Test #2 – Quantitative Analysis Flashcard

significant figures
the minimum number of digits needed to write a given value in scientific notation without any loss of accuracy
interpolation
estimate all readings to the nearest tenth of the distance between scale divisions
significant figures in arithmetic
in a series of calculations, carry the extra digits through to the final result then round.
significant figures in rounding
if the digit is to be removed and is less than 5, the preceding digit stays the same
if greater than 5, the preceding digit increases by 1
if equal to 5, preceding digit remains the same or increases by 1, whichever gives an even digit
significant figures and addition and subtraction
round according to the number with the most uncertainty, that is, the answer is limited by the least certain number
significant figures and multiplication and division
the answer is limited to the number of digits contained in the number with the fewest significant figures
significant figures and logarithms and antilogarithms
the number of digits in the mantissa of (log x) is the number of significant figures in x.
characteristic
the part of a logarithm to the left of the decimal point
mantissa
the part of a logarithm to the right of the decimal point
significant figures in graphs
depends on the purpose of the graph.
if to display qualitative behavior of data, then sig figs are irrelevant.
if to display precise values, then several sig figs
systematic error
determinate error
occurs in the same direction each time (high or low), often resulting from poor technique
how to detect systematic error
analyze samples of known composition, ‘blank’ samples containing none of the sought analyte; use different analytical methods to measure same quantity; Round Robin experiment
Round Robin experiment
assign different people/labs to analyze identical samples
random error
indeterminate error
measurement has an equal probability of being high or low; obeys laws of statistics
accuracy
agreement of a particular value with the “true” value.
precision
degree of agreement among several elements of the same quantity
absolute uncertainty
expression of the margin of uncertainty associated with a measurement
relative uncertainty
compares the size of the absolute uncertainty with the size of its associated measurement
percent relative uncertainty
100 * relative uncertainty
propagation of uncertainty from random error
addition and subtraction
if A=B+-C+-D
Ua=(Ub^2+Uc^2+Ud^2)^1/2
abs uncertainty used
propagation of uncertainty from random error
multiplication and division
A=B*/C*/D
%RUa=[(%RUb)^2+(%RUc)^2+(%RUd)^2]^1/2
percent relative uncertainty used
propagation of uncertainty
mixed operations
same manner as the calculations are performed
real rule of significant figures
THe first uncertain figure is the last significant figure
propagation of uncertainty
exponents
%RUy=a(%RUx)
propagation of uncertainty
logarithms
Uy=(1/ln10)*RUx
propagation of uncertainty
natural log
Uy=RUx
propagation of uncertainty
power of 10
RUy=(ln10)Ux
propagation of uncertainty
base e
RUy=Ux
uncertainty in molecular masses
Use rule for addition and subtraction, then multiply by n moles per identical atom
Gaussian distribution
Theoretical bell-shaped distribution of measurements when all error is random. The center of the curve is the mean, and the width is characterized by the standard deviation.
mean

average

 

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standard deviation

measure of how closely the data are clustered to the mean.

 

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degrees of freedom
the number of independent measurements
variance
standard deviation squared
relative standard deviation
100 * std. dev./ mean
significant figures in mean and standard deviation
where uncertainty begins according to std. dev., that’s where significant figures are.
formula for Gaussian curve
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Z
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confidence interval
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Student’s t
statistical tool used to express confidence intervals and to compare results from different experiments.
Student’s t test
used to compare one set of data with another to decide whether or not they are “the same”
null hypothesis
the two sets of data are the same
alternate hypothesis
the two sets of data are different
when to use Student’s t test
comparing a measured result with a known value, replicate measurements, individual differences
t calc equation known value
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t calc equation replicate measurements if std. devs. equal
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s pooled replicate measurements
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t calc equation replicate measurements if std. devs. inequal
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F test
compares standard deviations
F calc
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Grubbs test
determines whether one measurement can be thrown away — whether it is an outlier or not
G calc
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Real rule for bad data
Dropped sample? Pretty obvious
Be hesitant if not certain
Grubbs test is not very reliable
Calibration curve

a graph showing the value of some property versus concentration of analyte. When the same property of an unknown is measured, its concentration can be determined from the graph.

