Industries Information

X-ray fluorescence spectrometers (XRFs) use a spectroscopic technique that is commonly used with solids, in which X-rays are used to excite a sample and generate secondary X-rays.  The X-rays broadcast into the sample by X-ray fluorescence spectrometers eject inner-shell electrons. Outer-shell electrons take the place of the ejected electrons and emit photons in the process. The wavelength of the photons depends on the energy difference between the outer-shell and inner-shell electron orbitals. The amount of X-ray fluorescence is very sample dependent and quantitative analysis requires calibration with standards that are similar to the sample matrix.

The solid samples used with X-ray fluorescence spectrometers are usually powdered and pressed into a wafer or fused in a borate glass. The sample is then placed in the sample chamber of the XRF spectrometer, and irradiated with a primary X-ray beam. The X-ray fluorescence is measured either in simultaneous or sequential modes, and is recorded with either an X-ray detector after wavelength dispersion or with an energy-dispersive detector.

X-ray fluorescence spectrometers measure the emitted X-ray fluorescence in either a simultaneous fashion, or sequential.  Simultaneous mode typically measures the entire wavelength range around the emission line of interest simultaneously, while sequential mode typically measures one wavelength at time.

Wavelength dispersive detectors use a nondestructive analysis technique for the identification and quantification of elements in a material. Wavelength dispersive spectroscopy is the measurement x-ray energies emitted from the bombardment of an energy source impinged upon the material, producing characteristic x-rays.  Energy dispersive X-ray fluorescence spectrometers also use nondestructive analysis techniques for the identification and quantification of elements in a material. Energy dispersive spectroscopy is the measurement x-ray energies emitted from the bombardment of an energy source impinged upon the material, producing characteristic x-rays.

XRF was originally used to analyze geological samples. The advancement of computers and other technologies allowed the technique to develop even further.  XRF found its place in many different types of analytical laboratories and some industrial inspection systems. X-ray fluorescence spectrometers provide a number of distinct advantages including easy sample preparation, nondestructive rapid multi-element analysis, and the ability to screen unknowns in a wide array of sample matrices such as liquids, solids, slurries, powders, pastes, thin films, air filters, and many others.  Because of these advantages the technique, it is widely used for research, in industrial settings, and by quality assurance analysts.

Spectrometers, UV and visible, measure the amount of ultraviolet and visible light transmitted or absorbed by a sample placed in the spectrometer. The wavelength at which a chemical absorbs light is a function of its electronic structure and the intensity of the light absorption is related to the amount of the chemical between the light source and the detector, so a UV / Visible spectrum can be used to identify some chemical species.

UV and visible spectrometers may come with one of three common photometric design systems.  Scanning single beam systems can be one of two types of instrument, either a single wavelength light source or a selector for a single wavelength. The light from the lamp is dispersed before reaching the sample cell.  A scanning double beam instrument measures both the transmittance of the sample and solvent at each wavelength simultaneously and computes the ratio. The light from the lamp is dispersed before reaching the sample cell.  All wavelengths pass through the sample and the dispersing element is between the sample and the array detector. This allows the detector to simultaneously record the transmitted light power at multiple wavelengths.  Commonly UV spectrometers and visible spectrometers will have a monochromator, which is used to separate the wavelengths of the light source before the light passes through the sample and enters the detector.

Common detector types found in UV spectrometers and visible spectrometers include photomultiplier tubes, diode arrays and charge-coupled devices (CCDs).  A photomultiplier tube, useful for light detection of very weak signals, is a photo emissive device in which the absorption of a photon results in the emission of an electron. These detectors work by amplifying the electrons generated by a photo cathode exposed to a photon flux.  A diode array detects which light is absorbed and which is reflected.  A CCD chip, is an array of light-sensitive elements. Which are, in fact, some small electronic capacitors. The electrons generated by the light charge these capacitors. In fact, each light element (commonly called photon), that reaches the CCD array’s atoms, displaces some electrons, which are providing a current source. These current sources, are localized in small, delimited areas (the capacitors), called pixels.

