Laboratory Mixers

Laboratory mixers are used to mix, emulsify, homogenize, disintegrate and dissolve samples. There are several basic types of products. Dual-shaft mixers use a three-wing or helical anchor to generate flow and remove mixed materials from the vessel wall. Double-planetary mixers use a rectangular or finger-shaped blade to feed material to an orbiting high speed dispenser (HSD). Single-stage rotor/stator devices use a stationary stator to turn an immersed rotor at high speeds. The blades pass each port in the stator and expel material at a high velocity into the surrounding mix. Multi-stage rotor/stator mixers increase shearing to produce smaller particle sizes and more homogenous batches. When two to four rotor/stator pairs are nested concentrically, the mixed material that moves outward from the center of the unit is subjected to a rapid, sequential shearing. Some mixers can be operated at variable speeds. Others are designed for continuous speeds.

Selecting laboratory mixers requires an analysis of performance specifications. Speed range and accuracy are usually measured in revolutions per minute (rpm). Viscosity range is measured in cycles per second (cps). Capacity, the size of the mixing vessel, is expressed in either liters (L) or gallons (gal). Operating temperature and operating range are measured in degrees Fahrenheit (F) or degrees Celsius (C). There are two sample introduction methods for laboratory mixers. Continuous devices accept a continuous flow of the sample. By contrast, batch mixers accept only a measured flow or volume. In terms of temperature control, laboratory mixers with an internal heating or cooling elements are commonly available. Heating elements are usually made of ceramic materials, powered electrically, and measured in watts (W). Smooth cooling shovels that rotate within a drum are used to ensure maximum contact without inter-particle friction.

Laboratory mixers vary in terms of user interface options, display types, and special features. Analog front panels include potentiometers, dials, switches or other manually-actuated inputs that allow operators to adjust ranges and control the output. Digital front with numeric keypads or menus are used to perform these same functions. Video displays consist of a cathode ray tube (CRT), liquid crystal display (LCD), flat panel display (FPD) or other multi-line display. Intrinsically safe (IS) laboratory mixers will not produce sparks, electrical energy or other thermal effects that would cause an explosion under normal or abnormal conditions. Some laboratory mixers are handheld, but not necessarily portable. Others mount on an overhead stand. Programmable mixers and devices that use a timer are used in many applications.

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• Preparation of Samples for Aflatoxin Testing
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