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Chapter 0 The Analytical Process
1. Aliquot: portion.
2. Analyte: Substance being analyzed.
3. Composite sample: A representative sample prepared from a heterogeneous
material. If the material consists of distinct regions, the composite is made
of portions of each region, with relative amounts proportional to the size of
each region.
4. Interference: A phenomenon in which the presence of one substance changes
the signal in the analysis of another substance.
5. Masking: Process of adding a chemical substance (a masking agent) to a
sample to prevent one or more components from interfering in a chemical
analysis.
6. Random heterogeneous material: A material in which there are differences
in composition with no pattern of predictability and on a fine scale.
7. Random sample: Bulk sample constructed by taking portions of the entire
lot at random.
8. Sample preparation: Transforming a sample into a state that is suitable
for analysis.
9. Sampling: The process of collecting a representative sample for analysis.
10. Supernatant liquid (supernate): Liquid remaining above the solid after a
precipitation.
Chapter 1 Measurements
1. Abscissa: Horizontal (x) axis of a graph.
2. Ordinate: Vertical (y) axis of a graph.
Chapter 2 Tools of the Trade
1. Acid wash: Procedure in which glassware is soaked in 3~6M HCl for >1 h
(followed by rinsing well with distilled water and soaking in distilled
water) to remove traces of cations adsorbed on the surface of the glass and
to replace them with H+.
2. Ashless filter paper: Specially treated paper that leaves a negligible
residue after ignition. It is used for gravimetric analysis.
3. Buret: A calibrated glass tube, with a stopcock at the bottom, used to
deliver known volumes of liquid.
4. Calibration: Process of measuring the actual physical quantity
corresponding to an indicated quantity on the scale of an instrument.
5. Desiccant: A drying agent.
6. Desiccator: A sealed chamber in which samples can be dried in the presence
of a desiccant or by vacuum pumping or both.
7. Filtrate: Liquid that passes through a filter.
8. Gooch crucible: A short, cup-shaped container with holes at the bottom,
used for filtration and ignition of precipitates.
9. Hygroscopic substance: One that readily picks up water from its surface.
10. Ignition: The heating to high temperature of some gravimetric
precipitates to convert them into a known constant composition that can be
weighed.
11. Meniscus: Curved surface of a liquid.
12. Mother liquor: Solution from which a substance has crystallized.
13. Parallax: Apparent displacement of an object when the observer changes
position. Occurs when the scale of an instrument is viewed from a position
that is not perpendicular to the scale. The apparent reading is not the true
reading.
14. Rubber policeman: A glass rod with a flattened piece of rubber on the
tip. The rubber is used to scrape solid particles from glass surfaces in
gravimetric analysis.
15. Slurry: A suspension of a solid in a solvent.
16. Syringe: A device having a calibrated barrel into which liquid is sucked
by a plunger. The liquid is expelled through a needle by pushing on the
plunger.
17. Tare: (noun) The mass of an empty vessel used to receive a substance to
be weighed. (verb) setting the balance reading to 0 when an empty vessel or
weighing paper is placed on the pan.
18. Tolerance: Manufacturers’ stated uncertainty in the accuracy of a device
such as a buret or volumetric flask.
Chapter 3 Experimental Error
1. Absolute uncertainty: An expression of the margin of uncertainty
associated with a measurement. Absolute uncertainty also could refer to the
difference between a measured value and the “true” value.
2. Accuracy: A measure of how close a measured value is to the “true” value.
3. Characteristic: The part of a logarithm at the left of the decimal point.
4. Mantissa: The part of a logarithm to the right of the decimal point.
5. Precision: A measure of the reproducibility of a measurement.
6. Random error (indeterminate error): A type of error, which can be either
positive or negative and cannot be eliminated, based on the ultimate
limitations on a physical measurement.
7. Relative uncertainty: Uncertainty of a quantity divided by the value of
the quantity. It is usually expressed as a percentage of the measured
quantity.
8. Significant figure: The number of significant digits in a quantity is the
minimum number of digits needed to express the quantity in scientific
notation. In experimental data, the first uncertainty figure is the last
significant figure.
9. Systematic error (determinate error): Error due to procedural or
instrumental factors that cause a measurement to be consistently too large or
too small. The error can, in principle, be discovered and corrected.
Chapter 4 Statistics
1. Blank solution: A solution not intended to contain analyte. It could be
made from all reagents-except unknown-that would be used in an analytical
procedure. Analyte signal measured with a blank solution could be due to
impurities in the reagents or, possibly, interference.
2. Calibration curve: A graph showing the value of some property versus
concentration of analyte. When the corresponding property of an unknown is
measured, its concentration can be determined from the graph.
3. Confidence interval: Range of values within which there is a specified
probability that the true value lies.
4. Degree of freedom: In statistics, the degree of freedom is the number of
independent observations on which a result is based.
5. Dynamic range: Range of analyte concentration over which a change in
concentration gives a change in detector response.
6. F test: Statistical test used to determine whether two variances are
different.
7. Linear range: Concentration range over which the change in detector
response is proportional to the change in analyte concentration.
8. Linear response: The case in which the analytical signal is directly
proportional to the concentration of the analyte.
9. Normal error curve: A Gaussian distribution whose area is unity.
10. Null hypothesis: In statistics, the supposition that two quantities do
not differ from each other or that two methods do not give different results.
11. Q test: Statistical test used to decide whether to discard a datum that
appears discrepant.
12. Standard deviation: A statistic measuring how closely data are clustered
about the mean value.
13. Standard solution: A solution whose composition is known by virtue of the
way that it was made from a reagent of known purity or by virtue of its
reaction with a known quantity of a standard reagent.
