ACS Analytical Chemistry Final

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

confidence interval

(t)(s)/√N

Q test

determine if value can be rejected from a set of data

Qexp: |x-x nearest|/range

accuracy

indicates the closeness of the measurements to the accepted value and is expressed as error

precision

describes reproducibility of measurement. closeness of results obtained in exactly the same way

random (indeterminate) error

causes data to be scattered symmetrically around a mean value. affects precision

gross errors

often large errors which result from human error, outliers results

systematic (determinate) error

causes the mean to differ from the accepted value. Affects accuracy. Have a definite value, an assignable cause, and are often the same magnitude for replicates. leads to bias

sources of systematic error

instrumental, method, personal

instrumental error

malfunctions in equipment, faulty calibrations, leaky burets, varying temperatures

method error

non-ideal chemical or physical behavior of analytical systems, reagent problems

personal errors

carelessness, personal limitations, reading buret

systematic errors on analytical results

constant or proportional

constant error

stay the same as the sample size increases

as sample size increases, constant error decreases

proportional error

increases with sample size

usually from interferences

detection of method errors

independent analysis, analysis of standard samples, blank determinations, variations in sample size

analysis of standard samples

1. analysis with a previously validated reference method

2. analysis by 2 or more independent, reliable measurement methods

3. analysis by a network of co-operating labs that technically competent and thoroughly knowledgable

independent analysis

comparison of results from 2 independent methods

blank determination

a blank contains the reagent and solvent but no analyte

reveal errors due to interference and overestimations

variations in sample size

used to detect constant errors

w/w

w solute/w solution

w/v

weight solute g/volume solution mL

absorbance equation

2-log %T

e cell equation

Ecell=Ecathode-Eanode

henderson hasselbach

pH = pKa + log([A-]/[HA])

ppm

(grams analyte/grams sample)x10^6

Molarity

moles analyte/liter of solution

Volume Percent

(volume solute/volume soution)x100

Volume ppm

(volume solute/volume solution)x10^6

kilo-

10^3

deci-

10^-1

centi-

10^-2

milli-

10^-3

micro-

10^-6

nano-

10^-9

pico-

10^-12

femto-

10^-15

weight percent

(grams analyte/grams sample)x100

ppt

(grams analyte/grams sample)x10^3

ppt simplified

gram analyte/liter solution

ppm simplified

mg analyte/liter solution

ppb simplified

micrograms analyte/liter solution

pptr simplified

nanograms analyte/liter solution

buoyancy correction

m=(m'(1-(air density/weight density)))/(1-(air density/object density))

accuracy

closeness of the mean to the "true value"