In a series of posts, we are going to talk about method validation.

1. Part 1: Introduction-Is it valid, invalid or non-validated?
2. Part 2: What is method validation?
3. Part 3: Can we use some­one else’s val­i­dated method?
4. Part 4: What trig­gers ver­i­fi­ca­tion, re-validation or out right new val­i­da­tion of a method?
5. Part 5: What are the essen­tial terms in method validation?
6. Part 6: What is qual­ity assur­ance and qual­ity control?

Here are some of the essen­tial terms in ana­lyt­i­cal chem­istry in general.

Glos­sary of Impor­tant Ana­lyt­i­cal Chem­istry Terms

The learned fool writes his non­sense in bet­ter lan­guage than the unlearned, but it is still non­sense. —Ben­jamin Franklin (1706–1790) Amer­i­can states­man, sci­en­tist and philosopher.

From its cre­ation, lan­guage has been both a pow­er­ful weapon and a use­ful shield. As attor­neys, we use lan­guage as a means to pro­tect or to pun­ish. The sim­ple use of dis­junc­tive over the con­junc­tive can spell the dif­fer­ence between incar­cer­a­tion or free­dom— indeed, some­times between life or death. Yet, as it comes to lan­guage, we allow our­selves to be sloppy when it comes to sci­en­tific language.

Life and lan­guage are alike sacred. Homi­cide and ver­bi­cide –that is, vio­lent treat­ment of a word with fatal results to its legit­i­mate mean­ing, which is its life –are alike for­bid­den. —Oliver Wen­dell Holmes (1809–1894) Amer­i­can author and poet.

When it comes to sci­ence, we lawyers often think that sci­ence con­tains con­vo­luted terms that are arabesques of mean­ing­less jesuit­ics, and even pur­pose­fully cho­sen to allow the user to per­form acro­bat­ics of eva­sive­ness. For the longest time, our worlds (the legal and sci­en­tific) have remained dis­so­ci­ated parochial sand­boxes where one is not wel­come in the other. The best advo­cates are flu­ent in both.

If you want to tell the untold sto­ries, if you want to give voice to the voice­less, you’ve got to find a lan­guage… Use the wrong lan­guage, and you’re dumb and blind. —Salman Rushdie (1948-) Anglo-Indian novelist.

–ome­try: suf­fix mean­ing “to weigh.”

–scopy: suf­fix mean­ing “to look.”

Absorp­tion: The process of one mate­r­ial (absorbate) being retained by another (absorbent).

Abun­dance: (in mass spec­trom­e­try) The inten­sity (height) of each peak depends on the abun­dance of that iso­tope in the sam­ple and the unique loca­tion of the peak on the x-axis indi­cates the mass-to-charge ratio (m/z) of the iso­tope.

Accu­rate: A mea­sure of how closely the results are to the true value. It is char­ac­ter­ized by a high Stan­dard Devi­a­tion, but may or may not have a low aver­age devi­a­tion from the true (actual) value.

Adsorp­tion: The bind­ing of mol­e­cules or par­ti­cles to a sur­face, must be dis­tin­guished from absorption.

Ali­quant: A known amount of a homo­ge­neous mate­r­ial, assumed to be taken with neg­li­gi­ble sam­pling error. The term is usu­ally applied to flu­ids. The term is usu­ally used when the frac­tional part is not an exact divi­sor of the whole (e.g., a 15 mL por­tion is an ali­quant of 100 mL). This con­cept is impor­tant in the con­text of sampling.

Aliquot: A known amount of a homo­ge­neous mate­r­ial, assumed to be taken with neg­li­gi­ble sam­pling error. The term is usu­ally applied to flu­ids. The term is usu­ally used when the frac­tional part is an exact divi­sor of the whole. When a lab­o­ra­tory sam­ple or test sam­ple is “aliquoted” or oth­er­wise sub­di­vided, the por­tions have been called split sam­ples (e.g., a 10 mL por­tion is an aliquot of 100 mL). This con­cept is impor­tant in the con­text of sampling.

Alpha Cleav­age: The fis­sion of a bond orig­i­nat­ing at an atom which is adja­cent to one assumed to bear the charge.

