Instant Notes: Analytical Chemistry

● the application of statistical tests and chemometric procedures to assess

quantitative results and extract additional information from complex data;

● calculation of chromatographic parameters such as efficiency, resolution,

peak assymetry and detector response;

● comparison of chromatographic retention data for standards and samples to

enable unknown analyte peaks to be identified;

● measurement of chromatographic peak areas using a range of options for

defining baselines and separating overlapping peaks;

● display of developing chromatograms in real time, including scale and sensi-

tivity changes;

● processing and presentation of complex data from hyphenated techniques

such as gas or liquid chromatography-mass spectrometry and inductively

E5 Inductively coupled plasma spectrometry

Important areas of data processing include the use of chemometrics (Topic

B5) to simplify complex data for characterizing materials, quantitative spectro-

metric analysis using multiple wavelengths, and routines to optimize experi-

mental conditions for high-performance liquid chromatography.

Databases A databasemay consist of a simple look-up table relating two variables, such as
solvent composition and polarity, tables of statistical factors for tests of signifi-
cance (Q, F and t-tests), or archived sample data and analytical procedures.
Larger compilations of data may list chemical formulae and structures or char-
acteristic properties of elements, compounds, materials and commercial formu-
lations (e.g., boiling point, viscosity, dielectric constant, hardness and toxicity).
Spectrometric and chromatographic analytical databases are of particular value
in the characterization and identification of unknown substances, and some
examples are given in Table 1. The data is usually compressedand encoded to
maximize the amount of information that can be stored.

Table 1. Some analytical spectrometric and chromatographic databases

Technique Data base/source Data

Atomic emission spectrometry Plasma 2000/Perkin Elmer 50 000 atomic lines

Gas chromatography Sadtler Retention indices

Infrared spectrometry Aldrich/Nicolet >100 000 spectra

Mass spectrometry NIST/EPA/MSDC 50 000 spectra

Nuclear magnetic resonance Bruker 19 000 spectra

spectrometry

The formatting of a database involves the creation of several types of files

that are manipulated with specialized software. A source filecontaining raw

analytical data is converted to a library fileby reducing noise, eliminating

unimportant data and compression. Associated exchange filesenable data to be

transferred in a standard format such as JCAMP/DXfor spectrometric data and

JCAMP/CSfor chemical structures.

Library searches Search algorithmsare used to retrieve information from databases as quickly as
possible, often within a few seconds. User-defined criteria can be selected to
direct the search and/or to limit the amount of data retrieved and specify the
mode of presentation. Search algorithms are based on multivariate chemo-

334 Section H – Sensors, automation and computing