Instrumentation chemistry — a versatile strategy

202

3 4 5 6

trends in analytical chemistry, vol. 10, no. 7,1991

A.G. Marshall, Biophysical Chemistry: Principles, Techniques and Applications, Wiley, New York, 1978. D.V. Roberts, Enzyme Kinetics, Cambridge Chemistry Texts, Cambridge University Press, 1977. E. Biirgisser, Trends Pharmacol. Sci., 5 (1984) 143. B.F. Ryan, B.L. Joiner and T.A. Ryan, Minitab Handbook, Duxbury Press, Boston, MA, 1985.

I

W.A. Wood and I.C. Gunsalus, 171.

J. Biol. Chem.,

181 (1949)

Dr. M.E. Jones is at the National Centre for Epidemiology and Population Health, The Australian National University, Canberra, ACT 2601, Australia.

feature

Instrumentation strategy

chemistry - a versatile

Yohichi

A science dealing with the chemical information used to control a material system at present and in the future (applied science). These definitions are fundamental and should be transformed into more realistic expressions, such as: l Analytical chemistry is the branch of chemistry concerned with the knowledge of the components, composition or structure of a material system in order to understand it (basic science). l Analytical chemistry is the branch of chemistry concerned with the knowledge of the components, composition, structure or properties of a material system in order to control it or topredict its behavior (applied science). These expressions are fundamental and timeless. Analytical chemistry, however, has had and will have different features depending on its historical stage. Scientific activities are devoted to a specific point in the whole process of chemical information flow to solve a bottleneck at a specific historical stage. For example, quantitative conversion to stochiometric oxides was very important a long time ago, sampling became a hot issue in recent decades, and now contamination control is the most challenging part of chemical analysis. In each phase, the characteristic outlook of analytical chemistry was specific to it. Apparent features will change from time to time. Therefore, it is important to consider both essential and apparent features in the discussion of the perspective of analytical chemistry. The chemical inforl

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MACROSCOPIC

CONFIGURATION

ELEMENT (PROPERTY) t 1

CONFIGURATION

ELEMENT (PROPERTY) t 1

I Fig. 1. Analytical chemistry and its sub-functions.

The structure of material systems Analytical chemistry deals with chemical information. The information should be necessary and sufficient to describe or reproduce a material system. Two models are shown as examples of material systems in Fig. 2. The important feature is that the material systems can be described in an hierarchical way and each level of the hierarchy can be expressed by elements (components) and their configuration. Each

Fig. 3. Hierarchical approach.

element can be defined by the lower level components (elements) and their configuration. This relationship is shown in Fig. 3. Chemical information should correspond to this structure. The information concerning elements (components) is their properties. The information of configuration is well expressed by imaging. Therefore, a material system can be described by the concepts of element and configuration. From a chemical point of view, the atomic and molecular levels are important. Materials scientists will pay more attention to the molecular aggregate, crystallite or phase levels. It is a logical consequence that although the concept of chemical species is very important, it is but one of the various elements (components) in the hierarchy of material systems. Analytical methods should correspond to the information described above, Analytical method The above discussion leads to the model of analytical methods shown in Fig. 4. Any analytical method

Analytical

Melhod = _

F(Probe, Phenomenon, l”te,aCtlo”

_

F,(Prb,

=

Phn. Slg

Element Property

Fig. 2. Models of material systems.

CONFIGURATION

ELEMENT (PROPERTY)

MICROSCOPIC

Signal)

) xF,(Prb.

Phn. Slg

Co”fig”ratlo” imagtng

Fig. 4. Model of analytical method.

)

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trendsin analyticalchemistry,vol. 10, no. 7, 1991

Probe

Chemical Species

Chemical SpecK?s 1

Neutral (free)

particle

Sample

1

Interaction

Neutral

particle

(free) Reaction Electron

Electron Absorption

Photon

Photon Scattering

Heat

Heat Interierence Electric

Electric

field

field

DIffraction Magnetic

Magnetic

field

Mechanical

field

Mechanical

field

field

Fig. 5. Probes, interaction and signals.

has two functions: a property measuring capability and an imaging capability. Each function contains -three parameters, i.e. probe, interaction and signal. Probes, interactions and signals are summarized in Fig. 5. The classification in Fig. 5 is very approximate and a more detailed classification will be help-

TABLE

I. Combination

ofprobes and signals through

ful for further discussion. Examples of combinations of these three parameters are shown in Tables I and II. The imaging function is less complicated - as shown in Table III. I would like to call this combination “instrumentation chemistry”. Several examples are’ explained below. Chemical analysis (CA) is the most powerful method for obtaining information on a chemical species. On the other hand, chemical analysis has no imaging capability. An optical microscope has excellent imaging power, but is poor in providing chemical information. An electron probe microanalyzer (EPMA) has both functions. I would like to emphasize two points concerning Tables I-III. When a new probe, detector or interaction becomes available or is discovered, the blank boxes can be filled with the novel analytical method. Another point is the effect of scale in the hierarchical system. If we apply chemical analysis to a geological system, it functions as a one dimensional-one dimensional imaging method through sampling points. The analytical results of the sampling points provide a geological map which is typical imaging information.

