an introuduction to the basic terms and concepts of analytical chem

1. Basic Terms/Concept in
Analytical Chemistry
Course Instructor: Dr. Sajjad Ullah

2. Definitions of Basic Terms in Analytical Chemistry
Analyte: Constituent of the sample which is to be studied by quantitative measurements or identified qualitatively.
Or the chemical species to be identified or quantitated. Can be a pure substance or one constituent in a multi-component
sample.
Sample: A portion of material selected from a larger quantity of material.
Background:
• That proportion of a measurement which arises from sources other than the analyte itself. Individual contributions from
instrumental sources, added reagents and the matrix can, if desired, be evaluated separately.
• The detector signal for a physical measurement, concentration, spectrum, or chromatogram when no test portion is
present. May also refer to the normal or unperturbed concentrations in biological or environmental samples
Concentration: The amount of a substance present in a given mass or volume of another substance (w/w, w/v, v/v)
Matrix: The remainder of the sample of which the analyte forms a part. (sample = Analyte + Matrix)
Contaminant: A substance, which can include the analyte itself, that is introduced unintentionally into a
sample or test portion during collection, processing, or measurement.

3. OR
A standard that contains no analyte, i.e., a concentration of 0.0. The composition, solvent, electrolyte, etc,
should otherwise match the sample test portion. Variations include method, equipment, and instrument blanks
for blanks that go through all or only part of the sample processing procedures.
Calibration curve: A plot of signal versus analyte amount or concentration. Used to calibrate a measurement over
an extended range. Good practice is to measure five to ten standards that are equally spaced through the
measurement range
Calibration:
• To measure the response of an instrument by first measuring the response from a standard (Series of
standard for calibration curve)
• The process of measuring a known quantity to determine the relationship between the measurement signal and the
analyte amount or concentration.

4. Accuracy: The closeness of an experimental measurement or result to the true or accepted value (error/relative error)
Definitions of Basic Terms in Analytical Chemistry....continued
Precision (variability):
• The closeness of replicate experimental measurement with each other
• Precision describes the reproducibility of a result (SD, RSD)
(neither precise nor accurate) (accurate but not precise) (accurate and precise) (precise but not accurate)

5. Interference : An effect which alters or obscures the behavior of an analyte in an analytical procedure ( Sources:
contaminants, reagents, instrumentation used for the measurements)
Standards: Materials containing a known concentration of a substance. They provide a reference to determine unknown
concentrations or to calibrate analytical instruments
Primary Standard : A substance whose purity and stability are particularly well-established and with which other standards
may be compared. It is a pure substance which reacts in a quantitative and known stoichiometric manner with the analyte or
a reagent.
Primary standard is a reagent that is extremely pure, stable, has no waters of hydration, and has a high molecular weight
Criteria:
1. High Purity (testable easily)
2. High Stability in condition it is stored (non-hygroscopic, non-volatile, not deliquescent, unreactive towards atmosphere)
3. Larger molecular/equvivalent weight (to decrease relative error in weighing)
4. Cost-effectiveness

6. Primary Standards
Some Examples:
Sodium carbonate (Na2CO3)
Potassium hydrogen phthalate (KHP):
C8H5KO4, mol wt. = 204.23 g/mol,
Potassium hydrogen iodate: KH(IO3)2, mol wt. = 389.92 g/mol
sodium tetraborate Na2B4O7,
Secondary Standards: A secondary standard is a standard that is prepared in the laboratory for a specific analysis. It is
usually standardized against a primary standard.
NIST Standard Reference Materials: The National Institute of standards and Technology (NIST) provides a wide
variety of standard reference materials (SRMs) for validating and calibrating analytical methods
A standard solution is prepared by dissolving a definite weight of substance (a primary standard), in a definite volume. Its
concentration need to be known precisely (within specified limits).

7. Procedure :A description of the practical steps involved in an analysis.
Method: The overall description of the instructions for a particular analysis.
Technique: The principle upon which a group of methods is based (AAS, XPS etc.,)
Standardization: Determination of the concentration of an analyte or reagent solution from its reaction with a
standard or primary standard.
Certified reference material (CRM): A material that is verified to contain a known amount of analyte(s) or to have known
physical properties. Usually available from commercial suppliers. Also referred to simply as reference material (RM).4 See
http://nist.gov/srm/definitions.cfm for more details.
Speciation analysis: The determination of the specific forms of an analyte. Common examples are elemental
mercury versus organomercury and different oxidation states such as Cr(III) versus Cr(VI).

