test 1 Flashcards
measurement
a trial, replicate (specific)
determination
several trials (1 analyte) (general)
analysis
several analytes [ie blood panel]
technique
many times [with] a particular instrument
method
a way to determine an analyte using a particular technique
procedure
set of instructions that can be modified if needed
protocol
a specific set of instructions
What are the 10 Figures of Merit ?
- Accuracy
- Precision
- Sesitivity
- LOD (Limit of Detection)
- Linear Dynamic Range
- Robust/ Rugged
- Analysis time
- Selectivity
- Cost
- Sample size
sensitivity*
response vs concentration plot
the measure of the ability to establish that such differences are significant
LOD
Limit of Detection- the smallest amount of analyte that can be determined with confidence
-the minimum amount of analyte ( concen. or mass) that is “significantly different from the blank”
linear dynamic range
number of #s of orders of linearity of your calibration
robust/rugged
ability to minimize down-time
selectivity
the ability of the method to distinguish the analyte from the concomitants (forest) (needle in a haystack)
sample size
amount of sample one has to work with
Constituent Concentrations in a Sample (4)
1) major- 1-100%
2) minor- 10ppt-100ppm
3) trace- 100ppm-1ppb
4) ultratrace- = 1 ppb
Overall Sample Size (4)
1) macro- 100mg and up
2) meso/semi micro- 10-100mg
3) micro- 0.1-10mg
4) ultramicro-
replicates
(N) # of trials simulating the same conditions
mean (x-bar) (mu)
x-bar= (Sum of replicates)/ N
median
middle data point in rank order
4 Descriptors of Precision
1- range
2- standard deviation
--> relative standard deviation
3- coefficient of variation (CV)
4- variance (s^2)2 Descriptors of Accuracy
1- absolute error (E)
2- relative error
absolute error*
- descriptor of accuracy
- E = xi - xtrue
- shown with sign dependence
relative error*
- descriptor of accuracy
- %Er ={(| xi - xtrue |)/ xtrue}x 100
Types of Error
1- Systematic
2-Indeterminate
systematic error*
- type of error
- determinant
- can be corrected/avoided/minimized
- can be constant/ variable
constant systematic error** (EX)
ie. balance bias
variable systematic error** (EX)
ie. burret with varying diameter
3 Sources of Error
1- Instrument– any measuring device
2- Method– hardest to correct;
-ie. kinetics of method, degradation of product
3-Personal– its personal!
-ie. colorblindness, shakiness
SRM
Standard Reference Mixture
4 Types of Analysis
1- Qualitative
2-Quantitative
3- Characterization
4- Fundamentals
Qualitative Analysis*
What kinds of things are in your sample…
Quantitative Analysis*
How much of a particular analyte is in your sample…
Analytical Process [Scientific Method]
- Defining the problem
- Selecting the method of analysis: Cost VS Precision
- Handling the sample
- Where to obtain
- How to sample
- # of replicates
- # of dilutions
- Performing the required separations—isolate analyte
a. Interferences – another compound that adds or subtracts from the signal
b. Matrix—all constituents in a sample
- -rocks/ gold example - Performing the measurement= assay (obtaining the purity)
- Data presentation
- Check for anomalies
Methods of Analysis
1) Volumetric
2) Gravimetric
3) Spectroscopic
Volumetric method of analysis*
measure a well-known volume of substance that relates directly to your analyte
Gravimetric method of analysis*
determine the mass of ones analyte or derivative…
Spectroscopic method of analysis*
determine the analyte concentration after measuring the amount of interaction of light with matter
Concentration: Solid Analyte in Soluble Mixture
(gram analyte)/ (gram sample) x 100/1000/1000000... (pph) aka w/w% (ppt) (ppm) (ppb)
Concentration: Solid in Liquid Matrix
1 ppm = 1mg/L
Concentration: Liquid in Liquid
(w/v)% = (gram analyte/1,0mL sample)x 100
Molarity
M= mol/L
Normality
- N= equivalents analyte/ L solution
- N= (# reacting units)/(#moles)(L soln)
Equivalents =
= (#moles)/(#reacting units)
Equivalent weight
Formula weight/ # equivalents
Analytical Molarity
-does not consider the state of the solution
CHA = (#moles analyte)/(L soln)
Species Molarity
-molarity of one component in solution “[ ]”
p- function
p(anything)= -log(anything)
titration
procedure in which a known substance (titrant) is carefully added to a (titrand) analyte until the reaction is complete
titrant
known substance`
titrand
unknown concentration analyte
endpoint
where the titration ceases
equivalence point
equal # moles of analyte and titrant
titration error
the “distance” between the equivalence point and the end point
How do you minimize titration error?
run a blank
2 Titration Styles
1- direct – add titrant to endpoint
2-back– pass equivalence point on purpose, then add second titrant
5 1/2 Elements of a Successful Titration
- Rxn has to be Stoichiometric
- Rxn should be rapid
- No side rxns
3 1/2. no interferences - There must be a sharp change in solution property @ endpoint ie indicator
- You want the rxn to be quantitative
standard solution
a solution in which the concentration is very well known
Primary Standard Requirements:
The primary standard should be…
- pure
- stable to drying
- readily available
- best to have a high formula weight
- soluble
4 Classifications of Volumetric Methods:
1-Acid/Base
2-Redox– oxidizing agent and reducing agent
3-Complexometric– soluble analyte with color
-ie EDTA
4-Precipitation– endpoint is the persistence of a solid
Basic Equipment:
- analytical balance
- Buret
- volumetric flask
- volumetric pipet
- transfer pipet (glass)
- micropipet
tolerance
the allowable error associated with a device
indeterminate error*
accidental…
these errors are determined by making successive measurements (by the same analyst) using the same method
uncertainty
an expression that shows the range of values that are all possible for your determination (tolerance)
propagation of error: 1- addition/subtraction
s = [S(1)^2 + S(2)^2 +S(3)^2 + S(4)^2]^1/2
propagation of error: 2- multiplication/ division
s/y =
propagation of error: exponents
.
what is the difference between an analytical sample and a statistical sample?
analytical: sample= trial(discrete thing)
statistical: sample= the treatment of a group of data turned into sample
population
set of objects to be studied
N~30
