assay

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(ăs'ā', ă-sā') pronunciation
n.
    1. Qualitative or quantitative analysis of a metal or ore to determine its components.
    2. A substance to be so analyzed.
    3. The result of such an analysis.
  1. An analysis or examination.
  2. A bioassay.
  3. Archaic. An attempt; an essay.

v., -sayed, -say·ing, -says. (ă-sā', ăs'ā')

v.tr.
    1. To subject (a metal, for example) to chemical analysis so as to determine the strength or quality of its components.
    2. To bioassay.
  1. To examine by trial or experiment; put to a test: assay one's ability to speak Chinese.
  2. To evaluate; assess: assayed the situation before taking action. See synonyms at estimate.
  3. To attempt; try.
v.intr.
To be shown by analysis to contain a certain proportion of usually precious metal.

[Middle English, from Old French essai, assai. See essay.]

assayable as·say'a·ble adj.
assayer as·say'er n.


In chemical analysis, the process of determining proportions of metal, particularly precious metal, in ores and metallurgical products. The most important assaying technique grew largely out of the experiments of the ancient alchemists and goldsmiths. Precious metals tend to occur as scattered particles randomly distributed, so a large sample of ore is required. Such large samples (typically containing gold, silver, and lead) are still most economically assayed by this ancient method, which involves several steps of heating and cooling. More sophisticated recent methods, such as spectrochemical analysis, are not suited to assaying precious metal ores because the samples of the inhomogeneous ore that must be used are larger than the instruments can handle. parting.

For more information on assaying, visit Britannica.com.

test of a metal’s purity to verify that it meets the standards for trading on a commodities exchange. For instance, a 100 troy-ounce bar of refined gold must be assayed at a fineness of not less than 995 before the Comex will allow it to be used in settlement of a gold contract.

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noun

  1. A procedure that ascertains effectiveness, value, proper function, or other quality: essay, proof, test, trial, tryout. See investigate.
  2. A trying to do or make something: attempt, crack, effort, endeavor, essay, go, offer, stab, trial, try. Informal shot. Slang take. See try.

verb

  1. To subject to a procedure that ascertains effectiveness, value, proper function, or other quality: check, essay, examine, prove, test, try, try out. Idioms: bring to the test, make trial of, put to theprooftest. See investigate.
  2. To make a judgment as to the worth or value of: appraise, assess, calculate, estimate, evaluate, gauge, judge, rate, size up, valuate, value. Idioms: take the measure of. See value/worthlessness/evaluation.
  3. To make an attempt to do or make: attempt, endeavor, essay, seek, strive, try. Idioms: have a go at, havemaketakea shot at, havetakea whack at, make a stab at, take a crack at. See try.

assaying (əsā'yĭng, ăs'āyĭng), in metallurgy, process of determining the specific metallic content of an ore, alloy, or other substance, especially one containing precious metals. It consists, in some cases, of subjecting the substance to complete chemical analysis and, in others, of simply determining the quantity present of one or more of the metal constituents. An accurate assay depends first upon procuring a representative sample of the ore in question. Since distribution of the ore's components is not uniform, a common method employed in obtaining this sample is to procure several samples, crush and mix them together, and from the final mass take the sample to be assayed. Assays are said to be gravimetric when the weight of the metal is determined and volumetric when the analysis involves the volume of the metal in solution as compared to that in a standardized solution. A wet assay (one which involves the use of liquid reagents) is generally used in a determination of weight. In a dry assay the ore is fused and the metal is finally obtained in a pure state.


The act of testing the purity of precious metals.

Investopedia Says:
In futures contracts where the underlying commodities are precious metals, the quality must be assayed to ensure that they are of basis grade.

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For those who are new to futures but want a solid understanding of them, this tutorial explains what futures contracts are, how they work and why investors use them. Futures Fundamentals
The quest for this shiny commodity has made millionaires of paupers and, on the flip side, ruined many an investor. Using Technical Analysis In The Gold Markets
Despite its historic and symbolic appeal, this metal is simply a commodity. Here we explore its meaning as an investment. What Is Wrong With Gold?
Find out which currencies are most affected by fluctuations in gold and oil prices and improve your trading. Commodity Prices And Currency Movements
Learn what to watch out for to ensure your "sure thing" isn't another Bre-X. Strike Gold With Junior Mining
In this feature, we take an in-depth look at the various techniques that determine the value and investment quality of companies from an industry perspective. The Industry Handbook: Precious Metals
The quest for this shiny commodity has made millionaires of paupers and, on the flip side, ruined many an investor. Using Technical Analysis In The Gold Markets
Despite its historic and symbolic appeal, this metal is simply a commodity. Here we explore its meaning as an investment. What Is Wrong With Gold?
Find out which currencies are most affected by fluctuations in gold and oil prices and improve your trading. Commodity Prices And Currency Movements
Learn what to watch out for to ensure your "sure thing" isn't another Bre-X. Strike Gold With Junior Mining
In this feature, we take an in-depth look at the various techniques that determine the value and investment quality of companies from an industry perspective. The Industry Handbook: Precious Metals


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pronunciation

IN BRIEF: Chemical analysis of testing ore.

pronunciation The miners took five bags of ore to the assay office.