 

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method of least squares
process of fitting a mathematical function to a set of measured points by minimizing the sum of the squares of the distances from the points to the curve.
standard solutions
a solution whose composition is known by virtue of the way it was made from a reagent of known purity or by virtue of its reaction with a known quantity of standard reagent
blank solution
a solution that does not contain analyte; used to correct for interferences
linear range
the analyte concentration range over which response is proportional to concentration
dynamic range
the analyte concentration range over which there is a measurable response to analyte.
quality assurance
Quantitative indications that indicate whether data requirements have been met.

Also refers to the broader process that includes quality control, quality assessment, and documentation of procedures and results designed to ensure adequate data quality.

Use objective
states the purpose for which results will be used
specifications
describes how good analytical results need to be and what precautions are required in an analytical method.
false positive
a conclusion that the concentration of analyte exceeds a certain limit when, in fact, the concentration is below the limit
false negative
a conclusion that the concentration of analyte is below a certain limit when, in fact, the concentration is above the liimit.
selectivity
being able to distinguish analyte from other species in the the sample
sensitivity
the capability of responding reliably and measurably to changes in analyte concentration.

Slope of the calibration curve

method blank
a sample containing all components except analyte and is taken through all steps of the analytical process.

Response is subtracted from sample’s response.

reagent blank
a solution prepared from all of the reagents, but no analyte; for measuring response of analytical method to impurities in reagents and other effects caused by anything but the analyte
field blank
a blank sample exposed to the environment at the sample collection site and transported in the same manner as other samples between the lab and the field.
matrix
everything in the sample other than analyte

Also, the virtual reality which the machines have set us in while they harvest our bodies for energy. Ignore that it would be incredibly inefficient.

spike
addition of a known compound (with known concentration) to an unknown
spike recovery
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calibration check
the analysis of a solution formulated by the analyst to contain a known concentration of analyte

Ensures that procedures and instruments are functioning correctly.

performance test samples
inserted in a series of measurements to see if a procedures gives correct results when the analyst does not know the right answer
standard operating procedures
a written procedure that must be rigorously follow to ensure the quality of a chemical analysis
control chart
a visual representation of a confidence interval for a Gaussian distribution
assessment
the process of collecting data to show that analytical procedures operating within specified limits and verifying that final results meet use objectives
method validation
the process of proving that an analytical process is acceptable for its intended purpose
specificity
the ability of an analytical method to distinguish the analyte from everything else that might be in the sample
linearity
measures how well a calibration curve follows a straight line
square of the correlation coefficient
measure of goodness of fit of data points to a straight line.

Closer to 1 = better

how to demonstrate accuracy
Analyze a standard reference material
compare results of different methods
spike a blank sample with analyte
standard additions
reproducibility of results
precision

(alternate definition)

range
concentration interval over which linearity, accuracy, and precision are all acceptable
detection limit
the smallest quantity of analyte that is “significantly different” from the blank.

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procedure for detection limit determination
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quantitation limit
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reporting limit
the concentration below which regulatory rules say that a given analyte is reported as “not detected”
robustness
the ability of an analytical method to be unaffected by small, deliberate changes in operating parameters
standard addition
known quantities of analyte are added to the unknown and the responses are recorded. This keeps any matrix effect constant.
matrix effect
a change in the analytical signal caused by anything in the sample other than the analyte
standard addition equations
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standard addition with constant total volume
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standard addition with varying total volume
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internal standard
a known amount of a compound, different from analyte, that is added to the unknown. Signal from the analyte is compared with signal from the internal standard to find out how much analyte is present.
response factor, F
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