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.

Gas chromatography detectors (GC detectors) identify solutes as they exit the chromatographic column. As solutes are eluted from the gas chromatography column they interact with the detector. The GC detector converts this interaction into an electrical signal that is sent to the data system. The magnitude of the signal is plotted versus time (from the time of injection) and a chromatogram is generated.  GC detectors use one of several technology types to identify solutes as they exit the column.  These methods include thermal conductivity, flame ionization, atomic emission, electron capture, photoionization, flame photometric, chemiluminescence spectroscopy, and nitrogen phosphorous.

Thermal conductivity GC detectors consist of an electrically heated wire or thermistor. The temperature of the sensing element depends on the thermal conductivity of the gas flowing around it. Changes in thermal conductivity, such as when organic molecules displace some of the carrier gas, cause a temperature to rise in the element, which is sensed as a change in resistance.

Flame ionization GC detectors consist of a hydrogen / air flame and a collector plate. The effluent from the GC column passes through the flame, which breaks down organic molecules and produces ions. The ions are collected on a biased electrode and produce an electric signal.

Atomic emission GC detectors simultaneously determine the atomic emissions of many of the elements in analytes that elute from the GC capillary column. As the eluant comes off the capillary column it is fed into a microwave powered plasma (or discharge) cavity where the components are destroyed and their atoms are excited by the energy of the plasma. The light that is emitted by the excited particles is separated into individual lines via a photodiode array.

Electron capture detectors use a radioactive Beta emitter (electrons) to ionize some of the carrier gas and produce a current between a biased pair of electrodes. When organic molecules contain electronegative functional groups, such as halogens, phosphorous, and nitro groups pass by the detector, they capture some of the electrons and reduce the current measured between the electrodes.

Photoionization GC detectors use ultraviolet light as a means of ionizing an analyte exiting from a GC column. Electrodes collect the ions produced by this process. The current generated is therefore a measure of the analyte concentration.

Chemiluminescence spectroscopy detectors use quantitative measurements of the optical emission from excited chemical species to determine analyte concentration. Usually the emission is measured from energized molecules rather than excited atoms. The bands of light determined by this technique emanate from molecular emissions and are therefore broader and more complex than bands originating from atomic spectra.

Nitrogen phosphorous GC detectors burn the compound in plasma surrounding a rubidium bead supplied with hydrogen and air. Nitrogen and phosphorous containing compounds produce ions that are attracted to the collector. The number of ions hitting the collector is measured and a signal is generated.

In specifying a GC detector the detection limit or sensitivity, dynamic range and temperature range are all important parameters.  GC detectors also have important parameters that are specific to each technology type.

Gas chromatographs separate organic chemical mixtures according to physical properties. Instruments consist of a flowing mobile phase, an injection port, a separation column with a stationary phase, and a detector. Differences in partitioning behavior between the mobile phase and the stationary phase cause the separation of compounds. Gas chromatographs use many different detection methods. Choices include: thermal conductivity detectors (TCD), flame ionization detectors (FID), atomic emission detectors (AED), electron capture detectors (ECD), photo-ionization detectors (PID), flame photometric detectors, and nitrogen phosphorous detectors. Gas chromatography that uses chemiluminescence spectroscopy is also available. Some gas chromatographs are used with agricultural chemicals and pesticides, cosmetics and fragrances, drugs and pharmaceuticals, electronics, energy and environmental applications, food and beverage processing, forensics and narcotics, industrial gases, medical and biological applications, or metals and welding. Others are used with organic and inorganic chemicals; paint, castings, and inks; paper, pulp and wood; petroleum products; plastics, polymers, and resins; or soaps and cleaners.  

Oven operation, pump specifications, and injection operation are the main parameters for gas chromatographs. Devices with a column oven carry specifications such as operational method and oven temperature range. There are two operational methods for columnar ovens: isothermal or constant-temperature, and variable or temperature-programmable. Flow control and inlet pressure range are common pump specifications. In terms of injection operation, parameters include number of injection ports, injection method, and column injection. For optimum efficiency, a sample should not be too large for a column, and is best introduced as a "plug" of vapor. There are two choices for column injection method: split/split-less and packed column. With split or split-less column injection, the injector has an additional set of gas lines, providing another path for the vaporized sample. This extra line is sometimes called a split line or vent. Importantly, the amount of gas that exits the split line controls the amount of sample that enters the column. With packed column injection, all samples enter the column - including the gaseous sample, solvent, and analyte.

Specifications for gas chromatographs may include user interface options, display options, additional output options, and general features and functionality. Local interfaces use an analog front panel, a digital front panel, or a computer interface with parallel or serial communications. Analog meters, digital readouts, and video displays are common choices for display options. Additional output options include: analog voltage, frequency or modulated frequency, analog current, and switch or relay contacts. Some gas chromatographs are programmable, self-calibrating, or include a built-in chromatogram. Others provide data storage options and are designed for extreme environments. Gas chromatographs that accept liquid samples and include self-test diagnostics are also available. 

Digesters break down samples into their basic constituents for analysis.  While they function in a similar fashion to biological digestion, the constituents are not used for food, rather for study.  Sample digestion is often involved in hunts for trace metals, to prepare for such analyses as atomic absorption or inductively coupled plasma spectroscopy.  This classification of devices includes those used for laboratory research, sample testing, and process study.  Large-scale troughs, tanks, or silos used for sewage treatment, treatment of agricultural waste, or methane abatement are not covered. The two most common types of digesters are those that function via acid digestion or microwave digestion (although custom, specialized and proprietary technologies are available).

