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Achem 315 > Sample Prep/stats > Flashcards

Sample Prep/stats Flashcards

1
Q

What are makes a sample non ideal

A

It’s too complex (many components/analytes)

Poorly or insoluble

Volatile or short lived

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2
Q

What is sampling?

A

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)

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3
Q

What are the steps to sampling and analyzing

A

Lot
Representative bulk sample
Homogenous lab sample
Aliquot
Storage

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4
Q

What is lot in sampling

A

The population/whole

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5
Q

What comes after lot

What does it mean

A

Sampling

Choosing a sample from the lot that is representative of the whole

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6
Q

What comes after representative bulk sample

What does it mean

A

Sample prep to make the homogenous lab sample

Getting the sample ready to analyze through extracting, grinding, etc.

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7
Q

What do you watch out for during sample prep

A

Loss of analyte, addition of interferants, other introduction of bias in our preparation

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8
Q

What is the meaning of bias?

A

A systematic error that shifts the data up or down

Ex. Adding interferents shifts up
Losing analyte shifts down

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9
Q

Why do we need proper storage of samples

A

Due to oxidation, degradation, evaporation, leaching

Proper storage prevents this stuff from

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10
Q

What is the sampling variance equation

What does it tell us

A

Sn=(npq)^1/2

The standard deviation between multiple samples

q= probability of not sampling the analyte

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11
Q

If you want to find % sn of red beads what does you do

A

(Value of Sn x 100) /
(# of samples x prob of red beads)

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12
Q

How do you find value of n needed to reach a specific Sn

Ex. S=1%

A

S=(npq^1/2)

Insert s into

1= sx100/(n)(0.02)

Solve for n

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13
Q

What are the problems that can arise while trying to dissolve something

A

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)

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14
Q

What is a way to dissolve things if they aren’t easily dissolved?

It what is the downside to this

A

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

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15
Q

What is acid dissolution and digestion

A

Material that don’t dissolve in water, we dissolve them in concentrated acid by oxidation or reactions with hydrogen

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16
Q

What is aqua Regia, what does it do

What is piranha, what does it do

A

Aqua regia: 3:1concentrated HCL:HNO3
(Dissolves noble metals like gold and platinum)

Piranha: 3:1concentrated H2SO4:H2O2 (30%)

(Rapidly oxidizes organic material)

17
Q

What are fuming acids

A

Hot, near boiling acids

(Give off corrosive vapour)

18
Q

What is speacial about HCLO4

A

It’s very oxidizing (explosive)

19
Q

What can be used to dissolve silicates and calcium out of bones

A

HF

20
Q

How is acid digestion done

A

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

21
Q

What is melting (fusion)

What is used

A

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

22
Q

What is ashing

A

Combusting or pyrolyzing organic material until it decomposes, usually for atomic measurements

Can heat by thermal of thermal+chemical (acid)

23
Q

What is dervitization

Give an example

A

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

24
Q

What are the types of extractions

A

Liquid extraction
Solid phase extraction
Solid phase micro extraction

25
Q

What is liquid extraction

A

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

26
Q

What are some issues with liquid extraction

A

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)

27
Q

What is solid phase extraction

A

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.

28
Q

What is solid phase micro extraction

A

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

29
Q

What is special about solid phase micro extraction

A

It preconcentrates the analyte when it attaches to the silica

30
Q

When doing sample prep, what are we separating the things based on

A

Separating based on :

Particle size

Mass/ density

Complexation

Physical state change

Chemical state change

Partitioning between phases

31
Q

What are the techniques and errors in

Particle size

A

Filtration
Size exclusion/gels

Errors and if using filter you lose some sample to the filter paper

32
Q

What are the techniques and errors in
Mass/density

A

Can centrifuge: heavier goes lower, lighter goes higher

Errors: may get a clean separation (pellet) or a gradient

33
Q

What are the techniques and errors in
Complexation

A

Binding to edta, ex. Masking ……

Errors: controls reaction/side reactions

34
Q

What are the techniques and errors in

Physical state change

A

Distillation, freezing/concentrating

Error: good separation between the components but loss of sample

35
Q

What are the techniques and errors in

Chemical state change

A

Derivitization

36
Q

What are the techniques and errors in

Partitioning between phases

A

Chromatography
Liquid liquid extraction

Achem 315 (13 decks)

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