Information about Assay
An assay is a procedure where a property or concentration of an analyte is measured.
There are numerous types of assays, such as an antigen capture assay, bioassay, competitive protein binding assay, crude oil assay, four-point assay, immunoassay, microbiological assay, stem cell assay, and many others, including concentration assays.
There are methods of assay suitable for use on raw materials and other methods which are more properly suited for finished goods. Raw precious metals (bullion) are assayed by an assay office. Silver is assayed by titration, gold by cupellation and platinum by inductively coupled plasma optical emission spectrometry (ICP OES).[1],[2]
Precious metal items of art or jewelry are frequently hallmarked (depending upon the requirements of the laws of either the place of manufacture or the place of import). Where required to be hallmarked, semi-finished precious metal items of art or jewelry pass through the official testing channels where they are analyzed or assayed for precious metal content. While different nations permit a variety of legally acceptable finenesses, the assayer is actually testing to determine that the fineness of the product conforms with the statement or claim of fineness that the maker has claimed (usually by stamping a number such as 750 for 18k gold) on the item. In the past the assay was conducted by using the touchstone method but currently (most often) it is done using X-ray Fluorescence (XRF). XRF is used because this method is more exacting than the touchstone test. The most exact method of assay is known as fire assay or cupellation. This method is better suited for the assay of bullion and gold stocks rather than works or art or jewelry because it is a completely destructive method.
In the UK the Trial of the Pyx is a ceremonial procedure for ensuring that newly-minted coins conform to required standards.
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There are numerous types of assays, such as an antigen capture assay, bioassay, competitive protein binding assay, crude oil assay, four-point assay, immunoassay, microbiological assay, stem cell assay, and many others, including concentration assays.
Molecular biology assays
Assays are regularly utilized in molecular biology scientific research laboratories.DNA
Assays for studying interactions of proteins with DNA include:RNA
Protein
- Bicinchoninic acid assay (better known as the BCA assay)
- Bradford protein assay
- Lowry protein assay
- Secretion assay
Cytotoxicity
Assays for studying how toxic a compound is to cells:- MTT assay
- SRB (Sulforhodamine B) assay
Viruses
- Viral plaque assay: Used to calculate the number of viruses present in a sample. This technique requires counting the number of plaques formed by a virus sample, from which the actual virus concentration can be determined.
- Trofile assay: Used to determine HIV tropism.
Cellular secretions
A wide range of cellular secretions (say, a specific antibody or cytokine) can be detected using the ELISA technique. The number of cells which secrete those particular substances can be determined using a related technique, the ELISPOT assay.Drugs
Illegal drug testingEnvironmental contaminants
Methods of assay of precious metals
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A 19th century assay laboratory in Tombstone Courthouse State Historic Park, Arizona.
There are methods of assay suitable for use on raw materials and other methods which are more properly suited for finished goods. Raw precious metals (bullion) are assayed by an assay office. Silver is assayed by titration, gold by cupellation and platinum by inductively coupled plasma optical emission spectrometry (ICP OES).[1],[2]
Precious metal items of art or jewelry are frequently hallmarked (depending upon the requirements of the laws of either the place of manufacture or the place of import). Where required to be hallmarked, semi-finished precious metal items of art or jewelry pass through the official testing channels where they are analyzed or assayed for precious metal content. While different nations permit a variety of legally acceptable finenesses, the assayer is actually testing to determine that the fineness of the product conforms with the statement or claim of fineness that the maker has claimed (usually by stamping a number such as 750 for 18k gold) on the item. In the past the assay was conducted by using the touchstone method but currently (most often) it is done using X-ray Fluorescence (XRF). XRF is used because this method is more exacting than the touchstone test. The most exact method of assay is known as fire assay or cupellation. This method is better suited for the assay of bullion and gold stocks rather than works or art or jewelry because it is a completely destructive method.
The touchstone
The age-old touchstone method is particularly suited to the testing of very valuable pieces, for which sampling by destructive means, such as scrapping, cutting or drilling is unacceptable. A rubbing of the item is made on a special stone, treated with acids and the resulting color compared to references. Differences in precious metal content as small as 10 to 20 parts per thousand can often be established with confidence by the test. It is not indicated for use with white gold, for example, since the color variation among white gold alloys is almost unperceivable.X-ray fluorescence
The modern X-ray fluorescence is also a non-destructive technique that is suitable for normal assaying requirements. It typically has an accuracy of 2 to 5 parts per thousand and is well-suited to the relatively flat and large surfaces. It is a quick technique taking about three minutes, and the results can be automatically printed out by computer. It also measures the content of the other alloying metals present. It is not indicated, however, for articles with chemical surface treatment or electroplating.Fire assay/cupellation
The most elaborate but totally destructive assay method is fire-assay,also called cupellation, with an accuracy of 1 part in 10,000. In this process the article is melted, the alloys separated and constituents weighed.The assay of coins
An assayer is often assigned to each mint or assay office to determine and assure that all coins produced at the mint have the correct content or purity of each metal specified, usually by law, to be contained in them. This was particularly important when gold and silver coins were produced for circulation and used in daily commerce. Few nations, however, persist in minting silver or gold coins for general circulation. For example the U.S. discontinued the use of gold in coinage in 1933. The U.S. was perhaps the last nation to discontinue the use of silver in circulating coins in its 1969 half dollar coin, although the amount of silver used in smaller denomination coins was ended after 1964. Even with the half dollar, the amount of silver used in the coins was reduced from 90% in 1964 and earlier to 40% between 1965 and 1969. Copper, nickel, cupro-nickel and brass alloys now predominate in coin making. Notwithstanding, several national mints, including the Australian Mint at Perth, the Austrian Mint, the British Royal Mint, the Royal Canadian Mint, the South African Mint and the U.S. Mint continue to produce precious metal bullion coins for collectors and investors. The precious metal purity and content of these coins is guaranteed by the respective mint or government and therefore the assay of the raw materials and finished coins is an important quality control.In the UK the Trial of the Pyx is a ceremonial procedure for ensuring that newly-minted coins conform to required standards.
