The seventh member of group 18 is oganesson, an unstablesynthetic element whose chemistry is still uncertain because only five very short-lived atoms (t1/2 = 0.69 ms) have ever been synthesized (Template:As of<ref name="smits2020"/>). IUPAC uses the term "noble gas" interchangeably with "group 18" and thus includes oganesson;<ref name=Koppenol>Template:Cite journal</ref> however, due to relativistic effects, oganesson is predicted to be a solid under standard conditions and reactive enough not to qualify functionally as "noble".<ref name="smits2020">Template:Cite journal</ref>
Pierre Janssen and Joseph Norman Lockyer had discovered a new element on 18 August 1868 while looking at the chromosphere of the Sun, and named it helium after the Greek word for the Sun, Template:Lang (Template:Lang).<ref>Oxford English Dictionary (1989), s.v. "helium". Retrieved 16 December 2006, from Oxford English Dictionary Online. Also, from quotation there: Thomson, W. (1872). Rep. Brit. Assoc. xcix: "Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium."</ref> No chemical analysis was possible at the time, but helium was later found to be a noble gas. Before them, in 1784, the English chemist and physicist Henry Cavendish had discovered that air contains a small proportion of a substance less reactive than nitrogen.<ref name="Ozima 1">Template:Harvnb</ref> A century later, in 1895, Lord Rayleigh discovered that samples of nitrogen from the air were of a different density than nitrogen resulting from chemical reactions. Along with Scottish scientist William Ramsay at University College, London, Lord Rayleigh theorized that the nitrogen extracted from air was mixed with another gas, leading to an experiment that successfully isolated a new element, argon, from the Greek word Template:Lang (Template:Lang, "idle" or "lazy").<ref name="Ozima 1" /> With this discovery, they realized an entire class of gases was missing from the periodic table. During his search for argon, Ramsay also managed to isolate helium for the first time while heating cleveite, a mineral. In 1902, having accepted the evidence for the elements helium and argon, Dmitri Mendeleev included these noble gases as group 0 in his arrangement of the elements, which would later become the periodic table.<ref>Template:Harvnb</ref>
Ramsay continued his search for these gases using the method of fractional distillation to separate liquid air into several components. In 1898, he discovered the elements krypton, neon, and xenon, and named them after the Greek words Template:Lang (Template:Lang, "hidden"), Template:Lang (Template:Lang, "new"), and Template:Lang (Template:Lang, "stranger"), respectively. Radon was first identified in 1898 by Friedrich Ernst Dorn,<ref>Template:Cite journal</ref> and was named radium emanation, but was not considered a noble gas until 1904 when its characteristics were found to be similar to those of other noble gases.<ref name="brit">Template:Cite encyclopedia</ref> Rayleigh and Ramsay received the 1904 Nobel Prizes in Physics and in Chemistry, respectively, for their discovery of the noble gases;<ref>Template:Cite web</ref><ref name=nobelchem>Template:Cite web</ref> in the words of J. E. Cederblom, then president of the Royal Swedish Academy of Sciences, "the discovery of an entirely new group of elements, of which no single representative had been known with any certainty, is something utterly unique in the history of chemistry, being intrinsically an advance in science of peculiar significance".<ref name=nobelchem/>
The discovery of the noble gases aided in the development of a general understanding of atomic structure. In 1895, French chemist Henri Moissan attempted to form a reaction between fluorine, the most electronegative element, and argon, one of the noble gases, but failed. Scientists were unable to prepare compounds of argon until the end of the 20th century, but these attempts helped to develop new theories of atomic structure. Learning from these experiments, Danish physicist Niels Bohr proposed in 1913 that the electrons in atoms are arranged in shells surrounding the nucleus, and that for all noble gases except helium the outermost shell always contains eight electrons.<ref name="brit" /> In 1916, Gilbert N. Lewis formulated the octet rule, which concluded an octet of electrons in the outer shell was the most stable arrangement for any atom; this arrangement caused them to be unreactive with other elements since they did not require any more electrons to complete their outer shell.<ref>Template:Cite journal</ref>
Liquid helium will only solidify if exposed to pressures well above atmospheric pressure, an effect explainable with quantum mechanics</ref> || 24.7 || 83.6 || 115.8 || 161.7 || 202.2|| 325±15 (predicted)<ref name=og/>
