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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
Perform the
Measurement
Data Processing
and Report
Select a Method
Perform Any Necessary
Chemical Separations
Obtain a Representative Sample
Prepare the Sample for Analysis
1. Define the Problem
Factors:
• What is the problem--what needs to be found? Qualitative and/or
quantitative?
• 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?
• What is the budget?
• The analyst (the problem solver) should consult with the client to plan
a useful and efficient analysis, including how to obtain a useful
sample.
2. Select a Method
Factors:
• Sample type
• Size of sample
• Sample preparation needed
• Concentration and range (sensitivity needed)
• 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 ground
up prior to dissolution.
Analysis of grains from crops (rice, wheat, etc.) requires dehusking to yield
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 of
the 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 analytical
objectives.
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 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 in
the hyphenated techniques of GC-MS or LC-MS)
• Electrophoresis (may be done as part of the measurement step as in
CE-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 devices
must also be checked or calibarated
• 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 of
chemical identification and determination
•
•
Interpretation of data by correlating chemical parameters of analytes (formula
mass, 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 determine
quantitative 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, detection
limits, and etc.
• Relating qualitative and quantitative results to the objectives of
analyses (i.e. how C-14 results are used to determine the age of an
archaeological 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 Methods
Classical methods
• Gravimetry
• Titrimetry
Instrumental 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
Raw data
Machine-level commands
Control
Diagnostics
Processed data
(Information)
High-level
commands
Integrated
Computers
Data
Processing
Intelligent System
User Interface
User-level
commands
Explanation
(Knowledge)
Analyst
Output
Device
Components of a Typical Instrument
Signal
generator
Analytical
signal
Input
transducer
or
detector
Electrical
or
mechanical
input
signal
Meter
or
Scale
Signal
processor
Output
signal
Recorder
12.301
Digital
unit
Some Examples of Instrument Components
Selecting an Analytical Method
Defining the problem:
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
interference?
5. What are the physical and chemical properties of
the sample matrix?
6. How many samples are to be analyzed?
Validation involves
determining:
•selectivity
•linearity
•accuracy
•precision
•sensitivity
•range
•limit of detection
•limit of quantitation
•ruggedness/robustness
Standard reference
materials (SRMs) best for
determining accuracy.
General process for evaluation/validation of methodology
©Gary Christian, Analytical Chemistry,
6th Ed. (Wiley)
Other Characteristics to Be
Considered in Choosing a Method
1. Speed of analysis
2. Ease of use and automation
3. Cost and availability of instrument
4. Per-sample cost (consumables and reagents)
5. Training and learning curve
6. Software features and compatibility with
databases and data processing programs
COMPONENTS OF A QUALITY CONTROL
Well
trained
personnel
GLP
SOP
Suitable and
PROGRAM
well
maintained
facilities
Quality
Control
Evaluation
Samples
Maintained
and well
calibrated
equipment
GMP
Complete
Documentat
ion
IMPORTANT PROCEDURES IN QUALITY CONTROL
Measured parameter
Procedure
Accuracy
Analysis of reference materials or samples
of know concentration
Precision
Analysis of replicate samples
Extraction efficiency
Analysis of matrix spikes
Contamination
Analysis of blanks
POTENTIAL SOURCES OF SAMPLE CONTAMINATION
Steps in the analytical
process
Contamination sources
Sample collection
Equipment, Sample handling steps such as compositing, or
filtering, Sample preserving additives, Sample containers,
Ambient contamination
Sample transport and storage
Sample containers, Cross contamination from ear reagents or
other samples
Sample preparation
Sample handling, Dilutions, Glassware, Ambient
contamination
Sample analysis
Instrument memory effects or carry-over, Reagents, Syringes,
Glassware, Apparatus
TYPES OF ANALYTICAL BLANKS FOR QUALITY CONTROL
Blank type
Purpose
Process
System or Instrument blank
Establishes the baseline of an analytical
instrument, in the absence of sample
Determine the background signal with
no sample present
Solvent or Calibration blank
To measure the amount of the analytical signal
which arises from the dilution solvent. The zero
solution in the calibration series.
