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Every industry has its own special vocabulary that outsiders don’t understand. But in the lighting field, the technical lingo is sometimes confusing if not incomprehensible even to lighting industry insiders.

In a never ending battle to promote the advantages and technical superiority of their products, manufacturers are increasingly turning their efforts to enhancing ad copy and pouring on the technical jargon in specification sheets.

The idea is to impress specifiers with the image of quality and high technology. Some of this language is true and impressive, and some is just over-hyped copy.

There are also many time-honored catch phrases that are put in every lighting catalog and are never questioned but are nonetheless rarely understood by the very people who are specifying these fixtures.

This article offers a brief glossary of terms with an explanation in plain English as to what they mean and specifically how these attributes should affect fixture specification.

Commercial Lighting Specification Description Terminology

CRT Cathode Ray Tube, what is now called a computer monitor (see VDT).

Low Brightness This usually refers to a reflective surface that doesn’t produce an intense glare (or brightness) when looking directly at it.

Photometric Optimization When fixture manufacturers engineer lamp positions, reflectors and/or louver profiles ensure that the maximum amount of light leaving the lamp(s) will end up in the task area, as opposed to being trapped inside the fixture or bouncing uselessly around the room.

Rainbowing An effect that happens with certain types of fluorescent lamps (especially high-color-rendering triphosphor lamps) are used with certain types of lower-end anodized aluminum reflectors and louvers. It causes a noticeable and unacceptable rainbow reflection on the anodized surfaces of the fixtures.

Troffer As the name implies, troffers are trough-shaped recessed ceiling fixtures (the term is derived from the terms trough and coffer. They usually contain fluorescent lamps and have an open surface flush with the ceiling.

A parabolic troffer refers to a recessed fixture that has a louver with a parabolic cross section. The parabolic shape redirects light rays from the light source into parallel rays that shine in a controlled fashion into the room.

VCP Visual Comfort Probability. This is a fixture rating system that determines how many people would, when viewing this fixture, find it to have low glare and be comfortable to work near. The higher the number or percentage, the better.

VDT Video Display Terminal, what is now called a computer monitor (see CRT).

Commercial Lighting Specification Materials Glossary Of Terms.

OGa CRS 20-Gauge Cold Rolled Steel. This is the most common type of steel used in the lighting industry. Cold rolling indicates that the steel is not heat-treated or hardened, which allows for easy forming, piercing, stamping or shearing when manufacturing a lighting fixture.

Twenty-gauge CRS is in the general range of 0.036 in. in thickness.

l6Ga. Galvanized Steel A steel commonly used in internal or unseen functional parts of a fixture. This metal is used because it doesn’t require finishing or painting. Steel is galvanized by applying a layer of zinc to the raw metal sheets.

This process helps preserve the material and prevent it from rusting. Sixteen-gauge equals about 0.060 in. thickness.

Clear Specular Alzak Reflector Alzak is a registered trademark, originally of Alcoa. This is a proprietary anodizing process that allows maximum light reflection from the reflective surface with low brightness and glare.

Code Gauge This is a catch-all term used by many people to refer to the gauge of metal used in a fixture — acceptable to the certain prevailing national electrical or local code requirements for fixture construction.

Pre-Anodized Aluminum Anodizing is one of the most common finishing processes done to aluminum in the lighting industry. Anodizing is a controlled oxidation process that occurs when aluminum is exposed to an electrically charged chemical bath.

The end result is a hardening of the surface to resist abrasion and corrosion with an added protective transparent layer to preserve the decorative natural aluminum finish. Anodizing can also produce colored or dyed finishes that are locked into the aluminum surface.

Pre-anodizing is usually performed on the raw coil of aluminum before it is fabricated into a louver or reflector.

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Vinylcarbazole has been used in research labs since the early 1920’s. When produced from non-coal tar sources it is found to be most pure and typically is a more white/off-white crystalline material that melts at 65-67 degrees Celsius. The final monomer has good solubility in polar organic, aromatic, and chlorinated solvents, with only minimal solubility in non-polar systems that are not aromatic.

