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Medical Laboratory
Equipment …
made easy
Review & Summary
MASH 210
Prepared by
gtÜx~ XÄátÜÇtztãç
cÜÉyA tááÉvA WÜA XÇzA
Jan.2011
T. Elsarnagawy
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Spectrophotometer
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Most common spectrophotometers are used in the UV and visible regions of
the spectrum, and some of these instruments also operate into the nearinfrared region as well
Uses only one wavelength
This wavelength is obtained by using a Monochromator
A Monochromator with a diffraction grating or prism splits light into
individual wavelengths
A diffraction grating
o is an optical component with a periodic structure, which splits
and diffracts light into several beams travelling in different directions
To choose the wavelength optimum for maximum absorbance desired
color is centered on the exit slit to the sample solution
The absorbance for this color is measured and displayed
T. Elsarnagawy
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Colorimeter
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Working principle:
o Comparison of light intensities after going
through a standard solution and the sample
solution
How to change color of incident light:
o Optical filters
What is the optimum color:
o Color that is maximum absorbed by the
sample solution
Transmittance T = Iout/Iin
Transmittance
Absorbance
( I / I0 )
Absorbance A = -log T
1
o A is proportional to l (light path 0
0.1
0.79
length) & C (concentration)
0.25
0.56
o A=εbC
0.32
The output from a colorimeter may be 0.5
0.18
displayed by an analogue or digital 0.75
0.9
0.13
meter
and
may
be
shown
1
0.1
as transmittance (a linear scale from 00.01
100%) or as absorbance (a logarithmic 2
3
0.001
scale from zero to infinity)
Percent
transmittance
(100 * I / I0)
100
79
56
32
18
13
10
1
0.1
Beer's Lambert Law curve:
o Measure the absorbance of
different known concentrations
o Plot the curve (each point
(A1,C1), A2,C2), …)
Determination of the concentration of
an unknown solution:
o Measure Ax for the unknown
solution
o Look up on Beer;s Lambert
curve what concentration C is
for Ax
Calibration
o Ground the noniverting input of the amplifier
o Adjust R4 of amplifier so that Vamplifier = 0
o Remove grounding
o Put ref. solution in both cuvettes
o Adjust R1of ref sol so that Vamplifier=0
o Put the sample sol in one of the cuvettes Vampl T% or A%
Device block diagram
T. Elsarnagawy
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Flame-Photometer
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A photoelectric flame photometer is a device used in inorganic
chemical analysis to determine the concentration of certain metal ions, among
them sodium, potassium, lithium, and calcium.
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Separates compounds thermally in a flame
Atoms of each element are excited light is emitted from each element with
a characteristic wavelength
A filter picks out the light of the desired element (its intensity is depending on
the element concentration in the compound
Block diagram: burner, nebulizer, mixing chamber, sample solution beaker,
gas inlet, waste beaker, U-tube, filter selector, detector, amplifier, display
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T. Elsarnagawy
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PH-meter
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What does it measure?
o Acidity, alkalinity
Scale from 0-14 (7 is neutral pH)
PH = -10log H+
Main components of a pH-meter
o Measuring electrode
o Reference electrode
Gain: 17
Offset: 7 Volt
Output voltage: 59mV/pH unit
o 0V 0V x 17 + 7 = 7 pH 7
o -180mV -180mV x 17 + 7 pH 4
o +180mV 180mV x 17 + 7 pH 10
Calibration:
o Gain
o Offset
o Standard-pH solutions
T. Elsarnagawy
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Auto-Analyzer
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Airbubles sample segmentation (20-100 segments) add reagent tubing mixing coils dialyzer colorimeter electrical signal
(pulses or square wave)
Components:
o sampler, pump, mixing coils, optional sample treatments dialysis,
distillation, heating, detector, and data generator
T. Elsarnagawy
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Blood Cell Counter
A.
Impedance counting method (electrical):
What does it do?
• Counts the number of each type of cell found in whole blood.
• How?
• The WBC, RBC and PLT’s are counted using the “Coulter principle” where
the resistance of a circuit changes as the cells pass through a narrow aperture.
• The number of resistance changes and the amount of each change determine
the number and size (hence type) of cells
Units of measurement
• RBC, WBC, PLT are expressed in counts per micro litre (µL) Hb may be
grams per litre (g/L)
• A small opening (aperture) between electrodes is the sensing zone through
which suspended particles pass. In the sensing zone each particle displaces its
own volume of electrolyte.
• Volume displaced is measured as a voltage pulse; the height of each pulse
being proportional to the volume of the particle.
Coulter sensing cell
Impedance counter block diagram & Threshold detector
T. Elsarnagawy