14. Student’s t: A statistical tool used to express confidence intervals and
yo compare results from different experiments.
15. T test: Statistical test used to decide whether the results of two
experiments are within experimental uncertainty of each other. The
uncertainty must be specified to within a certain probability.
16. Variance: The square of the standard deviation.
Chapter 5 Quality Assurance and Calibration Methods
1. Assessment: In quality assurance, the process of (1) collecting data to
show that analytical procedures are operating within specified limits and (2)
verifying that final results meet use objectives.
2. Calibration check: In a series of analytical measurements, a calibration
check is an analysis of a solution formulated by the analyst to contain a
known concentration of analyte. It is the analyst’s own check that
procedures and instruments are functioning correctly.
3. Chain of custody: Trail followed by a sample from the time it is collected
to the time it is analyzed and, possibly, archived.
4. Coefficient of variation: A.k.a. relative standard deviation.
5. Control chart: A graph in which periodic observations of a process are
recorded to determine whether the process is within specified control limits.
6. Correlation coefficient: The square of the correlation coefficient R2, is
a measure of goodness of fit of data points to a straight line. The closer R2
is t o1, the better the fit.
7. Detection limit (lower limit of detection): The smallest quantity of
analyte that is “significantly different” from a blank. The detection limit
is often taken as the mean signal for blanks plus 3 times the standard
deviation if a low-concentration sample. If you have a recorder trace with a
signal plus adjacent baseline noise, the detection limit is sometimes taken
as twice the peak-to-peak noise level or 10 times the root-mean-square noise
level (which is 1/5 of the peak-to-peak noise level).
8. Dilution factor: Factor used to multiply the initial concentration of
reagent to find the diluted concentration.
9. False negative: A conclusion that the concentration of analyte is below a
certain limit when, in fact, the concentration is above the limit.
10. False positive: A conclusion that the concentration of analyte exceeds a
certain limit when, in fact, the concentration is below the limit.
11. Field blank: Ac blank sample exposed to the environment at the sample
collection site and transported in the same manner as other samples between
the labs and the field.
12. Instrument precision (injection precision): Reproducibility observed when
the
same quantity of one sample is repeatedly introduced into an instrument.
13. Interlaboratory precision: The reproducibility observed when aliquots of
the same sample are analyzed by different people in different labs.
14. Internal standard: A known quantity of a compound other than analyte
added to a solution containing an unknown quantity of analyte. The
concentration of analyte is then measured relative to that of the internal
standard.
15. Intra-assay precision: Precision observed when analyzing aliquots of a
homogeneous material several times by one person on one day with the same
equipment.
16. Linearity: A measure of how well data in a graph follow a straight line.
17. Lower limit of quantitation (quantitation limit): Smallest amount of
analyte that can be measured with reasonable accuracy. Usually taken as 10
times the standard deviation of a low-concentration sample.
18. Matrix: The medium containing analyte. For many analyses, it is important
that standards be prepared in the same matrix as the unknown.
19. Matrix effect: A change in analytical signal caused by anything in the
sample other than analyte.
20. Method blank: A sample without deliberately added analyte. The method
blank is taken through all steps of a chemical analysis, including sample
preparation.
21. Method validation: Process of proving that an analytical method is
acceptable for its intended purpose.
22. Noise: Signals originating from sources other than those intended to be
measured.
23. Performance test sample (quality control sample; blind sample): In a
series of analytical measurements, a performance test sample is inserted to
see if the procedure gives correct results when the analyst does not know the
right answer. The performance test sample is formulated by someone other than
the analyst to contain a known concentration of analyte.
24. Quality assurance: quantitative indications that demonstrate 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.
25. Range (spread): Difference between the highest and the lowest values in a
set of data. With respect to an analytical method, range is the concentration
interval over which linearity, accuracy, and precision are all acceptable.
26. Raw data: Individual values of a measured quantity, such as peak areas
from a chromatogram or volumes from a buret.
27. Reagent blank: A solution prepared from all of the reagents, but no
analyte. The blank measures the response of the analytical method to
impurities in the reagents or any other effects caused by any component
other than the analyte.
28. Reporting limit: Concentration below which regulations dictate that an
analyte is reported as “not detected”. The reporting limit is typically set
5 to 10 times higher than the detection limit.
29. Response factor (F): Relative response of a detector to analyte (X) and
internal standard (S):
30. Results: What we ultimately report after applying statistics to treated
data.
31. Robustness: Ability of an analytical method to be unaffected by small,
deliberate changes in operating parameters.
32. Ruggedness (intermediate precision): Precision observed when an assay is
performed by different people on different instruments on different days in
the same lab.
33. Selectivity (specificity): Capability of an analytical method to
distinguish analyte from other species in the sample.
34. Sensitivity: Response of an instrument or method to a given amount of
analyte.
35. Specifications: In quality assurance, written statements describing how
good analytical results need to be and what precautions are required in an
analytical method.
36. Spike (fortification): Addition of a known compound (usually at a known
concentration) to an unknown.
37. Standard addition: A technique in which an analytical signal due to an
unknown is first measured. Then a known quantity of analyte is added, and the
increase in signal is recorded. From the response, it is possible to
calculate what quantity of analyte was in the unknown.
38. Standard operating procedure: A written procedure that must be rigorously
followed to ensure the quality of a chemical analysis.
39. Treated data: Concentrations or amounts of analyte found from raw data
with a calibration curve or some other calibration method.
40. Use objectives: In quality assurance, use objectives are a written
statement of how results will be used. Use objectives are required before
specifications can be written for the method.