Ana­lyte: A sub­stance that under­goes analy­sis. A sub­stance or chem­i­cal con­stituent that is deter­mined in an ana­lyt­i­cal procedure.

Ana­lyt­i­cal Drift: A non-random change in sig­nal with time.

Anion: An ionic species hav­ing a neg­a­tive charge.

Anode: An elec­trode through which elec­tric cur­rent flows into a polar­ized elec­tri­cal device. The elec­trode at which oxi­da­tion takes place.

ASCLD/LAB: Asso­ci­a­tion of Crime Lab Directors/Laboratory Accred­it­ing Board. An ISO 17025 accred­it­ing body that can pro­vide cer­ti­fi­ca­tions to both gov­ern­ment and non-government labs.

ASCLD/LAB Inter­na­tional: The reg­is­tered trade­mark of ASCLD/LAB’s ver­sion and inter­pre­ta­tion of ISO 17025. ASLCD/LAB is not a par­tic­i­pat­ing or observ­ing mem­ber in the Coun­cil Com­mit­tee on Con­for­mity Assess­ment (ISO com­mit­tee) that sets ISO standards.

Assay: A set of oper­a­tions hav­ing the object of deter­min­ing the value of a quan­tity. In ana­lyt­i­cal chem­istry, this term is syn­ony­mous with measurement.

ASTM Inter­na­tional: Orig­i­nally known as the Amer­i­can Soci­ety for Test­ing and Mate­ri­als and founded over 100 years ago, ASTM Inter­na­tional is one of the largest vol­un­tary stan­dards devel­op­ment orga­ni­za­tions in the world-a trusted source for tech­ni­cal stan­dards for mate­ri­als, prod­ucts, sys­tems, and ser­vices. It is a par­tic­i­pat­ing or observ­ing mem­ber in the Coun­cil Com­mit­tee on Con­for­mity Assess­ment (ISO com­mit­tee) that sets ISO standards.

Autodi­luter: In the blood test­ing con­text, the autodi­luter is a vol­u­met­ric deliv­ery device that is designed to take a pre­cise por­tion of the blood sam­ple and add into it a very pre­cise amount of inter­nal stan­dard, which, for exam­ple in blood test­ing for Blood Alco­hol Con­tent in DUI cases is most typ­i­cally n-propanol.

Autosam­pler: The autosam­pler pro­vides the means to auto­mat­i­cally, with­out human input, intro­duce a sam­ple into the inlet of the chro­mato­graphic device.

Base Peak: Refers to the most intense peak in the mass spec­trum and is used as the ref­er­ence peak when nor­mal­iz­ing all peaks within the spectrum.

Base­line: Refers to the con­stant sig­nal pro­duced by the back­ground level of the instru­ment. It is usu­ally rep­re­sented after inte­gra­tion as a flat line on the chromatogram.

Base­line Drift: Refers to any devi­a­tion in the pos­i­tive or neg­a­tive as mea­sured along the y-axis on the chro­matogram to the expected baseline.

Blank: To be dis­tin­guished from a True Blank, infra, a blank is a sam­ple that is pre­pared using the same process that the unknown is to undergo, but does not con­tain the ana­lyte of inter­est or any other detectable ana­lyte (except­ing pur­pose­fully spiked sub­stances, such as the inter­nal stan­dard). It can be used to check for ana­lyt­i­cal carry-over.

Cal­i­bra­tion and Bias: The cur­rent pre­ferred method to describe the ana­lyt­i­cal instrument’s pre­ci­sion and accuracy.

Cal­i­bra­tion Curve: Despite its name, it is not a curve but rather, if well pre­formed, a straight line as deter­mined by var­i­ous mea­sures of lin­ear­ity. It is the ana­lyt­i­cal method that results in a plot of cal­i­bra­tion data. It is a gen­eral method for deter­min­ing the con­cen­tra­tion of a sub­stance in an unknown sam­ple by com­par­ing the unknown to a set of stan­dard sam­ples of known concentration.

Cal­i­bra­tor: It is the known amount of ana­lyte of inter­est that is placed within the batch of the run to insure that the ana­lyt­i­cal instru­ment is detect­ing the known within an estab­lished tol­er­ance. It is called a cal­i­bra­tor if it is placed before the unknowns are tested and a ver­i­fier if placed after the unknowns are tested.

