Chapter 6: Sampling, Standardization, and Calibration Flashcards
are traditionally classified as gravimetric methods, volumetric methods, or instrumental methods
quantitative methods
an analysis used for samples whose masses are greater than 0.1 g
macro analysis
is performed on samples in the range of
0.01 to 0.1 g
semi-micro analysis
is performed on samples in the range of
10^-4 to 10^-2 g
micro analysis
is performed on samples in less than 10^-4 g
ultramicro analysis
TRUE or FALSE
Techniques for handling very small samples are quite different from those for treating macro samples.
TRUE
species present in the range of 0.01 to 1% are usually termed
minor constituents
species present in the
range of 100 ppm (0.01%) and 1 ppb are called
trace constituents
Components present in amounts lower than 1 ppb are usually considered to be
ultratrace constituents
The analysis of real samples is complicated by the presence of the
sample matrix
can contain species with chemical properties similar to the analyte. can react with the same reagents as the analyte, or they can cause an instrument response that is not easily distinguished from the analyte.
Matrix
If the interferences are caused by
extraneous species in the matrix, they are often called
matrix effects
The process of acquiring a
representative fraction is termed
sampling
is often the most difficult
aspect of an analysis.
sampling
TRUE or FALSE
The composition of the gross
sample and the laboratory
sample must closely resemble
the average composition of
the total mass of material to be
analyzed
TRUE
Steps in obtaining a lab sample
identify the population
collect a gross sample
reduce the gross sample to a laboratory sample
representative portion of a whole analytical sample, which with further treatment, becomes the laboratory sample
gross sample
The items chosen for analysis are often called
sampling units or sampling increments
chemists usually call
the collection of sampling units or increments the
gross sample
gross sample is usually reduced in size and
homogenized to create the
laboratory sample
Statistically, the goals of sampling process are
obtain a mean analyte concentration for an unbiased estimate of population mean
obtain a variance in the measured analyte concentration for an unbiased estimate of the population variance
can reveal whether the between
samples variation (sampling variance plus measurement variance) is significantly
greater than the within samples variation (measurement variance).
analysis of variance
TRUE or FALSE
Errors due to invalid sampling
are unique in the sense that they are not controllable by the use of blanks and
standards or by closer control of experimental variables. For this reason, sampling errors are usually treated separately from the other uncertainties associated with an analysis
TRUE
is a miniature replica of the entire mass of material to be analyzed. It should correspond to the bulk material in chemical composition and in particle-size distribution if the sample is composed of particles.
gross sample
gross sample is acquired by
- uncertainty that can be tolerated
- degree of heterogeneity of the whole
- level of particle size, which heterogeneity begins
is a state intermediate between a suspension and a solution.
colloid
intermediate between heterogeneity that develops in particles that may have dimensions on the order of a centimeter or more and maybe several in grams are called
colloidal materials and solidified metals
the constant Ks is called the
Ingamells sampling constant
is a container that can be opened
and filled at any desired location in the solution.
sample thief
TRUE or FALSE
With large volumes of solutions, mixing may be impossible. It is then best to sample several portions of the container with a “sample thief,”
TRUE
What is used to collect vapor samples
gas-tight syringe or stainless steel canister
TRUE or FALSE
The laboratory sample should
have the same number of
particles as the gross sample.
TRUE
samples of metals are obtianed by
sawing
milling
drilling
TRUE or FALSE
With some materials, a representative sample can be obtained by sawing across the piece at
random intervals and collecting the “sawdust” as the sample.
TRUE
the steps in sampling a particulate solid includes
crushing
grinding
seiving
mixing
dividing the sample to reduce its mass
can lead to higher throughput (more
analyses per unit time), higher
reliability, and lower costs than
manual sample handling.
automated sample handling
two different methods for automated sample handling
batch or discrete approach
continuous flow approach
A method where Automated instruments that process samples in a discrete manner often mimic the operations that would be performed manually.
Discrete methods
In continuous flow methods, the sample is inserted into a flowing stream where a
number of operations can be performed prior to transporting it to a flow-through
detector. Hence, these systems behave as automated analyzers in that they can
perform not only sample-processing operations but also the final measurement step.
continuous flow methods
discrete methods do
dilute
filter
partition
grind
centrifuge
homogenize
extract
treat samples with reagent
continuous flow method do
reagent addition
dilution
incubation
mixing
dialysis
extraction
2 different types of continuous flow systems
segmented-flow analyzers
flow injection analyzers
divides the sample into discrete segments separated by gas bubbles
segmented-flow analyzer
is a more recent development, samples are
injected from a sample loop into a flowing stream containing one or more reagents
flow injection analysis
is a band-spreading
or mixing phenomenon that
results from the coupling of fluid
flow with molecular diffusion.
dispersion
is mass transport due to a
concentration gradient.
diffusion
the sample and reagent are both injected into carrier streams and merged
at a tee mixer.
