Sample Prep/stats Flashcards
What are makes a sample non ideal
It’s too complex (many components/analytes)
Poorly or insoluble
Volatile or short lived
What is sampling?
When you can’t measure the whole thing so you take a sample
due to it being too large to analyze all
The thing may represent a larger population that we want to know about
The thing may be part of a continuous object (river, atmosphere)
What are the steps to sampling and analyzing
Lot
Representative bulk sample
Homogenous lab sample
Aliquot
Storage
What is lot in sampling
The population/whole
What comes after lot
What does it mean
Sampling
Choosing a sample from the lot that is representative of the whole
What comes after representative bulk sample
What does it mean
Sample prep to make the homogenous lab sample
Getting the sample ready to analyze through extracting, grinding, etc.
What do you watch out for during sample prep
Loss of analyte, addition of interferants, other introduction of bias in our preparation
What is the meaning of bias?
A systematic error that shifts the data up or down
Ex. Adding interferents shifts up
Losing analyte shifts down
Why do we need proper storage of samples
Due to oxidation, degradation, evaporation, leaching
Proper storage prevents this stuff from
What is the sampling variance equation
What does it tell us
Sn=(npq)^1/2
The standard deviation between multiple samples
q= probability of not sampling the analyte
If you want to find % sn of red beads what does you do
(Value of Sn x 100) /
(# of samples x prob of red beads)
How do you find value of n needed to reach a specific Sn
Ex. S=1%
S=(npq^1/2)
Insert s into
1= sx100/(n)(0.02)
Solve for n
What are the problems that can arise while trying to dissolve something
The solvent to dissolve the sample doesn’t work with the analysis
The sample is only partially soluble
Sample is a big lump
The value we want to measure isn’t available with the sample in its current form (want to free the analyte if it’s bound to something else)
What is a way to dissolve things if they aren’t easily dissolved?
It what is the downside to this
Can use grinding to dissolve
Using mortar and pestle, ball mills, etc.
But it can contaminate due to grinding tool losing material from abrasion. The composition can change by loss or gain of water or atmospheric reactions
What is acid dissolution and digestion
Material that don’t dissolve in water, we dissolve them in concentrated acid by oxidation or reactions with hydrogen
What is aqua Regia, what does it do
What is piranha, what does it do
Aqua regia: 3:1concentrated HCL:HNO3
(Dissolves noble metals like gold and platinum)
Piranha: 3:1concentrated H2SO4:H2O2 (30%)
(Rapidly oxidizes organic material)
What are fuming acids
Hot, near boiling acids
(Give off corrosive vapour)
What is speacial about HCLO4
It’s very oxidizing (explosive)
What can be used to dissolve silicates and calcium out of bones
HF
How is acid digestion done
Put acid in closed container to increase pressure
Because of increased pressure, when heated in microwave the acid is heated beyond what is normal for it.
Essentially acid dissolution + heat
What is melting (fusion)
What is used
First dissolving inorganic compunds in hot molten salt(flux), then Dissolving that mix into acid
Li2B4O7 or liBO2 : don’t use too much because the introduce impurities
What is ashing
Combusting or pyrolyzing organic material until it decomposes, usually for atomic measurements
Can heat by thermal of thermal+chemical (acid)
What is dervitization
Give an example
Chemically modifying an analyte to make it easier to detect dissolves or separate
Reacting carbonyls with 2,4-dinitrophenylhydrazine gives them colour and make them easier to detect in hplc
What are the types of extractions
Liquid extraction
Solid phase extraction
Solid phase micro extraction
What is liquid extraction
Separation based on the relative solubility of the compounds (based on polarity and complex formation/chelation)
Dissolve analyte in desired solvent while leaving rest of the impurities/ stuff behind
What are some issues with liquid extraction
There’s never 100 percent separation, always some crossover
The solvents can mix with the analyte (some water in ether layer)
Emulsions can form
Rinsing and careful decanting is needed (this dilute the sample, may need to reconcentrate)
What is solid phase extraction
Add the analyte with red and blue parts
Red is not strongly attracted to the solid (silica) so it elutes quickly
The blue is retained in the solid
Either rinse out blue analyte to get its or keep in the tube.
What is solid phase micro extraction
Small needle which shoots out silica that the analyte binds to.
In sampling the silica shoots into the analyte and pick it up
In desorption the analyte coated silica takes in the concentrated sample by shooting back into the instrument
What is special about solid phase micro extraction
It preconcentrates the analyte when it attaches to the silica
When doing sample prep, what are we separating the things based on
Separating based on :
Particle size
Mass/ density
Complexation
Physical state change
Chemical state change
Partitioning between phases
What are the techniques and errors in
Particle size
Filtration
Size exclusion/gels
Errors and if using filter you lose some sample to the filter paper
What are the techniques and errors in
Mass/density
Can centrifuge: heavier goes lower, lighter goes higher
Errors: may get a clean separation (pellet) or a gradient
What are the techniques and errors in
Complexation
Binding to edta, ex. Masking ……
Errors: controls reaction/side reactions
What are the techniques and errors in
Physical state change
Distillation, freezing/concentrating
Error: good separation between the components but loss of sample
What are the techniques and errors in
Chemical state change
Derivitization
What are the techniques and errors in
Partitioning between phases
Chromatography
Liquid liquid extraction
