ANALYTICAL PROCESS

Audrius Maruškaa.maruska@gmf.vdu.lt

Vytautas Magnus UniversityDept. of Chemistry

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10 –14 November, 2003

Objectives• Role of analytical chemistry solving the

problems defined by clients• Importance of interaction between client

and analyst• Various steps in the total analytical

process• Basic characteristics of the performance

of analytical methods

Broad scope of samples

PigmentsRestoration/Ancient painting

BloodClinics/Cholesterol content

Metal analysisMining industry/Ores

Tap waterPublic health/Assessment of purity

Fresh water samplesEnvironment/Pollution degree

SoilAgrochemistry/Need for fertilizers

Raw materials and finished products

Chemical industry

SampleArea/Object

: WE NEED A COMMON LANGUAGE!!!

Investigation subject

Investigation subject Bulk matter/Object

Part of the object Sample

Compounds or elements Analytesof interest

Analytes are embedded in Matrix

• The analysis of objects or test samples must be performed with a clear objective

• The problem is formulated by others clients e.g. process engineer, farmer, water control authority, steel production

industry, physician, museum director.

• The problem often is not put in analytical terms. Analyst should recollect the information necessary to reformulate the problem in to analytically manageable dialog with client

• Extensive tool kit of the analysthow to select proper approach?

• The are no “best” methodsindividual problem will ask for a specific approach

• What you can learna feeling for the systematic development of analytical

procedures• What you need?

knowledge of the most important analytical techniques

• How to compare/evaluate different methods?objective way is to compare performance

characteristics

Other important factors1. Availability of equipment 2. Expertise

3. Presence of trained personnel

Scheme of the TOTAL ANALYTICAL PROCESS

Analyst Client9. ReportAnalyst8. ConclusionsAnalyst7. Evaluation of dataAnalyst6. MeasurementAnalyst5. Sample preparationClient Analyst4. SamplingAnalyst3. Selection of procedure

Client Analyst2. Specific analytical statement of problem, Definition of objective

Client1. General statement of problem

ALL STEPS AFFECT THE FINAL RESULT!!!

General definition of problem• Often beyond the field of expertise of the analyst• Often outside the chemical domain• Client often does not appreciate the opportunities

and technical aspects of analysisWhat is needed intensive discussion

before problem solving to make clear the real basis of the analysis

Specific analytical statement of problem

• Client and analyst what is the object of study, i.e.

1. What has to be analyzed?2. What can be analyzed?

Characteristic questions to be solved:1. The nature of the object or sample, functional

groups, molecular composition.2. Quantitative or qualitative analysis, what accuracy (in

case of quantitative analysis) is needed?3. Quantity of material available, approximate

concentration of analyte?4. Matrix composition?5. Single component or multicomponent analysis?6. How much time is available?7. Unique analysis or recurrent supply of samples, if so

with what frequency? Continuous monitoring?8. Should integrity of the sample be preserved? etc.

Selection of procedure• Of crucial importance • Determines the cost

a) instrumental b) personnel

• Also influenced by :a) sample sizeb) time availablec) information extracted out of analytical

investigation

Sampling

• Tendency to underestimate importance of sampling: when dealing with homogeneous samples

• Reliability of analytical result depends on the quality of the sample

• Whole object can be investigated by nondestructive method (antique ring by X-ray)

• Mostly samples have to be taken (ore samples from the carrier ship)

• Important operations:a) Definition of a sampling planb) Taking of the samples as suchNever start an analytical procedure without

knowledge of the sample history: sampling process, storage, preservation, pretreatment etc. and of its representativity to whole object

Avoid any alterations of sample compositionImportant to know type of analyte, concentration

level, composition of matrixSafety precautions

Solid materials

1. Representative2. Not be larger than necessary, size

depends on:a) Precision requiredb) Material heterogeneityc) Grain sizeAmount up to several kg or even several

hundreds kg

Liquid and gases

1. Usually sufficiently homogeneous2. Small samples therefore sufficient3. Adsorption may be risky due to large

surface–to–volume ratio in the sample vessels:

Deactivate or equilibrate the walls of vessels

Sampling tools are outside of the scope of this presentation

Transport and storage

• Avoid sample changes due to reactions induced by vigorous shaking

• Time between sampling and sample investigation is important

• Adsorption of trace compounds on the container walls should be avoided

Sample preparation

• Important: adaption of the state of the sample to that acceptable by the analytical technique

• Consider that the concentration range in the adapted sample is optimum: use dilution or enrichment

• Suppress the contribution of unwanted compounds: “masking” procedure

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Measurements/Determination

• Typical instrumental techniques are based on signal comparison of unknown composition sample and (series of) standard(s) of exactly known compositions: calibrate the instrument

Important: estimate unwanted fluctuations in signal-noise

Signal- to- noise ratio is optimized through data acquisition and data processing

Evaluation of data

• Most of the modern instruments are computerized mathematical processing is used to transfer data to analytically relevant (concentration, structural information etc.)

• Analyst can not check and does not have access the raw data: software should be validated

• Use “ library search” procedures for data evaluation

Conclusions and report

• Analyst is responsible for the analytical results presented in the report

• To warrant the quality:a) Test procedures on certified samples (various

methods in various laboratories)b) Compare the results obtained with proposed

procedure to the results obtained with other procedures

The conclusions to be drawn on the basis of the analytical results (by client) is responsibility of the analyst

Performance characteristics• Analytical method can be characterized

on the criteria based on the quality of the result and criteria of economic origin

•Costs of investment• Duration of analysis with regard to personnel costs•Special safety precautions•Costs of installation, housing•Degree of training of operator because of salary•Sample throughput•Costs of reagents

•Sensitivity•Precision•Bias•Accuracy•Limit of detection•Limit of determination•Selectivity•Dynamic range

Economic aspectsQuality criteria

• Accuracy – the agreement between the average of the measured values and the accepted reference value

• Precision – is the scatter of the measured values around the average value

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Accurate and precise

Inaccurate but precise

Accurate but not precise

Inaccurate and not precise

• Sensitivity – signal change dependence on change of concentration

S = dY/dc• Limit of detection – equal to k times the

standard deviation of the background noise. Typically k = 3.

• Limit of determination – used for quantitative analysis is always higher than the limit of detection

• Selectivity – gives an indication how strongly the result is affected by other sample components

You learned:• Role of analytical chemistry solving the

problems defined by clients• Importance of interaction between client

and analyst• Various steps in the total analytical

process• Basic characteristicsof the performanceof analytical methods