absorption and reaction (Function:

measurement)

Signal

Probe

Chemical species

Chemical species

Ion (free)

Electron (free)

Neutral particle (free)

Photon

Heat

CA u(P)

CIMS

PIES

MBSS

Chemical luminescence

AHads

SNMS

PIXE CL EPMA APS

EAM

EAM

PAS

Ion (free)

INS SIMS

Electron (free)

SSMS ESDI

EELS AEM SEM,TEM

ESDN

Neutral particle (free)

FABMS

MDS (PIES)

MBSS

Photon

PD LIMS (LAMMA)

XPS CEMS UPS OSEE AES, PEM

UV, LMA VIS , 7-w IR, SERS X-Ray

PAS PTD

TSEE

IR

Thermal Analysis

Heat Electric

property

field

FDMS Atom Probe

FEM

FIM

CDS

IETS STM NMR, NMR ESR

EXES

Magnetic field

Mechanical field

GDS

Magnetic field Mechanical field

Electric field

Triboluminescence

NMR ESR ESR NMR ESR Ultrasonic absorption internal friction

trends in analytical chemistry, vol. 10, no. 7,199l

TABLE

II. Combination

Probe

205

of probes and signals through

diffraction,

scattering and reflection (Function:

property-

measurement)

Signal Chemical species

Chemical species

Ion (free)

Electron

Neutral particle

Photon

Heat

Electric field

Magnetic field

Mechanical field

MBSS

Ion (free)

ICISS RBS, ISS

Electron

HEED RHEED LEED

Neutral particle

Neutron small angle scattering

Photon

Standing wave XPED PED SEXAFS

Standing wave XRD (Raman) EXAFS ELL TRXRF GIXRF

Heat Electric

field

Magnetic field Mechanical field

Acoustic microscope

Chemical information and chemical species As has been mentioned abovk, chemical species is a very important concept for material systems. TABLE

III. Imaging

Probe

Signal

methods

Dimension 1-D

2-D

1-D

Micro beam analysers STM

XRD CT

2-D

Micro beam analysers CT

Micro analysers (projection) CT microscope

3-D

Time

Holography

Photo acoustic microscope

3-D

Time

CT microscope Photo acoustic microscope Ultrasonic microscope

However, chemical information has a far broader meaning. Recent automated systems impose very severe requirements on analytical chemistry. For example, a combustion control system for cars or furnaces requires a rapid, small, inexpensive and rugged oxygen analyzer. The control system has to be installed to work under harsh environmental conditions and its 24-h continuous operation is necessary. In such a system, any human factor should be excluded. A zirconia galvanic sensor that has recently been developed meets these requirements and is widely used. In the combustion control system the output potential of the galvanic zirconia sensor is directly used as a control signal showing the oxidizing chemical potential of the exhaust gas and an explicit expression of oxygen concentration in the sample gas is not needed. An example of such a system is shown in Fig. 6. The important point is that chemical species are not necessarily the most important information. The direct transmission of chemical information is inevitable and a person who understands chemical information in terms of chemical species can often be excluded for various reasons (Table IV). Therefore the expansion of the concept of chemical information from chemical species to chemical properties is very important.

206

trends in analytical chemistry, vol. IO, no. 7,199l

iAMPLE \

ANALYSIS

TABLE

‘\ ‘\

MATERIAL

\

\

\

\

\

\\

J\

\

DETERMI‘NATION INTERPRETATION

A

ANALYVCAL

METHOD

-

Subject

//

Manpower

Future

Information saving

Man

saving

Information

(explicit)

\

urement which has capabilities for measuring properties and imaging. This approach will be effective for future development of analytical chemistry. In this short article, expression chemistry and chemical diagnosis (including prediction and simulation) are not discussed. These two fields will be of increasing importance in the future. A short discussion can be found in ref. 2 and I will address these topics in a future article.

PREPARATION

\\.

SYSTEM

)

DATA

Present

\

SAMPLE

ACTION.

system

AND

‘\

MATERIAL

analyzer-control

ANALYSl

\

SAMPLING

of automated

Aim \

SYSTEM

ACTION

IV. Significance

SENSORS

ETC.

PROCESSING

ANALYZER

Fig. 6. Information

flow

and control system.

Professor Chemistry, Japan.

Conclusions I have discussed a view of analytical chemistry as information flow. Analytical chemistry is divided into three fields, i.e., instrumentation chemistry, expression chemistry and chemical diagnosis. Instrumentation chemistry is defined as a field of meas-

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References 1 2 3

W. F. Pickering and D. E. Ryan, Trends Anal. (1989) 119. Bunseki (1987) 772. Fresenius J. Anal. Chem., 337 (1990) 149-246.

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