6-Step Strategy Flashcards
(15 cards)
Whatre the 6 steps that should be taken when analysing a sample?
1 - Define the problem
2 - Sample
3 - Sample prep
4 - Measurement
5 - Evaluation of data
6 - Analytical information
what should be considered when choosing an appropriate technique?
Sensitivity, detection & quantitation limits?
Amount required?
Specificity & selectivity?
Calibration & associated measurement errors
Accuracy & precision?
Reference materials & standards?
Method validation & quality assurance
Expand on why its important to define the problem.
What is to be measured?
- what is the analyte of interest?
Why is it to be measured?
- identify the reason & justify.
How can this be done in a safe, risk assessed manner?
- addressed by the analyst
Expand on why its important to acquire a representative sample.
- Sampling introduces the greatest error of all steps
- The sample must reflect the properties of interest in the parent population or be identical composition to the bulk material
How can representative samples be taken?
- Sampling from bulk media (core of rock)
- Random sampling for quality assurance
- Testing various samples at different stages of process/synthesis
- Concordant sample testing
- The sample must also be stable - shouldn’t change as a consequence of sampling
- Health, safety & ethics should be considered
Sample integrity must be maintained
What must be considered when preparing the sample for analysis?
- How much is needed? Grams, mg?
- Any pre-treatment required?
- Is it in a stable form for the testing required?
Solids: drying, dissolution?
Liquids: liquid digestion, drying?
Separation?
How can errors be minimised during sample preparation?
Sample prep procedure should be documented accurately so that other samples can be treated in the same way - in order to minimise errors
What questions should you ask prior to taking measurements?
Qualitative or quantitative?
Threshold level or specific value?
State of matter, number and type of components to identify?
Which technique? Which method? Why?
what is Limit of Blank (LoB)?
LoB is the highest analyte concentration expected to be found when replicates of a blank sample containing no analyte are tested.
Why is LoB an important metric?
By understanding LoB, we can determine the lowest concentration that can readily be distinguished from the blank, ensuring accurate & reliable results.
what is Limit of Detection (LoD)?
LoD is the lowest analyte concentration to be reliably distinguished from the LoB
- at which detection is feasible
what is Limit of Quantitation (LoQ)?
LoQ is the lowest concentration at which the analyte can be reliably detected, at which some predefined goals for bias and imprecision are met
How are LoQ and LoD relate to each other?
The LoQ may be equivalent or much higher than the LoD
What is done in Evaluation of data?
Data from measurements must be taken and converted into values
- i.e. mg/L or %
What is done in the final step of the analytical approach, Analytical information?
Statistical tests - fitness for purpose
Method validation
- LoB, LoD & LoQ measured, linearity range, selectivity & precision are attested.