The noble gas atoms, like atoms in most groups, increase steadily in atomic radius from one period to the next due to the increasing number of electrons. The size of the atom is related to several properties. For example, the ionization potential decreases with an increasing radius because the valence electrons in the larger noble gases are farther away from the nucleus and are therefore not held as tightly together by the atom. Noble gases have the largest ionization potential among the elements of each period, which reflects the stability of their electron configuration and is related to their relative lack of chemical reactivity.<ref name=greenwood891/> Some of the heavier noble gases, however, have ionization potentials small enough to be comparable to those of other elements and molecules. It was the insight that xenon has an ionization potential similar to that of the oxygen molecule that led Bartlett to attempt oxidizing xenon using platinum hexafluoride, an oxidizing agent known to be strong enough to react with oxygen.<ref name=bartlett/> Noble gases cannot accept an electron to form stable anions; that is, they have a negative electron affinity.<ref>Template:Cite journal; Template:Cite journal</ref>
The noble gases are colorless, odorless, tasteless, and nonflammable under standard conditions.<ref>Template:Cite book</ref> They were once labeled group 0 in the periodic table because it was believed they had a valence of zero, meaning their atoms cannot combine with those of other elements to form compounds. However, it was later discovered some do indeed form compounds, causing this label to fall into disuse.<ref name="brit" />
Template:Further
Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells resulting in trends in chemical behavior:
The noble gases have full valence electron shells. Valence electrons are the outermost electrons of an atom and are normally the only electrons that participate in chemical bonding. Atoms with full valence electron shells are extremely stable and therefore do not tend to form chemical bonds and have little tendency to gain or lose electrons.<ref>Template:Harvnb</ref> However, heavier noble gases such as radon are held less firmly together by electromagnetic force than lighter noble gases such as helium, making it easier to remove outer electrons from heavy noble gases.
As a result of a full shell, the noble gases can be used in conjunction with the electron configuration notation to form the noble gas notation. To do this, the nearest noble gas that precedes the element in question is written first, and then the electron configuration is continued from that point forward. For example, the electron notation of
phosphorus is Template:Nowrap, while the noble gas notation is Template:Nowrap. This more compact notation makes it easier to identify elements, and is shorter than writing out the full notation of atomic orbitals.<ref>Template:Harvnb</ref>
The noble gases cross the boundary between blocks—helium is an s-element whereas the rest of members are p-elements—which is unusual among the IUPAC groups. All other IUPAC groups contain elements from one block each. This causes some inconsistencies in trends across the table, and on those grounds some chemists have proposed that helium should be moved to group 2 to be with other s2 elements,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> but this change has not generally been adopted.
The noble gases show extremely low chemical reactivity; consequently, only a few hundred noble gas compounds have been formed. Neutral compounds in which helium and neon are involved in chemical bonds have not been formed (although some helium-containing ions exist and there is some theoretical evidence for a few neutral helium-containing ones), while xenon, krypton, and argon have shown only minor reactivity.<ref name=Ngcomp>Template:Cite journal</ref> The reactivity follows the order Ne < He < Ar < Kr < Xe < Rn ≪ Og.
Some of these compounds have found use in chemical synthesis as oxidizing agents; Template:Chem, in particular, is commercially available and can be used as a fluorinating agent.<ref>Template:Cite journal</ref> As of 2007, about five hundred compounds of xenon bonded to other elements have been identified, including organoxenon compounds (containing xenon bonded to carbon), and xenon bonded to nitrogen, chlorine, gold, mercury, and xenon itself.<ref name=Ngcomp/><ref>Template:Harvnb</ref> Compounds of xenon bound to boron, hydrogen, bromine, iodine, beryllium, sulphur, titanium, copper, and silver have also been observed but only at low temperatures in noble gas matrices, or in supersonic noble gas jets.<ref name=Ngcomp/>
Radon is more reactive than xenon, and forms chemical bonds more easily than xenon does. However, due to the high radioactivity and short half-life of radon isotopes, only a few fluorides and oxides of radon have been formed in practice.<ref>.Template:Cite journal</ref> Radon goes further towards metallic behavior than xenon; the difluoride RnF2 is highly ionic, and cationic Rn2+ is formed in halogen fluoride solutions. For this reason, kinetic hindrance makes it difficult to oxidize radon beyond the +2 state. Only tracer experiments appear to have succeeded in doing so, probably forming RnF4, RnF6, and RnO3.<ref name=Stein>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
Krypton is less reactive than xenon, but several compounds have been reported with krypton in the oxidation state of +2.<ref name=Ngcomp/> Krypton difluoride is the most notable and easily characterized. Under extreme conditions, krypton reacts with fluorine to form KrF2 according to the following equation:
Kr + F2 → KrF2
