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Hướng dẫn lựa chọn máy quang phổ theo ứng dụng

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Spectrometers, or spectrophotometers, are analytical instruments used to identify or confirm the chemical species, chemical structure, or concentration of substances in a sample. Spectrophotometers will emit an energy source to pass through a solution and measure light intensity at different wavelengths. If the solution is high in molecular concentration, then more light will be absorbed. In most cases, a sample submitted for spectrometric analysis must be very pure in order to avoid poor or contaminated results. Spectrometers are generally comprised of a light or energy source (typically a lamp), a filter (or monochromator) to set desired wavelengths of which to read, a place for cuvettes or blanks, and a radiation detector (or phototube) to convert the energy received during the experiment into a measurable signal.

Important criteria to consider when selecting proper spectrophotometer/spectrometer:

    • Detection limits
    • The density, shape, or size of the product you wish to measure
    • Wavelength range
    • Analytical working range
    • Sample throughput (single sample vs. multi-sample)
    • Data quality
    • Cost of instrument and associated consumables
    • Customizable and/or pre-configured method options
    • Measurement time
    • Footprint of instrument

What is the difference between single beam, double beam (dual-beam), and split beam spectrophotometers?

 

A single beam spectrophotometer has only one beam of light, while a double beam spectrophotometer has two beams of light, one passing through a reference solution and one passing through the sample. In single-beam instruments, because there is only one light path which passes through the sample, it therefore requires manually switching a reference cuvette with the sample cuvette for calibration. Double beam spectrophotometers operate faster and provide more reproducible results because they perform an automatic correction for the loss of light intensity as the beam passes through the sample and reference solution. Split-beam instruments are similar to dual-beam systems, but instead use a beam-splitter which rapidly alternates the light path between the reference and the sample while using one detector.

Guidelines for evaluating cuvettes

 

Windows: Cuvette windows should be uniformly clear, with no scratches, clouding, inclusions, bubbles, streaks, or “rainbowing,” as these issues will negatively affect the performance of the cuvettes. Scratches on non-optical sides are negligible.

Mold markings: Ideally, a single box of cuvettes should have identical mold markings. If they are not identical, then they may not have come from the same mold cavity and will be inherently more inconsistent in measurement.

Performance: Test your cuvette by running it several times in your spectrophotometer. It is always a good idea to rotate it 180 degrees and retest. Values should be very close. If results are inconsistent it could be due to poor molding or a poor fit in the cuvette holder. If values differ significantly, the cuvette windows are likely inconsistent from one side to another. Window inconsistencies, thickness, and quality of resins used make a big difference at critical wavelengths during testing and use.

Calibrating your instrument

To calibrate a spectrophotometer, a reference solution is used to zero out the instrument. This solution provides a base or zero reading. The device is then calibrated by placing the reference solution inside the spectrophotometer, zeroing out the settings, and running the instrument. You can then test your material with confidence that your machine is working properly.

A variety of spectrometers are available on the market. See below for more information on the common types Cole-Parmer carries.Personal weather stations

Visible Light Spectrophotometers: Simple spectrophotometers use only visible light (320 to 1000 nm) produced by a tungsten lamp. Portable and benchtop models with a continuous wavelength range are most commonly used for routine laboratory work. Choose from analog and digital models that feature optional data acquisition software for your PC.

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UV/Visible Spectrophotometers: A second lamp—usually deuterium—turns a visible light spectrophotometer into a UV-visible unit that can measure from 190 nm to 1100 nm. UV-visible models are available with a variety of features including scanning function, multiple cells, integral printers, and user interfaces.

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Near-Infrared (IR or NIR) Spectrophotometer: IR spectrometers operate on a similar principle as UV spectroscopy, however they measure the response of a sample when exposed to infrared light. NIR offers non-invasive analysis and quantitive determinations with minimal sample preparation. It is particularly useful for monitoring highly absorbing solids, and providing information such as protein, fat, fiber, and starch content. Our scanning infrared spectrophotometers provide data over a full range of wavelengths from 7800 to 350 cm-1 in seconds.

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NMR: Nuclear Magnetic Resonance (NMR) spectroscopy is arguably the most powerful tool available for determining the structure of organic compounds—giving structural information of the whole molecule, and dynamic insights of organic reactions. Cole-Parmer carries a miniature, technologically advanced high-resolution true NMR instrument that is an excellent tool for teaching and applications.

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Atomic Absorption Spectrophotometer: A high-temperature flame evaporates water from the sample which then dissociates the sample into ions. This results in a change in light intensity as measured by the detector to determine sample concentration. This high-precision analysis is ideal for environmental testing, toxicology, and quality control laboratories. An optional continuous-flow hydride/cold vapor system lets you test for arsenic, selenium, or mercury.

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Mercury Spectrophotometer or Analyzer: An economical alternative to atomic absorption systems, the mercury analyzing spectrophotometer quickly measures trace amounts (0 to 9 µg) of mercury in potable, surface, saline, or wastewater.

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Fluorometers: Fluorometers measure the fluorescence released when a sample is exposed to a single wavelength of light. Select one of our compact and efficient fluorometers for unlimited analysis testing in biotechnical, food-testing, pharmaceutical, life-science and environmental applications.


Comparison Table
Industry Surface Color meter and spectrophotometer models
Painted surfaces Flat panels

12-mm 45/0 cone, 12-mm hemisphere,
26-mm, 11-mm benchtop

Curved surfaces 3-mm, use foam baffle
Masonry, stucco, cement 20-mm D with window and baffle
Plastics Flat areas 12-mm cone
Small parts 3 mm
Curved surfaces 3-mm, use foam baffle
Wire and cable Small wire and fiber special, 3-mm and fixture
Fibers and small tubes Up to 5-mm D, wire and fiber special
Textured surfaces 20-mm D with window, 12-mm hemisphere
Powders 12-mm or 20-mm with window,
30-mm bench top
Transparent 12-mm with white background
Foods and
agriculture
Cheese, meats 12-mm w/window, 20-mm D w/window
Powders, flour, sugar 20-mm D w/window, 30-mm bench top
Fruits, outside 12-mm cone
Fruits, inside and fish 12-mm with window
Leaves, small areas 3 mm
Soil and grass clippings 20-mm D w/ window, 30-mm bench top
Coffee, grains, snack foods 30-mm bench top
Opaque liquids, sauces, dips 30-mm bench top
Graphic arts Litho printing 3 mm
Other printing small 3 mm
Ink proofs, larger print targets 12-mm cone
Paper Finished paper 12-mm, 11-mm bench top
Paper pulp and paper board 20-mm D w/ window
Textile Textile printing 3 mm
Hard weave 12-mm cone
Solid colors soft weave 20-mm D w/window, 30-mm bench top
Packages 12-mm cone
Cosmetics Foundation drawdowns 12-mm cone, 11-mm bench top
Skin, cosmetics on skin 12-mm flat head
Powders and creams 12-mm or 20-mm with window, 
30-mm bench top
Lipstick 12-mm with thin film press
Packaging 3 mm

 Reference source:  http://www.coleparmer.com/TechLibraryArticle/1415