merging zones flow injection analysis
sample dispersion is controlled
by the sample size, the flow rate, and the length and diameter of the tubing. It is also
possible to stop the flow when the sample reaches the detector to allow concentrationtime profiles to be measured for kinetic methods
flow injection analysis/ merging zone FIA
determines the relationship between the analytical response and the analyte concentration
calibration
the relationship of analytical response and the analyte concentration (calibration) is determined by
chemical standards
Constituents of a sample other than
the analyte are called
concomitants
Concomitants that interfere
with the determination of an
analyte may be referred to as
interferences or interferents
needs to indicate whether the threshold has been exceeded
comparator
Some analytical procedures involve comparing a property of the analyte (or the product of a reaction with the analyte) with standards such that the property being tested matches or nearly matches that of the standard are called as
null comparison or isomation methods
are among the most accurate of all analytical procedures, the analyte reacts with a standardized reagent (the titrant) in a known stoichiometric manner.
titration
a type of calibration process in which a series of standard solutions is prepared separately from the sample, The standards are used to establish the instrument calibration function, which is obtained from analysis of the instrumatrment response as a function of the known analyte concentration.
external standard calibration
A plot of instrument response versus
known analyte concentrations is used
to produce a
calibration curve or working curve
provides the means for objectively determining such a line and also for specifying the uncertainties associated with its subsequent use
regression analysis
Least squares method two assumptions
linear relationship between the measured response y (absorbance in Figure 6-10) and the
standard analyte concentration x
any deviation of the individual points from the straight line results from error in the individual measurements
The vertical deviation of each point from
the straight line is called a
residual
simple least-squares analysis may
not be appropriate when the uncertainties in the y values vary significantly with x. In
that instance, it may be necessary to apply different weighting factors to the points
and perform a
weighted least square analysis
is a rough measure of
the magnitude of a typical deviation
from the regression line.
SD abour regression/ standard error of the estimate/ standard error
measures the fraction of the observed variation in y that is explained by the linear relationship and
coefficient of determination R^2
The process of relating multiple
instrument responses to an analyte or a mixture of analytes is known as
multivariate calibration
The least-squares procedure just described is an example of a
univariate calibration
The use of multivariate statistical methods for
quantitative analysis is part of the subdiscipline of chemistry called
chemometrics
involves adding the interfering species to all the samples, standards, and blanks so that the interference effect becomes independent of the
original concentration of the interfering species in the sample
saturation method
is a species, not itself an interfering species, added to samples, standards, and blanks in sufficient amounts to make the analytical
response independent of the concentration of the interfering species
matrix modifier
is added that reacts selectively with the interfering species to form a complex that does not interfere
masking agent
can sometimes be used if the interfering species produces no significant effect below a certain concentration level.
dilution method
attempts to duplicate the sample matrix by adding
the major matrix constituents to the standard and blank solutions
matrix-matching method
a type of calibration method in which a known amount of a reference species is added
to all the samples, standards, and blanks
internal standard method
We use the _______________ when it is difficult or impossible to duplicate the sample matrix. a known amount of a standard solution of analyte is
added to one portion of the sample
method of standard additions
additions of known amounts of
standard analyte solution are made to several portions of the sample, and a multiple additions calibration curve is obtained.
multiple additions method
is a general term that applies to many fields including analytical
chemistry. It is a numerical expression representing the
performance or efficiency of a given device, material, method,
or procedure.
figures of merit
Analytical procedures are characterized by a number of figures of merit
accuracy
precision
sensitivity
detection limit
dynamic range
the change in the measured quantity per unit change in analyte concentration. slope of the calibration curve
calibration sensitivity
Scatter in the response is also called as
noise
is the smallest concentration that can be reported with a certain level of confidence
detection limit
TRUE or FALSE
A k value of 2 corresponds to a confidence level of 92.1%, while a k value of 3 corresponds to a 98.3% confidence level
TRUE
of an analytical method most often refers to the concentration range over which the analyte can be determined using a linear calibration
curve
linear dynamic range
is a sequentialplot of some characteristic that is a
criterion of quality.
control chart
if the value is within the upper control limit and lower control limit, the balance is said to be in
statistical control
determines the suitability of an analysis for providing the sought-for information and can apply to samples, to meth odologies, and to data
validation
is the final step before release of the results
data validation
a known amount of
a standard solution of analyte is
added to one portion of the sample
method of standard additions/ standard addition method
This standard
additions method assumes a linear
response
multiple additions method
is a rough measure of the magnitude of a typical deviation
from the regression line
standard deviation about
regression, also called the standard
error of the estimate or just the
standard error
is identical to the sample but without the analyte.
ideal blank
Most often a real blank is either a ___________, containing the same solvent in which the sample is dissolved
solvent blank
containing the solvent plus all the reagents used in sample preparation.
reagent blank
contains the solvent or the solvent plus all the reagents used to prepare the samples.
blank
is the ratio of the calibration curve slope to the standard deviation of the analytical signal at a given analyte concentration.
analytical sensitivity
