Analytical Chemistry
Chapter 4 Summary
Sampling, Standardizations and Calibration
Sampling
- Instead of one huge sample per population, its better take “bulk” sample per
population
- To ensure the sample represent the population (kurgkan bias)
- Sample size (depends on mass)
o Ultramicro <0.0001
o Micro
o Semimicro
o Macro
- Constituent types (to measure or quantitate)
o Constituent – choc chip, sample-whole cookie
o Types of constituents:
▪ Ultratrace <ppb (sikit gila choc chip tu)
▪ Trace
▪ Minor
▪ Major (major of the cookie is choc chip) – usually this wont come up
- How to obtain representative sample?
reduce gross sample
identify population collect gross sample
to laboratory sample
- Important terms:
o Representative sample
o Sample storage
▪ To avoid undesirable losses, contamination or other things that could
affect the analysis result
▪ Eg.;
• temp may lead to loss of volatile analytes, thermal or
biological degradation and chemical reactivity
• temp lead to formation of deposits or precipitates of
analytes with low solubility
o Sample pre-treatment
▪ Necessary before suitable form for analysis is obtained by the chosen
technique and method (separation, [analyte] or removal of matrix
component that is expected to interfere with the analysis
o Sample preparation
▪ Need to be brough into suitable form for measurements to be made
under controlled conditions (dissolution, grinding, fabricating into
specific size and shape, pelletizing/mounting in a sample holder
, - How to minimize errors in analytical procedure?
o Separations (untuk interference in simple matrix)
▪ Techniques: filtration, precipitation, solvent extraction
▪ Cons: time consuming, chances are some analytes may loss and
sample has high chance to be contaminate
o Saturation method
▪ Adding interfering species so the interference effect becomes
independent of the original concentration
▪ Cons: degrade sensitivity and detectability of the analyte
o Matrix modifier
▪ Sufficient amount of ‘species’ is added to make the analytical
response independent of concentration of the interfering species
(cth: addition of abuffer)
o Masking agent
▪ Selectively added with the interfering species to form complex that
does not interfere
o Dilution method
▪ Interference effect can be minimized
o Matrix-matching method
▪ Duplicate sample matrix by adding major matrix cnstituents to the
standard and blank solution ( to trace metal in ppm)
Standardizations
- Calibration and standardization is the same thing
- What is a chemical standard?
o High purity material or substance with known composition that can be used
to standardize a reagent or calibrate an instrument
o Has higher relative molar mass to minimize weighing error
o Readily soluble in water
o Impurities <0.02% by weight
- What is a reference material?
o Has one or more properties that is sufficiently homogenous and well
established in order for it to be used for calibrating apparatus, assessment
of a measurement method or assigning values to materials
- Preparing standard solution
o Volumetric flask (diluting)
o Serial dilution (larger range of concentration)
Chapter 4 Summary
Sampling, Standardizations and Calibration
Sampling
- Instead of one huge sample per population, its better take “bulk” sample per
population
- To ensure the sample represent the population (kurgkan bias)
- Sample size (depends on mass)
o Ultramicro <0.0001
o Micro
o Semimicro
o Macro
- Constituent types (to measure or quantitate)
o Constituent – choc chip, sample-whole cookie
o Types of constituents:
▪ Ultratrace <ppb (sikit gila choc chip tu)
▪ Trace
▪ Minor
▪ Major (major of the cookie is choc chip) – usually this wont come up
- How to obtain representative sample?
reduce gross sample
identify population collect gross sample
to laboratory sample
- Important terms:
o Representative sample
o Sample storage
▪ To avoid undesirable losses, contamination or other things that could
affect the analysis result
▪ Eg.;
• temp may lead to loss of volatile analytes, thermal or
biological degradation and chemical reactivity
• temp lead to formation of deposits or precipitates of
analytes with low solubility
o Sample pre-treatment
▪ Necessary before suitable form for analysis is obtained by the chosen
technique and method (separation, [analyte] or removal of matrix
component that is expected to interfere with the analysis
o Sample preparation
▪ Need to be brough into suitable form for measurements to be made
under controlled conditions (dissolution, grinding, fabricating into
specific size and shape, pelletizing/mounting in a sample holder
, - How to minimize errors in analytical procedure?
o Separations (untuk interference in simple matrix)
▪ Techniques: filtration, precipitation, solvent extraction
▪ Cons: time consuming, chances are some analytes may loss and
sample has high chance to be contaminate
o Saturation method
▪ Adding interfering species so the interference effect becomes
independent of the original concentration
▪ Cons: degrade sensitivity and detectability of the analyte
o Matrix modifier
▪ Sufficient amount of ‘species’ is added to make the analytical
response independent of concentration of the interfering species
(cth: addition of abuffer)
o Masking agent
▪ Selectively added with the interfering species to form complex that
does not interfere
o Dilution method
▪ Interference effect can be minimized
o Matrix-matching method
▪ Duplicate sample matrix by adding major matrix cnstituents to the
standard and blank solution ( to trace metal in ppm)
Standardizations
- Calibration and standardization is the same thing
- What is a chemical standard?
o High purity material or substance with known composition that can be used
to standardize a reagent or calibrate an instrument
o Has higher relative molar mass to minimize weighing error
o Readily soluble in water
o Impurities <0.02% by weight
- What is a reference material?
o Has one or more properties that is sufficiently homogenous and well
established in order for it to be used for calibrating apparatus, assessment
of a measurement method or assigning values to materials
- Preparing standard solution
o Volumetric flask (diluting)
o Serial dilution (larger range of concentration)