Compounds in which krypton forms a single bond to nitrogen and oxygen have also been characterized,<ref>Template:Cite journal</ref> but are only stable below Template:Convert and Template:Convert respectively.<ref name=Ngcomp/>
Krypton atoms chemically bound to other nonmetals (hydrogen, chlorine, carbon) as well as some late transition metals (copper, silver, gold) have also been observed, but only either at low temperatures in noble gas matrices, or in supersonic noble gas jets.<ref name=Ngcomp/> Similar conditions were used to obtain the first few compounds of argon in 2000, such as argon fluorohydride (HArF), and some bound to the late transition metals copper, silver, and gold.<ref name=Ngcomp/> As of 2007, no stable neutral molecules involving covalently bound helium or neon are known.<ref name=Ngcomp/>
Extrapolation from periodic trends predict that oganesson should be the most reactive of the noble gases; more sophisticated theoretical treatments indicate greater reactivity than such extrapolations suggest, to the point where the applicability of the descriptor "noble gas" has been questioned.<ref>Template:Cite journal Translated into English by W. E. Russey and published in three parts in ChemViews Magazine: Template:Cite magazine Template:Cite magazine Template:Cite magazine</ref> Oganesson is expected to be rather like silicon or tin in group 14:<ref name=primefan>Template:Cite web</ref> a reactive element with a common +4 and a less common +2 state,<ref name="BFricke">Template:Cite journal</ref><ref>Russian periodic table poster by A. V. Kulsha and T. A. Kolevich</ref> which at room temperature and pressure is not a gas but rather a solid semiconductor. Empirical / experimental testing will be required to validate these predictions.<ref name=og/><ref name=semiconductor>Template:Cite journal</ref> (On the other hand, flerovium, despite being in group 14, is predicted to be unusually volatile, which suggests noble gas-like properties.)<ref>Template:Cite journal</ref><ref>Template:Cite web</ref>
The noble gases—including helium—can form stable molecular ions in the gas phase. The simplest is the helium hydride molecular ion, HeH+, discovered in 1925.<ref>Template:Cite journal</ref> Because it is composed of the two most abundant elements in the universe, hydrogen and helium, it was believed to occur naturally in the interstellar medium, and it was finally detected in April 2019 using the airborne SOFIA telescope. In addition to these ions, there are many known neutral excimers of the noble gases. These are compounds such as ArF and KrF that are stable only when in an excited electronic state; some of them find application in excimer lasers.
In addition to the compounds where a noble gas atom is involved in a covalent bond, noble gases also form non-covalent compounds. The clathrates, first described in 1949,<ref>Template:Cite journal</ref> consist of a noble gas atom trapped within cavities of crystal lattices of certain organic and inorganic substances. The essential condition for their formation is that the guest (noble gas) atoms must be of appropriate size to fit in the cavities of the host crystal lattice. For instance, argon, krypton, and xenon form clathrates with hydroquinone, but helium and neon do not because they are too small or insufficiently polarizable to be retained.<ref>Template:Harvnb</ref> Neon, argon, krypton, and xenon also form clathrate hydrates, where the noble gas is trapped in ice.<ref>Template:Cite journal</ref>
Noble gases can form endohedral fullerene compounds, in which the noble gas atom is trapped inside a fullerene molecule. In 1993, it was discovered that when Template:Chem, a spherical molecule consisting of 60 carbon atoms, is exposed to noble gases at high pressure, complexes such as Template:Chem can be formed (the @ notation indicates He is contained inside Template:Chem but not covalently bound to it).<ref>Template:Cite journal</ref> As of 2008, endohedral complexes with helium, neon, argon, krypton, and xenon have been created.<ref>Template:Cite journal</ref> These compounds have found use in the study of the structure and reactivity of fullerenes by means of the nuclear magnetic resonance of the noble gas atom.<ref>Template:Cite journal</ref>
Noble gas compounds such as xenon difluoride (Template:Chem) are considered to be hypervalent because they violate the octet rule. Bonding in such compounds can be explained using a three-center four-electron bond model.<ref>Template:Harvnb</ref><ref>Template:Harvnb</ref> This model, first proposed in 1951, considers bonding of three collinear atoms. For example, bonding in Template:Chem is described by a set of three molecular orbitals (MOs) derived from p-orbitals on each atom. Bonding results from the combination of a filled p-orbital from Xe with one half-filled p-orbital from each F atom, resulting in a filled bonding orbital, a filled non-bonding orbital, and an empty antibonding orbital. The highest occupied molecular orbital is localized on the two terminal atoms. This represents a localization of charge that is facilitated by the high electronegativity of fluorine.<ref>Template:Cite journal</ref>
The chemistry of the heavier noble gases, krypton and xenon, are well established. The chemistry of the lighter ones, argon and helium, is still at an early stage, while a neon compound is yet to be identified.