Tutor's tip: An "assay" (examination of characteristics) following a blood test can help diagnose a disease, but can't help you with the "essay" (analytic or interpretive written composition) portion of your English test!

LearnThatWord.com is a free vocabulary and spelling program where you only pay for results!

n.
  1. the determination of the activity, potency, strength, etc. of a substance, either on an absolute basis or in comparison with that of a standard preparation.
  2. the determination of the relative amount(s) of one or more components of a mixture, or of the degree of purity of a substance.
  3. to carry out such a determination. See also bioassay, immunoassay, microbiological assay, radioassay.

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Determination of the purity of a substance or the amount or activity of any particular constituent of a mixture.

  • biological a. — bioassay; determination of the potency of a drug or other substance by comparing the effects it has in a biological system with those of a reference standard.
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categories related to 'assay'

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Random House Word Menu by Stephen Glazier
For a list of words related to assay, see:
  • Mining - assay: analysis of ore or alloy to determine proportion and purity of components; (vb) make such an analysis
  • Verbs of Sight - assay: examine and evaluate


  See crossword solutions for the clue Assay.

An assay is an investigative (analytic) procedure in laboratory medicine, pharmacology, environmental biology, and molecular biology for qualitatively assessing or quantitatively measuring the presence or amount or the functional activity of a target entity (the analyte) which can be a drug or biochemical substance or a cell in an organism or organic sample.[1][2]

Generally in an assay the quantity of the exogenous materials (the reagents) are kept fixed (or in excess) so that the quantity (and quality) of the target is the only limiting factor for the reaction/assay process, and the difference in the assay outcome is used to deduce the unknown quality or quantity of the target in question. Some assays (e.g., biochemical assays) may be similar to or have overlap with chemical analysis and titration. But generally assays involve biological material or phenomena which tend to be intrinsically more complex either in composition or in behavior or both. Thus reading of an assay may be quite noisy and may involve greater difficulties in interpretation than an accurate chemical titration. On the other hand older generation qualitative assays especially bioassays may be much more gross and less quantitative (e.g., counting death or dysfunction of an organism or cells in a population, or some descriptive change in some body part of a group of animals).

An assay (analysis) is never an isolated process and needs to be preceded by certain necessary procedures which are the preanalytic steps and must be followed by certain necessary post analytic steps. The information communication (eg request to perform an assay and further information processing) or specimen handling (eg collection transport and processing) done before and till the point of beginning of an assay are the preanalytic steps. Similarly after the actual assay is done the result may be documented, verified and transmitted/communicated in steps which are called post-analytic steps related to an assay. Like any multistep information handling and transmission systems, variation and errors in the communicated final results of an assay involves corresponding parts in every such step ie not only analytic variations and errors intrinsic to the assay itself but also variations and errors involved in preanalytic and post analytic steps. Since the assay itself (the analytic step) gets a lot of attention[3], steps that get less attention by the chain of users ie the preanalytic and the post analytic steps are often less stringently regulated and generally more prone to errors- eg preanalytic steps in medical laboratory assays may contribute to 32-75% of all lab errors[4].

In modern practice Assays have become routine part of medical, environmental, pharmaceutical, forensic and many other business at various scales from industrial to curbside or field level. Those assays that have very high commercial demand have been well investigated in research and development sectors of professional industries and have gone through various generations of development of better and sophisticated assays that have become copyrighted intellectual properties through highly competitive process patenting. These kind of industrial scale assays are often done in well equipped laboratories and use high level of automation in organizing the procedure, right from ordering of an assay, to pre-analytic sample processing (sample collection, necessary manipulations eg spinning for separation or other processes, aliquoting if necessary, storage, retrieval, pipetting/aspiration etc) and are generally tested in high thruput AutoAnalyzers and the results are verified, and transmitted automatically back to the ordering service providers and the end users. These are made possible through use of advanced Laboratory informatics system that interfaces with multiple computer terminals with end users as well as central servers and the physical autoanalyser instruments and other automata.

