be purchased as customized commercial software packages or developed by a company's 'in-house'
programmers. Privileged access to various parts of the system can be built in so that, for example, only
specified personnel can change the parameters associated with a particular method of analysis or the
availability of confidential information can be restricted. An overall picture of sample flow through the
laboratory can be used to pinpoint sources of delay so that changes in the operation can be introduced to
improve efficiency. A diagrammatic representation of a LIMS is shown in Figure 13.1(b).
Expert Systems
These consist of sophisticated software packages and data banks of information that act as sources of
knowledge and advice on a particular subject area, e.g. chromatography, atomic emission techniques,
the analysis of polyurethane plastics, the quality control of anti-depressant drugs. They can be accessed
interactively by the user to extract information and develop ideas. Systems become more 'expert' as
additional data and opinions from numerous sources are fed into them. The software currently available,
and which is likely to evolve into a form of artificial intelligence, is already capable of making logical
deductions after rationalizing the information fed into the computer and will in the future be able to
explain the reasoning processes leading to its decisions and advice. A diagrammatic representation of an
expert system for an analytical separation is shown in Figure 13.2.
A brief description of computers, microprocessors and computer/instrument interfacing in the context of
analytical chemistry is given in the following sections.
13.2—
Computers and Microprocessors
Digital computers contain three main components which are termed the hardware. These are the central
processing unit (CPU), the memory and the input/output (I/O) systems. The CPU consists of an
arithmetic logic unit, which performs the computations, registers for the temporary storage of
information, a clock to enable the various operations to be synchronized, and a control unit. The latter
passes instructions, results of computations and data to and from the arithmetic logic unit, the memory
and the I/O devices, generally under the control of a program (software) stored in the memory. All
instructions and data are stored, transmitted and received, and computations executed in a machine code
consisting of groups of binary numbers, i.e. 0 and 1, which are easily represented electrically by one of
two states (voltages) (usually 0 V and 5 V). Groups of signals are passed between the various
components along sets of parallel lines known as the bus system. Thus the computer operates at
extremely high speed, the various hardware components consisting essentially of very large networks of
on/off switches corresponding to binary 1 and 0 and connected by printed circuits. The term binary
number or binary digit is commonly abbreviated to bit and com-