Template:Clear
The abundances of the noble gases in the universe decrease as their atomic numbers increase. Helium is the most common element in the universe after hydrogen, with a mass fraction of about 24%. Most of the helium in the universe was formed during Big Bang nucleosynthesis, but the amount of helium is steadily increasing due to the fusion of hydrogen in stellar nucleosynthesis (and, to a very slight degree, the alpha decay of heavy elements).<ref>Template:Cite web</ref><ref>Template:Cite journal</ref>
Abundances on Earth follow different trends; for example, helium is only the third most abundant noble gas in the atmosphere. The reason is that there is no primordial helium in the atmosphere; due to the small mass of the atom, helium cannot be retained by the Earth's gravitational field.<ref name=morrison>Template:Cite journal</ref> Helium on Earth comes from the alpha decay of heavy elements such as uranium and thorium found in the Earth's crust, and tends to accumulate in natural gas deposits.<ref name=morrison /> The abundance of argon, on the other hand, is increased as a result of the beta decay of potassium-40, also found in the Earth's crust, to form argon-40, which is the most abundant isotope of argon on Earth despite being relatively rare in the Solar System. This process is the basis for the potassium-argon dating method.<ref>Template:Cite web</ref>
Xenon has an unexpectedly low abundance in the atmosphere, in what has been called the missing xenon problem; one theory is that the missing xenon may be trapped in minerals inside the Earth's crust.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Radon is formed in the lithosphere by the alpha decay of radium. It can seep into buildings through cracks in their foundation and accumulate in areas that are not well ventilated. Due to its high radioactivity, radon presents a significant health hazard; it is implicated in an estimated 21,000 lung cancer deaths per year in the United States alone.<ref>Template:Cite web</ref> Oganesson does not occur in nature and is instead created manually by scientists.
Neon, argon, krypton, and xenon are obtained from air using the methods of liquefaction of gases, to convert elements to a liquid state, and fractional distillation, to separate mixtures into component parts. Helium is typically produced by separating it from natural gas, and radon is isolated from the radioactive decay of radium compounds.<ref name="brit" /> The prices of the noble gases are influenced by their natural abundance, with argon being the cheapest and xenon the most expensive. As an example, the adjacent table lists the 2004 prices in the United States for laboratory quantities of each gas.
Helium is used as a component of breathing gases to replace nitrogen, due its low solubility in fluids, especially in lipids. Gases are absorbed by the blood and body tissues when under pressure like in scuba diving, which causes an anesthetic effect known as nitrogen narcosis.<ref name=Fowler>Template:Cite journal</ref> Due to its reduced solubility, little helium is taken into cell membranes, and when helium is used to replace part of the breathing mixtures, such as in trimix or heliox, a decrease in the narcotic effect of the gas at depth is obtained.<ref>Template:Harvnb</ref> Helium's reduced solubility offers further advantages for the condition known as decompression sickness, or the bends.<ref name="brit"/><ref>Template:Cite journal</ref> The reduced amount of dissolved gas in the body means that fewer gas bubbles form during the decrease in pressure of the ascent. Another noble gas, argon, is considered the best option for use as a drysuit inflation gas for scuba diving.<ref>Template:Cite web</ref> Helium is also used as filling gas in nuclear fuel rods for nuclear reactors.<ref>Template:Cite journal</ref>
In many applications, the noble gases are used to provide an inert atmosphere. Argon is used in the synthesis of air-sensitive compounds that are sensitive to nitrogen. Solid argon is also used for the study of very unstable compounds, such as reactive intermediates, by trapping them in an inert matrix at very low temperatures.<ref>Template:Cite journal</ref> Helium is used as the carrier medium in gas chromatography, as a filler gas for thermometers, and in devices for measuring radiation, such as the Geiger counter and the bubble chamber.<ref name=kirk/> Helium and argon are both commonly used to shield welding arcs and the surrounding base metal from the atmosphere during welding and cutting, as well as in other metallurgical processes and in the production of silicon for the semiconductor industry.<ref name="ullmann" />