When multiple assays measure the same target their results and utility may or may not be comparable depending on the natures of the assay and their methodology, reliability etc. Such comparisons are possible through study of general quality attributes of the assays eg principles of measurement (including identification, amplification and detection), dynamic range of detection (usually the range of linearity of the standard curve), analytic sensitivity, functional sensitivity, analytic specificity, positive, negative predictive values, turn around time ie time taken to finish a whole cycle from the preanalytic steps till the end of the last post analytic step (report dispatch/transmission), thruput ie number of assays done per unit time (usually expressed as per hour) etc. Organizations or laboratories that perform Assays for professional purposes eg medical diagnosis and prognostics, environmental analysis, forensic proceeding, pharmaceutical research and development must undergo well regulated quality assurance procedures including method validation, regular callibration, Analytical quality control, Proficiency testing, test accreditation, test licensing and must document appropriate certifications from the relevant regulating bodies in order to establish the reliability of their assays, especially to remain legally acceptable and accountable for the quality of the assay results and also to convince customers to use their assay commercially/professionally.

Contents

Etymology

According to Etymology Online[5] the verb assay, at least since the 13th century meant "to try, endeavor, strive; test the quality of," from Anglo-Fr. assaier, from assai (n.), from O.Fr. essai "trial". And the noun assay thus means "trial, test of quality, test of character," mid-14c., from Anglo-Fr. assai and Meaning "analysis" is from late 14c. For assay of currency coins this litterally meant analysis of the purity of the gold or silver or whatever precious component used to represent the true value of the coin. This might have translated later (possibly after 14th century) into a generalized meaning of analysis eg of important/principle component of a target inside a mixture such as active ingradient of a drug inside the inert excepients in a pharmacological formulation which originally used to be measured by its actual action on an organism (eg lethal dose or inhibitory dose).

General steps of any assay

Assays can be very diverse, but generally involve the following general steps:

  1. Sample processing/manipulation in order to selectively present that target in a discernible/measurable form to a discrimination/identification/detection system. It might involve a simple centrifugal separation or washing or flitration or capture by some form of selective binding or it may even involve modifying the target eg epitope retrieval in immunological assays or cutting down the target into pieces eg in Mass Spectrometry. Generally there are multiple separate steps done before an assay and are called preanalytic processing. But some of the manipulations may be inseparable part of the assay itself and will not thus be considered pre-analytic.
  2. Target specific DISCRIMINATION/IDENTIFICATION principle: to discriminate from background (noise) of similar components and specifically identify a particular target component ("analyte") in a biological material by its specific attributes. (eg in a PCR assay a specific oligonucleotide primer identifies the target by base pairing based on the specific nucleotide sequence unique to the target).
  3. Signal (or target) AMPLIFICATION System: The presence and quantity of that analyte is converted into a detectable signal generally involving some method of signal amplification, so that it can be easily discriminated from noise and measured - eg in a PCR assay among a mixture of DNA sequences only the specific target is amplified into millions of copies by a DNA polymerase enzyme so that it can be discerned as a more prominent component compared to any other potential components. Sometimes the concentration of the analyte is too large and in that case the assay may involve sample dilution or some sort of signal diminution system which is a negative amplification.
  4. Signal DETECTION (and interpretation) system: A system of deciphering the amplified signal into a interpretable output that can be quantitative or qualitative. It can be visual or manual very crude methods or can be vary sophisticaed electronic digital or analog detectors.
  5. Signal enhancement and noise filtering: may be done at any/all of the steps above. Since the more downstream a step/process during an assay, the higher the chance of carrying over noise from the previous process and amplifying it, multiple steps in a sophisticated assay might involve various means of signal-specific sharpening/enhancement arrangements and noise reduction or filtering arrangements. These may simply be in the form of a narrow band-pass optical filer, or a blocking reagent in a binding reaction that prevents nonspecific binding or a quenching reagent in a fluorescence detection system that prevents "autofluorescence" of background objects.

Assay types based on the nature of the assay process

Depending on whether an assay just looks at a single time point or timed readings taken at multiple time points, an assay may be:

  1. end point assay: when the only reading that matters is the end result after a fixed assay incubation period.
  2. kinetic assay: when readings are taken multiple times at fixed time intervals during an assay and a kinetic graph of the readings is important.

Depending on how many targets or analytes are being measured:

  1. Usual assay are simple or single target assays which is usually the default unless it is called multiplex.
  2. Multiplex assays are assays that in a same reaction detect multiple analytes simultaneously.

