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EVISA is providing a list of terms used in the area of speciation and fractionation analysis. Since speciation analysis is a field of analytical chemistry that is specified by a pronounced interdisciplinary cooperation between different sciences such as biochemistry, medicine, biology, environmental sciences, nutritional sciences and material sciences its terminology is a complex mixture of terms used in all these.

You may search for a term or browse the glossary alphabetically.

(In case that you cannot find the term you may consult more special glossaries or handbooks about nomenclature. For more details please consult EVISA's Link pages related to terminology,



Arsphenamine, also known as Salvarsan and 606, is a drug containing arsenic that was used to treat syphilis and trypanosomiasis. The organoarsenic compound was the first modern chemotherapeutic agent. Arsphenamine was marketed under the trade name Salvarsan in 1910. It was also called 606, because it was the 606th compound synthesized for testing. Salvarsan was the first organic anti-syphillitic, and a great improvement over the inorganic mercury compounds that had been used previously. A more soluble (but slightly less effective) arsenical compound, Neosalvarsan, (neoarsphenamine), became available in 1912. These arsenical compounds came with considerable risk of side effects, and they were supplanted as treatments for syphilis in the 1940s by penicillin.

Source: Wikipedia

A portion or piece of a whole. A selected subset of a population or subset of whatever is being studied. For example, in a study of people the sample is a number of people chosen from a larger population [see population]. An environmental sample (for example, a small amount of soil or water) might be collected to measure contamination in the environment at a specific location.

sample matrix
- a collective term referring to all of the sample constituents other than the analyte(s).

sampling error
That part of the total error (the estimate from a sample minus the population value) associated with using only a fraction of the population and extrapolating to the whole, as distinct from analytical or test error.

Note: Sampling error arises from a lack of homogeneity in the parent population.

An orally administered third generation platinum compound with potential antineoplastic activity. Satraplatin forms highly reactive, charged, platinum complexes which bind to nucleophilic groups in DNA, inducing intrastrand and interstrand DNA cross-links, as well as DNA-protein cross-links. These cross-links result in cell growth inhibition and apoptosis.

saturated solution
A solution which has the same concentration of a solute as one that is in equilibrium with undissolved solute at specified values of temperature and pressure.

Source:  IUPAC

Stir bar sorptive extraction (SBSE) is a solid phase extraction (SPE) method in which the sorbent is a coating of a solid magnetical stir bar. SBSE applies stir bars varying in length from 1 to 4 cm coated with a relatively thick layer (0.3-1 mm) of  polydimethylsiloxane (PDMS) resulting in PDMS volumes varying from 55 µL to 220 µL. After a certain stirring time, the stir bar is removed from the aqueous sample and thermally desorbed on-line with a gas chromatograph. Due to the much larger volume of the PDMS-phase extraction efficiency is far better than for SPME.

scanning electron microscopy (SEM)
A method employing an electron microscope and a finely focused beam of electrons that is moved across a sample allowing the surficial textures to be examined at high resolution and the image displayed. By collecting the emitted electrons from a single spot (size 1-10 microns)
chemical analysis of portions of the sample, i.e. a specific mineral species, can be made using energy dispersive x-ray analysis (SEM/EDXA).

scanning tunneling microscopy
Technique belonging to the group of scanning probe microscopy (SPM) used to directly observe individual atoms on surfaces. In STM a solid specimen in air, liquid or vacuum is scanned by a sharp tip located within a few Å from the surface. A quantum -mechanical tunneling current flows between atoms on the surface and those on the tip. The magnitude of the current depends upon the separation between the surface and tip atoms, so that it is possible to obtain surface topography with atomic resolution.

A naturally occurring organoselenium compound found in many plants, including garlic, onions, and broccoli, with potential antioxidant and chemopreventive activities. Se-Methyl-seleno-L-cysteine (MSC) is an amino acid analogue of cysteine in which a methylselenium moiety replaces the sulphur atom of cysteine. This agent acts as an antioxidant when incorporated into glutathione peroxidase and has been shown to exhibit potent chemopreventive activity in animal models.