Car­rier Gas: A gas intro­duced in order to trans­port a sam­ple for ana­lyt­i­cal pur­poses. In gas chro­matog­ra­phy it is the gas which is passed con­tin­u­ously through the col­umn and whose pas­sage pro­motes the elu­tion of the com­po­nents of the sam­ple. The car­rier gas together with the por­tions of the sam­ple present in this phase con­sti­tutes the mobile phase

Carry-Over: A process by which mate­ri­als are car­ried into a reac­tion mix­ture to which they do not belong. It can be either uni­di­rec­tional or bidi­rec­tional in a series of spec­i­mens or assays. The term carry-over effect is used for carry-over from spec­i­men to specimen.

Cath­ode: Elec­trode at which reduc­tion takes place.

Cation: An ion or group of ions hav­ing a pos­i­tive charge and char­ac­ter­is­ti­cally mov­ing toward the neg­a­tive elec­trode in electrolysis.

Chem­i­cal Ion­iza­tion: A process used in mass spec­trom­e­try that uses a lower energy process than elec­tron ion­iza­tion. The lower energy yields less frag­men­ta­tion, and usu­ally a sim­pler spec­trum. A typ­i­cal CI spec­tra has an eas­ily iden­ti­fi­able mol­e­c­u­lar ion.

Chem­Sta­tion: Pro­pri­etary soft­ware devel­oped by Agi­lent avail­able in the inter­na­tional stream of com­merce that records the raw data of a given ana­lyt­i­cal con­fig­u­ra­tion and allows the ana­lyst to alter the recorded data.

Chi­ral Com­pounds: A spe­cific type of iso­mer that is char­ac­ter­ized as a type of mol­e­cule that lacks an inter­nal plane of sym­me­try and has a non-superimposable mir­ror image

Chro­matogram: The printed graph­i­cal rep­re­sen­ta­tion of the record of the ana­lyt­i­cal and inter­pre­ta­tive process of the test per­formed. The printed paper graph­i­cal record of the instru­ment process that may or may not be sub­ject to inter­pre­ta­tion by the chro­matog­ra­pher, the soft­ware or both.

Chro­mato­graph: The actual ana­lyt­i­cal device. It is not the graph­i­cal rep­re­sen­ta­tion of the test.

Chro­matog­ra­phy: From Greek χρώμα:chroma, mean­ing color and γραφειν:graphein mean­ing to write. It is the col­lec­tive term for a set of lab­o­ra­tory tech­niques for the sep­a­ra­tion of mix­tures into its con­stituent parts. In two words, it can be summed up as “sep­a­ra­tion science.”

Co-elution: When two or more ana­lytes elute from the col­umn with­out suf­fi­cient resolution.

Col­li­sion Cell: A method in tan­dem mass spec­trom­e­try (MS-MS) wherein after ini­tial frag­men­ta­tion occurs in the first mass ana­lyzer pur­pose­ful col­li­sion of the remain­ing frag­mented ions occurs with the mol­e­cules or atoms of some col­li­sion gas.

Col­umn: The tube and the sta­tion­ary phase con­tained within, through which the mobile phase passes.

Con­clu­sory Report: A report that is issued typ­i­cally by the crime that that sim­ply states a con­clu­sion of the test­ing with­out data to sup­port the pur­ported result.

Con­fi­dence Inter­val: Is a par­tic­u­lar kind of inter­val esti­mate of a pop­u­la­tion para­me­ter. Instead of esti­mat­ing the para­me­ter by a sin­gle value, an inter­val likely to include the para­me­ter is given. Thus, con­fi­dence inter­vals are used to indi­cate the reli­a­bil­ity of an esti­mate. How likely the inter­val is to con­tain the para­me­ter is deter­mined by the con­fi­dence level or con­fi­dence coef­fi­cient. Increas­ing the desired con­fi­dence level will widen the con­fi­dence interval.

Con­trol: The test por­tion or test solu­tion used for assess­ment of the per­for­mance of an ana­lyt­i­cal procedure.