8. Method development: Determining the experimental conditions for sample collection, preparation, and measurement that
produce accurate and repeatable results.
Validation of Method:
• to validate the method by analyzing standards which have an accepted analyte content, and a matrix similar to that of
the sample.
• Performing control experiments to verify the accuracy, sensitivity, specificity, and reproducibility of test methods.
Signal : The detector output that is displayed or recorded.
Noise: Random fluctuations in the signal. Usually quantified using the standard deviation of multiple measurements of a blank.
Selectivity: The ability of a method or instrument to measure an analyte in the presence of other constituents of the sample
or test portion. [Pure & Appl.Chem. 2001, 73(8), 1381–1386.]
Sensitivity: The change in the response from an analyte relative to a small variation in the amount being determined. The
sensitivity is equal to the slope of the calibration curve (the change in detector signal versus the change in amount of
analyte), being constant if the curve is linear. In other words, it is the ability of a method to facilitate the detection or
determination of an analyte. A higher sensitivity may allow measurement of a lower analyte concentration, depending on
the signal-to-noise ratio.

9. Detection Limit: The smallest amount or concentration of an analyte that can be detected by a given procedure and with
a given degree of confidence. It is the minimum measured concentration at which an analyte may be reported as being
detected in the test portion or sample.
Limit of linearity (LOL): The concentration at which the signal deviates from linearity.
Limit of quantitation (LQ):An analytical value, XLQ, above which quantitative determinations are possible with a given
minimum precision.
Determination: A quantitative measure of an analyte with an accuracy of considerably better than 10% of the amount
present.
Estimation: A semi-quantitative measure of the amount of an analyte present in a sample, with accuracy no better than
about 10% of the amount present.
Equivalent : That amount of a substance which, in a specified chemical reaction, produces, reacts with or can be
indirectly equated with one mole (6.023 × 1023) of hydrogen ions. This confusing term is obsolete but its use is still to
be found in some analytical laboratories.

10. Internal Standard
A compound or element added to all calibration standards and samples in a constant known amount. Sometimes a major
constituent of the samples to be analysed can be used for this purpose. Instead of preparing a conventional calibration curve
of instrument response as a function of analyte mass, volume or concentration, a response ratio is computed for each
calibration standard and sample, i.e. the instrument response for the analyte is divided by the corresponding response for the
fixed amount of added internal standard. Ideally, the latter will be the same for each pair of measurements but variations in
experimental conditions may alter the responses of both analyte and internal standard. However, their ratio should be
unaffected and should therefore be a more reliable function of the mass, volume or concentration of the analyte than its
response alone. The analyte in a sample is determined from its response ratio using the calibration graph and should be
independent of sample size.

11. What is Analytical Science?
• Analytical Chemistry provides the methods and tools needed for insight into our
material world…for answering four basic questions about a material sample?
• What?
• Where?
• How much?
• What arrangement, structure or form?
(Fresenius’ J. Anal. Chem. 343 (1992):812-813)
• Qualitative and Quantitative Analysis (What and How much?)
• Chemical Characterization of matter (what and How much?)
• Seeks ever improved means of measuring the chemical composition
of materials
• Research to discover new principles of measurements. Develops
new measurement methods on existing principles to solve new
analysis problems.
Analytical Chemistry?
“Science of Chemical Measurements”

12. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
Qualitative analysis is what.
Quantitative analysis is how much.

13. Areas of Chemical Analysis and Questions
They Answer
• Quantitation:
– How much of substance X is in the sample?
• Detection:
– Does the sample contain substance X?
• Identification:
– What is the identity of the substance in the sample?
• Separation:
– How can the species of interest be separated from the sample matrix for
better quantitation and identification?

16. Scope of Analytical Chemistry
• Agriculture: Nitrogen content of fertilizers, P and Fe contents of soils
• Environment: As, Pd, Co, Hg and other heavy metals, pesticides etc in environment
• Forensic: trace elements from gun’s powder on accused’s hands
• Clinical: Vitamins, hormones, glucose level, diagnostic of diseases
• Manufacturing: Quality control (C-content of steel), testing of raw materials (fuels, paints, pharmaceuticals)
• Metallurgy: ore-content of desired elements
• Pharmaceuticals: quality control, purity of drugs, active ingredients in drugs

17. Fig. 1.1. Steps in an analysis
An analysis involves several
steps and operations which
depend on:
•the particular problem
• your expertise
• the apparatus or
equipment available.
The analyst should be
involved in every step.
©Gary Christian,
Analytical Chemistry,
6th Ed. (Wiley)
Gross sample
Lab sample (few g)
Analysis sample (few mg)

18. Different methods provide a range of precision, sensitivity, selectivity,
and speed capabilities.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)

19. The sample size dictates what measurement techniques can be used.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)