Se-methylselenoneine is a Se-metabolite found in human urine most likely as a result of methylation of dietary selenoneine. Higher concentrations of this species in human urine are probably associated with the consumption of tuna which is a rich source of selenoneine.

secondary standard
Standard whose value is assigned by comparison with a primary standard of the same quantity.

Particulate material consisting of eroded soil and rock material, and plant debris, transported and deposited by water.

sediment pore water
The water that occupies the spaces between sediment particles.

sedimentation field-flow fractionation
SdFFF is a set of high resolution liquid chromatography-like elution methods used for sizing and separating colloidal matter into size fractions. SdFFF separations are performed within a flat open channel, usually having a rectangular cross-section and triangular end pieces where the sample and carrier fluid enters and leaves. The mechanism for particle separation involves only physical interactions. The sample is introduced into the channel through a septum or injection valve, and then the flow is turned off. A centrifugal field is then applied at right angles to the flat face of the ribbon-like channel. This flat channel sits within a centrifuge basket and the centrifugal field drives the particles towards the accumulation wall. There they form equilibrium clouds whose average thickness or elevation above the accumulation wall  depends on how strongly the particles interact with the field and also their diffusivity.

selected ion monitoring
Selected ion monitoring (SIM) is the practice of monitoring and  recording ion currents at one or more selected ion m/z values  with time, rather than recording full mass spectra, as sample  is introduced into the ion source. Because the detector is integrating signal for a longer time at the relevant ion, limits of  detection can be lowered, albeit at a cost of susceptibility of  the experiment to unexpected interferences. Use of the terms  multiple ion detection, multiple ion (peak) monitoring, and  mass fragmentography have also been used but are discouraged. The terms single ion monitoring or multiple ion monitoring are sometimes used.  

selected reaction monitoring
Selected reaction monitoring (SRM) is used to describe a mode of data acquisition in tandem mass spectrometry where precursor and product ions are selected in the first and second stages of mass spectrometry, respectively

selectivity (in analysis)
Qualitative – the extent to which other substances interfere with the determination of a substance according to a given procedure.
Quantitative – a term used in conjunction with another substantive (e.g. constant, coefficient, index, factor, number, etc.) for the quantitative characterization of interferences.

Selenates are analogous to sulfates and have similar chemistry. Unlike sulfate, selenate is a somewhat good oxidizer; it can be reduced to selenite or selenium. In strongly acid conditions, hydrogen selenate ion, HSeO4-, is formed; the selenic acid, H2SeO4, is very strong

selenic acid
Selenic acid, H2SeO4, is an oxygen acid of selenium. Selenic acid is analogous to sulfuric acid and has similar properties; however, it is a stronger oxidizer.

The selenide ion is Se2-. A selenide is a chemical compound in which selenium serves as a anion with oxidation number of -2, much as sulfur does in a sulfide.


Selenium is a chemical element with atomic number 34, with the chemical symbol Se. Selenium occurs only rarely in the free state in nature. It is a nonmetal that is chemically related to sulfur and tellurium. It is toxic in large amounts, but trace amounts of it, forming the active center of certain enzymes such as glutathione peroxidase(GSH-Px), are necessary for the function of all cells in (probably) all animals. Selenium requirements in plants differ by species, with some plants apparently requiring none.

Isolated selenium occurs in several different forms, but the most stable of these is a dense purplish-gray semimetal (semiconductor) form that is structurally a trigonal polymer chain. It conducts electricity better in the light than in the dark, and is used in photocells (see allotropic section below). Selenium also exists in many nonconductive forms: a black glass-like substance, as well as several red crystalline forms built of eight-membered ring molecules, like its lighter cousin sulfur.

Selenium is found in economic quantities partially replacing sulfur in sulfide ores such as pyrite. Minerals that are selenide or selenate compounds are also known, but all are rare.

Amino acids such as selenocysteine and selenomethionine that contain selenium instead of sulfur in their structure.

The organoselenium compound selenocystamine has been used in some trials as a Se-supplement for its anticarcinogenic activity.

