Industries Information

 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.

Infrared (IR) spectrometers measure the wavelength and intensity of the absorption of infrared light by a sample. Infrared light lies between the visible and microwave portions of the electromagnetic spectrum and has a range of wavelengths. Near infrared light is closest in wavelength to visible light. By contrast, far infrared light is closest to the microwave region. Mid-infrared light is energetic enough to excite molecular vibrations to higher energy levels. These vibrations, which are caused by changes to a molecule’s dipole moment, occur only at those frequencies where the molecule absorbs infrared light. Because the wavelengths of infrared absorption bands are characteristic of specific types of chemical bonds, infrared spectrometers are often used to identify organic and organometallic molecules.

There are two basic types of infrared spectrometers. Fourier transform infrared (FTIR) spectrometers are single-beam instruments that use an interferometer to spread a sample with infrared light and measure the intensity of the infrared light not absorbed by the sample. The application of a Fourier transform converts the resulting time domain digital signal into a frequency domain digital signal. Dispersive infrared spectrometers use visible lasers, a grating, and charged coupled devices (CCDs) to collect data. The laser acts as a light source and irradiates the sample. Most of the radiation scatters elastically at the same energy as the incoming laser radiation. A small amount, approximately one photon in a million (0.00001%), scatters from the sample at a wavelength shifted slightly from the original wavelength.

Selecting infrared spectrometers requires an analysis of performance specifications such as wavelength range, resolution, accuracy, and infrared range. Wavelength range is the dispersion of the grating across the linear array, or the “size” of the spectra on the array. Resolution, a measure of an instrument’s ability to separate two overlapping peaks, is the width of an analytical peak at half its height. Typically, resolution is measured in nanometers (nm). At the point of resolution, two peaks of equal height are said to be resolved if the dip between the tops of the peaks is visible. Accuracy, another important specification, is the agreement between a mean-measured value and a true or accepted value as quantified by error. Three are three infrared ranges for infrared spectrometers: near (0.75 – 3.00 µm ), mid (3.00 – 6.00 µm) and far (6.00 – 15.00 µm). Operating temperature and operating humidity are other performance specifications.   

There are several system configurations for infrared spectrometers. Monochromatic instruments such as Czerny-Turner designs consist of fixed entrance and exit slits, fixed focusing mirrors and a rotatable diffraction grating. As the grating rotates, a different wavelength is focused on the exit slit. Filter systems or polarizers use near infrared filters that are mounted on a temperature-controlled filter wheel and controlled by a microprocessor. Acousto-optical tunable frequency (AOTF) devices include a single-element detector and overcome many of the mechanical problems associated with multi-wavelength filter instruments. Michelson interferometers split infrared energy into beams which are then recombined optically. The  two beams interfere with each other to produce a complex waveform.

There are many detector types for infrared spectrometers. Examples include deuterated triglycine sulfate (DTGS), deuterated lanthanum triglycine sulfate (DLATGS), indium antimonide (InSb), lithium tantalate (LiTaO3), and silicon (Si). Mercury cadmium tellurium (MCT) exhibits a wavelength cutoff proportional to its alloy composition. In the long wavelength spectral region, photoconductive detectors (PC-MCT) are best suited for meeting low-noise requirements. At shorter wavelengths, photovoltaic devices (PV-MCT) are suitable choices. Photoacoustic detectors measure the energy transfer from a modulated infrared beam into a mechanical vibration.

Fluorometers are instruments that measure the amount of fluorescent radiation produced by a sample exposed to monochromatic radiation. They contain filters for excitation and emission but no wavelength scanning. Light is collected at 90 degrees from the incident light (excitation) direction.  Fluorescence is a very reliable and accurate means for quantifying and detecting a compound or substance.  It is a phenomenon in which light energy is absorbed by a molecule and then re-emitted again as a photon of light with a slightly longer wavelength. The phenomenon is common among organic molecules including groups of strongly fluorescent dyes, such as fluorescein (absorbs blue, emits yellow-green light), the rhodamines (absorb green light, emit orange-red), and the family of stilbene optical brighteners, which absorb U/V light and emit blue.  Fluorescence has become an indispensable tool in a wide range of research disciplines such as: molecular and cellular biology, genetics, environmental assessment, pharmaceutics, forensics, food processing, oceanography, and biohazard detection.  Fluorometers are also sometimes referred to as luminescence spectrometers, fluorimeters, fluorescence spectrometers or spectrofluorometers.