21. Deer Kill
• Case Study # 2: Deer Kill
• Problem: Dead whitetail deer near pond in the Land
Between the Lakes State Park in south central Kentucky.
• Chemist state veterinary diagnostic laboratory helped find
the cause
Source: Fundamentals of Analytical Chemistry by Douglas A. Skoog, Donald M. West, F. James Holler, Stanley R. Crouch

22. Site Investigation
• Careful visual observation of a two acre area around the
site:
• Observation: grass around nearby power-poles was wilted
and discolored.
• Speculation: Herbicide used on grass.
• Ingredient: Arsenic in a variety of forms (Arsenic trioxide,
sod arsenite) is a common ingredient of herbicides
– Disodium methane arsenate (salts of CH3AsO(OH)2) very soluble
in water.

23. Select Method
• Association of Official Analytical Chemists (AOAC)
• Distillation of arsenic as arsine (AsH3) which is then
determined by colorimetric measurements.

24. Representative Sample
• Dissect both deer. Removed kidneys for analysis.
• Laboratory Sample Preparation: Cut kidney into pieces and
blend in a high speed blender to homogenize the sample.

25. Defining Replicate Samples
• Three 10-g samples of the homogenized tissue were placed
in porcelain curcibles and dry ashed.
• Dry ashing serves to free the analyte from organic material
and convert the arsenic present to As2O5. Samples of the
discolored grass were treated in a similar manner.

26. Dissolving the Samples
• The dry solid in each of the sample crucibles was dissolved
in dilute HCl, which converted the As2O5 to soluble
H3AsO4.

27. Eliminating Interferences
• H3AsO4 + SnCl2 + 2HCl --> H3AsO3 + SnCl2 + H2O
• H3AsO3 + 3Zn + 6HCl --> AsH3(g) + 3ZnCl2 + 3H2O
• Bubble gas into collectors with silver diethyldithiocarbamate to form a
colored complex compound shown below.
Reactions to Eliminate Interferences:
As can be separated from other substances that might interfere in analysis by converting into Arsine
(AsH3), a colorless, toxic gas that is evolved when H3AsO3 (obtained from reduction of H3AsO4 with
SnCl2) is treated with Zn.

28. Measuring the Amount of Analyte
• Spectrophotometer: Highly colored complex of arsenic was
found to absorb light at a wavelength of 535 nm.

29. Absorbance vsConcentration
y=0.0282x+0.005
R2
=0.9961
0
0.2
0.4
0.6
0.8
0 5 10 15 20 25 30
Conc.,ppm
Absorbance
Conc. Absorbance
ppm
0 0
5 0.16
10 0.28
15 0.41
20 0.595
25 0.7
deer 1 0.61
deer 2 0.43

30. Calculating the Concentration
• ppm = (Absorbance -.005)/0.0282
• Deer 1: (0.61 - 0.005)/0.0282 = 22 ppm
• Deer 2: (0.43 -0.005)/0.0282 = 15 ppm
• Arsenic in the kidney tissue of animals is toxic at levels
above about 10 ppm.
• Grass Samples showed about 600 ppm arsenic.

31. Laboratory safety is a must!
Learn the rules.
See Appendix D.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)

32. BIBLIOGRAPHYS
1 IUPAC Compendium of Chemical Terminology - the Gold Book (International Union of Pure and Applied Chemistry: Research Triangle Park,
NC, 2005-2009); available: http://goldbook.iupac.org/index.html, 2010-12-22: Release 2.2.
2 IUPAC Compendium on Analytical Nomenclature (1997); available: http://iupac.org/publications/analytical_compendium/.
3 Currie, L. A. “Nomenclature in Evaluation of Analytical Methods Including Detection and Quantification Capabilities,” Pure & Appl.Chem.
1995, 67(10), 1699–1723.
4 NIST Standard Reference Materials: Definitions. http://nist.gov/srm/definitions.cfm.
5 Analytical Detection Limit Guidance & Laboratory Guide for Determining Method Detection Limits, Wisconsin Department of Natural
Resources Laboratory Certification Program, April 1996, PUBL-TS-056-96; http://dnr.wi.gov/regulations/labcert/documents/guidance/-
lodguide.pdf.
6 Templeton, D. M. et al. “Guidelines for terms related to chemical speciation and fractionation of elements. Definitions, structural aspects, and
methodological approaches (IUPAC Recommendations 2000),” Pure & Appl.Chem. 2000, 72(8), 1453–1470.
7 Glossary of Analytical Terms ver. 27 June 2015
by Brian M. Tissue, https://www.tissuegroup.chem.vt.edu/a-text/
8. https://www.nist.gov/srm/srm-definitions https://link.springer.com/chapter/10.1007/978-3-642-13609-2_1
9. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)