Formula:  C7H14N2O4Se
Mass 270.0119

Selenocysteine is an amino acid that is present in several selenoproteins (seleno-enzymes) in plants and animals (for example glutathione peroxidases, tetraiodothyronine 5' deiodinases, thioredoxin reductases, formate dehydrogenases, glycine reductases and some hydrogenases).
Selenocysteine has a structure similar to cysteine, but with an atom of selenium taking the place of the usual sulfur. Selenium is incorporated into amino acid sequences of selenoproteins by the specific codon to SeCys residue. 

The selenoamino acid selocystine has been found in seagull eggs. 

Selenols are organic compounds that contain the functional group with the connectivity C–Se–H. Selenols are sometimes also called selenomercaptans and selenothiols. Selenols are one of the principal classes of organoselenium compounds. The best known member of the group is the amino acid selenocysteine.

Selenomethionine is an selenoamino acid (amino acid containing selenium). The L-isomer of selenomethionine, known as Se-met, is a common natural food source of selenium. It can not be synthesized by higher animals, but can be obtained from plant material.
Chemical formula: C5H11NO2Se
IUPAC name: 2-amino-4-methylselanyl-butanoic acid

A histidine derivative that is Nα,Nα,Nα-trimethyl-L-histidine substituted by a selenoxo group at position 2 on the imidazole ring. This selenium-containing antioxidant was found in tuna blood and is a major selenium compound in fish muscle. Ths compound has strong antioxidant capacity and binds to heme proteins, such as hemoglobin and myoglobin, to protect them from iron auto-oxidation, and it reacts with radicals and methylmercury (MeHg).

Formula: C9H15N3O2Se
Mol. Weight: 276.19000

Formula H3O3PSe
Mass 161.8985

A selenoprotein is any protein that includes a selenocysteine residue. Selenoproteins exist in all major forms of life, eukaryote, eubacteria and archaea. Among eukaryotes, selenoproteins appear to be common in animals, but rare or absent in other phyla (one has been identified in the green alga Chlamydomonas, but none in other plants or in fungi). Among eubacteria and archaea, selenoproteins are only present in some lineages, while they are completely absent in many other phylogenetic groups.

A glycoprotein synthesized mostly by the liver that serves as the main plasma selenoprotein. Its role is thought to involve extracellular antioxidant activity and Se transport.

The part of the proteome incorporating selenoamino acids, selenomethionine and selenocysteine.
The use of the term is often limited to proteins with genetically encoded selenocysteine only.

Poisoning due to excessive intake of Se. Symptoms include hair and nail loss, skin lesions, damage to the nervous, immune and reproductive systems, convulsions, paralysis, gastrointestinal and circulatory

Compounds where a selenium atom replaces the endocyclic oxygen atom of a carbohydrate.

Scanning Electron Microscopy (SEM) – A scanning electron microscope is a microscope that uses electrons as an "illuminating" medium to resolve very fine features (i.e., thousands of times magnification are typical) in a particular specimen. The concept is similar to a light microscope, but since it uses electrons that have a much smaller wavelength than light, very small features can be resolved.

An electron beam microprobe for X-ray-fluorescence analysis. Commonly associated with electronic microscopy (scanning electron microscopy), energy-dispersive X-ray analysis permits spatially resolved measurments of the elementary composition of materials.

The change in the response of a measuring instrument divided by the corresponding change in stimulus.

sequential injection analysis
In sequential injection manifolds, a stack of well-defined unsegmented zones is assembled in a holding coil using a pump or liquid driver and a selection device. On transporting this stack of zones to the detector, the zones penetrate one another and mixing between their components gives rise to one or more detectable species. These products are measured as the zone stack reaches a suitable (flow-through) detector. The multiposition selection valve allows sequential injection analytical systems to be extremely versatile with many changes to the methodology being achievable through software control of the system parameters rather than actual physical changes to the hardware. Each port of the valve can be dedicated to a specific purpose, and the combinations of sample, standards, reagents, and detectors around the valve are easily modified to suit a particular analysis.