Crimp: Is the phys­i­cal act of attach­ing both the sep­tum (the mem­brane that the nee­dle passes through) and the cap (the metal ring) to the head­space vial. The devise used to do so is called a crimp (it is sim­i­lar in appear­ance to a wal­nut cracker).

Dex­tro­ro­ta­tory: The prop­erty of a mol­e­cule that exhibits on a rotat­ing plane polar­ized light clockwise.

Diode: In elec­tron­ics, a diode is a two-terminal elec­tronic com­po­nent that con­ducts elec­tric cur­rent in only one direction.

Dupli­cate: Two mea­sure­ments made con­cur­rently and in the same loca­tion, or side-by-side. Used to eval­u­ate the pre­ci­sion of the mea­sure­ment method.

Elec­tro­Spray Mass Spec­trom­e­try: A method of ion­iza­tion in mass spec­trom­e­try most typ­i­cally used in Liq­uid Chro­matog­ra­phy. The liq­uid con­tain­ing the analyte(s) of inter­est is dis­persed by elec­tro­spray into a fine aerosol. Because the ion for­ma­tion involves exten­sive sol­vent evap­o­ra­tion, the typ­i­cal sol­vents for elec­tro­spray ion­iza­tion are pre­pared by mix­ing water with volatile organic com­pounds (e.g. methanol, acetonitrile).

Elec­tron Impact Mass Spec­trom­e­try: Elec­tron Impact (EI) is the orig­i­nal mass spec­trom­e­try (MS) ion­iza­tion method and is still prob­a­bly the most widely used of all ion­iza­tion meth­ods. In the EI process, the sam­ple of inter­est is vapor­ized into the mass spec­trom­e­ter ion source, where it is impacted by a beam of elec­trons with suf­fi­cient energy to ion­ize the mol­e­cule caus­ing fragmentation.

Elu­ci­da­tion: Lit­er­ally means to make clear through analy­sis. Typ­i­cally, it is used in chem­istry to explain the con­cept of tak­ing raw data and com­ing to a con­clu­sion. It is must fre­quently used in spec­tral inter­pre­ta­tion and in mass spectrometry.

Elute: Describes the emer­gence of ana­lytes from the col­umn of a chromatograph.

Equi­lib­rium: A con­di­tion in which a chem­i­cal reac­tion is occur­ring at equal rates in its for­ward and reverse direc­tions, so that the con­cen­tra­tions of the react­ing sub­stances do not change with time.

Error: The result of a mea­sure­ment minus the true value of the measurand.

Exter­nal Stan­dard: A com­pound present in a stan­dard sam­ple of known con­cen­tra­tion and vol­ume which is ana­lyzed sep­a­rately from the unknown sam­ple under iden­ti­cal con­di­tions. It is used to facil­i­tate the qual­i­ta­tive iden­ti­fi­ca­tion and/or quan­ti­ta­tive deter­mi­na­tion of the sam­ple components.

EZChrom Élite: Pro­pri­etary soft­ware devel­oped by Agi­lent avail­able in the inter­na­tional stream of com­merce that records the raw data of a given ana­lyt­i­cal con­fig­u­ra­tion and allows the ana­lyst to alter the recorded data.

Fer­rell: It is bush­ing or metal ring or cap like item that is designed to keep the col­umn in its place.

Flame Ion­iza­tion Detec­tor: A spe­cific type of detec­tor that is used to arrive at a quan­ti­ta­tive result. It counts the increase in the num­ber of ions that occurs as hydro­car­bon bonds are burned. A polar­iz­ing volt­age attracts these ions to a col­lec­tor located near the flame. The cur­rent is sensed by an elec­trom­e­ter, con­verted to a dig­i­tal form and sent to an out­put device that gives the peak.

Fronting: May be a pre­sen­ta­tion of co-elution, supra. It occurs when the A sym­met­ri­cal hemi­sphere is greater than the B sym­met­ri­cal hemi­sphere in a chro­mato­graphic peak.

