ACS Analytical Chemistry

standard deviation (s)

the square root of the variance

% relative standard deviation (%RSD)

Standard deviation divided by mean times 100

Grubbs test (Gcalc)

|Questionable value - mean/ std dev|

If that is larger than the Gtable value then the value is thrown out. Locate Gtable value based on number of values in data set.

Used to define outliers

z score

(x- xavg)/s

F Test

used to compare precision

(s2)^2/(s1)^2 (should always be >1)

Use n-1 to find on table.

Fcalc> Ftable -- There is some noise or error

External standard

use standard solutions spanning a range of conc, measure response

Internal standard

substance similar to analyte (ie deuterated); used to normalize signal by reducing random error

Standard Addition

ideal for analyzing sample in a complex matrix; add known standard to constant amount of sample; x-int =[sample]

Box car average

minimizes distance between data points and best fit line/ minimizes standard deviation

Limit of detection (LOD)

3*std dev

Limit of quantitation (LOQ)

10* std dev

sigma--> sigma* absorbs at

~100nm

proteins absorb at

~ 280 nm (bc of aromatic R groups)

d-->d absorb

visible light

(transition metals)

IR spectroscopy

responds to change in dipole moment

Raman

responds to change in polarizability

photomultiplier tube

detects single photon, is highly sensitive

Jablonski Diagram

shows movement from ground state to excited state

Fluorescence

occurs when LUMO--> HOMO releases energy;

generally occurs in rigid molecules

X ray fluorescence

Useful when sample cannot be put into sol'n

capacity factor (k')

tells efficiency of a separation

k'= time in SP /time for MP to elute= mol SP/mol MP

Van Deemter Equation

A (in van deemter Eq)

accounts for path

A=2(lambda)dp

decrease particle diameter, increase speed of separation

B (in van deemter Eq)

accounts for diffusion

B= 2(gamma) Dm

affected by temp, [ ], solubility, density, viscosity,

gamma-- channel uniformity

C (in van deemter Eq)

accounts for equilibration

Cs = f'(k') * (df^2/Ds)

Cm = f(k') * (r^2/Dm)

Gas chromatography

A term is eliminated

Liquid chromatography

no terms eliminated

capillary electrophoresis

A and C terms eliminate; VERY efficient

electrophoretic mobility

allows separation based on charge

electroosmotic flow

'drag' of analyte because of friction

apparent mobility

= electrophoretic mobility + electroosmotic flow

thermal conductivity detector

non destructive, but not sensitive

electron capture detector

e- emitted from Ni, analyter accepts e-, decreased current

works well for halogens, organometallics, and nitriles

very sensitive

Flame ionization detector

best for organic cmpds

Mass Spec instrument set up

reduction potential > 0

desire for e-

reduction potential < 0

desire to lose e-

Nerst Equation

Delta G= -nFEcell

nonspontaneous electrochemical reaction

Ecell < 0

spontaneous electrochemical reaction

Ecell > 0

Students t test

compares two means from two different samples

compare t to alpha

determinate error (systematic error)

Sampling, method, measurement or personal errors. Can be traced to a source. Affect accuracy.

indeterminate error (random error)

Affect precision. Can be traced to sample collection, manipulation and or measurement.

uncertainty

The range of possible values for a measurement. can be added or subtracted via squaring each standard deviation, performing the necessary operations (+,-) and taking the square root.

relative uncertainty

Uncertainty of a quantity divided by the value of the quantity. It is usually expressed as a percentage of the measured quantity.

multiplying or dividing uncertainty

use relative uncertainty. Square, add, then square root. Absolute uncertainty can be obtained by multiplying by R.

Binomial Distribution

The probability distribution of X with parameters n and p. Homogenous mixtures.

confidence interval

a range of values so defined that there is a specified probability that the value of a parameter lies within it. Xi = µ ± zσ : Where z is from a table.

degrees of freedom

The number of individual scores that can vary without changing the sample mean. Statistically written as 'N-1' where N represents the number of subjects.

Normal Phase HPLC

polar stationary phase, non-polar mobile phase. Therefore non-polar will come out first, polar last.

Reverse phase HPLC (High Performance Liquid Chromatography)

Non-polar stationary phase, polar mobile phase. This polar comes out first.

Gradient elution

Faster separation

standard solution

a solution whose concentration is accurately known

matrix effect

is a change in the analytical signal caused by anything in the sample other than analyte

For Gaussian distribution of points...

2/3 of points lie in +/- 1 std deviation

Q test

A rough test to justify ejecting an outlying data point from a set