Noble gases are commonly used in lighting because of their lack of chemical reactivity. Argon, mixed with nitrogen, is used as a filler gas for incandescent light bulbs.<ref name=ullmann>Template:Cite book</ref> Krypton is used in high-performance light bulbs, which have higher color temperatures and greater efficiency, because it reduces the rate of evaporation of the filament more than argon; halogen lamps, in particular, use krypton mixed with small amounts of compounds of iodine or bromine.<ref name=ullmann/> The noble gases glow in distinctive colors when used inside gas-discharge lamps, such as "neon lights". These lights are called after neon but often contain other gases and phosphors, which add various hues to the orange-red color of neon. Xenon is commonly used in xenon arc lamps, which, due to their nearly continuous spectrum that resembles daylight, find application in film projectors and as automobile headlamps.<ref name=ullmann/>
The noble gases are used in excimer lasers, which are based on short-lived electronically excited molecules known as excimers. The excimers used for lasers may be noble gas dimers such as Ar2, Kr2 or Xe2, or more commonly, the noble gas is combined with a halogen in excimers such as ArF, KrF, XeF, or XeCl. These lasers produce ultraviolet light, which, due to its short wavelength (193 nm for ArF and 248 nm for KrF), allows for high-precision imaging. Excimer lasers have many industrial, medical, and scientific applications. They are used for microlithography and microfabrication, which are essential for integrated circuit manufacture, and for laser surgery, including laser angioplasty and eye surgery.<ref>Template:Cite book</ref>
Some noble gases have direct application in medicine. Helium is sometimes used to improve the ease of breathing of people with asthma.<ref name=ullmann/> Xenon is used as an anesthetic because of its high solubility in lipids, which makes it more potent than the usual nitrous oxide, and because it is readily eliminated from the body, resulting in faster recovery.<ref>Template:Cite journal</ref> Xenon finds application in medical imaging of the lungs through hyperpolarized MRI.<ref>Template:Cite journal</ref> Radon, which is highly radioactive and is only available in minute amounts, is used in radiotherapy.<ref name=brit />
Noble gases, particularly xenon, are predominantly used in ion engines due to their inertness. Since ion engines are not driven by chemical reactions, chemically inert fuels are desired to prevent unwanted reaction between the fuel and anything else on the engine.
Oganesson is too unstable to work with and has no known application other than research.
The relative isotopic abundances of noble gases serve as an important geochemical tracing tool in earth science.<ref name=Mukhopadhyay-2019/><ref name="Burnard-2013">Template:Cite book</ref> They can unravel the Earth's degassing history and its effects to the surrounding environment (i.e., atmosphere composition<ref>Template:Citation</ref>). Due to their inert nature and low abundances, change in the noble gas concentration and their isotopic ratios can be used to resolve and quantify the processes influencing their current signatures across geological settings.<ref name="Burnard-2013"/><ref name="Ballentine-2002b">Template:Cite journal</ref>
Neon has three main stable isotopes:20Ne, 21Ne and 22Ne, with 20Ne produced by cosmic nucleogenic reactions, causing high abundance in the atmosphere.<ref name="Ballentine-2002b"/><ref name="Wetherill 679–683">Template:Cite journal</ref> 21Ne and 22Ne are produced in the earth's crust as a result of interactions between alpha and neutron particles with light elements; 18O, 19F and 24,25Mg.<ref>Template:Cite journal</ref> The neon ratios (20Ne/22Ne and 21Ne/22Ne) are systematically used to discern the heterogeneity in the Earth's mantle and volatile sources. Complimenting He isotope data, neon isotope data additionally provide insight to thermal evolution of Earth's systems.<ref>Template:Cite journal</ref>
Argon has three stable isotopes: 36Ar, 38Ar and 40Ar. 36Ar and 38Ar are primordial, with their inventory on the earth's crust dependent on the equilibration of meteoric water with the crustal fluids.<ref name="Ballentine-2002b"/> This explains huge inventory of 36Ar in the atmosphere. Production of these two isotopes (36Ar and 38Ar) is negligible within the earth's crust, only limited concentrations of 38Ar can be produced by interaction between alpha particles from decay of 235,238U and 232Th and light elements (37Cl and 41K). While 36Ar is continuously being produced by Beta-decay of 36Cl.<ref name="Wetherill 679–683"/><ref>Template:Cite journal</ref> 40Ar is a product of radiogenic decay of 40K. Different endmembers values for 40Ar/36Ar have been reported; Air = 295.5,<ref name="Burnard-1997">Template:Cite journal</ref> MORB = 40,000,<ref name="Burnard-1997" /> and crust = 3000.<ref name="Ballentine-2002b"/>