In acid digestion the sample is digested under elevated pressure (100-500 psi) and temperature (50-180 degrees C) conditions using conventional acids, such as nitric and hydrochloric acids.

Microwave digesters heat microwave-absorbing reagents containing a sample inside a pressurized, microwave-transparent container. Pressurization allows higher temperatures to be achieved, thus increasing the speed of digestion. Pressure and temperature inside the control vessels may be monitored and used to determine the amount of microwave energy applied.

Laboratory digesters are all of a batch-type design.  Sample material, generally organic matter, is placed within the device and is allowed to digest. The retention time depends on temperature and other factors. Once the digestion is complete, the effluent is removed and the process is repeated.  Installation of a fume hood is helpful to remove gases produced by the digestion process.

One of two methods is used to process samples: open flask or closed flask digestion.  As the name implies, in open flask digestion, the reaction takes place in an open container.  This is the more commonly used method; calling for lower pressure to perform the procedure, although gas build up is more likely.  Closed flask reaction takes place in a closed container.  The elevated pressures that can be achieved in closed reaction vessels decrease digestion time.  Generally, high-pressure vessels are used for biological and organic chemical samples, while lower pressure vessels are used for soil/sediment, environmental samples, and catalysts.

Digesters can be preset to process a batch of samples over a specific period of time. Automated operation frees key laboratory personnel from managing the long and tedious digestion processes and provides a head start on analysis.

Degassers are used to filter or remove gases from solvents and samples. The primary methods employed include vacuum degassing, flow degassing and helium degassing. Flow degassers function via a gentle flow of dry gas over the surface of the sample particles.  This function serves to quickly wick moisture and other contaminants away from the sample.  In many cases, needle valves are employed, which allow careful control of flow rate while avoiding elutriation (blowing out) of fine powders.

Vacuum degassers remove atmospheric interferences and diffused gases from solvents, mobile phases, and reagents during use.  Within these degassers, water trickles through the system where its flow is interrupted up by a packed filtration medium. The water flow is broken down into a very thin film, which allows gases to escape at an enhanced rate. An internal vacuum system inside the filter increases the rate at which gases can be extracted from the sample. 

Solvent or membrane degassers remove gaseous components such as O₂, N₂, and CO₂ from solvents by passing the solvent through a special fluoropolymer membrane tube with the pressure outside the tube reduced. This is a popular degassing method, because membrane separation is carried out under such mild conditions, that the process has virtually no effect leaving the composition of the solvent relatively unchanged. In addition, it is highly efficient, yielding results similar to that of degassing by the helium sparging method.

In helium degassers, the dissolved air within the solvent is expelled by continuously passing helium through the solvent. This is the most effective method of degassing and is particularly recommended for trace analysis, and for avoiding the fluorescence quenching due to the affect of dissolved oxygen on the analytes. The disadvantages associated with helium degassing are the high price of helium, and the fact that the helium can release more volatile solvent components, like tetrahydrofuran, over a period of time. This can give rise to changes in retention times.

Other important configurations to consider include the vacuum rating of the degasser, the number of input channels in the device, and the maximum flow rate per channel.  The more channels that degassers have, and the higher the flow rate, the more rapidly the devices can dissipate gases from a sample.

electrophoresis (CZE), Capillary electrophoresis (CE) is a group of related separation techniques that use narrow-bone fused-silica capillaries to separate a complex array of large and small molecules. Capillary electrophoresis (CE) is used for the analysis of ions, and both basic and chiral pharmaceuticals. There are many types of capillary electrophoresis (CE) depending on the type of capillaries and the electrolytes used. Examples include micellular electrokinetic chromatography (MEKC), capillary zonecapillary gel electrophoresis (CGE), and capillary isoelectric focusing (CIEF). Micellular electrokinetic chromatography (MEKC) is used for separating mixtures containing both ionic and neutral species. Capillary zone electrophoresis (CZE) is known as free solution CE and it provides constant field strength throughout the length of the capillary. A capillary gel electrophoresis (CGE) is used to separate the proteins and nucleic acids. Capillary isoelectric focusing (CIEF) separates amphoteric molecules such as proteins by electrophoresis in a pH gradient that is generated between cathode and the anode. Other capillary electrophoresis (CE) are commonly available.

There are several ways in which capillary electrophoresis (CE) function. In micellular electrokinetic chromatography (MEKC), the surfactants are added to a buffer solution and the separation is done by differential partition between the solvent and micelle. Capillary zone electrophoresis (CZE) fills the capillary tube with aqueous buffer solution that contains both positive and negative ions. The surface of the capillary has a net negative charge because of Si-O chemical groups present in the glasslike material. Capillary gel electrophoresis (CGE) uses gel which builds heat and is detrimental to separation. It is used for DNA sequencing and genotyping. Capillary isoelectric focusing (CIEF) combines with capillary reversed-phase liquid chromatography (CRPLC) using a micro injector as the interface for performing the 2-D protein separations from complex protein mixtures. Capillary electrophoresis (CE) is designed and manufactured to meet most industry specifications.

Capillary electrophoresis (CE) is used in many applications. Some examples include genetic analysis, analysis of pharmaceuticals (containing nitrogenous bases), gunshot residue analysis, and counter-ion analysis in drug discovery. Capillary electrophoresis (CE) adheres to ICC standards.