Since the system works sequential, the drawback of such versatility is a reduced sample throughput.

sequential leaching
In sequential leaching (extraction) procedures, chemical extractants of various types are applied to the solid sample, e.g. soil, plants, airborne particles, sludge and wastes, each successive treatment being more drastic in chemical action than the previous one.

A batch leaching test where a solid sample is leached in successive volumes of different types of leaching solutions (compare with serial batch leaching, leaching test, column leaching, and batch leaching).

serial batch leaching
A batch leaching test where a solid sample is leached in successive volumes of fresh aliquots of the same leaching solution (compare with sequential batch leaching, leaching test, column leaching, and batch leaching).

serial dilution
The progressive dilution, by the same factor, of standard or sample in a row of tubes so that the first tube contains the highest concentration of test substance

Surface Enhanced Raman Spectroscopy, or Surface Enhanced Raman Scattering, often abbreviated SERS, is a surface sensitive technique that results in the enhancement of Raman scattering by molecules adsorbed on rough metal surfaces. The enhancement factor can be as much as 1014-1015, which allows the technique to be sensitive enough to detect single molecules.

1. Watery proteinaceous portion of the blood that remains after clotting.

2. Clear watery fluid especially that moistening the surface of serous membranes or that exuded through inflammation of any of these membranes.

sheat liquid
A liquid that is added to the sample flow towards the sample introduction system, often via a concentric capillary, to help produce a stable spray especially in techniques creating very low sample flow rates such as CE.

sheath flow interface
A sheath flow interface is a method for coupling capillary electrophoresis to electrospray ionization that uses a coaxial flow of makeup liquid that is introduced through a tube that is concentric with the separation capillary.

shot noise
Noise caused by the randomness in arrival time of ions/photons at the detector. It is proportional to the number of ions/photons arriving at the detector in a given time interval.

shotgun proteomics
Shotgun proteomics is a method of identifying proteins using a combination of high performance liquid chromatography and mass spectrometry in which the proteins in the mixture are digested and the resulting peptides are separated by liquid chromatography and identified by tandem mass spectrometry.

The sensitive high-resolution ion microprobe (also sensitive high mass-resolution ion microprobe or SHRIMP) is a large-diameter, double-focusing secondary ion mass spectrometer (SIMS) sector instrument produced by Australian Scientific Instruments in Canberra, Australia. Like other SIMS instruments, the SHRIMP microprobe bombards a sample under vacuum with a beam of primary ions that sputters secondary ions that are focused, filtered, and measured according to their energy and mass.

EVISA Instrument Database: SHRIMP

Siderophores (Greek: "iron carrier") are small, high-affinity iron chelating compounds secreted by organisms such as bacteria, fungi or plants. Siderophores are amongst the strongest soluble Fe3+ binding agents known.

signal-to-noise ratio
Magnitude of the observed datastream related to the sum of sought-for and interfering substances plus background, and fluctuations unrelated to the sought-for measurements.

Organosilicon compounds unlike their carbon counterparts do not have a rich double bond chemistry due to the large difference in electronegativity. Existing compounds with organosilene Si=C bonds are laboratory curiosities such as the silicon benzene analogue silabenzene. Disilenes have Si=Si double bonds and disilynes are silicon analogues of an alkyne.

Polymerized siloxanes with organic side chains (R ≠ H) are commonly known as silicones or as polysiloxanes. Representative examples are [SiO(CH3)2]n (polydimethylsiloxane) and [SiO(C6H5)2]n (polydiphenylsiloxane). These compounds can be viewed as a hybrid of both organic and inorganic compounds. The organic side chains confer hydrophobic properties while the -Si-O-Si-O- backbone is purely inorganic.

Siloles, members of a larger class of compounds called metalloles, are the silicon pendants of pyrroles and are of current academic interest due to their electroluminescence and other electronic properties. Siloles are efficient in electron transport. They owe their low lying LUMO to a favorable interaction between the antibonding sigma silicon orbital with a antibonding pi orbital of the butadiene fragment.