A summary of key physical property and research information for vinylcarbazole -

Alternate names 9-vinyl-9H-carbazole; vinyl-9H-carbazole; N-vinylcarbazole
CAS 1484-13-5
Molecular weight 193.24 g/mol
Formula C14H11N
Melting point 65-66 degrees Celsius

Monomer Synthesis

As indicated earlier, carbazole from coal-tar distillation is the main starting material for industrial synthesis of vinylcarbazole. Typically, vinylation of the carbazole in the presence of a metal hydroxide is arguably the safest industrial route. However, acetylene reactions with alkali metal salts are used by organizations that are allowed, and capable, of undertaking acetylene-based reactions. Acetylene reactions are often undertaken at moderate to high pressures in order to affect this route. Recently a slightly better route using acetylene carbonate has been developed, but the yields indicate a higher end cost per Kg of the material.

Laboratory preparations have the advantage of using more expensive starting materials and more elegant chemistry. This in turn allows the production of vinylcarbazole that may be purer, and free of the impurities that exist with coal-tar sourced vinylcarbazole. An example synthesis is the dehydration of N(2-hydroxyethyl)carbazole which is obtained by the reaction of potassium carbazole with 2-chloroethanol.

For the organometallic and catalyst chemists among us, PdCl2 has been used to effect ethylenation of carbazole starting materials. These laboratory synthesis methods are important for scientists who need very high purity material. When researching vinylcarbazole production researchers should be careful to determine the source of their material as it may impact their results.

Some key impurities from coal-tar distillation include sulfur compounds, aromatics and polyaromatic rings such as anthracene.

One synthetic and handling note - Always read the material safety data sheet for full information, but take prior note that vinylcarbazole should be handled with care because it may cause skin irritations and is believed to be carcinogenic.

Polymer Synthesis

There are many methods for the polymerization of vinyl carbazole:
(i)Radical polymerization
(ii)Cationic polymerization
(iii)Charge-Transfer polymerization
(iv)Solid-State polymerization

Each of these utilizes very different conditions and initiators, ultimately resulting in a wide variety of polymer properties. The overriding goal is to produce a homo- or co-polymer of vinylcarbazole. Poly(vinylcarbazole), or PVK, polymers are well known for their thermal stability and optoelectronic properties when doped. That broad discussion is beyond the scope of this article.

If you would like to learn more about vinylcarbazole visit http://www.monomerpolymer.com.

Amino acid analysis refers to a variety of methodologies which are used to determine the amino acid content of peptides, proteins and other samples. Amino acids, of course, are organic compounds which contain an amino group and a carbolic acid group as well as any of many possible side groups. These side groups are typically linked by peptides, forming proteins or compounds which are employed as intermediates in the metabolic process or as chemical messengers within living organisms.

Proteins and peptides are organized as linear polymers; these macromolecules are composed of covalently bonded amino acid residues. The properties of a given organic molecule (such as a peptide or protein) are determined by the sequence of amino acids present - data which is gathered through amino acid analysis. A peptide is a smaller molecule, often consisting of only a few amino acids. Proteins, by comparison are large and are generally folded into a specific structural model containing a larger number of amino acids.

Identification and quantification of proteins and peptides can be determined through analysis; it is also used to detect atypical amino acids present in a peptide or protein analyzed as well as for the evaluation of fragmentation strategies in peptide mapping applications. Before the analysis proper can be performed, proteins and peptides must be hydrolyzed to separate their constituent amino acids. After hydrolysis, amino acid analysis can be performed in the same manner as is used for free amino acids (such as is done in preparing pharmaceuticals).

The most common methodology for the analysis of amino acids in a sample involved chromatographic separation of the amino acids present. Automated chromatographic instruments with post column derivation are the most commonly used technologies at present; most analysis of amino acids is most commonly done with a liquid chromatograph (low or high pressure) which can generate mobile phase gradients. This procedure separate the amino acid analytes in the column.

Background contamination is always a concern when performing amino acid analysis. High purity reagents are absolutely necessary. For instance, low purity hydrochloric acid can contribute to glycine contamination. Analytical reagents are changed routinely every few weeks using only high-pressure liquid chromatography (HPLC) grade solvents. Potential microbial contamination and foreign material that might be present in the solvents are reduced by filtering solvents before use, keeping solvent reservoirs covered and not placing instruments in direct sunlight.

The accuracy and reliability of the analysis process can be ensures through basic best laboratory practices. The lab must be sterile, instruments installed in a relatively low traffic area and pipettes cleaned (or replaced) and calibrated regularly. Vials containing samples must be opened only when absolutely necessary; contamination by dust can cause elevated glycine, alanine and serine.

