analytical selectivity and sensitivity, assay quality control and statistical computations

Question 1

what are the 5 steps to analytical methodology

Answer 1

plan
sampling
sample prep
analytical measurement
data analysis

Question 2

plan

Answer 2

Qualitative, quantitative or both?

What kind of information do we have?

What technique is suitable?

Question 3

sampling

Answer 3

Accuracy depends on proper sampling, characteristic of sample is important, required good representative sample (from top, middle and bottom and mix up and take average sample)

Question 4

sample prep

Answer 4

Depends on analytical techniques

Question 5

analytical measurement

Answer 5

Which techniques are best?

Question 6

data analysis

Answer 6

Whether data acquires make sense or not

Question 7

what 7 points should be considered when choosing an instrument for any measurement

Answer 7

Accuracy and precision required

Available sample amount

Concentration range of the analyte

Interference in sample

Physical and chemical properties of the sample matrix

Number of samples to be analysed

Speed, ease, skill and cost of analysis

Question 8

6 figures of merit for an analytical method

Answer 8

Precision

Bias

Sensitivity

Detection limit

Concentration range

Selectivity

Question 9

what is precision

Answer 9

How close the same measurements made on the same material are to one another. The degree of mutual agreement amongst data that have been obtained in the same manner. Precision provides a measure of the random or indeterminate error of an analysis.

Question 10

what is accuracy

Answer 10

How close the measurement approached the real value?

Question 11

what is bias

Answer 11

Bias provides a measure of the systematic, or determine error of an analytical method

bias: x’ = x + δ + 

where is x’ is the population mean, δ is the bias (perhaps caused by an interfering component),  is a random component (experimental error), and x is the true value.

Question 12

see powerpoint for

Answer 12

terms on calculation precision

Question 13

see powerpoint for

Answer 13

normal distribution

Question 14

see powerpoint for

Answer 14

standard deviation

Question 15

absorption - concentration relationships

Answer 15

If various different concentrations of a sample are subjected to

UV/Vis radiation the different absorbance readings obtained

can be plotted on a graph against concentration.

Question 16

see powerpoint for

Answer 16

absorbance - concentration relationships graph

Question 17

correlation and regression

Answer 17

Is there a relationship between x and y?

What is the strength of this relationship?
- Pearson’s r

Can we describe this relationship and use it to predict y from x?

• Regression
• Fitting a line using the Least Squares solution

Is the relationship we have described statistically significant?
- Significance tests

Question 18

what do correlation coefficient values tell us

Answer 18

how well our data fit a LINEAR relationship

Question 19

see powerpoint for

Answer 19

person’s correlation coefficient

Question 20

best line fit

Answer 20

Aim of linear regression is to fit a straight line, ŷ = ax + b to data that gives best prediction of y for any value of x
This will be the line that minimises distance between data and fitted line, i.e. the residuals

Question 21

see powerpoint for

Answer 21

best fit line equation graph

Question 22

how to find a from the equation

Answer 22

now we find the value of a that gives the least sum of squares

trying out different values of a is equivalent to changing the slope of the line, while b stays constant

Question 23

how to find b from the equation

Answer 23

First we find the value of b that gives the least sum of squares

Trying different values of b is equivalent to shifting the line up and down the scatter plot

Question 24

what are two regression fit warnings

Answer 24

outliners

more than 1 different population or contrast