Industries Information

Laboratory balances are used to measure an object’s mass to a very high degree of precision. They consist of a beam with a friction-free fulcrum, a pointer which attaches to the beam and amplifies deviation from the balance position, and fractional weights which are applied along the beam’s measuring arm. Often, the weighing pan is sealed to prevent the ingress of dust or other contaminants. Samples are maintained at room temperature to prevent the formation of air currents inside the enclosure. Other sources of error for laboratory balances include buoyancy, friction, improper miscalibration, misalignment, condensation, evaporation, gravitational abnormalities, and seismic disturbances. For best results, laboratory balances provide high readability, a broad weighting range, and a high degree of accuracy.  

There are many types of laboratory balances. Examples include beam balances, equal-arm balances, unequal-arm balances, spring balances, analytical balances, moisture balances, top-loading balances, and platform balances. An equal-arm balance is the simplest type of beam balance. A uniform bar or beam is suspended at its exact center. By contrast, an unequal-arm balance is suspended at a point a very short distance from one of its ends. A spring balance consists of a coiled spring fixed to a support at one end, with a hook at the other to which the body to be weighed is applied. An analytical balance is designed for quantitative chemical analysis. A moisture balance is used to measure the moisture content in a material sample. A top-loading balance uses a glass or plastic breeze-break atop the scale. A platform balance is a form of equal-arm balance in which two flat platforms are attached to the top side of the beam, one at each end.  

Specifications for laboratory balances include capacity, resolution, platform width and length, display, interface, and ratings or certifications. Some laboratory balances have an analog display such as a needle. Others have a digital display such as a liquid crystal display (LCD), light-emitting diode (LED), or vacuum fluorescent display (VFD). Laboratory balances with remote displays are also available. There are four choices for laboratory balance interface: serial, parallel, universal serial bus (USB), and wireless. Ratings for laboratory balances include Ingress Protection (IP) standards, ratings from the National Electronic Manufacturers Association (NEMA), and certification by the National Type Evaluation Program (NTEP). Laboratory scales that sold in Europe must meet the Waste Electrical and Electronics Equipment (WEEE) directive from the European Union (EU).

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.

Laboratory homogenizers are high-speed, high-shear mixers that reduce samples to uniformed-sized molecules through maceration, cutting, and blending. They are used to process liquids, slurries, or granular substances. Product specifications for laboratory homogenizers include media viscosity, capacity, feed rate, motor speed, motor power, pressure range, and operating temperature. Viscosity is a measure of a fluid’s thickness. Capacity is the volume of product that a laboratory homogenizer can accommodate. Feed rate measures product flow over a given period of time. Media characteristics such as pH concentration and specific gravity are also important considerations. Some laboratory homogenizers include an integral heating or cooling element. Others are intrinsically safe, explosion proof, or designed for sanitary applications.   

There are three basic types of laboratory homogenizers: fluidized bed, rotor-stator, and ultrasonic. Fluidized-bed homogenizers are durable vessels which fluidize the complete product bed. Efficient and thorough, these laboratory homogenizers can achieve relatively fast rotational speeds, but require higher levels of applied horsepower (hp). Rotor-stator homogenizers are single-shaft mixers with an impeller which rotates in close proximity to a stationary housing. The rotor imparts high shear forces mechanically while the stator directs the flow. Ultrasonic or vibrational homogenizers apply ultrasonic waves in a mixed medium to produce a steep gradient of acoustical pressure and, therefore, fluid movement and a very-fine level of mixing action. Though inaudible to the human ear, these ultrasonic waves are capable of exerting pressures of more than 500 atmospheres (atm) and achieving temperatures of 5,000° C.     

Laboratory homogenizers differ in terms of mounting styles and user interface. Handheld, benchtop, portable, overhead, stand-mounted, and floor-mounted products are commonly available. Display type and local interface define the user interface. There are three basic display types: analog meter, digital numerical display, and video display. Analog meters have a dial or indicator lights. Video displays use a cathode ray tube (CRT), liquid crystal display (LCD), or other multi-line display. As a local interface, laboratory homogenizers may include an analog or digital front panel. An analog front panel has user inputs such as potentiometers, dials and switches for the adjustment of outputs and ranges. A digital front panel features digital menus or keypads.  

Laboratory homogenizers are used with a wide range of materials, but are best suited for high-moisture, high-fat, or fibrous products. In addition to homogenization, they are used in comminuting, deagglomerating, disintegrating, dispersing, and dissolving processes. Some laboratory homogenizers are also used in emulsification, extraction, gassing, mixing, precipitation, process reactions, shredding and wetting applications.

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.