A siloxane is any chemical compound composed of units of the form R2SiO, where R is a hydrogen atom or a hydrocarbon group. A siloxane has a branched or unbranched backbone of alternating silicon and oxygen atoms -Si-O-Si-O-, with side chains R attached to the silicon atoms.
The word siloxane is derived from the words silicon, oxygen, and alkane.

Fig.: Decamethylcyclopentasiloxane

silver sulfadiazine
Silver (I) sulfadiazine is a metallodrug used to prevent and treat bacterial or fungus infections of the skin.

Secondary ion mass spectrometry (SIMS) is a mass-spectrometric technique that is used for microscopic chemical analysis. A beam of primary ions with an energy of 5- 20 kiloelectronvolts (keV) bombards a small spot on the surface of the sample under ultra- high vacuum conditions. Positive and negative secondary ions sputtered from the surface are analyzed in a mass spectrometer in regards to their mass-to-charge ratio.

EVISA Instrument Database: SIMS systems

single filament method
The single filament method is a surface ionization method used for TIMS wherein a single filament is used to vaporize and ionize the sample.

single-focusing mass spectrometer
In a single-focusing mass spectrometer, a single magnetic sector is used to generate the magnetic field that differentiates  ions according to their m/z values (strictly, according to their  momenta). The addition of an electric sector in a specified  configuration provides a double-focusing mass spectrometer  that can achieve higher mass resolution than a single-focusing mass spectrometer.

size fractionation
Size fractionation is the process of classification of an analyte or a group of analytes from a certain sample acoording to molecular or particular size.

size-exclusion chromatography
An HPLC method, different from reversed-phase chromatography, used mainly to separate high-molecular-weight samples and to determine their molecular-weight distribution. SEC, also called Gel Filtration Chromatography (GFC) or Gel Permeation Chromatography (GPC) is based on the molecular sieve effect and enables species to be separated according to their size and to a lesser extend, shape. The average time a substance spends in the pores of the packing can usually be correlated with its molecular weight.

sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)
Analytical separation technique, often used to characterize proteins or mixtures, that uses a charged gel environment through which molecules of varying sizes and electric charges migrate from one pole to the other. Unlike gel-filtration chromatography, larger molecules move more slowly than smaller molecules because their migration rate is not dependent on diffusion into and out of particles. The SDS detergent denatures and binds to proteins, aiding in their separation.

sodium stibogluconate
Sodium stibogluconate belongs to the class of medicines known as the pentavalent antimonials used  to treat leishmaniasis.  Sodium stibogluconate is sold in the UK as Pentostam (manufactured by GlaxoSmithKline) and is only available for administration by injection. Widespread resistance has limited the utility of sodium stibogluconate, and in many parts of the world, amphotericin or miltefosine are used instead.

soft ionisation
Mass spectrometric methods leading to the formation of ions with low internal energies meant to avoid fragmentation of the molecular structure.

soft ionization
Ionization in which a minimum of excess energy is imparted to the newly formed ion, producing little resultant fragmentation. Distinguished from high-energy ionization, sometimes called ‘hard’
ionization, typified by the products of EI.

First generation water-soluble gold(1) thiolate metallodrug used for treatment of rheumatoid arthritis. Serious side effects led to the development of second generation gold drugs such as auranofin.
IUPAC name : auriothioglucose

solid phase extraction
(SPE) - A sample-preparation technique that uses a solid-phase packing contained in a small plastic cartridge. The solid stationary phases are the same as HPLC packings; however, the principle is the same as in frontal chromatography. The process as most often practiced requires four steps: conditioning the sorbent, adding the sample, washing away the impurities, and eluting the sample in as small a volume as possible with a strong solvent.

solid-phase micro-extraction (SPME)
SPME is a solvent-free solid-phase preconcentration technique based on the sorption of analyte species present in a liquid phase or, more often in a headspace gaseous phase, on a microfiber coated with a chromatographic sorbent.
When the equilibrium is reached, the fiber is transferred to a GC injector by means of a microsyringe, and the analytes are thermally desorbed inside the heated injector.

