Prof. of Clinical Chemistry, Mansoura University

Implies a self – regulating process with an element of feed-back which detect any tendency to malfunction

and readjusts the equipment so that it continues to function correctly.

Definitions and processing concepts:

Continuous flow analyser: The reagent are pumped continuously by

syring pump The samples are introduced at regular

intervals The flow is segmented to separate one

specimen from anothor This type is used as batch analyzer e.g

technicon .Two types :

a) single channel continuous flow: analyse one constituent in each specimen .

b) Multichannel continuous flow: determination of several components in each sample

Discrete analyser:

Samples are processed in separate

reaction tubes.

The instrument contain a variety of

receptacle in which the sample and

reagents are mixed.

The reaction occurs: cuvettes, dry

film slides.

Some containers contain the

reagents and only the specimen

need to be added.

Others add both reagents and

specimen.

Reaction vessels and cuvets in discretes: Reused or discarded

Used as cuvet or just reaction tube,

aspirated in tube then to another tube

for measurement For wash reused reaction vesseles or cuvets

aspiration of the reaction mixture

a detergent ,alkaline or acid wash soln . is

then dispensed into and aspirated out of

the cuvets

Parallel analysis: All specimens are subjected to a series of

analytical processes at the same time in a

parallel fashion:

Discretionary multiple – channel

analysis. The specimen can be analyzed by any

one or by more than one of the

available processes (methods,

channels).

- A number of specimens are processed in the same analytical session , or run:

Batch analyzer.

The components steps in automated system

1. Specimen identification.2. Specimen preparation.3. Specimen handling, transport and delivery.4. Specimen processing.5. Sample transport and delivery. 6. Reagent handling and storage. 7. Reagent delivery.8. Chemical reaction phase.9. Measurement approach.10. Signal processing data handling and process

control.

These operations are usually performed sequentially but in some instrument, they may be combined and occur in parallel.

Specimen identification:

Specimen Preparation:

Specimen Handling, Transport and Delivery:

Specimen processing:

Sample transport and delivery:

In continuous – flow system: the sample is aspirated through the

sample probe into continuous reagent stream

In Discrete analyzers: the sample is aspirated into sample probe and

delivered, with reagent into reaction tube or cup .

Carry over:

Carry over occurs when a previous sample or reagent contaminates

successive tests in a run causing the next sample to have an aberrantly

higher or lower results . Carry over occurs when anlytes occur in extremely high levels e.g. enzyme

or h CG in pregnancyCarry over also occurs in systems

that reuse cuvettes that are insufficiently washed after each

testing cycle.In discrete systems with disposable reaction vessels and measuring cuvettes carry over is caused by the pipeting system

Disadv: one analyte per rotor but now recent models allow multiple analysis 24 rotors can be loaded at one time.

In Continuous flow: by glass coils passing through the samples and

reagents.

Measurement approaches:

Spectrophotometry Fluorimetry e.g. IMX

Chemiluminescenc e.g. IMMULITE

Electrochemical for electrolytes

Examples:

Automated immunoassay systems differ from chemical analyzers in that they require the use of:

1.solid – phase reagents to separate bound and unbound

2.More sensitive detection methods e.g fluorescence and chemiluminescence

3.Special handling of the reagents:

e.g. 1. Thermal conditioning to keep chemilum substrate stable. 2. Constant agitation to keep microparticles suspended.

4-Multiple Calibrators: (upto 6)

• Calibration usually nonlinear

Example : ACS : 180

• benchtop • R-A • Imm . AS.S ay

IMMULITE :

• bench – top • R-A • Imm. Assay

Automated immunoassay

Selection of instruments

Role of an automated system in the workflow of

the laboratory.

Identification of candidate system (RA or

batch).

Cost effectiveness of the system.

User-friendiness (interface between the

machine and the human operator).

Analytical performance.

Advantages of automation:

Large number of samples may be processed with minimal technician.

Two or more methods may be performed simultaneously.

precision is superior to that of manual performance.

calculations may not be required.

Disadvantages of automation: limitation of the methodology "closed

system".Expensive.

Many systems, are impractical to use for small numbers of samples.

Therefore, back up manual methods may be required for individual

emergency analysis. Back up methods must also be available in the event of

instrumental failures.