ANALYTICAL SELECTIVITY AND SENSITIVITY, ASSAY QUALITY CONTROL, AND STATISTICAL COMPUTATIONS

Question 1

analytical methodology

Answer 1

1. Plan
2. Sampling
3. Sample preparation
4. Analytical measurements
5. Data analysis

Question 2

plan

Answer 2

Qualitative, quantitative or both?; what kind of information do we have?; which technique is suitable?, etc.

Question 3

sampling

Answer 3

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

Question 4

sample preparation

Answer 4

Depends on analytical techniques.

Question 5

analytical measurements

Answer 5

Which techniques are best?

Question 6

data analysis

Answer 6

Where data acquired make sense or not

Question 7

Selecting an analytical method

Answer 7

 In order to select an analytical method correctly, it is essential to define clearly the nature of the analytical problem. In general, the following points should be considered when choosing an instrument for any measurement.

1. Accuracy and precision required
2. Available sample amount
3. Concentration range of the analyte
4. Interference in sample
5. Physical and chemical properties of the sample matrix
6. Number of samples to be analysed
7. Speed, ease, skill and cost of analysis

Question 8

figures of merit for an analytical method

Answer 8

• Precision
• Bias
• Sensitivity
• Detection limit
• Concentration range (Dynamic range)
• Selectivity

Question 9

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

accuracy

Answer 10

How close the measurement approaches the real value.

Question 11

Bias

Answer 11

Bias provides a measure of the systematic, or determinate 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

equations for analytical methods

Answer 12

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Question 13

Distribution and probability: normal distribution

Answer 13

If we know something about the distribution of events in a population, we know something about the probability of these events

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Question 14

Formula for standard deviation

Answer 14

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Question 15

Standard error of the mean (SEM)

Answer 15

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Question 16

Summary of samples collectable from participants

Answer 16

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Question 17

Diagnosis of periodontal diseases using 1H NMR linked metabolics

Answer 17

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Question 18

Electronic absorption spectrum of sodium chlorite

Answer 18

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Question 19

Absorbance- concentration relationships

Answer 19

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 20

Absorbance- concentration relationships reading graph

Answer 20

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Question 21

Correlation and regression

Answer 21

• 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 22

Correlation coefficient tells us

Answer 22

How well our data fit a linear relationship

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Question 23

Formula for Pearson’s correlation coefficient

Answer 23

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Question 24

Best fit line

Answer 24

• 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

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Question 25

finding a

Answer 25

• 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

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Question 26

finding b

Answer 26

• 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 27

Regression fit warning – dodgy correlations

Answer 27

1. outliers
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2. more than 1 different population or contrast
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