The analytical concentration of a solute in a saturated solution. The analytical concentration includes those of all the species formed by the dissolved substance in the solution. Numerical data for solubility always have to be defined in relation to the values of temperature, pressure and concentrations of other dissolved substances.

Source: IUPAC

- analytical procedure for bringing biological materials into solution. It can be achieved by alkaline, acidic or enzymatic hydrolysis. Following the solubilization, an aqueous solution of species is obtained but the matrix is not eliminated.

The minor component of a solution which is regarded as having been dissolved by the solvent.

Source: IUPAC

Homogeneous liquid phase comprising at least two different substances.

Source: IUPAC

A liquid (usually the major component of a solution) which is used to dissolve a solute or

Source: IUPAC

solvent extraction
The removal of a soluble material from a solid mixture by means of a solvent or the removal of one or more components from a liquid mixture by use of a solvent with which the liquid is immiscible or nearly so.

sonic spray ionization (SSI)
Sonic spray ionization is the process of gas phase ion formation during atmospheric pressure droplet formation in a supersonic pneumatic spray. Ions are formed due to a statistically unbalanced charge distribution in the nebulized droplets

A solid material that removes chemical species from liquids or gases through adsorption and/or
absorption (compare with absorbent and adsorbent).  Common sorbents are polymers, silica gel, alumina, titania, zirconia, and chemically modified materials.Sorbents are used as packing materials in liquid chromatography or solid phase extraction cartridges.

It is sometimes difficult or impossible to discriminate experimentally between adsorption and absorption : in such cases it is convenient to use the noncommittal term sorption. In ion exchange, sorption is the uptake of electrolytes or nonelectrolytes by ion exchangers through mechanisms other than pure ion exchange.
With respect to surface phenomena, this term is also used when the retention mechanism at a
surface is unknown. Adsorption, surface precipitation, and polymerization are all examples of sorption.

Optical spectrometry:
In optical spectrometry, the source of the spectrometer is the device from which the radiation is emitted. This may be a flame or plasma source.

Mass spectrometry:
The source is the device within the mass spectrometer in which ionization of sample molecules occurs. The source may be under vacuum, or it can operate at atmospheric pressure. A chromatographic method may interface with the source, or samples may be introduced via a probe or an automated sample introduction system. Ions are accelerated out of the source into the mass analyzer of the instrument.

space charge effect
The space charge effect is the mutual repulsion of particles of like charge that limits the current in a charged-particle beam and causes beams or packets of charged particles to expand radially over time.

Transient plasma triggered by imposing so high a voltage across a small gap between conducting electrodes that the intervening gas ionizes.Spark devices are used as sources both for atomiuc emission spectrometry (Spark-OES) as well as mass spectrometry (SS-MS),

spark source mass spectrometry
Spark source mass spectrometry is a technique using a mass spectrometer with a spark ionization source.

Distribution of an element amongst defined chemical species in a system.

speciation analysis
analytical chemistry: analytical activities of identifying and /or measuring the quantities of one or more individual chemical species in a sample.

species-specific isotope dilution
Species-specific isotope dilution (sometimes also called speciated isotope dilution) is an isotope dilution technique using a spike compound identical to the compound under investigation but labeled with a specific isotope of the target element. Species-specific ID analysis is only possible for element species well defined in their structure and composition. The equilibration of the spike and the analyte in the sample, attainable in classical IDMS by multiple sequential dissolution and evaporation cycles, cannot be guaranteed to be achieved for species-specific ID analysis of solid samples. If applicable, the method can correct for loss of analyte during sample preparation following the spike addition, incomplete derivatisation yield and for intensity suppression/enhancement during detection.

spectral interferences
the class of interference related to spectral properties of components other than atomized analyte. Three sources of spectral interference can be identified including spectral line interference, scattering, and broad band spectral interference.

spectral skewing
Spectral skewing is the deviation of the peak intensities in a mass spectrum from their expected values that occurs when the relative concentration of the various analytes change during acquisition of the mass spectrum.

