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ACS Analytical Chemistry
Terms in this set (56)
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
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
use standard solutions spanning a range of conc, measure response
substance similar to analyte (ie deuterated); used to normalize signal by reducing random error
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)
Limit of quantitation (LOQ)
10* std dev
sigma--> sigma* absorbs at
proteins absorb at
~ 280 nm (bc of aromatic R groups)
responds to change in dipole moment
responds to change in polarizability
detects single photon, is highly sensitive
shows movement from ground state to excited state
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
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)
A term is eliminated
no terms eliminated
A and C terms eliminate; VERY efficient
allows separation based on charge
'drag' of analyte because of friction
= 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
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-
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.
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.
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.
The probability distribution of X with parameters n and p. Homogenous mixtures.
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.
a solution whose concentration is accurately known
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
A rough test to justify ejecting an outlying data point from a set