Gas Chro­matog­ra­phy: A pow­er­ful, yet not per­fect, ana­lyt­i­cal method whose goals are to uniquely sep­a­rate and iden­tify ana­lytes of inter­est (qual­i­ta­tive mea­sure) from a mix­ture and if desired arrive at a unique amount of that unique ana­lyte of inter­est (quan­ti­ta­tive mea­sure). The mobile phase is that of a gaseous matrix as opposed to Liq­uid Chro­matog­ra­phy whose mobile phase is liquid.

Gauss­ian: Nor­mal dis­tri­b­u­tion, char­ac­ter­ized by a bell-shaped curve and hav­ing a mean at the cen­ter of the curve with tail widths pro­por­tional to the stan­dard devi­a­tion of the data about the mean.

Good Lab­o­ra­tory Prac­tices: Gen­er­ally refers to a sys­tem of man­age­ment con­trols for lab­o­ra­to­ries and research orga­ni­za­tions to ensure the con­sis­tency and reli­a­bil­ity of results as out­lined in the Orga­ni­za­tion for Eco­nomic Co-operation and Devel­op­ment (OECD) Prin­ci­ples of GLP and national reg­u­la­tions. GLP embod­ies a set of prin­ci­ples that pro­vides a frame­work within which lab­o­ra­tory stud­ies are planned, per­formed, mon­i­tored, recorded, reported and archived. There is no equiv­a­lent to this in foren­sic sci­ence gen­er­ally and specif­i­cally in DUI foren­sic test­ing for BAC determinations.

Golden Seal: A con­sum­able used in Gas Chro­matog­ra­phy. It is housed within the injec­tor por­tion of the instru­ment. Its pri­mary func­tion is to seal the inlet to help main­tain the chro­mato­graphic conditions.

Head­space: It is the gaseous por­tion over the liq­uid por­tion in a closed sys­tem. It is also a method of indi­rect analy­sis of the gaseous phase relat­ing the gaseous phase mea­sure to the liq­uid phase mea­sure based upon par­ti­tion ratio once equi­lib­rium is achieved.

Henry’s Law: Henry’s Law states that at a con­stant tem­per­a­ture, the amount of a given gas dis­solved in a given type and vol­ume of liq­uid is directly pro­por­tional to the par­tial pres­sure of that gas in equi­lib­rium with that liq­uid. Or stated dif­fer­ently, an equiv­a­lent way of stat­ing the law is that the sol­u­bil­ity of a gas in a liq­uid at a par­tic­u­lar tem­per­a­ture is pro­por­tional to the pres­sure of that gas above the liq­uid. Head­space gas chro­matog­ra­phy requires a closed sys­tem (i.e. no pres­sure leak­ing from the gaseous phase).

His­togram: A graph­i­cal rep­re­sen­ta­tion, show­ing a visual impres­sion of the dis­tri­b­u­tion of exper­i­men­tal data.

Hit Histogram: A feature in certain software versions of mass spectral data systems wherein the unknown which is reduced to a chromatogram is compared against the knowns in the spectral library displayed in a histogram. Hit histograms indicate how the best matching units of a data set/some data sets are distributed.

Hit List: A panel in some mass spec­tral soft­ware pro­grams that dis­plays Match Fac­tor scor­ing, Rel­a­tive Match and Prob­a­bil­ity scor­ing based upon com­puter assisted pat­tern recog­ni­tion to a loaded spec­tral library.

Hyphen­ated Tech­nique: A com­bi­na­tion of chro­mato­graphic and spec­tral meth­ods to exploit the advan­tages of both. It is a com­bi­na­tion of two or more uncor­re­lated techniques.

Iden­tity Search: A method of search algo­rithms pre­formed by the soft­ware typ­i­cally used to per­form pat­tern recog­ni­tion of a spec­tral library. An Iden­tity search is designed to find exact matches of the com­pound that pro­duced the sub­mit­ted spec­trum and there­fore pre­sumes that the unknown com­pound is rep­re­sented in he ref­er­ence library. Only exper­i­men­tal vari­abil­ity pre­vents a per­fect match. The “Sim­i­lar­ity” search is opti­mized to find sim­i­lar com­pounds and is intended for use when a com­pound can­not be iden­ti­fied by the “Iden­tity” search.

Injec­tor: A device by which a liq­uid or gaseous sam­ple is intro­duced into the apparatus.