Instrument to display light of various wavelengths at separated physical positions simultaneously.

Any instrument used to study light as a function of wavelength.

An instrument to quantitatively measure the intensity of light as a function of wavelength, typically for making absorbance measurements.

spiked sample
A spiked sample is a sample prepared by adding a known quantity of analyte to a matrix which is close to or identical to that of the sample of interest. Spiked samples may be used in method validation experiments to help identify matrix effects and determine the recovery of an analyte or the selectivity of the method.

Spiroplatin is a second generation metallodrug and analgue for cisplatin, developed for cancer therapy. Spiroplatin induces DNA cross-links, thereby inhibiting DNA replication and RNA and protein synthesis. Similar to other platinum compounds, this agent has been shown to be mutagenic and carcinogenic.
IUPAC name: aqua-1,1-bis(aminomethyl)-cyclohexanesulfatoplatinum(II)

spray chamber
Comparison of spray chambersThe spray chamber is part of the sample introduction system for liquid samples of a spectroscopic source such as a flame or plasma. The function of the spray chamber is to filter the aerosol produced by the nebulizer (primary/secondary aerosol) so that only the smallest reach the source (tertiary aerosol). The most commonly used spray chambers in plasma spectrochemistry are the cyclonic, barrel (or Scott-type), and conical (see figure). 
The cyclonic and Scott-type spray chambers are available as both single and double pass (or baffled) versions. The double-pass mode acts as a secondary filter to further reduce the mean droplet site distribution (reducing the aerosol transport efficiency and reducing the noise level). The conical spray chamber uses an impact bead to break-up larger droplets. In all three designs gravity is used to remove the larger drops from the transport gas stream and divert them to the drain. Total transport efficiency is typically below 5 %. In the cyclonic spray chamber this action is assisted by centrifugal forces.

The ejection of atoms from a surface by the impact of high-energy ions and atoms.

stable isotopes
Nuclei that do not decay to other isotopes on geologic timescales, but may themselves be produced by the decay of radioactive isotopes.

A procedure of labeling tissues, organisms, or molecules (such as DNA or proteins) with colored or fluorescent dyes to allow visualization by microscopic or marcroscopic techniques.

standard addition method (SAM)
The standard-addition  method  is a calibration method applied to reduce the effect of matrix interferences. It involves adding one or more increments of a standard solution to a sample  aliquots of the same size. Each spiked sample is then diluted to a fixed volume before analyzing. When  the amount of sample is limited, standard additions can also be carried out by successive introductions of increments  of the standard to a single measured aliquot of the unknown. Measurements are made on the original and after each addition. Placing a regression line through the absorptive data points obtained from the series of additions and interpolating it till crossing the abscissa, yields the initial analyte concentration of the sample.  

standard deviation
A measure of dispersion or variation, usually taken as the square root of the variance.

standard operating procedure (SOP)
A detailed (step-by-step), instruction to achieve uniformity in the performance of a specific process or or pioece of equipment, which are approved by the quality control unit and used for GMP/GLP operations.

static nanoelectrospray
Static nanoelectrospray is a variant of nanoelectrospray in which the flow of liquid is driven by the capillary action induced by droplets leaving the electrospray needle with no additional pumping.

static secondary ion mass spectrometry (SSIMS)
SIMS method featuring primary ion current densities (corresponding to SIMS gun flux) of 2 ~ 3 nA/cm2 or less and primarily used in analysis of sample surface components. The method is therefore distin-guished from dynamic SIMS, which is used for analysis of components in the depth direction. When the sample is an organic molecule in solid form, the term is changed to organic SIMS or molecular SIMS.

stationary phase
The non-mobile phase in the chromatographic bed, on which the separation depends. For example, in gas solid chromatography and liquid—solid chromatography the active solid is the stationary phase, and in gas—liquid and liquid liquid chromatography the liquid, but not the solid support, is
the stationary phase.

