Centrifuges - "The Gravity of It All"

Centrifuges separate particles and structures suspended in liquid by applying thousands of gravitational force equivalents to the sample through spinning. Laboratories use centrifuges to clarify suspensions, separate liquids, isolate suspended particles, perform density measurements, and for many other applications.

Many users, and some manufacturers, specify centrifuges and centrifugation in terms of rotor revolutions per minute (rpm), but as Dr. Lars Borrmann, group marketing manager at Eppendorf (Hauppauge, NY), notes, rpm is a vague term that says nothing about separation power: “Customers still ask about rpm, but that only tells you what the motor can do and nothing about the force being applied.”

Currently, the operative term is RCF, relative centrifugal force, a function of rotor radius and the square of the rotational speed. Two centrifuges with the same RCF provide comparable resolving power. Transferring methods between centrifuges is difficult without knowing the instruments’ RCF values.

Dr. Borrmann places centrifuges into two basic categories: inexpensive instruments that provide basic speed and capacity, and ergonomic and “eco-friendly” units.

Labs are noisy, with numerous devices contributing to the din. A loud centrifuge can tip the noise balance into the intolerable range. “You don’t want a screaming loud instrument right next to where you’re working,” Dr. Borrmann says.

Accessibility is another oftenoverlooked ergonomic issue. Dr. Borrmann advises buyers to consider units with a low profile and easyopen- and-close lids for increased safety. The final ergonomic consideration is ease of operation.

For Maurizio Merli, senior product manager for benchtop centrifuges at Thermo Fisher Scientific (Milford, MA), improved construction materials have been the most significant trend in centrifugation, providing levels of biological and workplace safety that did not exist 15 years ago.

When a centrifuge spinning at tens of thousands of rpm crashes, the device becomes a kind of centrifugal fragment bomb that can destroy a lab and cripple or kill anyone nearby. Most units today employ high-quality covers and paneling to keep flying metal inside.

Manufacturers have focused on rotor design to minimize the effects of a crash, particularly for highspeed units. Aluminum alloys and lightweight metal amalgams provide mechanical integrity and high performance. Composite rotor materials, which Thermo has pioneered, do even better by providing the highest strength-to-weight ratings.

Most use glass-reinforced plastics, similar to materials used to make surfboards and aircraft. Carbon fiber-based composites do an even better job, according to Mr. Merli. Carbon fiber rotors are stronger than metal of equivalent weight, contain potential biological hazards better than do conventional rotor designs, and resist corrosion—a major source of catastrophic failure and centrifuge crashes.

Industrial and regulated applications are driving the application of data logging in centrifugation, observes Randy Pawlovich, strategic marketing manager at Beckman Coulter (Indianapolis, IN). “In the old days, the traditional customers were research and academic labs and data wasn’t a big deal.” Today, he says, regulated industries (like diagnostics) routinely collect centrifuge operation data.

Even in non-regulated settings, companies facing tight budgets are documenting who uses instruments and for how long, and what mishaps may have occurred during a particular run.

Allegra X-30 Series Benchtop

18-inch-wide instrument is now available individually or packaged with the appropriate rotors and labware to provide high-level performance in a range of applications
The SX4400, a 1.6-liter swinging-bucket rotor, and the S6096 microplate rotor that accommodates 3 x 2 microplates or 2 x 1 deep-well plates are also available
Offers intuitive operation and large interface

Beckman Coulter
www.beckmancoulter.com

Clinical Centrifuge Package
QuickSpin® PLUS

Ideal for stat and coagulation applications, including platelet poor plasma
Features a maximum RPM of 8,000 and RCF of 6,153
8-place rotor is ideal for small sample quantities
Accommodates a wide variety of tube sizes

HELMER
www.helmerinc.com

Mini

Includes three rotors: a 6 x 1.5mL rotor, a PCR Strip rotor and a 1” x 3” slide rotor
Also includes two adapters for 0.5 to 0.65mL and 0.4mL
Features a safety interlock which automatically shuts off unit when lid is opened
Cold room compatible

Scie-Plas
www.scie-plas.com

Sorvall® RC 12BP Plus Floor-Standing

For blood banking and bioprocessing applications
Features a maximum capacity of 12 L
Accumulated Centrifugal Effect™ (ACE) function automatically compensates for any variations in acceleration due to full or partial rotor loading

Thermo Fisher Scientific
www.thermoscientific.com