Important parameters in specifying spectrometers, UV and visible are wavelength range, resolution and accuracy.  Wavelength range is the dispersion of the grating across the linear array; also expressed as the "size" of the spectra on the array.  The spectral resolution is the width of an analytical peak at half its height expressed in nanometers. A measure of the instruments ability to separate two overlapping peaks. At the point of resolution, two peaks of equal height are said to be resolved if you can see a dip between the tops of the two peaks separate two overlapping peaks. At the point of resolution, two peaks of equal height are said to be resolved if you can see a dip between the tops of the two peaks.  The wavelength accuracy is the agreement between a mean measured value and a true or accepted value as quantified by error. Related to determinate errors and quantified by bias.  Detector sample volume and sample flow rate range are also important specifications pertaining to UV and visible spectrometers.

Many UV spectrometers and visible spectrometers will give measurement values for transmittance, absorbance and reflectance.  Transmittance is the ratio of the radiant power transmitted by a sample to the radiant power transmitted by a blank in an equivalent cell or by some other means of compensation for solvent absorption, reflection losses, etc.  Absorbance is a measure of concentration of material present: negative log (base 10) of Transmittance [- log 1/ T] of product of extinction coefficient, path length, and concentration, written as A = e bc.  Reflectance is the ratio of the radiant energy reflected by a body to the energy incident on it. Spectral reflectance is the reflectance measured within a specific wavelength interval.

Spectrometers are analytical instruments which disperse an emission (such as particles or radiation) according to some property of the emission (such as mass or energy) in order to measure the amount of the dispersion. This product area includes visible, infrared (IR), ultraviolet (UV), atomic absorption (AA), optical emission (OE), Raman, X-ray fluorescence (XRF) and mass spectrometers. Specific search forms are also available. Performance specifications for spectrometers include: spectral range, spectral resolution, mass range, mass resolution, and mass accuracy. Spectral range is the dispersion of the grating across the linear array, or the “size” of the spectra on the array. Spectral resolution is the width of an analytical peak at half its height as measured in nanometers (nm). This value indicates the spectrometer’s ability to separate two overlapping peaks. Spectral accuracy is the agreement between a mean measured value and a true or accepted value as quantified by error. Mass range is a measurement of atomic mass that is expressed in atomic mass units (amu) or Daltons (Da). Mass resolution is the ratio of the mass divided by the change in mass over the area of two peaks.  

There are many different types of spectrometers. UV and visible spectrometers measure the amount of ultraviolet (UV) and visible light transmitted or absorbed by a sample placed in the spectrometer. Infrared (IR) spectrometers measure the wavelength and intensity of the absorption of infrared light by a sample. Atomic absorption (AA) spectrometers use the absorption of light to measure the concentration of gas-phase atoms. Atomic emission (AA) and optical emission (OE) spectrometers determine analyte concentration via a quantitative measurement of the optical emission from excited atoms. Raman spectrometers are used to measure the wavelength and intensity of inelastically scattered light from molecules. X-ray fluorescence spectrometers (XRF) use a spectroscopic technique that is commonly used with solids, in which X-rays are used to excite a sample and generate secondary X-rays.  Mass spectrometers separate ions by their mass-to-charge (m/z) ratios. They are used to identify compounds by the mass of one or more elements in the compound. They are also used to determine the isotopic composition of one or more elements in a compound.

Specialty spectrometers and accessories are specialty or proprietary products and accessories related to spectrometers, analytical instruments that are used measure the amount of dispersion of a property such as mass or energy. Like other types of spectrometers, specialty spectrometers are used to determine chemical composition and to perform electromagnetic radiation analysis by measuring light intensity across the visible, ultraviolet (UV), and infrared (IR) spectrums. A specialty spectrometer can be built using optical detectors such as charged coupled devices (CCD) or photo diode arrays, or fiber optics.

Specialty spectrometers and accessories are often application-specific and differ in terms of performance specifications such as wavelength range, optical resolution, sensitivity or absorption, and data capture speed. Products used in thin film analysis are different from those used in biomedical applications, or for monitoring inline process control. Some specialty spectrometers are used in medical imaging applications. For example, nuclear magnetic resonance (NMR) spectroscopy is used to determine physical and chemical information about a specific molecule, typically organic compounds. Resonance spectroscopy is based on the magnetic property of an atom’s nucleus and its response to an electromagnetic field. This is the technique used in magnetic resonance imaging (MRI).

Many other types of specialty spectrometers are available. Secondary ion mass spectrometry (SIMS) is a technique for analyzing the surface of a thin film test sample. An ion mass spectrometer is used to analyze the particles emitted by an object after it is bombarded with a stream of ions or charged particles. Electron auger spectroscopy is also used to analyze surface composition of materials. Auger electron spectroscopy (AES) measures the energies of Auger electrons, which are created by bombarding the sample with an electron beam. Auger electron energies are tabulated based on the Auger effect or process.