Source: IUPAC

statistical quality control
Those aspects of quality control in which statistics are applied, in contrast to the broader scope of quality control which includes many other procedures, such as preventive maintenance, instrument function checks, and performance validation tests. Statistical QC procedures are often used to monitor routine performance of a method and to alert the laboratory when the performance of a method changes.

steady state
1. (in chemistry): State of a system in which properties do not change with time.

2. (in toxicology): State of a system in which the conditions do not change in time.

steam distillation
Steam distillation is a special type of distillation (a separation process) for temperature sensitive materials that tend to decompose at sustained high temperatures. Separation by normal distillation would then not be an option, so water or steam are introduced into the distillation apparatus. By adding water or steam the boiling point of the compounds is depressed, allowing them to evaporate at lower temperatures, preferably below the temperatures at which the deterioration of the material becomes appreciable. If the substances to be distilled are very sensitive to heat, steam distillation can also be combined with vacuum distillation. After destillation the vapors are condensed as usual, usually yielding a two-phase system of water and the organic compounds, allowing for simple separation.

Steam distillation has been evaluated as a technique for the separation of methylmercury from different environmental sample materials.

Stibine (SbH3) is a precursor for chemical vapor deposition (CVD) of antimony atom in the production of semiconductors.
In the environment, traces of stibines have been found in contaminated soils.
CAS Number : 7803-52-3
Other names: Antimony trihydride

stock solution
This is generally a standard or reagent solution of known accepted stability, which has been prepared in relatively large amounts, of which portions are used as required. Frequently, such portions are used following further dilution.

properly refers to the set of chemical and physical principles applied to determine the relationships between reactants and products in a chemical process. In stoichiometric calculations, it is the mass relationship existing between the chemical reactants and products, which are of the primary interest. As an adjective, "stoichiometric" is often taken to refer to the quantities of reactants and products as determined by the reaction equation for a specific chemical reaction, which produces no by-products.

stray light
Any radiation reaching the detector that is not remitted or transmitted from, or through, the sample
at the selected measurement wavelength. In the specific case of Raman spectroscopy, stray light generally consists of the elastic stray light as Rayleigh scattering of the main laser frequency energy.

structure analysis
Analytical efforts aiming on structural identification of molecules. The techniques that have been developed for the identification of chemical structures include mass spectrometry (MS), nuclear magnetic resonance spectroscopy (NMR), infrared/ultraviolet spectrometry (IR/UV), X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) spectroscopy.

Passing directly from a solid to a vapor state without first melting into a liquid.

sulfate-reducing bacteria
Microbes found commonly in sediments that transform inorganic mercury into organic methylmercury as a by-product of their metabolism.

supercritical fluid
A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned". Supercritical fluids are suitable as a substitute for organic solvents in a range of industrial and laboratory processes.

supercritical fluid chromatography (SFC)
An HPLC technique which employs the use of supercritical fluids as the mobile phase to enhance the separation of samples that are typically problematic for standard LC analysis.

supercritical fluid extraction (SFE)
A special type of mixture extraction employing the unique benefits of supercritical fluid.

Material floating on the surface of a liquid mixture (often the liquid component that has the lowest density); the overlying fluid layer that remains after precipitation of a solid componentr through centrifugation.

surface complex
The interaction of a surface functional group with an ion or molecule present in the soil solution can create a stable molecular entity called a surface complex. The overall reaction is referred to as surface complexation.

surface water
Water above the surface of the land, including lakes, rivers, streams, ponds, floodwater, and runoff [compare groundwater].

surface-induced dissociation
Surface-induced dissociation (SID) is the fragmentation of an ion  induced by an energetic collision of that ion with a solid surface, which can be placed between two mass analyzers. The surface then takes the place of the neutral gas molecule that is the collision target in collision-induced dissociation.   

Any substance that changes the characteristics of a surface, such as lowering the surface tension of water.

suspended particulate matter (SPM)
Mineral and/or organic particles in suspension in natural or polluted waters.

Particles floating in (not necessarily on) a liquid medium, or the mix of particles and liquid itself.

Pharmacological or toxicological interaction in which the combined biological effect of two or more substances is greater than expected on the basis of the simple summation of the toxicity of each of the individual substances

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