Centrifuges and Spectrophotometers

How are materials separated in centrifuges?

by density

What are centrifuges used for in the clinical lab?

to separate serum or plasma from blood cells

(separate precipitated solids froma liquid and separate liquids of varying density)

Horizontal rotor

a type of centrifuge head

cups in vertical position at rest and become horizontal when in operation

up to 3000 rpms

Fixed angle rotor

cups are at a fixed angle

lower friction and operated up to 7000 rpms

particles have shorter distance to travel (more efficient)

Microcentrifuges

high speed

small volume

measures red blood cell percentage (microhematocrit)

Ultracentrifuges

up to 100,000 rpms

Serofuges

small table top

set speed and timers

used for blood bank

What are the components of a centrifuge?

brush (electrical contact; gradually wears down)

potentiometer (raises and lowers voltage to control speed)

tachometer (indicates speed)

timer (turns off at a preset time)

brake (rapid deceleration; mechanical or electical; only used in emergency situations)

Relative Centrifugal Force (RCF)

(1.12)r (rpm/1000)²

r=radius of rotor in millimeters

rpm=number of revolutions per minute

What are some rules for the centrifuge?

always balance it

be sure cover is closed

make sure it has completely stopped before opening lid

all tubes have to be capped or topped with parafilm

Spectrophotomer

measures light transmittance of a solutino in order to determine the concentration of the substance in the solution

light source

usually white light

monochromator

selects the specific wavelength and color that will be passed through the solution

has a prism or something to defract the light

has an entrance and exit slit to block out other light

How does visible light work in relatino to wavelength?

the color seen depends on the wavelength not absorbed

cuvettes

precision made containers that are free of all imperfections

need all of them to have constant widths

they all have to be the exact same

photocell or phototube

measure light transmitted by the solution

galvanometer

records teh amount of electical current received from the photcell

beer’s law

Absorbance =(absorption coefficient)(light path in cm)(concentration)

A = abc

a and b have to be constant so that A is proprtional to C