Suppliers of specialty spectrometers are located across the United States and around the world. They conform to various quality standards and regulatory requirements.

Residual gas analyzers (Rags) are spectrometers that are used to identify the gases present in vacuum environments.  Residual gas analyzers perform this function by producing ionizing molecules of the gas sample, separating the resulting mixture of ions according to their charge-to-mass ratios, providing an output signal, which is a measure of the relative species present, and counting the rate at which the ions hit the detector. The spectrometers within residual gas analyzers analyze the process by which a mixture of ionic species is separated according to the mass-to-charge ratio (m/z). The analysis may be qualitative and/or quantitative.  There are two common styles of spectrometric analysis used, quadrupole and magnetic sector analysis, although there are specialized and custom designs available.

Quadrupole mass spectrometers consist of an ion source, ion optics to accelerate and focus the ions through an aperture into the quadrupole filter, the quadrupole filter itself with control voltage supplies, an exit aperture, an ion detector, detection electronics, and a high-vacuum system.  The mass spectrometer operates only in a high vacuum whereas the gas it is being used to analyze is often at atmospheric pressure. To reduce the pressure the gas is sampled twice using a "double sniffer" configuration.

Magnetic sector residual gas analyzers use one of two methods to read and identify samples.  Single focusing analyzers focus a circular beam in a path of 180, 90, or 60 degree. A variety of forces influence the particles and separate the ions due to their different mass-to-charge ratios. In double focusing analyzers, an electrostatic analyzer is added to separate particles with difference in kinetic energies.

Residual gas analyzers ionize their samples using a variety of technologies and methods including electron impact ionization (EI), field ionization (FI), and chemical ionization (CI).  EI uses an electron beam, usually generated from a tungsten filament, to ionize gas-phase atoms or molecules. An electron from the beam knocks an electron off of analyte atoms or molecules to create ions.  FI removes the electrons from any species by interaction with an intense electrical field. CI forms new ionized species when gaseous molecules interact with ions. The process may involve transfer of an electron, a proton or other charged species between the reactants.

Finally, there are two distinct detector types that can be found within residual gas analyzers. Electron multiplier tubes are similar in design to photomultiplier-tubes. They consist of a series of biased dynodes that eject secondary electrons when they are struck by an ion. They therefore multiply the ion current and can be used in analog or digital mode.

Faraday cup residual gas analyzers use a metal cup that is placed in the path of the ion beam. It is attached to an electrometer, which measures the ion-beam current. Since a Faraday cup can only be used in an analog mode it is less sensitive than other detectors that are capable of operating in pulse-counting mode.

 Refractometers are widely used to measure the amount of dissolved substances in solutions containing mainly sucrose. The relationship between refractive index and the amount of dry substance content is well known for sucrose and is the basis of the BRIX scale, which is the measure of the number of grams of sucrose present per 100 grams of aqueous sugar solution. That is, 50 BRIX means 50 grams of solid per 100 grams of solution. This relationship holds for a large number of similar substances and so the BRIX scale is widely used in the food industry. Unfortunately the refractive index of a sugar solution changes with temperature while its solid content remains the same.

Refractometers measure the critical angle of refraction through a sample. The critical angle of refraction will change with concentration. It will normally increase with an increase in concentration. Color, gas and dissolved particles do not affect measurement results. Refractometers can be designed for either continuous or sample monitoring.

Important specifications for refractometers are the refractive index range or BRIX range, depending on which is being used, and the accuracy. The pressure range of the refractometers is important, as are the maximum flow velocity and the sample size.

Sample temperature control is a popular feature available for some refractometers. Another special feature is an automatic prism wash system, which will clean the prism without having to remove it from the refractometer. Other features include temperature compensation, temperature sensing, sanitary ratings, programmability, self-calibration and alarms.

Common display types for refractometers include analog meters or gauges, digital displays and video terminal displays. They can be handheld, as a field instrument might be, portable with wheels or handles for ease in transporting, or more permanently fixtured instruments. Analog outputs such as current, voltage and frequencies are often available. Computer signals and other digital outputs can be found in these devices as well.

