Prof. of Clinical Chemistry, Mansoura University
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.