Instru­ment Con­fig­u­ra­tion: The con­stel­la­tion of vari­ables that the instru­ment itself is set for. Adjust­ing the instru­ment con­fig­u­ra­tion will result in the change of the raw data gen­er­ated. This is to be con­trasted with soft­ware con­fig­u­ra­tion which does not alter the raw data accumulated.

Inte­gra­tion: The act of alter­ing the raw data. There are any num­ber of dif­fer­ent ways one can arrange the data col­lected. It comes in two forms: man­ual or soft­ware produced.

Inter­nal Stan­dard: A com­pound pur­pose­fully added to a sam­ple in known con­cen­tra­tion to facil­i­tate the qual­i­ta­tive iden­ti­fi­ca­tion and/or quan­ti­ta­tive deter­mi­na­tion of the sam­ple components.

Invalid: Proven to be not valid, not the same as “not val­i­dated” as “not val­i­dated” means that it may be valid or it may be invalid.

Ion Source: Gen­er­ally an assem­bly com­posed of: (1) an ion­iza­tion cham­ber in which a stream of elec­trons flows from a hot fil­a­ment across a stream of gas to col­lec­tor (the poten­tial between fil­a­ment and col­lec­tor is usu­ally between 50 and 70 v), and (2) a device for the accel­er­a­tion of these ions.

Ion­iza­tion: Is the phys­i­cal process of con­vert­ing an atom or mol­e­cule into an ion by adding or remov­ing charged par­ti­cles such as elec­trons or other ions.

ISO 17025: ISO 17025 is a con­cep­tual frame­work that was adopted by an inter­na­tional com­mit­tee com­prised of peo­ple not in the law enforce­ment com­mu­nity, but rather in the sci­en­tific com­mu­nity as a whole as well as those who are in indus­try. It does not specif­i­cally address the foren­sic sci­ence com­mu­nity, but rather cov­ers any and all lab­o­ra­to­ries involved in test­ing and cal­i­bra­tion services.

Iso­mers: Com­pounds with the same mol­e­c­u­lar for­mula but dif­fer­ent struc­tural formulas

Isother­mic: A char­ac­ter­is­tic of a ther­mo­dy­namic process dur­ing which the tem­per­a­ture remains constant.

Lev­oro­ta­tory: The prop­erty of a mol­e­cule that exhibits on a rotat­ing plane polar­ized light counter-clockwise.

Limit of Detec­tion: Is the low­est amount of ana­lyte in a sam­ple that can be detected, but not nec­es­sar­ily quan­ti­fied as an exact value. In other words, it is known that the ana­lyte of inter­est is there but the ana­lyst can­not tell how much of it is present (i.e., the quan­tity). LOD is the low­est quan­tity of a sub­stance that can be dis­tin­guished from the absence of that sub­stance (a blank value) within a stated con­fi­dence limit (gen­er­ally 1%). At the LOD, no quan­tifi­ca­tion can occur. Hyper-technically, the LOD may be expressed as LOD=3.3*SD/S where SD=the stan­dard devi­a­tion of the response and S=the slope of the cal­i­bra­tion curve.

Limit of Lin­ear­ity: Is the high­est point on a cal­i­bra­tion curve that has been demon­strated to be lin­ear in that a data point from a CRM was used to estab­lish the upper most level of lin­ear­ity. In other words, the LOL is set at the con­cen­tra­tion of the high­est stan­dard ana­lyzed even though in the­ory it could be extended beyond this. It is the max­i­mum level where lin­ear­ity is proven.

Limit of Quan­tifi­ca­tion: Is the limit at which we can rea­son­ably tell the dif­fer­ence between two dif­fer­ent val­ues (zero and non-zero). It is a demon­strated point where quan­tifi­ca­tion can begin.

Lin­ear Dynamic Range: Is the con­cen­tra­tion range over which the ana­lyt­i­cal work­ing cal­i­bra­tion curve has been demon­strated to remain lin­ear. It is only between the lower and upper lim­its of the ref­er­ence points used that the Demon­strated Lin­ear Dynamic Range exists. Only when unknown val­ues fall between the extremis points along the Cal­i­bra­tion Curve can sci­en­tif­i­cally valid con­clu­sions con­cern­ing quan­tifi­ca­tion be drawn.

