Clinical laboratory instrumentation
1- Draw a schematic diagram for Spectrophotometer and explain how it is work
Answer
- The spectrophotometer measures light absorption by a liquid substance at
various wavelengths.
- The components of an unknown material can be determined or the concentration
of a number of known substances can be measured.
a- A monochrometer uses a diffraction grating or prism to disperse the light from the lamp
(slit S1).
b- The light is broken into its spectral components as it arises from slit S2 and falls on the
sample in the cuvette,
c- The angle of the diffraction grating determines light wavelength.
d- The mirror reduces equipment size.
e- Light output, photodetector sensitivity, and sample substance absorbance changes with
wavelength, and this necessitates zero calibration for each wavelength measurement.
f- The double-beam spectrophotometer accomplishes this automatically by beam path
switching (sample to reference) via a mechanical shutter or rotating mirror
g- Single Beam Instrument
Single Beam Instrument
Slit
Light
Source
(Tungsten
Lamp)
Filter,
MonoChromator,
Grating
Sample
Detector
Quartz
Cuvette
Photomultiplier
h- Double Beam Instrument
Double Beam Instrument
Beam Chopper
Semi-transparent
Mirror
Sample
Tungsten
Lamp
Slit
Grating
Quartz
Cuvette
Photomultiplier
Reference
Mirror
Mirror
i-
Draw an electrical circuit for water bath;
Mirror
022
‫فولت‬
‫ فولت‬42 ‫محول‬
‫ترموستاات‬
‫حماية‬
‫منبع تغذية‬
‫ فولت‬03
‫وحدة التحكم فى‬
‫درجة الحرارة‬
‫مقاومة‬
‫الختيار درجة الحرارة‬
j-
‫ريالى‬
‫لمبة بيان عمل‬
‫وحدة التحكم‬
‫لمبة‬
‫بيان‬
‫عنصر تسخين‬
Draw a schematic diagram for autoanalyzer and give the function of each components
 Sampler- aspirates sample, standards, and wash solutions to the autoanalyzer
system.
 Proportioning pump and manifold- introduces (mixes) samples with reagents to
effect the proper chemical reaction to be read by the colorimeter. It also pumps
fluids at precise flow rates to other modules, as the proper colour development
depends on reaction time and temperature
 Dialyzer- separates interfacing substances from the sample material by permitting
selective passage of sample components through a semi permeable membrane.
 Heating bath- heats fluids continuously to exact temperature (typically 37oC
incubation equivalent temperature). Temperature is critical to colour development
 Colorimeter- monitors the changes in optical density of the fluid stream flowing
through tubular flow cell. Colour intensities (optical densities) proportional to
substance concentrations, are converted to equivalent electrical voltages.
 Recorder- converts optical density electrical signal from the colorimeter into a
graphic display on a moving chart.
 The heart of the autoanalyzer system is the proportioning pump
k- What are the main components of water bath?
a. Container
b. Temperature selection bottom
c. Heater Element
d. Temperature gauge
e. Control unit
f. Switches
g. Indicator
Complete:1- Maintenance of spectrophotometer includes:
a. Calibration adjustment
b. Replacement of light source bulbs and photo detectors.
c. Mechanically rotating assembles (mirrors, diffraction grating) will
occasionally malfunction.
d. The electronics is very reliable
2- The most important components of a spectrophotometer are:a. The light source
b. The monochromator
c. The sample carrier
d. The detector system
e. The reading system
3- Depending on the type of spectrophotometer, the light source can be
a. a tungsten lamp for visible light or
b. a deuterium arc lamp for ultraviolet light.
c. Some manufacturers have designed spectrophotometers with long lasting
xenon lamps emitting light in the visible and ultraviolet ranges.
4- The typical radiating energy emitted from a tungsten lamp is between 2600 and
3000°K (Kelvin degrees).
5- The monochomator is a set of elements used to disperse white light into waves of
different wavelengths, one of which is used in the sample reading.
6- In general, monochromator has:a. Inlet slit;
b. a set of mirrors for transmitting light through the optic system;
c. an element for separating the light radiation wavelengths (which may be a
prism or a diffraction (or transmission) grating); and
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d. an exit (outlet slit) opening for selecting the wavelength required to
illuminate the sample.
Diffraction gratings have the advantage of eliminating the non-linear dispersion and
being insensitive to changes in temperature.