Analytical instrument is run with
dilution solvent only
Method blank
To detect contamination from reagents, sample
handling, and the entire analytical process
A simulated sample containing no
analyte is taken through entire
analytical procedure
Matched-matrix blank
To detect contamination from field handling,
transportation, or storage
A synthetic sample which matches the
basic matrix of the sample is carried to
the field and is treated in the same
fashion as the samples
Sampling media or trip
blank
To detect contamination in sampling media such
as filters and sample adsorbent traps
Analyze samples of unused filters or
traps to detect contaminated batches
Equipment blank
To determine contamination of equipment and
assess the efficiency or equipment clean-up
procedures
Samples of final equipment cleaning
rinses are analyzed for contaminants
REGULATORY LEVELS OF TCLP CONTAMINANTS
Metals
Regulatory
level (mg/l)
Pesticides
Regulatory
level (mg/l)
Other organics
Regulatory
level (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
1,4Dichlorobenzene
10.8
Mercury
0.2
2,4,5-TP
(Silvex)
0.14
Pentachlorophen
ol
3.6
Lead
5
Heptachlor
0.001
Trichloroethylene 0.07
Silver
5
Methoxychlor
1.4
Toluene
Vinyl chloride
14.4
0.05
REGULATORY LEVELS FOR AMBIENT AIR POLLUTANTS
Compound
Regulatory concentration
Averaging period
0.12 ppm
1h
Carbon monoxide
35 ppm
9 ppm
1h
8h
Nitrogen dioxide
0.05
1 year
Sulfur dioxide
0.14 ppm
0.03 ppm
24h
1 year
Particulate matter
150 µg/m3
50 µg/m3
25 µg/m3
24h
1 year
24h
Sulfates
25 µg/m3
24h
Vinyl chloride
0.01 ppm
24h
Lead
1.5 µg/m3
3 months
Ozone
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.
©Gary Christian,
Analytical Chemistry,
6th Ed. (Wiley)
Normal error curve (Gaussian Curve)
Bias
Bias = m - xi
where
m => population mean
xi => measured concentration
Sensitivity
2 factors limiting sensitivity:
• slope of calibration curve
– steeper slope, greater sensitivity
• reproducibility of measurements
– equal slope, better reproducibility, greater
sensitivity
Sensitivity
IUPAC defined calibration sensitivity
S = mc + Sbl
where
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
- independent of units
disadvantage:
- standard deviation of signal can vary with
concentration
Detection Limit & Quantitation Limit
Instrumental detection limit refers to the minimum
concentration or weight of analyte that can be
detected at a known confidence level and is
usually defined as being equivalent to 3 times the
signal background noise or the 3s-level.
Method or practical quantitation limit refers to the
level at which reliable quantitative analysis can
be performed and is commonly defined at 9s to
15s levels.
Detection Limit
minimum distinguishable analytical signal => Sm
Sm = Sbl + ksbl
where Sbl => mean blank signal
k => some multiple (normally 3)
sbl => absolute standard deviation of the blank
measure 20-30 blanks over extended period of
time to determine Sbl and sbl
detection limit => cm = (Sm - Sbl)/m
Raman spectra of Calcium ascorbate
SNR=17
100 ms, 50 um slit
SNR= 5
10 ms, 50 um
SNR=2.8
10 ms, 20 um
SNR < 2
10 ms, 10 um
400
600
800
1000
1200
1400
Raman shift, cm-1
1600
1800
2000
Signal averaging improves S/N
0.1 sec*
1.0 sec
30 sec
400
600
800
1000
1200
1400
1600
Raman shift, cm-1
* spectra were accumulated for period indicated
1800
2000
Instrument response
Linear Dynamic Range
LOL
LOQ => limit of quantitative
measurement
LOQ
Useful range
Concentration
LOL => limit of linear
response
Selectivity
degree to which a method is free from
interference by other species contained in
the matrix
S = 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
Selectivity
kB,A = mB/mA and kC,A = mC/mA
where kB,A => selectivity coefficient for
B
with respect to A
kC,A => selectivity coefficient for
C
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.
m
m
m
©Gary Christian, Analytical Chemistry,
6th Ed. (Wiley)
m
m
This is a time plot for analysis of the same sample, assumed to have only
random 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)
F = s12/s22
You compare the variances of two different methods to see if there is a
significant 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
small numbers of observations.
