LU1: Analytical Chemistry Overview Steps in Typical Quantitative…
LU1: Analytical Chemistry Overview
Steps in Typical Quantitative Analysis
8. Measure property of analyte and calibration
The physical or chemical property proportional to the analyte concentration is measured.
Suitable standards must be measured to determine the relationship btw analyte quantity & physical / chemical property being measured (i.e., calibration).
C = kX
C = concentration
kX = technique response
to establish relationship, 1 or more standard solutions is needed.
relationship btw measured response & [analyte]
Standards – prepared identically to the samples, have a similar compositions or matrix, &prepared in a range that is expected as the sample or the unknown samples.
National Institute of Standards and Technology (NIST)
Standard Reference Material (SRM)
9. Data analysis
using raw data, stoichiometry of reaction (s) & instrumental factors to calculate [analyte]
Evaluating the results & estimating their reliability (statistics)
5. Replicate samples
portions of material of approximately the same size that are carried through an analytical procedure at the same time & in the same way
Replication improves the quality of the results; minimize error
4. Preparation of laboratory sample
convert sample to usable form for chemical analysis –drying, sample weighing, mixing (ie.solid samples are ground to suitable particle size, mixed to assure homogeneity & stored before the analysis)
Most difficult step
Obtaining small mass of a material whose composition accurately represent the bulk sample
1. Define a problem
How accurate and precise does it have to be?
What is the budget?
When will it be needed?
The analyst should consult the client to plan a useful and efficient analysis including how to obtain a useful sample.
What will the information be used for? Who will use it?
What is the problem? What needs to be found
Size of sample
Sample preparation needed
[ ] & range (sensitivity needed)
Selectivity needed (interferences)
Does it need to be automated
Are methods available in the chemical literature
Are standard methods available
7. Eliminating interferences
interferences are substances that prevent direct measurement of the analyte & must be removed.
6. Preparing solutions of the sample
Solvent chosen should dissolve the entire sample completely without decomposing the analyte.
Various types of solvents in dissolution method – nitric acid, sulphuric acid, hydrochloric acid etc.