Accuracy in amino acid analysis depends on proper maintenance of the instruments, which should be checked for leaks daily if the equipment is in regular use. The stability of the lamp, detector and the column’s ability to provide proper resolution of individual amino acids should all be checked and filters and other consumables replaced regularly.

Andrew Long writes for scientific websites and a main area for content covers lab suppliers and services like amino acid analysis and amino acid analyzer products.

There are a variety of different gel dryer units which are commercially available for different gel drying applications in the laboratory. The exact drying methods used differ depending on the nature and size of the gels involved.

Polyacrylamide gels of standard size can be dried by oven-like air drying systems, while gels containing corrosive compounds must instead be dried by vacuum dryers which feature filter traps. Sequencing gels (and other larger gels) or multiple standard size gels need a large drying surface with drying enhanced by a vacuum.

The gels are normally dried between two sheets of porous cellophane and come out of the gel dryer completely flat and clear with a glossy finish. The dried gels can be used for further detection and analysis by photodocumentation, densitometry or autoradiography. This gel drying process also makes them suitable for long-term storage. There are also heat vacuum method dryers available which can dry gels rapidly and evenly. These types of dryers come with separator traps which capture corrosive liquids and vapors from the gels as they dry.

A manual gel dryer process is also used in some laboratories. Manual drying uses a solution containing 10% glycerol and 20% ethanol, drying frames and as with other methods, cellophane sheets. In a manual gel dryer procedure, the gel to be dried must first be equilibrated in a drying solution for a minimum of half an hour to reduce swelling and make the gel more flexible once dried.

The next step in the gel drying procedure is to place the gel between two sheets of moistened cellophane after pipetting 1.2 ml of drying solution on top of the gel. The cellophane sheets containing the gel are then clipped together and left to dry for a minimum of two days. As you can imagine, this is a much lengthier and labor intensive process than that offered by an automated gel dryer unit. There are also quite a few things which can go wrong along the way in the manual process, which leads to the commercially available units being preferred in most laboratories where resources and bench space permit.

Yet another alternative to manual drying as well as the more expensive vacuum-based gel drying units is also available. This is a lower-tech but simple and cost effective method of drying gels; both agarose and polyacrylamide gels can be dried using gel drying film; essentially pre-treated film which is used along the same lines as the manual method but resulting in much more rapid drying. This allows the gels to be viewed even as they are drying and provides a virtually gas-impermeable barrier.

The exact type of gel dryer which is preferable for a given application depends on the requirements of the gel and the other parameters of the application in question. Other factors such as available space in the laboratory, resources available and the throughput of gel drying required all come into play in the question as well. For those facilities which have a large volume of gels, however, the commercially available automated dryer units are a very welcome addition to the laboratory worth every millimeter of bench space that they occupy.

Andrew Long writes for scientific websites and a main area for content covers lab suppliers and services like gel drying and gel dryer products.

Sieving in its most elemental definition is the separation of fine material from coarse material by means of a meshed or perforated surface. The technique was used as far back as the early Egyptian days as a way to size grains. In order to understand sieving today, it is essential to examine the definition of test sieves, limitations of the test sieve procedure, test sieve standards, sieve certifications, and sieve calibration.

Certifications

A sieve certification is an assurance that a new sieve will perform in a predictable way. The closer the tolerance required in a manufacturing process, the higher the level of certification needed. Learn the fundamental differences between Mesh Certified Sieves, Mid-Point Sieves, and generic certifications.

Sieve Certificates

Sieve certifications are statements that a test sieve meets or exceeds published criteria. It is an assurance that a new sieve will perform in a predictable way. The closer the tolerance required in a manufacturing process, the higher the level of certification needed. Similarly, a master set of test sieves against which working sieves (sieves in everyday use) are checked for wear and predicted performance need a high level of certification. When test sieves are part of a process that is required to meet traceability prerequisites, such as a specific ISO level, a certification will document the needed traceability.

Many sieve manufacturers provide a certificate which states that the sieve was manufactured in conformance with a specific standard (ASTM, ISO). The Manufacturing Conformance Certificate references that the mesh was in conformance with a standard. Most manufacturers supplying a Conformance Certificate will analyze the mesh in a sieve and provide a mesh certification for an extra charge.

