Analytical Analysis

Question 1

Step 1 in an Analytical Analysis

Answer 1

Formulating a Question
Asking a meaningful question. What specifically do you want to know?
What are we analyzing for? What kind of sample is it?
How much silver is in a trainload of ore? (accuracy)
Did an athlete cheat? vs. how much clenbuterol is present? (sensitivity, specificity)

Question 2

Step 2 in an Analytical Analysis

Answer 2

Selecting analytical procedure
What analytical method will we use? Availability, cost, sensitivity, sample volume
Literature search method, or make a new method.
Is a Regulatory method available and needed?

Question 3

Step 3 in an Analytical Analysis

Answer 3

Sampling
How do we get a “representative sample” to analyze; “Garbage in – Garbage out”.
Protocol, selection, homogenization, containers, contamination, loss

Question 4

Step 4 in an Analytical Analysis

Answer 4

Sample preparation or pretreatment:
Convert sample to be suitable for analysis
Copper Lab: conversion of solid into liquid with HNO3
Fluoride Lab: buffer pH 5 so fluoride as F- not un-dissociated HF
Total Salt Lab: convert Mn+ into nH+
for titration with a base
Eliminate interferences from sample matrix
Copper Lab: add NH4HF2
to complex Fe3+ leaving Cu2+ for analysis
Fluoride Lab: add EDTA in buffer solution to complex metals
Concentrate sample
Trace Cu2+ could be concentrated using cation exchange resin

Question 5

Step 5 in an Analytical Analysis

Answer 5

Analysis/Measurement
Perform analysis of the analyte with replicate aliquot (portion) measurements
Allows assessment of uncertainty and reliability
Standardize method - Quality control

Question 6

Step 6 in an Analytical Analysis

Answer 6

Calculation and Evaluation of Results
Clearly written report of results and observations
Check for calculation errors, evaluate quality of results (Qtest, statistics)
Decide to repeat if need be

Question 7

Step 7 in an Analytical Analysis

Answer 7

Drawing Conclusions
Usually done by the person asking for the information
Interpretation of the statistical significance of result to answer the question

Question 8

The Lab Notebook

Answer 8

The Lab Notebook – understanding what you did and observed so it can be repeated

Question 9

Why sample?

Answer 9

– Resources (time, money) and workload
– Gives results of whole with known accuracy and error
Analysis is meaningless unless you begin with meaningful sample

Question 10

Lot

Answer 10

total material from which sample taken

Question 11

Sample

Answer 11

– a smaller, representative, collection of units from the lot used to determine
something about the lot

Question 12

Sampling

Answer 12

process of selecting representative material to analyze from the lot – can be the largest source of uncertainty.
Sample must be representative

Question 13

Representative Sample

Answer 13

Sampling is about asking how to get an representative sample to analyze

Question 14

Homogeneous

Answer 14

having same composition everywhere
– [Li] in salt brine pool
Construct representative sample
divide into even 10 x 10 cm sections
random select 100 of 20,000 sections
sampling 0.5% of total

Question 15

Heterogeneous

Answer 15

having non uniform composition
– [Li] in salt flats
Construct representative sample
random samples based on %
select 100 of 20,000 based on location
66 from A, 14 from B, 20 from C

Question 16

Judgemental Sampling

Answer 16

– professional/expert judgement based on prior information

– used for screening purposes, cheap and easy

Question 17

Random sampling

Answer 17

– arbitrary collection, same probability any sample unit picked from lot
– space and time non-critical, assumed homogenous samples,
small sample areas

Question 18

Systematic sampling

Answer 18

– grid overlaid on lot and random grid samples picked

– uniform distribution over space and time; best for large sample areas

Question 19

Stratified random sampling

Answer 19

– lot divided into specific zones based on homogenous characteristic
– random sampling then done per zone
– can create composite sample or more accurately measure different spaces

Question 20

Transect sampling

Answer 20

– variation of systematic – line drawn over sample

– sample along regular interval of transect line

Question 21

Sampling standard deviation for many samplings

Answer 21

S=npq^-2
p = probability of grabbing a particle of A
q = probability of grabbing a particle of B

Question 22

Statistics of Sampling

Answer 22

Sampling uncertainty due to random nature
of drawing particles from the mixture.
To minimize sampling error we need to
increase sample size