 Raman spectrometers measure the wavelength and intensity of inelastically scattered light from molecules. They are used to determine the chemical composition of a sample based on the wavelength and intensity of the light passing through the sample. Raman spectroscopy is based on the theory of Raman scattering, which states that light is scattered due to the vibrations of the molecules in the substance or substrate through which light passes. This vibration scatters the light and changes its energy from that of the incident light. In this way, Raman spectrometers use the Raman effect by comparing the different energies of the incident light and the scattered photons.

Raman spectrometers are similar to infrared (IR) spectrometers in that both an IR spectrometer and Raman spectometer measure the vibrational energies of the molecules in a sample. Infrared spectroscopy or IR spectroscopy measures the absorption of light of certain energies that correspond to the vibrational energy of the molecule. Since Raman scattering is different from infrared absorption, the two methods of spectroscopy are often used to provide complementary data.

Raman spectrometers often use lasers, the most typical being an argon ion laser. A laser spectrometer offers many benefits, including focused, high-powered excitation of the tested substance which results in a high incidence of light scattering. Because the Raman effect measures the difference between scattered and incident light, Raman spectrometers are particularly useful in gathering data from a small section of a sample. Consequently, Raman spectrometers are being used to develop confocal microscopy techniques. The incident laser radiation of the Raman spectrometer is focused with the microscope objective on a point in the sample. The resulting Raman spectrum contains data almost exclusively from a point within the sample.

Suppliers of Raman spectrometers are located across the United States and across the world. They meet a variety of regulatory requirements and quality standards.

Polarimeters are instruments used to measure the rotation of the plane of vibration in polarized light. Light polarization can be measured using a Stokes vector polarimeter. The polarization properties of a particular material can be measured with a Mueller matrix polarimeter. Typically, Mueller matrix polarimeters are used to determine the purity of materials such as sugar, vitamins, steroids, and antibiotics. Polarimetry of thin films and surfaces is called ellipsometry, which is used to provide information about layers that are thinner than the wavelength of the light itself, down to a single atomic layer or less. An interferometer uses the interference pattern of two beams of light to make very precise measurements. Interferometers can measure minute surface irregularities in optical devices such as mirrors. In astronomy, interferometers can measure the distances between celestial objects and their diameters. The most sensitive polarimeters are based on interferometers, while more conventional polarimeters use polarizing filters, wave plates or other devices.

Choices for polarimeters include: complete vs. incomplete, sequential vs. simultaneous, monochromatic vs. polychromatic, non-imaging polarimeter vs. imaging polarimeter, and manual (visual) vs. electronic (automatic). For pharmaceutical testing, most work is done using 589 nm light (sodium D line). For electronic (automatic) polarimeters, total accuracies of 0.01° are possible. The light source in a polarimeter can be a spectral arc lamp (sodium or mercury), or an incandescent lamp (tungsten). Spectral arc lamps can be designed for visible, ultraviolet (UV) and infrared (IR) wavelengths, and are suitable for stability of wavelength and long-term calibration. Incandescent lamps are less expensive than spectral arc lamps, but limited to visible and IR radiation.

ASTM International (formerly called the American Society for Testing and Materials (ASTM), maintains ASTM C1426 regarding the standard practices for verification and calibration of polarimeters. Other standards describe how to use polarimeters in standard tests (i.e. ASTM F218 for analyzing stress in glass). The Society of Manufacturing Engineers (SME) maintains SME EM930116 for the rapid contour measurement of composite structures utilizing a three-dimensional (3D) tracking interferometer.

Water quality photometers and colorimeters are ion-specific computer-interfaced probes designed to determine the concentration of a solution from its color intensity. The color of a solution may be inherent or derived by adding another reagent to it. Monochromatic light from an LED light source passes through a cuvette containing a solution sample. Some of the incoming light is absorbed by the solution. As a result, light of a lower intensity strikes a photodiode. The amount of light that penetrates a solution is known as transmittance. Transmittance can be expressed as the ratio of the intensity of the transmitted light, It, and the initial intensity of the light beam, Io, as expressed by the formula:

T = It / Io

Photometers and colorimeters produce an output voltage, which varies in a linear way with transmittance, allowing a computer to monitor transmittance data of a solution thus producing an output that can be converted to concentration.

Mounting options for water quality photometers and colorimeters are quite varied. They can be handheld, portable meters or benchtop or fixtured instruments. Handheld meters are popular for laboratory use, where a scientist may be taking readings from many different samples. Portable meters typically have wheels, handles or another device for transportation. Benchtop and fixtured instruments are permanently mounted for long-running use.