Depending on the quality of the result produced, assays may be classified into:

  1. Qualitative assay, i.e. assays which generally give just a pass or fail, or positive or negative or some such sort of only small number of qualitative gradation rather than an exact quantity.
  2. Semi-quantitative assays, i.e. assays that gives the read-out in an approximate fashion rather than an exact number for the quantity of the substance. Generally they have a few more gradations than just two outcomes, positive or negative, e.g. scoring on a scale of 1+ to 4+ as used for blood grouping tests based on RBC agglutination in response to grouping reagents (antibody against blood group antigens).
  3. Quantitative assays, i.e. assays that gives accurate and exact numeric quantitative measure of the amount of a substance in a sample. An example of such an assay used in coagulation testing laboratories for the commonest inherited bleeding disease - Von Willebrand disease is VWF antigen assay where the amount of VWF present in a blood sample is measured by an immunoassay.
  4. Functional assay, i.e. an assay that tries to quantitative functioning of an active substance rather than just its quantity. The functional counterpart of the VWF antigen assay is Ristocetin Cofactor assay, which measures the functional activity of the VWF present in a patients plasma by adding exogenous formalin-fixed platelets and gradually increasing quantities of drug named ristocetin while measuring agglutination of the fixed platelets. A similar assay but used for a different purpose is called Ristocetin Induced Platelet Aggregation or RIPA, which tests response of endogenous live platelets from a patient in response to Ristocetin (exogenous) & VWF (usually endogenous).

Depending on the general substrate on which the assay principle is applied:

  1. Bioassay: when the response is biological activity of live objects e.g.
    1. Organism (e.g. mouse injected with a drug)
    2. ex vivo body part (e.g. leg of a frog)
    3. ex vivo organ (e.g. heart of a dog)
    4. ex vivo part of an organ (e.g. a segment of an intestine).
    5. tissue (e.g. limulus lysate)
    6. cell (e.g. platelets)
  2. Ligand binding assay when a ligand (usually a small molecule) binds a receptor (usually a large protein).
  3. immunoassay when the response is an antigen antibody binding type reaction.

Depending on the nature of the signal amplification system assays may be of numerous types, to name a few:

  1. Enzyme activity assay: Enzymes may be tested by their highly repeating activity on a large number of substrates when loss of a substrate or the making of a product may have a measurable attribute like color or absorbence at a particular wavelength or light or chemiluminiscence or electrical/redox activity.
  2. Light detection systems that may use amplification e.g. by a photodiode or a photomultiplier tube or a cooled charge coupled device.
  3. Radioisotope labeled substrates as used in radioimmunoassays and equilibrium dialysis assays and can be detected by the amplification in GM counters or [X-ray plate]]s, or phosphorimager
  4. Polymerase Chain Reaction Assays that amplifies a DNA (or RNA) target itself rather than the signal

Assays may be a combination of the above eg Enzyme Immuno assay or EIA, enzyme linked immunosorbent assay.

Depending on the nature of the Detection system assays can be based on:

  1. colony forming: e.g. by multiplying bacteria or proliferating cells.
  2. Photometry /Spectrophotometry When the absorbence of a specific wavelength of light while passing through a fixed path-length through a cuvette of liquid test sample is measured and the absorbance is compared with a blank and standards with graded amounts of the target compound. If the emitted light is of a specific visible wavelength it may be called colorimetry, or it may involve specific wavelength of light eg by use of laser and emission of fluorescent signals of another specific wavelength which is detected via very specific wavelength optical filters.
  3. Transmittance of light may be used to measure eg clearing of opacity of a liquid created by suspended particles due to decrease in number of clumps during a platelet agglutination reaction.
  4. 'Turbidimetry when the opacity of straight-transmitted light passing through a liquid sample are measured by detectors placed straight across the light source.
  5. Nephelometry when the scattered lights are measured by detectors placed at fixed angles to the path of light.
  6. Reflectometry When color of light reflected from a (usually dry) sample or reactant is assessed e.g. the automated readings of the strip urine dipstick assays.
  7. Viscoelastic measurements eg viscometry, elastography (eg thromboelastography)
  8. Counting assays: e.g. optic Flowcytometric cell or particle counters, or coulter/impedance principle based cell counters
  9. Imaging assays, that involve image analysis manually or by software:
    1. Cytometry: When the size statistics of cells is assessed by an image processor.
  10. Electric detection eg involving amperometry, voltametry, coulometry may be used directly or indirectly for many types of quantitative measurements.
  11. Other physical property based assays may use
    1. Osmometer
    2. Viscometer
    3. Ion Selective electrodes

Assay types based on the targets being measured

DNA

Assays for studying interactions of proteins with DNA include:

Protein

RNA

Cell counting, viability, proliferation or cytotoxicity assays

A cell-counting assay may determine the number of living cells, the number of dead cells, or the ratio of one cell type to another, such as numerating and typing red versus different types of white blood cells. This is measured by different physical methods (light transmission, electric current change). But other methods use biochemical probing cell structure or physiology (stains). Another application is to monitor cell culture (assays of cell proliferation or cytotoxicity). A cytotoxicity assay measures how toxic a chemical compound is to cells.