The important parameters measured by fluorometers are the spectral or wavelength range and the accuracy and resolution of that reading.  Common detector configurations of fluorometers include photomultiplier tubes and photodiodes.  A photomultiplier tube is a photo-detector, with adjustable voltage, that translates optical tube (PMT) signals into electrical current. Increasing the PMT voltage increases the output signal for a given amount of light.  A photodiode is a semiconductor device used to detect light and generate an electrical current. Photodiode detectors are typically used in forward scatter (FSC) detection.

Fluorometers can be configured for either continuous or flow through monitoring to monitor samples on a process line or in-situ in the field.  Fluorometers can also be configured to monitor single samples.  The samples are individually injected into the fluorometer.

Common features for fluorometers include shutters, microscope, automatic temperature compensation ability, temperature measurement ability, programmability, self-calibration and alarms.

Flame photometers use atomic emission for the routine detection of metal salts, principally sodium (Na), potassium (K), lithium (Li) and calcium (Ca). A flame photometer is an instrument used for measuring the spectral intensity of metals present in the metallic salt. A flame photometer at low temperature measures the concentration of sodium and potassium present in the metallic salt. To measure the concentration of potassium present in the soil, the soil is grind and then passed through a 2 mm mesh sieve. Next, approximately 20g of air dried soil is transferred into a bottle and about 50 ml of ammonium nitrate solution is poured into it. Before shaking, this mixture is passed through a flame ionization detector. The mixture is shaken using a shaking machine for 30 minutes and at a rate of 275 strokes per minute. The shaken mixture is filtered using filter paper to retain the extract of the solution. The amount of potassium in the extract is determined using flame photometry. This is a very effective salt detection process. There are many types of flame photometers. Examples include PFP7 and PFP7/C flame photometers. A PFP7 flame photometer is a single channel photometer used for measuring sodium and potassium salts. A PFP7/C is a clinical flame photometer and is used for salt detection at low temperature. Other flame photometers are commonly available.

There are several ways in which flame photometers function. Flame photometers are also generally known as spectrometers and work by vaporizing metallic salts in a very hot flame. The quantitative analysis of vaporized metallic salt is then performed to measure the intensity of metals present in the metallic salt. The size of a flame detector in a flame photometer should be 420*360*300mm. A flame photometer for performing atomic emission of salt requires an electrical voltage of 90 - 125 volts. In addition, it requires air as moisture and an oil free specification of 6 liter/minute. Flame photometers are designed and manufactured to meet most industry specifications.

Flame photometers are used in many applications. Some examples include analysis of salt presence in biological material, and identifying the composition of alkali and alkaline salts present in the earth composition. Flame photometers should adhere to the standards used for the construction of a model 410 clinical flame photometer.

Fiber optic probes collect light or spectra from extreme environments inside reaction vessels at high temperatures or pressures. Product types include UV-Vis spectroscopy probes, Raman spectroscopy probes, and refractometry probes. UV-Vis spectroscopy probes track the electronic transitions of molecules as they absorb light in the ultraviolet (UV) and visible (Vis) regions of the electromagnetic spectrum. These fiber optic probes can be used with a wide range of samples and are suitable for biochemical, biological, and pharmaceutical research. Raman spectroscopy probes collect scattered light from a sample that is illuminated with a laser. Molecular components are identified through an analysis of the wavelengths and intensities of the scattered light. Because of their ability to avoid sample contamination, Raman spectroscopy probes are often used in polymer and semiconductor applications. Refractometry probes are fiber optic probes that detect the deviation of light by a solution as a measure of specific gravity. They are sometimes used in the identification of gemstones.

Fiber optic probes differ in terms of optics technology. Choices include holographic optics, immersion optics and insertion optics. Holographic optics produce a hologram through the use of high-precision optical hardware such as collimators, mirrors, spatial filters, optical lenses, camera lenses, exposure meters and beam splitters. Immersion and insertion optics feature single, double or triple-window designs and can be directly inserted into high-temperature reaction vessels and process streams. Like holographic optics, immersion optics and insertion optics provide high signal-to-background measurements along various lengths of optic fiber. Optics working distance and optical fiber specifications are also important considerations when selecting fiber optic probes. As a rule, single fibers or single collection fibers are less expensive than multi-fiber fiber optic probes. In some products, standard telecommunications fibers are used to provide enhanced mechanical stability.

Fiber optic probes differ in terms of applications. Raman spectroscopy probes can be used to analyze samples, obtain chemical intermediate information from automated laboratory reactors, monitor in-situ crystallization, detect end-points, and identify polymorphs. UV-Vis spectroscopy probes are available in both dual beam and diode array designs. Dual-beam fiber optic probes offer superior flexibility and precision. Diode array fiber optic probes combine flexibility with relatively high speeds. Refractometry probes are used in medical fields such as hematology.