Liner: Is a con­sum­able com­po­nent of the inlet injec­tor sys­tem. It is where flash vapor­iza­tion occurs if there is a direct injec­tion, not of the head­space. It is also the last point where a col­lec­tion of alien mate­r­ial such as pieces of septa can be pre­vented from com­ing into con­tact with the col­umn. There are many dif­fer­ent types of liners.

Make-up Gas: In the con­text of a flame ion­iza­tion detec­tor is gas injected into the efflu­ent stream that elutes off the col­umn to serve as a method of dilut­ing the con­cen­tra­tion so to not over­whelm the detec­tor and also the insure con­stant pres­sure and flow.

Mass Ana­lyzer: In mass spec­trom­e­try the method that the frag­mented ions are selected and then trans­ported by mag­netic or elec­tri­cal fields to the detec­tor or caused to be pumped out through the vac­uum not to be ana­lyzed by the detector.

Mass Hunter: A type of pro­pri­etary soft­ware offered by Agi­lent that can be used in mass spectrometry.

Mass Spec­trom­e­try: The branch of sci­ence deal­ing with all aspects of mass spec­tro­scopes and the results obtained with these instru­ments. It mea­sures the mass-to-charge ratio of charged par­ti­cles. It is used for deter­min­ing masses of par­ti­cles, for deter­min­ing the ele­men­tal com­po­si­tion of a sam­ple or mol­e­cule, and for elu­ci­dat­ing the chem­i­cal struc­tures of mol­e­cules. The MS prin­ci­ple con­sists of ion­iz­ing chem­i­cal com­pounds to gen­er­ate charged mol­e­cules or mol­e­cule frag­ments and mea­sure­ment of their mass-to-charge ratios.

Mass-to-Charge Ratio: (m/z) rep­re­sents the mass of a given par­ti­cle (Dal­tons or Da) to the num­ber (z) of elec­tro­sta­tic charges (e) that the par­ti­cle car­ries. The term ”m/z” is mea­sured in Da/e.

Match Fac­tor: One of the fea­tures of mass spec­trom­e­try soft­ware wherein through a process of com­puter algo­rithm com­puter assisted pat­tern recog­ni­tion is employed to arrive at the “match fact.” A per­fect match is 999.

Matrix: The com­po­nents of the sam­ple includ­ing the analyte.

Matrix Effect: The com­bined effect of all com­po­nents of the sam­ple other than the ana­lyte on the mea­sure­ment of the quantity.

Mean: Arith­metic mean (aver­age) is the sum of a series of obser­va­tions divided by the num­ber of observations.

Method: A way of doing some­thing, espe­cially a sys­tem­atic way; implies an orderly log­i­cal arrange­ment, usu­ally in steps.

Metrol­ogy: The sci­en­tific study of measurement.

Mobile Phase: A fluid which per­co­lates through or along the sta­tion­ary phase of a col­umn, in a def­i­nite direc­tion. It may be a liq­uid (liq­uid chro­matog­ra­phy) or a gas (gas chro­matog­ra­phy). In gas chro­matog­ra­phy the expres­sion car­rier gas may be used for the mobile phase.

Mol­e­c­u­lar Ion: An ion formed by the removal from (pos­i­tive ions) or addi­tion to (neg­a­tive ions) a mol­e­cule of one or more elec­trons with­out frag­men­ta­tion of the mol­e­c­u­lar struc­ture. The mass of this ion cor­re­sponds to the sum of the masses of the most abun­dant nat­u­rally occur­ring iso­topes of the var­i­ous atoms that make up the mol­e­cule (with a cor­rec­tion for the masses of the electron(s) lost or gained).

Neu­tral Loss Scan: In mass spec­trom­e­try, a scan which deter­mines, in a sin­gle exper­i­ment, all the par­ent ion mass-to-charge ratios which react to the loss or gain of a selected neu­tral mass.

NIST: National Insti­tute for Stan­dards and Tech­nol­ogy is the fed­eral tech­nol­ogy agency that works with indus­try to develop and apply tech­nol­ogy, mea­sure­ments, and standards

Noise: The always present ran­dom fluc­tu­a­tions occur­ring in a sig­nal that are inher­ent in the com­bi­na­tion of instru­ment and method.