Krypton has several isotopes, with 78, 80, 82Kr being primordial, while 83,84, 86Kr results from spontaneous fission of 244Pu and radiogenic decay of 238U.<ref name=Mukhopadhyay-2019>Template:Cite journal</ref><ref name="Ballentine-2002b"/> Krypton's isotopes geochemical signature in mantle reservoirs resembling the modern atmosphere. preserves the solar-like primordial signature.<ref name="Holland-2006">Template:Cite journal</ref> Krypton isotopes have been used to decipher the mechanism of volatiles delivery to earth's system, which had great implication to evolution of earth (nitrogen, oxygen, and oxygen) and emergence of life.<ref>Template:Cite journal</ref> This is largely due to a clear distinction of krypton isotope signature from various sources such as chondritic material, solar wind and cometary.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
Template:MainXenon has nine isotopes, most of which are produced by the radiogenic decay. Krypton and xenon noble gases requires pristine, robust geochemical sampling protocol to avoid atmospheric contamination.<ref>Template:Cite journal</ref> Furthermore, sophisticated instrumentation is required to resolve mass peaks among many isotopes with narrow mass difference during analysis.
Noble gas measurements can be obtained from sources like volcanic vents, springs, and geothermal wells following specific sampling protocols.<ref>Template:Cite journal</ref> The classic specific sampling protocol include the following.
Copper tubes - These are standard refrigeration copper tubes, cut to ~10 cm³ with a 3/8” outer diameter, and are used for sampling volatile discharges by connecting an inverted funnel to the tube via TygonⓇ tubing, ensuring one-way inflow and preventing air contamination. Their malleability allows for cold welding or pinching off to seal the ends after sufficient flushing with the sample.
File:Giggenbach Bottle.jpgSampling of noble gases using a Giggenbach bottle, a funnel is placed on top of the hot spring to focus the stream of sample towards the bottle via the Tygon tube. A geochemist is controlling the flow of the sample inlet using a Teflon valve. Note the condensation process inside the evacuated Giggenbach bottle.Giggenbach bottles - Giggenbach bottles are evacuated glass flasks with a Teflon stopcock, used for sampling and storing gases. They require pre-evacuation before sampling, as noble gases accumulate in the headspace.<ref>Template:Cite web</ref> These bottles were first invented and distributed by a Werner F. Giggenbach, a German chemist.<ref>Template:Cite journal</ref>
Noble gases have numerous isotopes and subtle mass variation that requires high-precision detection systems. Originally, scientists used magnetic sector mass spectrometry, which is time-consuming and has low sensitivity due to "peak jumping mode".<ref>Template:Cite journal</ref><ref name="Mark-2009">Template:Cite journal</ref> Multiple-collector mass spectrometers, like Quadrupole mass spectrometers (QMS), enable simultaneous detection of isotopes, improving sensitivity and throughput.<ref name="Mark-2009" /> Before analysis, sample preparation is essential due to the low abundance of noble gases, involving extraction, purification system.<ref name="Burnard-2013"/> Extraction allows liberation of noble gases from their carrier (major phase; fluid or solid) while purification remove impurities and improve concentration per unit sample volume.<ref name="Mtili-2021">Template:Cite journal</ref> Cryogenic traps are used for sequential analysis without peak interference by stepwise temperature raise.<ref name="Li-2021">Template:Cite journal</ref>
Research labs have successfully developed miniaturized field-based mass spectrometers, such as the portable mass spectrometer (miniRuedi), which can analyze noble gases with an analytical uncertainty of 1-3% using low-cost vacuum systems and quadrupole mass analyzers.<ref>Template:Cite journal</ref>
The color of gas discharge emission depends on several factors, including the following:<ref>Template:Cite book</ref>
discharge parameters (local value of current density and electric field, temperature, etc. – note the color variation along the discharge in the top row);
gas purity (even small fraction of certain gases can affect color);
material of the discharge tube envelope – note suppression of the UV and blue components in the bottom-row tubes made of thick household glass.