And the range times a factor (K) may be a better measure of spread than the
standard 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)
Main Purposes of Solid Phase Extraction
Purpose
How Performed
Usage
Application Examples
Removal of interferences
Interferences are allowed to pass
unretained through the cartridge with
analytes remained sorbed, or analytes
pass through the cartridge, with
interferences remaining on the cartridge
50%
Removal of proteins from biological fluids,
fats and lipids from food, ionic compounds
from aqueous samples and drugs of abuse
from urine, and extractions of dioxans from
waste water.
Analyte Concentration
Conditions are chose to achieve strong
retention values (retentive stationary
phase/ weak mobile phase); elution in a
small volume of volatile organic solvent.
35
Trace enrichment of ppb of polynuclear
aromatics from water, trace pesticides in
urine, caffeine from beverages, and
therapeutic drugs from plasma.
Phase exchange
Analyte present in emulsion, suspension,
or undesirable solvent is sorbed on SPE
cartridge, dried, and eluted with desired
solvent
5
Exchange of aqueous solvent for
nonaqueous one with intermediate dry
nitrogen flush.
Specifically coated SPE phases
selectively derivatize analytes as they
pass through the cartridge.
5
2,4-dinitrophenyl hydrazine-coated
cartridges that selectively derivatize
carbonyl-containing compounds; amines
and polyamines in air; organic acids in
water.
Vapor or liquid samples are collected at
factory or in field on an SPE cartridge or
disk and transported to laboratory.
5
Soil gas analysis; trace organics in water.
Solid-phase derivatization
Sample storage and
transport
Comparison of Extraction Methods for Sample Preparation of Solids
Parameter
Sonication
Soxhlet
(traditional)
Soxhlet
(modern)
SFE
ASE (ESE)
MicrowaveAssisted
(closed
container)
MicrowaveAssisted (open
container)
Sample size, g
20-50
10-20
10-20
5-10
5-15
2-5
2-10
Solvent
volume, 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
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 of
Automation**
0
0
++
+++
+++
++
++
Number of
Samples***
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
Modern Extraction Methods for Solid Samples
Method of Sample
Principles of Technique
Comments
Accelerated
(enhanced) solvent
extraction (ASE or
ESE)
Sample is placed in a sealed container
and heated to above its boiling point,
causing pressure in vessel to rise;
extracted sample is automatically
removed and transferred to vial for
further treatment
Greatly increased speed of liquid-solid extraction process and is
automated. Vessel must withstand high pressure; extracted sample
in diluted form requires further concentration; safety provisions are
required.
Automated Soxhlet
extraction
A combination of hot solvent leaching
and Soxhlet extraction; sample in
thimble is first immersed in boiling
solvent then thimble is raised for
Soxhlet extraction with solvent
refluxing.
Manual and automated versions are available; uses less solvent than
traditional Soxhlet and solvent is recovered for possible reuse.
Extraction time is decreased due to two-step process.
Supercritical fluid
extraction (SFE)
Sample is placed in flow-through
container and supercritical fluid (such
as CO2) is passed through sample; after
depressurization, extracted analyte is
collected in solvent or trapped on
adsorbent, followed by desorption by
rinsing with solvent.
Automated and manual versions are available; to affect "polarity"
of supercritical fluid, density can be varied and solvent modifiers
added. Collected sample is usually concentrated and pure because
CO2 is removed after extraction; matrix has an effect on extraction
process.
Microwave-assisted
extraction (MASE)
Sample is placed in an open or closed
container and heated by microwave
energy, causing extraction of analyte.
Extraction solvent can range from microwave-absorbing (MA) or
non-microwave-absorbing (NMA); in MA case, sample is placed in
high-pressure, non-microwave-absorbing container and heated well
above its boiling point. Also in MA case, the sample and solvent
can be refluxed at atmospheric pressure, analogous to solid-liquid
extraction, in NMA case, container can be open, with no pressure
rise, safety provisions are required.
Modern Extraction Methods for Solid Samples
Method of Sample
Principles of Technique
Comments
Accelerated
(enhanced) solvent
extraction (ASE or
ESE)
Sample is placed in a sealed container
and heated to above its boiling point,
causing pressure in vessel to rise;
extracted sample is automatically
removed and transferred to vial for
further treatment
Greatly increased speed of liquid-solid extraction process and is
automated. Vessel must withstand high pressure; extracted sample
in diluted form requires further concentration; safety provisions are
required.
Automated Soxhlet
extraction
A combination of hot solvent leaching
and Soxhlet extraction; sample in
thimble is first immersed in boiling
solvent then thimble is raised for
Soxhlet extraction with solvent
refluxing.