Displays for the instruments can be analog meters, a numeric or alphanumeric digital display or video, CRT or LCD. Another option is to have no local display at all and have the data gathered by another instrument. Likewise, the user controls can also be analog or digital or can be operated through a host computer. To simplify the instruments, preprogrammed devices without user controls are available.

Electrical output options for water quality photometers and colorimeters are the standard voltage and current outputs as well as an analog pulse or frequency or a change in state of switches or an alarm. Serial and parallel interfaces can help connect these instruments to a host computer.

Some features for water quality photometers and colorimeters are battery power for greater mobility, auto wavelength selection and automatic calibration. Temperature compensation is available in some models, as are self-test diagnostic routines to verify sensitivity, zero point, etc. Water resistant housings and data storage and logging capabilities enhance the versatility of these instruments.

 Mass spectrometers are used in both quantitative and qualitative analysis, including high-resolution accurate mass measurements for the determination of elemental compositions. Mass spectrometry (MS) is an analytical spectroscopic tool primarily concerned with the separation of molecular (and atomic) species according to their mass. MS can be used in the analysis of many types of samples, from elemental to large proteins and polymers.

Important performance parameters to consider when specifying mass spectrometers include mass range, resolution, mass accuracy and mass spectrum.  Mass range is a measure of the atomic mass range detected by the spectrometer in Atomic Mass Units. May also be measured in Daltons.  The resolution is the ratio of the mass divided by the change in mass over the area of two peaks. (m/dm).  The mass spectrum is a spectrum obtained when ions (usually in a beam) are separated according to the mass-to-charge (m/z) ratios of the ionic species present. This plot is a graphical representation of m/z values versus measured ion abundance information.

Mass spectrometers have one of five common mass analyzer designs.  The mass analyzer is the part of the spectrometer that analyzes the process by which a mixture of ionic species is separated according to the mass-to-charge ratio (m/z). The analysis may be qualitative and/or quantitative.  Time of Flight (TOF) instruments utilize the times taken by ions to pass (fly) along an evacuated tube as a means of measuring m/z values and therefore of obtaining a mass spectrum.  Quadrupole mass spectrometers consist of an ion source, ion optics to accelerate and focus the ions through an aperture into the quadrupole filter, the quadrupole filter itself with control voltage supplies, an exit aperture, an ion detector, detection electronics, and a high-vacuum system.  The ion-trap mass spectrometer uses three electrodes to trap ions in a small volume. The advantages of the ion-trap mass spectrometer include compact size and the ability to trap and accumulate ions to increase the signal-to-noise ratio of a measurement.  Fourier-transform mass spectrometry takes advantage of ion-cyclotron resonance to select and detect ions.  Single focusing analyzers use a  circular beam path of 180, 90, or 60 degrees. The various forces influencing the particle separate ions with different mass-to-charge ratios. Double focusing analyzers have an electrostatic analyzer added to separate particles with difference in kinetic energies.

Mass spectrometers use one of four ionization methods to ionize the sample for analysis.  The electrospray ionization (ESI) source consists of a very fine needle and a series of skimmers. A sample solution is sprayed into the source chamber to form droplets. The droplets carry charge when they exit the capillary and, as the solvent evaporates, the droplets disappear leaving highly charged analyte molecules. ESI is particularly useful for large biological molecules that are difficult to vaporize or ionize.  In fast atom bombardment (FAB) a high-energy beam of neutral atoms, typically Xe or Ar, strikes a solid or low-vapor-pressure liquid sample causing desorption and ionization. It is used for large biological molecules that are difficult to get into the gas phase. The sample is usually dispersed in a matrix such as glycerol. FAB causes little fragmentation and usually gives a large molecular ion peak, making it useful for molecular weight determination.  An electron impact ionization (EI) source uses an electron beam, usually generated from a tungsten filament, to ionize gas-phase atoms or molecules. An electron from the beam knocks an electron off of analyte atoms or molecules to create ions.  Matrix-assisted laser deposition/ionization (MALDI) is a LIMS method of vaporizing and ionizing large biological molecules such as proteins or DNA fragments. The biological molecules are dispersed in a solid matrix such as nicotinic acid or dihydroxybenzoic acid. A UV laser pulse ablates the matrix that carries some of the large molecules into the gas phase in an ionized form so they can be extracted into a mass spectrometer.