A Mesh-Certified Sieve will be provided with a certificate that states the sieve was a) manufactured in accordance with a specified standard, B) was submitted for laboratory analysis and C) is certified that the mesh conforms a specific specification/standard (ASTM, ISO).

There is a third and still higher level of assurance. This is a certificate that states A) the manufacturing standard was met, B) the mesh was submitted for laboratory analysis and C) the sieve openings fall in the middle of the specific standard. (ASTM, ISO). This is effectively a 30% tighter tolerance than the mesh standard. This is known as a Mid-Point Sieve and the certificate contains the inspection measurements.

These three levels of sieve certification enable the a comparability of expected performance of one sieve to another of the same size.

Until the development of the Mid-Point Sieve, high levels of comparability were achieved by providing sieves that were optically matched to a user’s standard sieve. A time consuming and costly procedure was needed to accomplish this level of comparability and the results were not significantly better than those achieved by using Mid-Point Sieves.

Other Sieve Mesh Types

There are three lower grade levels of sieve mesh available to meet special need and lower levels error tolerance .

The first is Market Grade. These sieves have a weave that uses a larger diameter wire resulting in a high strength square-mesh cloth suitable for general purpose screening. There are no official standards for Market Grade test sieves.

The second, Mill Grade, is a class of woven mesh using smaller wire, which results in larger open areas in the screen mesh.

There is also a Twill Weave in which the weft and warp wires alternatively run over and under two wires rater than over and under alternate wires as in standard mesh.

As none of these have official standards against which to measure the expected performance, none of these are provided with a mesh certificate.

New Developments

In 2009, the ASTM Specification E11-09 was issued. This new standard specifies three new categories of compliance with the mesh specifications. Beginning with “Compliance Sieves”, a basic standard deviation of holes sizes was established. The second category, “Inspection Sieves”, was defined with a lower acceptable standard deviation A third category, “Calibration Sieves”, was also established with an even tighter tolerance expressed in terms of allowable maximum standard deviation.

When these new standards are fully integrated in to sieve testing practice, new certificates of conformance can be expected to be developed using these new allowable deviation definitions.

Summary

During the last 20 years the different levels of sieve certification emerged to help users predict operating performance and develop easy methods of checking on the condition of sieves used repeatedly. These levels can be classified as 1) Manufacturing Conformance for day to day working sieves, 2) Mesh Certification for a higher level of assurance and 3) Mid-Point Sieves that often replace matched sets for in-house calibration.

The new 2009 ASTM specification may provide the basis for an official gradation and certification levels in the new categories of 1) Compliance Sieves, 2) Inspection Sieves and 3) Calibration Sieves. Practical adoption of these new categories could eliminate a serious level of confusion.

Arthur(Art) Gatenby has been involved in measurement and control for more
than 30 years.


Art is President of CSC Scientific Company, Inc.

CSC Web Site

Sieve Info
Email: agatenby@cscscientific.com
Phone: 703-876-4030

Induction lighting is an emerging technology that is energy efficient and environmentally friendly. Many of the larger induction lighting fixtures now house lamps of up to 400W in power.

These, along with smaller, self ballasted induction lamps, wireless and remote controlled dimmable functions, motion sensor integration capability, and an extensive array of customized fixtures represent some commercial lighting firms growing and comprehensive inventory of this remarkable new technology.

BENEFITS

Induction lighting offers benefits to both large scale and small scale projects. With the longest rated lamp life of outdoor lighting technologies, induction lights provide an ideal lighting source in places where replacements must be minimized for the sake of cost effectiveness and where routine maintenance represents a major inconvenience.

Places such as tunnels, bridges, rail yards, and airports can easily recover their front-end investment by reducing both equipment replacement costs and man-hours associated with labor. Many municipalities are now turning to induction lighting for a similar reason.

Smaller cities and towns often lack funding for street and highway lighting, so the purchases they make when they do invest in new equipment often has to last a good 10-20 years before more funding becomes available for procurement. The short ignition time that characterizes induction lights also makes them ideal for security lighting systems, where motion detectors can pinpoint potential invasion and instantly turn the lights on to ward off suspected intruders.

Due to the high color rendering capabilities of induction lighting, these lamps are also ideally suited to high-end commercial lighting and hospitality lighting. Contractors are installing more and more of these lamps in conference rooms, hotel lobbies, banquet rooms, and special event facilities.