Manual and automated versions are available; uses less solvent than
traditional Soxhlet and solvent is recovered for possible reuse.
Extraction time is decreased due to two-step process.
Supercritical fluid
extraction (SFE)
Sample is placed in flow-through
container and supercritical fluid (such
as CO2) is passed through sample; after
depressurization, extracted analyte is
collected in solvent or trapped on
adsorbent, followed by desorption by
rinsing with solvent.
Automated and manual versions are available; to affect "polarity"
of supercritical fluid, density can be varied and solvent modifiers
added. Collected sample is usually concentrated and pure because
CO2 is removed after extraction; matrix has an effect on extraction
process.
Microwave-assisted
extraction (MASE)
Sample is placed in an open or closed
container and heated by microwave
energy, causing extraction of analyte.
Extraction solvent can range from microwave-absorbing (MA) or
non-microwave-absorbing (NMA); in MA case, sample is placed in
high-pressure, non-microwave-absorbing container and heated well
above its boiling point. Also in MA case, the sample and solvent
can be refluxed at atmospheric pressure, analogous to solid-liquid
extraction, in NMA case, container can be open, with no pressure
rise, safety provisions are required.
Comparison of Extraction Methods
Parameter
Sonication
Soxhlet
(traditional)
Soxhlet
(modern)
SFE
ASE (ESE)
MicrowaveAssisted (closed
container)
MicrowaveAssisted (open
container)
Sample size, g
20-50
10-20
10-20
5-10
5-15
2-5
2-10
Solvent
volume, 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
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 of
Automation**
0
0
++
+++
+++
++
++
Number of
Samples***
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
Extraction Methods for Various Types of Samples and Analytes
Sample
Solid
Liquid
Organic
Analytes
Metals
Organic
Analytes
Supercritical
Fluid
Extraction
Accelerated
Solvent
Extraction
Microwave
Digestion
Soxhlet
Extraction
Acid
Digestion
Ultrasonic
Extraction
Solid Phase
Extraction
Solid Phase
Microextraction
Dissolved Metals
Chelation/Organic
Extraction
Ion Exchange Solid
Phase Extraction
Liquid/liquid
Extraction
METHODS FOR ANALYSIS OF AIR POLLUTANTS BY IMPINGER METHODS
Compound
Ammonia
Absorbing solution
Dilute sulfuric acid
Analytical method
React with phenol to form blue
indenophenol, Colorimetric
measurement
Range
20-700
micrometers/m3
Interferences
Some metal ions
(EDTA prevents some
interference)
LOD 0.2
micrometers/ml in
solution
Nitrogen
dioxide
Triethanol amine, omethyl-phenol, sodium
metabisulfite
React with sulfanilamide and 8anilino-1-naphthalenesulfonic
acid- colorimetric measurement
20-700
micrometers/m3
HNO2, N2O3
Sulfur
dioxide
Sodium
tetrachloromercurate
React with formaldehyde and
pararosaniline, Colorimetric
measurement
500 ml/m3 to 10
micrometers/m3
None (note high
toxicity of abs. soln)
Phosgene
4-(4’-nitro-benzyl)
pyridine in
diethylphthalate
Colorimetric measurement
Down to 40
microliters/m3
Acid chlorides, high
humidity
Chlorine
Methyl orange at pH3
Bleaching of the methyl orange is
measured colorimetrically
Down to 1 ml/m3 in
air. 5-100
micromoles/ 100 ml
of soln
Free bromine, SO2,
NO2, (used for Cl
spills, in emergences)
Ozone and
oxidizers
Buffered KI soln
I3 formed is measured
colorimetrically
0.01-10 ml/ m3 in
air
NO2
Acrolein
4-hexyl-resorcinol in ethyl
alcohol and trichloroacetic
acid
Colorimetric measurement
Down to 0.01
ml/m3 in air
Dienes (slight)
EXAMPLES OF COLORIMETRIC AIR SAMPLING TUBES
Compound
Range
Description
Interference
Mercury vapor 0.1-2
mg/m3
Hg reacts with CuI reagent to give a
yellow-orange complex
Cl2 gives low
readings
Carbon
monoxide
5-150
ml/m3
CO reacts with iodine pentoxide giving I2,
and a preconditioning layer removes
halogenated hydrocarbons, benzene, etc.