See also
References
Bioassay is a shorthand commonly used term for biological assay and is a type of scientific experiment. Bioassays are typically conducted to measure the effects of a substance on a living organism . Bioassays may be qualitative or quantitative .
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A crude oil assay is essentially the chemical evaluation of crude oil feedstocks by petroleum testing laboratories. Each crude oil type has unique molecular, chemical characteristics. No crude oil type is identical and there are crucial differences in crude oil quality.
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An immunoassay is a biochemical test that measures the concentration of a substance in a biological liquid, typically serum or urine, using the reaction of an antibody or antibodies to its antigen. The assay takes advantage of the specific binding of an antibody to its antigen.
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Molecular biology is the study of biology at a molecular level. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell,
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laboratory (informally, lab) is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory
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Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as percy puddles to a one-way causal effect.
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Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
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DNase footprinting assay is a technique from molecular biology that detects DNA-protein interaction using the fact that a protein bound to DNA will often protect that DNA from enzymatic cleavage. This makes it possible to locate a protein binding site on cellular DNA.
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electrophoretic mobility shift assay (EMSA), also referred as a gel shift assay, gel mobility shift assay, band shift assay, or gel retardation assay, is a common technique used to study protein-DNA or protein-RNA interactions.
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A nuclear run-on assay is conducted to identify the genes that are being transcribed at a certain point in time. Cell nuclei are isolated rapidly, and incubated with labelled nucleotides and the results are hybridized to a slot blot, which is then exposed to film.
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The bicinchoninic acid assay (also known as the BCA assay or Smith assay) is a biochemical assay for determining the total level of protein in a solution, similar to Lowry protein assay, Bradford protein assay or biuret reagent.
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Bradford Protein Assay is a spectroscopic analytical procedure used to measure the concentration of protein in a solution.
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Principle
The Bradford assay, a colorimetric protein assay, is based on an absorbance shift in the dye Coomassie when the previously red form..... Click the link for more information.
The Lowry protein assay, or Lowry Method, is a biochemical test to measure the amount of protein in a sample.
Copper(II) ion in alkaline solution reacts with protein to form complexes, which react with the Folin-phenol reagent, a mixture of phosphotungstic acid and
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Copper(II) ion in alkaline solution reacts with protein to form complexes, which react with the Folin-phenol reagent, a mixture of phosphotungstic acid and
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Secretion assay is a process used in cell biology to identify cells that are secreting a particular protein (usually a cytokine). It was first developed by Manz et al in 1995.
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MTT assay is a laboratory test and a standard colorimetric assay (an assay which measures changes in color) for measuring cellular proliferation (cell growth). It can also be used to determine cytotoxicity of potential medicinal agents and other toxic materials.
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A viral plaque is a visible structure formed within a cell culture, such as bacterial cultures within some nutrient medium (e.g. agar). The bacteriophage viruses replicate and spread, thus generating regions of cell destructions known as plaques.
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The Trofile (TM) assay is a blood test that identifies the tropism of a patient's HIV.
A molecular assay, Trofile was developed by Monogram Biosciences for use in HIV treatment.
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A molecular assay, Trofile was developed by Monogram Biosciences for use in HIV treatment.
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HIV tropism refers to the cell type that the human immunodeficiency virus (HIV) infects and replicates in. HIV tropism of a patient's virus is measured by the Trofile assay.
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Antibodies (also known as immunoglobulins) are proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses.
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Cytokines are a group of proteins and peptides that are used in organisms as signaling compounds. These chemical signals are similar to hormones and neurotransmitters and are used to allow one cell to communicate with another.
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Elisa (born Elisa Toffoli on 19 December, 1977) is an Italian singer and solo artist, writing and performing within several genres, notably rock, blues, soul and ambient.
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The Enzyme-linked immunosorbent spot (ELISPOT) is a common method for monitoring immune responses in humans and animals. It was developed by Cecil Czerkinsky in 1983.
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screening test, and this is applied to all samples that go through the lab. The second, known as the confirmation test, is only applied to samples that test positive during the screening test.
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2
(Amphoteric oxide)
Electronegativity 2.33 (scale Pauling)
Ionization energies
(more) 1st: 715.6 kJmol−1
2nd: 1450.5 kJmol−1
3rd: 3081.
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(Amphoteric oxide)
Electronegativity 2.33 (scale Pauling)
Ionization energies
(more) 1st: 715.6 kJmol−1
2nd: 1450.5 kJmol−1
3rd: 3081.
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Coliform bacteria are a commonly-used bacterial indicator of sanitary quality of foods and water. They are defined as rod-shaped Gram-negative organisms which ferment lactose with the production of acid and gas when incubated at 35 °C.
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3, 5
(mildly acidic oxide)
Electronegativity 2.18 (scale Pauling)
Ionization energies
(more) 1st: 947.0 kJmol−1
2nd: 1798 kJmol−1
3rd: 2735 kJmol−1
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(mildly acidic oxide)
Electronegativity 2.18 (scale Pauling)
Ionization energies
(more) 1st: 947.0 kJmol−1
2nd: 1798 kJmol−1
3rd: 2735 kJmol−1
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Assay offices are institutions set up to assay (test the purity of) precious metal items, to protect consumers. Upon successful completion of the assay, (i.e. the metallurgical content is found to be equal or better than that claimed by the maker and it otherwise conforms to the
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