TECHNOLOGY

How an induction lamp produces light is basically a current loops through a primary coil and induces a magnetic field.

This, in turn, induces a secondary current in the mercury vapor within the induction lamp. As free electrons subsequently accelerate, they collide with mercury atoms and create excited electron orbits for a brief period of time.

When the electrons finally settle back into their normal orbits, they emit UV radiation that interacts with fluorescent powder coating on the lamps interior and creates visible light in the process.

FEATURES

A number of features characterize induction lighting as an across-the-board improvement over HID and incandescent light sources. Induction lamps do not require an electrode or a filament to operate and last for up to 100,000 hours.

Because they lack electrodes and filaments, they are vibration resistant and do not flicker when they power on. They produce a very high quality white light ranging between 4,000-5,000K Kelvin, and rate 82 on the color rendering index.

They are also highly resistant to cold, having been known to operate reliably at temperatures as low as -40C.

Perhaps more than anything, the energy saving abilities of induction lighting makes it a milestone in illumination sourcing. LPW efficiency ranges from 70-90W, even in larger fixtures operating at 200W and 400W.

Small wattage lamps feature a medium base and internal ballast. Induction lights are also dimmable, making them ideal for indoor commercial and residential lighting where additional energy savings through lighting control may be required.

ADVANTAGES OF INDUCTION LIGHTS

The following table shows the many competitive advantages induction lighting offers to commercial designers seeking to bid projects for clients on a budget. In all but one attribute, induction lighting offers a clear superiority to other light sources.

While incandescent sourcing does rate slightly higher than induction sourcing on the color rendering index (100 versus 82), this margin is negligible, and the many disadvantages of incandescent both from an energy standpoint and a replacement cost standpoint hardly justify any consideration of this slight aesthetic differentiation.

TYPES OF INDUCTION LIGHTING LAMPS

Commonly used induction lighting lamps are globe type induction lamps (40W~ 250W), circular type induction lamps (40W~300W) and rectangular type induction lamps (70W~400W). Fixture types vary per application and include all the major architectural area, site lighting, outdoor lighting, and street lighting fixtures types.

You could also incorporate Cobra-head and Shoebox roadway lights, post-top mounted street lights, lights for tunnels, canopy lights for gas stations, wall-mounted architectural site lighting fixtures, high bay/low bay lights, office lights, and many more.

RLLD Commercial Lighting offers energy efficient tennis court lighting and parking lot lighting sales.

HPLC analysis (high performance liquid chromatography) is a variety of chromatography which is often used in biochemistry and analytical chemistry laboratories whose purpose is to identify, separate and quantify compounds in a sample.

The method is a type of column chromatography using a column which contains a chromatographic packing known as the stationary phase, a pump whose purpose is to move the mobile phase or phases through the column and a detector which is used to determine and display the retention time of the compounds in the column. The retention time (which is the time elapsed from introduction to elution) will vary based on the interactions of the analyte, the solvents used and the stationary phase in the column.

In an HPLC analysis procedure, a small volume of the sample is introduced to the mobile phase stream; the pace of progress of the analyte through the column will be quicker or slower depending on the physical and/or chemical interactions between the analyte and the stationary phase as the sample travels through the column. As stated above, the time between introduction of the sample and elution is referred to as the retention time; this time provides a relatively unique characteristic of the analyte which is useful in identification of the compounds contained in the sample.

In order to create a higher back pressure and a higher linear velocity of the analyte through the column, the stationary phase used in columns for HPLC analysis applications tends to be in small particle sizes. This gives the compounds in the sample being analyzed less time to diffuse; meaning that the resulting chromatogram will be of higher resolution.

The solvents commonly used in HPLC procedures are water combined with methanol or acetonitrile, though any miscible combination of water and/or organic solvents may be used depending on the specific requirements of the application. The water used as a solvent often contains salts or chemical buffers added to assist in separating the constituent components of the analyte. Ion pairing agents like trifluoroacetic acid are also commonly used.

The mobile phase composition may be varied during the HPLC analysis, a practice known as gradient elution. In a reversed phase liquid chromatography process, a typical gradient may be 5% methanol in water at the beginning of the procedure, with a linear progression to 50% methanol in water over the space of 25 minutes. The exact gradient used is dependent on how hydrophobic (or hydrophilic) the analyte is. The analyte mixtures are separated by the gradient as a function of how strong of an affinity the analytes has for the mobile phase composition relative to the composition of the stationary phase.

The process of portioning in a gradient elution HPLC analysis procedure is similar to what is seen in liquid-liquid extraction, but rather than being sequential, the gradient elution method results in a continuous partitioning. With a water/methanol gradient, the components of an analyte which are more hydrophobic will elute when the gradient of the mobile phase is higher in ethanol; the more hydrophilic compounds elute when the gradient of the mobile phase is at a point of lower methanol and higher water content.

The solvents, buffers and other additives and the gradient (if the gradient elution method is being used) in HPLC analysis are entirely dependent on the composition of the analyte and the stationary phase. In many cases, preliminary tests are run to find the method which provides the best separation of eluting peaks.

Andrew Long writes for scientific websites and a main area for content covers lab products and services like HPLC method and spectrophotometers products.

Chromatography analysis is used to determine the presence and concentration of analytes in a sample.

Chromatography refers to a set of laboratory methods and techniques for the separation of mixtures. It involves passing a mixture that dissolved in a mobile phase through a medium known as the stationary phase. This separates the analyte to be measured from other components of the mixture and allows it to be isolated.

Chromatography may be preparatory or analytical in nature. Preparatory chromatography is performed to separate the components of a mixture for further analysis as well as for cleansing and purification applications. Analytical chromatography is usually done with smaller amounts of material and is used to measure the relative proportions of analytes in a mixture.

In chromatography analysis, chemical substances are introduced into a vertical glass tube containing an adsorbent. The various components of the substance move through the adsorbent material at different rates of speed according to their degree of attraction to it. This produces bands of color at different levels of the adsorption column.

Analysis techniques by physical state of the mobile phase fall into several categories. Gas chromatography (sometimes called gas-liquid chromatography) is a separation technique in which the mobile phase is a gas. Gas chromatography is always performed in a column, typically packed or capillary. Liquid chromatography is a separation methodology in which the mobile phase is a liquid and can be performed either in a column or a plane. Present day liquid chromatography analysis generally utilizes very small packing particles and a relatively high pressure; a method referred to as high performance liquid chromatography or HPLC.

Affinity chromatography is based on selective non-covalent interaction between an analyte and particular molecules. It is frequently used in biochemistry in the purification of proteins bound to tags.

Other techniques use a variety of separation mechanisms. Ion exchange chromatography employs the ion exchange mechanism to separate analytes. It is usually performed in columns but can also be useful in planar mode. Ion exchange chromatography uses a charged stationary phase to separate charged compounds including amino acids, peptides, and proteins.

Size exclusion chromatography analysis (also known as gel permeation chromatography or gel filtration chromatography) separates molecules according to their size (or more accurately according to hydrodynamic diameter or volume). Smaller molecules are able to enter the pores of the media and take longer to elute, while larger molecules are excluded from the pores and elute more rapidly.

Special chromatography methodologies are sometimes needed. Reversed-phase chromatography is an elution procedure used in liquid chromatography analysis, using a mobile phase which is significantly more polar than the stationary phase.

If the chemistry within a given column is insufficient to separate some analytes, two-dimensional chromatography can be used, making it possible to direct a series of unresolved peaks onto a second column with different properties. This method allows for the separation of compounds which are indistinguishable from one another when using one-dimensional chromatography methods.

Additional specialized chromatography analysis techniques include simulated moving-bed chromatography, pyrolysis gas chromatography, fast protein liquid chromatography, countercurrent chromatography and chiral chromatography.

Andrew Long writes for scientific websites and a main area for content covers lab suppliers and services like autosampler and GC analysis products.

An autosampler is an instrument which is used in a variety of different laboratory applications, especially gas-liquid chromatography, where it is used (as the name implies) to automatically introduce a sample into the inlets of the apparatus being employed in a given test. While it is possible to manually insert samples with many instruments, this is no longer the common practice, since autosamplers offer a more efficient and reproducible method.

Autosamplers may be classified by their capacity, such as autosamplers as opposed to auto-injectors; the latter instrument is capable of running more than one sample at once. Robotic instruments offer another classification of autosampler, with rotating/SCARA robots being among the most widely used.

