1 ml/m3 inair. 5-100micromoles/ 100 mlof soln
Free bromine, SO2,NO2, (used for Clspills, in emergences)
Ozone andoxidizers
Buffered KI soln I3 formed is measuredcolorimetrically
0.01-10 ml/ m3 inair
NO2
Acrolein 4-hexyl-resorcinol in ethylalcohol and trichloroaceticacid
Colorimetric measurement Down to 0.01ml/m3 in air
Dienes (slight)
Compound Range Description Interference
Mercury vapor 0.1-2mg/m3
Hg reacts with CuI reagent to give ayellow-orange complex
Cl2 gives lowreadings
Carbonmonoxide
5-150ml/m3
CO reacts with iodine pentoxide giving I2,and a preconditioning layer removeshalogenated hydrocarbons, benzene, etc.
Acetylene willinterfere
EXAMPLES OF COLORIMETRIC AIR SAMPLING TUBES
Ozone 0.05-1.4ml/m3
Blue indigo dye is cleaved and bleached towhite
Cl2 and NO2 whenpresent above 5ml/m3 will turnindigo gray
Sulfur dioxide 0.5-5ml/m3
SO2 react with blue complex of I2 andstarch, changing to white
H2S will makeindicator gray
Tetrachloro-ethylene
5-50 ml/m3 First layer contains MnO4- which cleavesthe analyte forming Cl2, which reacts insecond layer with N,N’-diphenylbenzidineto give a gray-blue product
Free halogens,hydrogen halidesand easily cleavedhalocarbons
Sorbent Useful for Desorption method
Tenax (polyphenylene oxide) Nonpolar VOC with BP fromapprox. 40-200 ̊C
Thermal desorption
Carbon molecular sieve C2-C5 hydrocarbons Thermal desorption
Activated charcoal Low to medium boiling polarand nonpolar organics
Solvent extraction
SORBENT MATERIALS FOR AIR SAMPLING
Polyurethane foam Polar and nonpolarsemivolatile compounds
Solvent extraction
Activated silica Amines and polar organics Solvent extraction
Graphitized carbon C4 to C14 hydrocarbons,heavy organics such as PCBs
Thermals desorption, Solventdesorption
XAD-2 resin Semivolatiles, PAH Solvent desorption
Analyte Color system Measurement wavelength(nm)
Metals
Cr (VI) 1,5-Diphenylcarbazide 540
Pb Dicyclohexyl-18-crown-6-dithizone 512
Fe(III) Thiocyanate 460
Fe(II) Pyrocatecol violet 570
Cd Iodide/Malachite green 685
Hg 2-Pyridylketone 2-quinolylhydrozone
SOME COMMON COLORIMETRIC REAGENTS
Hg 2-Pyridylketone 2-quinolylhydrozone
Organics
Phenol 1-nitroso-2-napthol/Ce(IV)
Inorganic Ions
NO2- TiCl3/sulfanilamide 530
SO42- Fe(III)/HClO4 355
CN- Isonicotinic acid, 3-methyl-1-phenyl-2-pyrazoline-5-one
548
Gases
O3 KI 352
NH3 Glutamate dehydrogenase 340
Candidates for electrochemical detection: Biomedical
Acetylcholine* Neutral phenols
Amino acids* Nitrosothiols
Benzoic acids Oxalate
Cinnamic acids Peptides*
Coenzymes Phenylpropionic acids
DNA adducts Phenylpyruvic acidsDNA adducts Phenylpyruvic acids
Enzymes Thiols and disulfides
Estrogenic hormones Tryptophan metabolites
Glucose* Tyrosine metabolites
Lactic acid* Vitamins
Mandelic acids
* Require chemical or enzymatic derivatization before detection.
Bromide Nitrite
Cyanide Sulfite
Candidates for electrochemical detection: Ions
Alkaloids Disulfides
Analgesics L-DOPA and related
Candidates for electrochemical detection: Pharmaceutical
Analgesics L-DOPA and relatedcompounds
Antibiotics Nitrogen heterocycles
Anticancer Phenothiazines
Antimalarial Thiols
β-mimetics and β-blockers Tricyclic antidepressants
Environmental and Industrial
Analines Herbicides
Antioxidants Naphthols
Aromatic amines PCB metabolites
Candidates for electrochemical detection:
Aromatic amines PCB metabolites
Biphenyls Peroxides
Chelating agents Pesticides
Ethylenethiourea Phenols
Explosives
Typical Functional Groups
Oxidizable Reducible
Aromatic amines Aliphatic nitro
Ascorbic acids Aromatic nitro
Hydroquinones Azo compounds
Indoles AzomethineIndoles Azomethine
Phenols Nitrosamines
Phenothiazenes N-oxides
Thiols Organometallics
Vanillyl Peroxides
Xanthines Quinones and Thioamides
Standard Calomel Reference Electrodes of the Type //KCl/MCl(satd.)/M
MCl/M KCl E˚’ at 25˚C25
D(E˚’)dt
(mV deg-1 at25˚C)
AgCl/Ag 3.5 M (at 25˚C) 0.205 -0.73
Saturated 0.199 -1.01Saturated 0.199 -1.01
Hg2Cl2/Hg 0.1 M (at 25˚C) 0.336 -0.08
1.0 M (at 25˚C) 0.283 -0.29
3.5 M (at 25˚C) 0.250 -0.39
Saturated 0.244 -0.67
Electrode Type ConcentrationRange
Interferences
Ammonia Gas sensing 1-5 X 10-7 M Volatile Amines
Chloride Solid state 1-5 X 10-5 M OH-, S-2, Br-, I-, CN-
Fluoride Solid state Saturated to 0.02 ppm OH-
Lead (Pb+2) Solid state 0.1-10-6 M Ag+, Hg+2, Cu+2, high
EXAMPLES OF ION-SELECTIVE ELECTRODES
Lead (Pb+2) Solid state 0.1-10-6 M Ag+, Hg+2, Cu+2, highCd+2 or Fe+
Oxygen Gas sensing 0-14 ppm
Silver or Sulfide Solid state 1-10-17 M (Ag+ or S-2) Hg+2
Water hardness (M+2) Liquid membrane 1-6 X 10-6 M Na+, Cu+2, Zn+2, Fe+2,Ni+2, Sr+2, Ba+2, K+
Calcium (Ca+2) Liquid membrane 1.0-5 X 10-7 M Pb+2, Na+, Hg+2, H+,Fe+2, NH4, Mg+2
Relative Sensitivity of Some Electrochemical Techniques
Technique Limit of Detection forPb(II)
Ion selective electrode 10-5 M
DC polarography at DME 10-6 M
Differential pulsepolargraphy at SMDE
10-7 Mpolargraphy at SMDE
Differential pulse ASV atHMDE
10-10 M*
DC ASV at mercury film 10-11 M*
Square-wave ASV atmercury film
10-12 M*
* Deposition for 360 seconds; LOD varies with deposition time;S(H)MDE = (hanging)mercury drop electrode