Surfactants

Other cell assays

Many cell assays have been developed to assess specific parameters or response of cells (biomarkers, cell physiology. Techniques used to study_cells include :

Petrochemistry

Virology

The HPCE-based viral titer assay uses a proprietary, high-performance capillary electrophoresis system to determine baculovirus titer.

The Trofile assay is used to determine HIV tropism.

The viral plaque assay is to calculate the number of viruses present in a sample. In this technique the number of viral plaques formed by a viral inoculum is counted, from which the actual virus concentration can be determined.

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

See also

References

  1. ^ The American Heritage Dictionary of the English Language. Fourth Edition. Houghton Mifflin Company: 2000.
  2. ^ McKean, Erin (ed.). The New Oxford American Dictionary. Second edition. Oxford University Press: 2005.
  3. ^ Minireview: Pierangelo Bonini, Mario Plebani, Ferruccio Ceriotti, and Francesca Rubboli Errors in Laboratory Medicine Clinical Chemistry 2002; v. 48, p.691-698.
  4. ^ Featured Article: Julie A. Hammerling A Review of Medical Errors in Laboratory Diagnostics and Where We Are Today. Lab Medicine 2012 43:41-44; doi:10.1309/LM6ER9WJR1IHQAUY
  5. ^ http://www.etymonline.com/index.php?term=assay
  6. ^ Lowry OH, Rosebrough NJ, Farr AL, Randall RJ (November 1951). "Protein measurement with the Folin phenol reagent". J. Biol. Chem. 193 (1): 265–75. PMID 14907713. http://www.jbc.org/cgi/pmidlookup?view=long&pmid=14907713. 
  7. ^ http://www.animal.ufl.edu/hansen/protocols/LOWRY.htm

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Dansk (Danish)
n. - probering, finhedsanalyse
v. tr. - probere, finhedsbestemme
v. intr. - probere, finhedsbestemme

Nederlands (Dutch)
het analyseren van metaal/erts, analyseerbaar materiaal, metaal/erts analyseren, goud-/zilvergehalte toetsen, pogen

Français (French)
n. - essai
v. tr. - essayer (du minerai), essayer, tenter de (arch)
v. intr. - être analysé, contenir de l'or

Deutsch (German)
n. - Probe, Analyse
v. - prüfen, analysieren

Ελληνική (Greek)
v. - δοκιμάζω, καρατάρω ή αναλύω (πολύτιμο) μέταλλο
n. - δοκιμασία, τεστ, έλεγχος καθαρότητας μετάλλου

Italiano (Italian)
esaminare

Português (Portuguese)
v. - ensaiar, testar, analisar
n. - ensaio (m), teste (m), análise (f)

Русский (Russian)
производить количественный анализ, пробовать, пытаться, испытание

Español (Spanish)
n. - prueba, ensayo
v. tr. - probar, ensayar
v. intr. - someter a prueba, probarse

Svenska (Swedish)
v. - pröva, analysera
n. - prövning, justering

中文(简体)(Chinese (Simplified))
化验, 分析, 尝试, 被验明成分

中文(繁體)(Chinese (Traditional))
n. - 化驗, 分析
v. tr. - 嘗試, 化驗, 分析
v. intr. - 被驗明成分

한국어 (Korean)
n. - 분석 시험, 시험
v. tr. - 을 분석하다, 을 시험하다, 을 평가하다
v. intr. - 금속을 함유하다

日本語 (Japanese)
v. - 分析する
n. - 分析試験, 試金

العربيه (Arabic)
‏(فعل) يجرب, يختبر, يفحص, يحلل (الاسم) اختبار, فحص, تحليل‏

עברית (Hebrew)
n. - ‮בחינת המרכיבים, האיכות והריכוז של מתכת או חומר-גלם‬
v. tr. - ‮בדק, בחן, קבע את הריכוז של‬
v. intr. - ‮הכיל שיעור מסוים של מתכת יקרה‬


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