The detection system can be designed with photocells, phototubes, photodiodes or
photomultipliers. This depends on the ranges of wavelength, the sensitivity and the
required speed of response. The detection system receives light from the sample
and converts it into an electrical signal proportional to the energy received. This
electrical signal can be processed and amplified to be interpreted by the reading
system.
The signal which leaves the detector goes through various transformations. It is
amplified and transformed until its intensity becomes a proportional
transmittance/absorbance percentage.
Give advantages and disadvantages of the following photo detection devices:a. Photocells
b. Phototubes
c. Photodiodes
d. Photomultiplier tubes
Answer
11- For the correct functioning of a spectrophotometer, the following is required:
a. An electric supply source
b. A clean, dust free, environment.
c. A stable work table
12- Electrical installation of spectrophotometer must be verified and tested for ensuring
the following:
a. There is an electrical outlet or receptacle with a ground pole.
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b. The receptacle is in good condition and is no further than 1.5 m from the
spectrophotometer.
c. The voltage is of an appropriate level and must not vary by more than 5% of
the voltage specified on the equipment’s plate.
d. The receptacle’s polarity is correct.
For spectrophotometer installation area you must:
a. Check that there is free space around the spectrophotometer
b. Verify that there is no equipment installed that can transmit vibrations in
proximity. (E.g. centrifuges).
c. Verify that it is not affected by excessively humid conditions, dust or high
temperatures.
d. Avoid installing the equipment where it receives direct solar radiation.
e. Do not install the equipment where there are magnetic fields or intense
electromagnetic radiation.
f. Ensure installation area is free from the influence of gases and corrosive
substances.
In case of a leak in the sample holder or carrier, the spill must be cleaned according
to the following procedure:
a. Turn off the spectrophotometer and disconnect the cable from the electrical
feed.
b. Use a syringe for cleaning the sample holder. Absorb as much liquid that can
possibly be extracted.
c. Dry the sample holder with a medicinal cotton bud.
d. Use lens paper or a clean piece of soft textured cloth for cleaning the
window of the photocell.
e. Clean the exterior of the instrument with a piece of cloth moistened with
distilled water.
To maintain quartz cuvettes in good condition:
a. Wash the cuvettes using a diluted alkaline solution such as NaOH 0.1 M and
a diluted acid such as HCl, 0.1 M.
b. Rinse cuvettes several times with distilled water.
c. Conduct rigorous and careful cleaning procedures on cuvettes if samples
used can deposit films.
d. Some manufacturers recommend using special detergents for cleaning
cuvettes.
If low battery indication appears on the instrument’s screen.
a. Turn off the spectrophotometer.
b. Disconnect the electrical feed cable.
c. Open the battery compartment and remove the worn out batteries.
d. Clean the electrical contact points.
e. Install new batteries with the same specifications as the originals.
f. Close the compartment.
g. Reconnect the equipment.
h. Adjust the date and time information.
Common lamp change steps are as follows:
a.
b.
c.
d.
e.
f.
g.
Verify that the bulb is not functioning .
Turn off the spectrophotometer.
Disconnect the feed cable.
Undo the screws securing the top of the lamp’s compartment.
Undo the screws keeping the lamp’s mechanism fixed.
Undo the screws fastening the electrical connection cable to the lamp
Install a new lamp with the same characteristics as the original. Use gloves
to avoid getting fingerprints on the surface of the lamp.
h. Reconnect the electrical feed cables to the lamp.
i. Reinstall the screws keeping the lamp in place.
j. Replace the screws securing the lamp’s compartment’s cover.
k. Reconnect the spectrophotometer.
l. Turn the equipment ON and carry out the equipment’s recalibration
procedure stipulated by the manufacturer.
18- Preventive Maintenance of spectrophotometer:a. Clean the spectrophotometer externally using a piece of fine cloth
dampened with distilled water.
b. Inspect and clean the electrical feed cable.
c. Verify that the lamp is clean and in good state.
d. Check the protection fuse.
e. Put the instrument in the operational configuration.
f. Activate the “on” switch and allow it to warm up for five (5) minutes. Verify
that:
g. The lights or pilot indicators work.
h. The reading indicators stay on zero (0).
i. The light source works.
j. Carry out an escaping current test in the “on” and “off ” position.
k. Calibrate the front panel of the spectrophotometer according to the
manufacturer’s instructions.
l. Measure the equipment’s sensitivity.
m. Conduct a test according to Beer’s law.
n. Return the spectrophotometer to the initial configuration .
19- What the probable causes and solutions of the following spectrometer faults: