Industries Information

Laboratory centrifuges are used for separating particles from solutions according to their size, shape, density, viscosity of the medium and rotor speed. The theoretical basis of this technique is the effect of gravity on particles (including macromolecules) in suspension. Two particles of different masses will settle in a tube at different rates in response to gravity. Centrifugal force (measured as xg, gravity) is used to increase this settling rate depending on the rotation to induce centrifugal force, which accelerates the separation of the liquid from the solids. Centrifugal force causes the solid phase to move through the liquid phase in a straight line and away from the center of rotation. Solid-phase characteristics such as particle density, size, shape, and consistency and the rotation speed for the laboratory centrifuges’ chamber (a basket or bowl, depending on the centrifuge type) of a given diameter also influence how fast the solid phase moves away from the center of rotation. The higher the rotation speed, the higher the G force exerted on the solid phase and the faster the solids accumulate.

The two most common types of laboratory centrifuges are analytical and preparative; the distinction between the two is based on the purpose of centrifugation.

Preparative laboratory centrifuges are used to isolate specific particles. This classification is divided into two types: differential and density. Differential centrifuges are used to separate particles from a liquid medium or to separate particles of different masses into separate fractions of the supernatant. Density centrifuges work by spinning two fluids of different densities within a rotating container or rotor the heavier fluid is forced to the wall at the inside of the rotor while the lighter fluid is forced toward the center of the rotor.

Analytical laboratory centrifuges measure the physical properties of particle, such as sedimentation coefficient or molecular weight. Optimal methods are used in analytical ultra centrifugation. Molecules are observed by optical system during centrifugation, to allow observation of macromolecules in solution as they move in gravitational field. The samples are centrifuged in cells (tubes with quartz windows) having windows that lie parallel to the plane of rotation of the rotor head. As the rotor turns, the images of the cell (proteins) are projected by an optical system on to film or a computer. The concentration of the solution at various points in the cell is determined by absorption of a light of the appropriate wavelength (Beer’s law is followed). This can be accomplished either by measuring the degree of blackening of a photographic film or by the pen deflection

High performance liquid chromatograph (HPLC) detectors pass a beam of light through a column effluent as the fluid passes through a low-volume flow cell. Variations in light intensity are recorded and a chromatograph is generated. HPLC detectors use several detection methods. Ultraviolet (UV) detectors measure the ability of a sample to absorb light at one or more wavelengths. Light scattering detectors nebulize the effluent, vaporize the solvent, and then detect droplets in a light scattering cell. Electrochemical detectors measure the current from the oxidation/reduction reaction of an analyte at a suitable electrode. Radiochemical detectors use tritium or carbon-14 to detect the fluorescence associated with beta-particle ionization. Mass spectroscopy detectors ionize a sample and use a mass analyzer to detect the ion current. Nuclear magnetic resonance detectors irradiate nuclei that are placed between the poles of a strong magnet. The radiation is absorbed, the parallel nuclei enter a higher energy state, and each atom produces a spectra specific to its location and chemical composition. Some HPLC detectors measure the change in the refractive index of the column effluent passing through the flow cell. Others detect the fluorescence that occurs when compounds are excited by shorter wavelength energy and emit higher wavelength radiation.

Important specifications for HPLC detectors include dynamic range, detector wavelength, response time, flow cell volume and flow cell rate. Dynamic range allows for the quantification of unknown samples using a multi-point calibration curve. It indicates when the peak area is directly proportional to the solute amount so that, for example, doubling the solute amount results in a doubling of peak area. Detector wavelength indicates the emission wavelength. Response time is the amount of time between a solute’s entry into an HPLC detector and the generation of a chromatogram. Flow cell volume and flow cell rate are measurements of capacity and efficiency, respectively. Maximum pressure rating is another important specification to consider when searching for HPLC detectors.

HPLC detectors vary in terms of general features, display options, and interface options. General features include self-calibration, self-test diagnostics, data storage, and programmability. Devices with a built-in chromatograph and application software are commonly available. Some HPLC detectors are suitable for extreme temperatures. Others output an analog voltage, analog current, frequency, or pulse. Examples include amplitude modulation (AM), frequency modulation (FM), pulse width modulation (PWN), sine waves and pulse trains. Analog devices usually include an analog meter and a front panel with switches and knobs. Digital devices often provide a serial or parallel computer interface and a video display. Serial protocols include universal serial bus (UBS), RS232, RS422, and RS485.

 High performance liquid chromatography (HPLC) is a separation technique that uses liquid mobile phase to separate the components of a mixture. The sample is first dissolved in a solvent, then forced to flow through a chromatographic column under high pressure. Within the column, the mixture is resolved into its component parts. Individual HPLC columns may use any one of a number of different phases or processes to induce this resolution including normally bonded phase, reversed phase, size exclusion, ion exclusion, and ion exchange.

Normally bonded phase HPLC columns are composed of a stationary bed, which is strongly polar in nature, and a mobile phase that is non-polar. Polar samples are thus retained on the polar surface of the column packing longer than less polar materials. This technique works well with water-sensitive samples, analytes that are insoluble in water, certain geometric isomers that are difficult to separate by reversed-phase, and class separations. Organic solvents used in normal-phase separations are more Mass Spectroscopy (MS) friendly than some of the typical buffers used in HPLC. In reversed-phase HPLC, operating conditions sometimes must be dramatically modified to allow compatibility with MS detection.

Reversed phase HPLC columns are the inverse of normal phase chromatography. The stationary bed is non-polar (hydrophobic) in nature, while the mobile phase is a polar liquid, such as mixtures of water and methanol or acetonitrile. The lower the polar differential, the longer the material is retained.

In size exclusion the HPLC column is filled with material having precisely controlled pore sizes, and the sample is screened or filtered by the stationary phase according to its solvated molecular size. Larger molecules are rapidly washed through the column, and smaller molecules penetrate the pores of the packing particles and elute later.

In ion exclusion the anions are retained longer on the stationary phase than on anion-exchange columns. Quantification is therefore simplified in the event large amounts of cationic contaminants are present in the sample.

In ion exchange, the stationary bed with the HPLC column has an ionically charged surface of opposite charge to the sample ions. This technique is used almost exclusively with ionic or ionizable samples. The stronger the charge on the sample, the stronger it will be attracted to the ionic surface and thus, the longer it will take to elute. The mobile phase is an aqueous buffer, where both pH and ionic strength are used to control elution time.

High performance liquid chromatographs (HPLC) use a liquid mobile phase to separate the components of a mixture. The components are dissolved in a solvent and forced to flow through a chromatographic column under high pressure. In the column, the mixture is resolved into its components. The components flow through a detector and a chromatogram is generated. Most high performance liquid chromatographs (HPLC) use high-pressure pumps to force solvents through packed stationary beds. Isocratic pumps use constant mobile phase composition to elute compounds. By contrast, gradient pumps vary the strength of the organic solvent to elute different compounds. Pumps with flow control are well-suited for high performance liquid chromatographs (HPLC) that deliver gradients automatically. Specifications such as flow rate, maximum pump pressure, and pump accuracy vary among devices. In simple systems, the sample is introduced with an injection valve. More complex high performance liquid chromatographs (HPLC) incorporate an autosampler with a microprocessor.

High performance liquid chromatographs (HPLC) use several detection methods. Ultraviolet (UV) detectors measure the ability of a sample to absorb light at one or more wavelengths. Light scattering detectors nebulize the column effluent, vaporize the solvent, and then detect droplets in a light scattering cell. Electrochemical detectors measure the current from the oxidation/reduction reaction of an analyte at a suitable electrode. Radiochemical detectors use tritium or carbon-14 to detect the fluorescence associated with beta-particle ionization. Mass spectroscopy detectors ionize a sample and use a mass analyzer to detect the ion current. Nuclear magnetic resonance detectors irradiate nuclei that are placed between the poles of a strong magnet. The radiation is absorbed, the parallel nuclei enter a higher energy state, and each atom produces a spectra specific to its location and chemical composition. Some high performance liquid chromatographs (HPLC) measure the change in the refractive index of the column effluent passing through the flow cell. Others detect the fluorescence that occurs when compounds are excited by shorter wavelength energy and emit higher wavelength radiation.

High performance liquid chromatographs (HPLC) vary in terms of general features, display options, and interface options. General features include self-calibration, self-test diagnostics, data storage, and programmability. Devices with a built-in chromatograph and application software are commonly available. Some high performance liquid chromatographs (HPLC) are suitable for extreme temperatures. Others output an analog voltage, analog current, frequency, or pulse. Examples include amplitude modulation (AM), frequency modulation (FM), pulse width modulation (PWN), sine waves and pulse trains. Analog devices usually include an analog meter and a front panel with switches and knobs. Digital devices often provide a serial or parallel computer interface and a video display. Serial protocols include universal serial bus (UBS), RS232, RS422, and RS485.

Gel electrophoresis equipment is used to separate macromolecules, either nucleic acids or proteins, on the basis of size, electric charge, and other physical properties. Gel electrophoresis equipment allows researchers to maintain a uniform electric field across a gel. It also provides for a cooling effect that prevents thermal artifacts and allows access to the gel for convenient loading and monitoring.

An essential piece of gel electrophoresis equipment is the gel electrophoresis apparatus, which uses a positive and a negative charged pole generated by electrical currents to separate molecules. These apparatuses come in horizontal or vertical forms. Horizontal gel electrophoresis units are boxes divided into two compartments by a middle platform and are generally used for separating, visualizing samples, and analyzing restrictions. Vertical gel electrophoresis products are typically used for DNA sequencing and consist of negative and positive electrode chambers, sample wells, gel plates, and cooling plates.

Gel electrophoresis equipment uses an electrophoresis power supply attached to a running tank to provide a regulated electric current to separate the charged molecules. Gel electrophoresis tanks, or running tanks, comprise of a flat bed, column, and slab. Another important component to gel electrophoresis equipment are electrophoresis DNA sequencers, which are made of a slab of gel with electrophoresis migration paths sandwiched between two planes of glass. Different DNA samples are inserted into each migration path and moved under the influence of electrophoresis.

Acrylic electrophoresis equipment, such as an acrylic tank, is used to ensure that there are no leaks during the electrophoresis process. The acrylic material allows for durability and full view of contents due to its transparent material. Platinum electrodes for gel electrophoresis provide gel electrophoresis equipment with a uniform, corrosion resistant, electrical field and are embedded in acrylic tanks for an even current flow. Nucleic acid electrophoresis equipment is used for analytical and preparative studies of nucleic acids and usually comprises of a removable UV-transparent gel-casting tray, end gaskets that allow the gel to be cast directly in the running tank, and buffer recirculation ports.