analytical chemistry acs review ):

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])