Acetylene will
interfere
Ozone
0.05-1.4
ml/m3
Blue indigo dye is cleaved and bleached to Cl2 and NO2 when
white
present above 5
ml/m3 will turn
indigo gray
Sulfur dioxide
0.5-5
ml/m3
SO2 react with blue complex of I2 and
starch, changing to white
Tetrachloroethylene
5-50 ml/m3 First layer contains MnO4- which cleaves
the analyte forming Cl2, which reacts in
second layer with N,N’-diphenylbenzidine
to give a gray-blue product
H2S will make
indicator gray
Free halogens,
hydrogen halides
and easily cleaved
halocarbons
SORBENT MATERIALS FOR AIR SAMPLING
Sorbent
Useful for
Desorption method
Tenax (polyphenylene oxide)
Nonpolar VOC with BP from
approx. 40-200 ̊C
Thermal desorption
Carbon molecular sieve
C2-C5 hydrocarbons
Thermal desorption
Activated charcoal
Low to medium boiling polar
and nonpolar organics
Solvent extraction
Polyurethane foam
Polar and nonpolar
semivolatile compounds
Solvent extraction
Activated silica
Amines and polar organics
Solvent extraction
Graphitized carbon
C4 to C14 hydrocarbons,
heavy organics such as PCBs
Thermals desorption, Solvent
desorption
XAD-2 resin
Semivolatiles, PAH
Solvent desorption
SOME COMMON COLORIMETRIC REAGENTS
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
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-phenyl2-pyrazoline-5-one
548
O3
KI
352
NH3
Glutamate dehydrogenase
340
Gases
Candidates for electrochemical detection: Biomedical
Acetylcholine*
Amino acids*
Benzoic acids
Cinnamic acids
Coenzymes
DNA adducts
Enzymes
Estrogenic hormones
Glucose*
Lactic acid*
Mandelic acids
Neutral phenols
Nitrosothiols
Oxalate
Peptides*
Phenylpropionic acids
Phenylpyruvic acids
Thiols and disulfides
Tryptophan metabolites
Tyrosine metabolites
Vitamins
* Require chemical or enzymatic derivatization before detection.
Candidates for electrochemical detection: Ions
Bromide
Cyanide
Nitrite
Sulfite
Candidates for electrochemical detection: Pharmaceutical
Alkaloids
Disulfides
Analgesics
Antibiotics
L-DOPA and related
compounds
Nitrogen heterocycles
Anticancer
Phenothiazines
Antimalarial
Thiols
β-mimetics and β-blockers
Tricyclic antidepressants
Candidates for electrochemical detection:
Environmental and Industrial
Analines
Herbicides
Antioxidants
Aromatic amines
Naphthols
PCB metabolites
Biphenyls
Peroxides
Chelating agents
Pesticides
Ethylenethiourea
Phenols
Explosives
Typical Functional Groups
Oxidizable
Aromatic amines
Ascorbic acids
Hydroquinones
Indoles
Phenols
Phenothiazenes
Thiols
Vanillyl
Xanthines
Reducible
Aliphatic nitro
Aromatic nitro
Azo compounds
Azomethine
Nitrosamines
N-oxides
Organometallics
Peroxides
Quinones and Thioamides
Standard Calomel Reference Electrodes of the Type //
KCl/MCl(satd.)/M
MCl/M
KCl
E˚’ at 25˚C
25
D(E˚’)
dt
(mV deg-1 at
25˚C)
AgCl/Ag
Hg2Cl2/Hg
3.5 M (at 25˚C)
0.205
-0.73
Saturated
0.199
-1.01
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
EXAMPLES OF ION-SELECTIVE ELECTRODES
Electrode
Type
Concentration
Range
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
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
Ag+, Hg+2, Cu+2, high
Cd+2 or Fe+
Relative Sensitivity of Some Electrochemical Techniques
Technique
Ion selective electrode
DC polarography at DME
Differential pulse
polargraphy at SMDE
Differential pulse ASV at
HMDE
DC ASV at mercury film
Square-wave ASV at
mercury film
Limit of Detection for
Pb(II)
10-5 M
10-6 M
10-7 M
10-10 M*
10-11 M*
10-12 M*
* Deposition for 360 seconds; LOD varies with deposition time;S(H)MDE = (hanging)
mercury drop electrode