Pharmaceutical analysis: Measurement and data reliability Flashcards
What are the steps in drug analysis (5)
- Take representative sample
2, Extract analyte(s) from interfering matrix - separate analytes
- identify, detect and quantify analytes
- determine reliability/validity of results
What does a ‘representative sample’ represent?
represents a large portion of batch. taking sample from different places within the sample to ensure its homogeneously mixed
What is an analyte?
What we want to detect - drug/metal etc
What step must be taken to test if it is highly susceptible to impurities?
purification
What is data validity?
Determine through stats, comparison with standards and/or another method.
How can you present data?
- Group it: frequency table/histogram/bar chart
- Only one parameter changed: line graph
- More than one parameter changed: scatter graph
Are analytical measures exact?
NO
What can you assume about the last digit quotes in a measured value?
That it is uncertain
If a value of weight is 44.2239672g and the accuracy of the balance is +/- 0.1mg, what is the final weight?
- 2240g
0. 1mg = 0.0001g
When adding and subtracting, what number of decimal places should you round off to?
The SAME number of decimal places as the value having the FEWEST decimal places;
100 + 28.621 = 129
When multiplying and dividing, what number of significant figures should you round off to?
The same number of sf as the value with the least.
2.1 x 11.31 = 24
When is zero significant?
Zeroes between non-zero digits are significant:
4.06ml (3 sig fig)
zeros to the left of first non-zero digits are not significant: 0.014 g has 2 significant figures
zeroes to the right of a decimal point in a number are significant: 0.0130 mL has 3 significant figures
Zero at the end of a number without decimal point may or may not be significant: 4600 calories may be 2, 3, 4 significant figures.
When taking measurement on a SCALED instrument, how should you read the value?
Go ONE more figure than you can actually read. e.g. when measuring thirty ml of solvent, the accuracy is only 30.00ml
What 3 types of errors is the validity of analytical measurement affected by?
- Indeterminate (random) error: evaluate with statistics - affects precision more than accuracy
- Determinate (systematic) error: evaluate with standards - affects accuracy more than precision
- Gross error: big mistake, like spilling everything on the floor, sample evaporated etc
What is the difference between accuracy and precision?
Accuracy is how close a value is to its true value. An example is how close an arrow gets to the bull’s-eye centre.
Precision is how repeatable a measurement is. An example is how close a second arrow is to the first one (regardless of whether either is near the mark).
