Laboratory Testing Equipment

Spectrophotometer

conNz — Mon, 28 May 2007 20:08:52 +0000

Basic components of a Spectrophotometer consist of the exciter lamp, the entrance slit, the monochromator, the analytical cell or cuvette, and the photodltector. Components of a single beam spectrophometer. A, exiter lamp, B entrance slit C monochromator, D exit, E cuvetter, F photodetector and G meter. An exciter lamp provides electromagnetic radiation as visible, infrared, or UV light that will pass through the monochromator to be separated into discrete wavelengths. Light of a selected wavelength will be incident on the cuvette containing the solution of which the absorption is to be measured. For spectrophotometric work in the visible and near-infrared ranges, tungsten and halogen quartz lamps are good sources of radiant energy. Several types of vapor lamps are available for ultraviolet range. The hydrogen lamp is widely used. A mercury lamp is less desirable owing to its uneven emission spectrum. A xenon lamp gives a brilliant light that is ideal for applications requiring a narrow slit, but it is not suited for routine application owing to problems with stray light. For infrared spectrophotometry, a silicone carbide rod heated to 1200 degree Celsius works well. Collimating lenses are often inserted between the exciter lamp and the entrance slit to focus the light into a beam of parallel light rays.

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Double-Beam Spectrophotometer

conNz — Mon, 28 May 2007 20:06:38 +0000

In a double beam system monochromatic light from either a single or two identical monochromators pass through both a reference and sample compartment. The intensity of these two light beams is then measured by one or two photo detectors. The sample beam intensity is compared with the reference one as a ratio. Double-beam designs include double beam in space and double beam in time.

In a double beam in space spectrophotometer, the light is split with a half-silvered mirror, called a dichroic mirror. The dichroic mirror splits the beam so half the light passes through the specimen aliquot and the other half to the reference cell. Both beams pass simultaneously through different components separated in space. This arrangement compensates for changes in intensity of the light source. However, photo detectors may age differently, resulting in different responses. This design also does not compensate for fluctuation in the photo detector output. In a double beam in time spectrophotometer, the light beam is split with a rotating chopper that alternately presents a mirror and an opening. One beam passes through the sample and the other through a reference solution or blank. The open part of the chopper passes the beam directly to one path, while the mirrored part reflects the beam to the second path. Each beam, consisting of a pulse of electromagnetic radiation separated in time by a dark interval, is directed onto a photo detector. The output of the detector is an alternating current that has amplitude proportional to the difference in intensity of the two beams.

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Common Laboratory Measurements

conNz — Mon, 28 May 2007 19:59:12 +0000

Turbidimetry

Turbidimetry is the measurement of the reduction in light transmission caused by particle formation. Light transmitted in the forward direction is detected. The amount of light absorbed by a suspension of particles depends on the specimen concentration and on the particle size. Solutions requiring quantitation by turbidimetry are measured using visible photometers or visible spectrophotometers. High sensitivity has been achieved through photodetectors that can quantify small changes in signals. Sensitivity comparable to nephelometry can be attained using low wavelengths and high-quality spectrophotometers.

Many clinical applications exist for turbidimetry. Various microbiology analyzers measure turbidity of samples to detect bacterial growth in broth cultures. Turbidimetry is routinely used to measure the antibiotic sensitivity from such cultures. In coagulation analyzers, turKdimetric measurements detect clot formation in the sample cuvettes. Turbidimetric assays have long been available in clinical chemistry to quantitate protein concentration in biological fluids, such as urine and cerebrospinal fluid.

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Nephelometer

conNz — Mon, 28 May 2007 19:57:11 +0000

Nephelometry

Two useful methods available for measuring the concentration of a solution that contains particles too large for absorption spectroscopy are nephelometry and turbidimetry. These nonabsorptive methods may be suitable for quantitative assays using antigen-antibody complexes or measuring the amount of proteins in fluids.

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Autoclave: A Spore-Breaker Equipment for Hardy Bacteria

laboratorytestingequipment — Fri, 18 May 2007 05:33:00 +0000

Inside the laboratory, the risks of being contaminated and infected with the pathogens inherent in each specimen handled are deadly real. Aside from the obvious way of having these infective microorganisms enter the system via blood spill out, air droplets and direct skin contacts, their ever persistent presence and dormancy in the occupational area pose as lethal as other factors could be. That is why it is always observed that within the laboratory premises, each individual, especially the laboratory workers and technicians, is strictly advised to wear protective suits and observe aseptic precautions. (more…)

Equally Equipped with Equipment

laboratorytestingequipment — Fri, 18 May 2007 05:31:37 +0000

Accuracy and precision are very critical within the laboratory. As clinical specimens were received, preserved, processed and examined, clinical laboratory technologists or laboratory scientists, as other people would call it, see to it that not even a single speck of the procedure is taken lightly and left into mere chance and opportunities. Instead, highly organized protocols of assuring the observance of quality control are kept in place as the final diagnosis of diseases lies at such early phase of medical examination. (more…)