In gas-liquid chromatography, the column inlet (or injector) provides for the introduction of samples into a continuous flow of carrier gas. Common inlet types are the split/splitless injectors, on-column inlets, PTV injectors, the gas source inlet (also called a gas switching valve), purge and trap systems and SPME (solid phase micro extraction) systems. In the split/splitless injector, the sample is introduced to a heated chamber using a syringe.

With an on-column inlet, the sample is introduced in its entirety without the use of heat. PTV injectors introduce the sample through a heated liner at a controlled rate. In the gas source inlet method, the sample is inserted into the gas stream from collection bottles, a method which allows samples to be introduced without interrupting the carrier gas flow.

Purge and trap autosampler systems involve bubbling an inert gas through aqueous samples, purging insoluble volatile compounds from the matrix. These volatile compounds are then trapped in an absorbent column which is then heated - the volatiles are directed into the carrier stream. Solid phase micro extraction (SPME)is a more economical alternative to purge and trap systems which provides greater ease of use and a lower cost.

The type of automatic sampling system used depends largely on the specific application; in gas chromatography alone, there are two different types of columns used - with the different types of autosampler being more appropriate for one or the other. There are packed columns (usually made of glass or stainless steel and containing an inert, solid and highly granular material which is coated with a liquid or solid stationary phase).

The other type are capillary columns; these columns feature a very small internal diameter, with the inside of the column being coated with the phase. Other capillary columns are made with a semi-solid construction and parallel micropores; this style allows for great flexibility, so a long column can be wound into a tight coil which takes up far less room.

While it is gas and liquid chromatography which often first come to mind when discussing different types of autosampler, there are samplers used in many different applications from the life sciences to geological surveys, the pharmaceutical industry, water quality testing and nearly every other application in the materials and life sciences as well as quality control testing of all types. These instruments allow laboratories to handle higher sample throughputs while increasing reproducibility and efficiency.

Andrew Long writes for scientific websites and a main area for content covers lab suppliers and services like autosampler and GC analysis products.

High-performance liquid chromatography (HPLC method) is a powerful type of column chromatography. Rather than allowing a solvent to drip through the column using only gravity, it is forced through the column using pressures of as much as 400 atmospheres.

This makes it significantly faster than standard column chromatography and also allows for the use of column packing material which has a much smaller particle size. This in turn provides a much greater surface area for interactions between the stationary phase and the molecules flowing through it, providing a much better separation of the mixture’s components. The other advantages of using the HPLC method over traditional column chromatography are the more sensitive and easily automatable detection methods that can be used.

HPLC is commonly used in biochemistry and analytical chemistry to separate, distinguish and quantify compounds. HPLC employs a column containing chromatographic packing material (the stationary phase), a pump that moves the mobile phase (or phases) through the column and a detector showing the retention times of the various molecules; this varies depending on the interactions between the stationary phase, the molecules being analyzed and the type of solvent used.

A small volume of the sample to be analyzed is introduced to the mobile phase stream in the HPLC method. The analyte’s movement through the column is slowed by specific chemical or physical interactions with the stationary phase as it navigates the length of the column. The time at which a specific analyte elutes is called the retention time, which is a unique characteristic of a particular analyte.

The use of smaller particle size column packing increases the linear velocity, giving the components less time to diffuse within the column. This allows for higher resolution chromatograms. Common solvents used include any miscible combination of water or organic liquids, the most common being methanol and acetonitrile. The water that is used may contain buffers or salts to assist in the separation of the components of the analyte. Compounds such as trifluoroacetic acid, which acts as an ion pairing agent, may also be used.

A further refinement to the HPLC method has been to vary the mobile phase composition during the analysis, something which is known as gradient elution. A typical gradient for reversed phase chromatography may be water with 5% methanol progressing linearly to 50% methanol over a span of 25 minutes. The gradient chosen depends on how hydrophobic the analyte is.

When using a water/methanol gradient, the more hydrophobic components will elute when the mobile phase consists mostly of methanol. This produces a comparatively hydrophobic mobile phase. By contrast, hydrophilic compounds will elute under conditions of a relatively low methanol and a relatively high water mixture.

The choice of solvents, additives and gradient used depend on the nature of the stationary phase and the analyte. Often a series of tests are performed on the analyte and a number of trial runs may be processed in order to determine the HPLC method which provides the best separation of peaks with a given analyte.

Andrew Long writes for scientific websites and a main area for content covers lab products and services like HPLC method and spectrophotometers products.

related material.