Oven: In gas chro­matog­ra­phy, the heated enclo­sure that is designed to be of a low ther­mal mass to per­mit more rapid pro­grammed tem­per­a­ture changes, and to pro­vide good oven cool­ing for work on the columns between analy­ses. It is where the col­umn can be found.

Par­ti­tion Ratio: The ratio of the con­cen­tra­tion of a sub­stance in a sin­gle def­i­nite form in the extract to its con­cen­tra­tion in the same form in the other phase at equi­lib­rium (e.g. for an aque­ous form to a gaseous one).

Pat­tern Recog­ni­tion: The iden­ti­fi­ca­tion of objects, images or data by their shapes, forms, out­lines, or other attrib­utes, some­times by auto­matic means.

Peak-tailing: Can be a pre­sen­ta­tion of co-elution, defined supra. It occurs when the B sym­met­ri­cal hemi­sphere is greater than the A sym­met­ri­cal hemi­sphere in a chro­mato­graphic peak.

Pre­cise: A mea­sure of how closely the results can be to one another. It is char­ac­ter­ized by a low Stan­dard Devi­a­tion, but may or may not have a high aver­age devi­a­tion from the true (actual) value.

Pro­to­nate: An ion formed by inter­ac­tion of a mol­e­cule with a pro­ton abstracted from an ion, as often occurs in chem­i­cal ion­iza­tion accord­ing to the reac­tion. The sym­bol­ism [M + H]⁺ may also be used to rep­re­sent the pro­to­nated mol­e­cule. The widely used term ‘pro­to­nated mol­e­c­u­lar ion’ to describe the MH⁺ ion is not rec­om­mended, since it sug­gests an asso­ci­ated prod­uct of a pro­ton with a mol­e­c­u­lar ion.

Quadra­pole or Quadru­pole: A type of mass ana­lyzer, infra. An arrange­ment in which ions with a desired quo­tient mass/charge are made to describe a sta­ble path under the effect of a sta­tic and a high-frequency elec­tric quadru­pole field, and are then detected. Ions with a dif­fer­ent mass/charge are sep­a­rated from the detected ions because of their unsta­ble paths and a “pumped out” b the vacuum.

Qual­i­ta­tive Mea­sure: Seeks to answer the ques­tion, “What is it?” The goal of such mea­sur­ing is to report­ing one unique mol­e­cule to the exclu­sion of all other mol­e­cules or possibilities.

Qual­ity Assur­ance: The guar­an­tee that the qual­ity of a prod­uct (ana­lyt­i­cal data set, etc.) is actu­ally what is claimed on the basis of the qual­ity con­trol applied in cre­at­ing that prod­uct. Qual­ity assur­ance is not syn­ony­mous with qual­ity con­trol. Qual­ity assur­ance is meant to pro­tect against fail­ures of qual­ity control.

Qual­ity Con­trol: Pro­ce­dures which give insight into the pre­ci­sion and accu­racy of analy­sis results. The main­te­nance and state­ment of the qual­ity of a prod­uct (data set, etc.) specif­i­cally that it meets or exceeds some min­i­mum stan­dard based on known, testable criteria.

Quan­ti­ta­tive Mea­sure: Seeks to answer the ques­tion, “How much?” The goal of such mea­sure­ment is to report one unique amount of the mol­e­cule selected to the exclu­sion of all other mol­e­cules or possibilities.

Ran­dom Error: Varies when a mea­sure­ment is repeated under the same conditions.

Ran­dom Sam­pling Error: It is the fail­ure of sam­ple selec­tion wherein the selec­tion method does not accu­rately reflect the pop­u­la­tion. It can lead peo­ple to draw incor­rect con­clu­sions in research.

Raw data: The data recorded in real time as the analy­sis occurs that is saved by the inte­grated com­puter sys­tem. The GC itself does not record the data, but the PC based and linked sys­tem does. As the data comes off the instru­ment itself, the inte­grated machine cap­tures it into a series of files. The raw data is the pre-interpretation and pre-software manipulation/editing infor­ma­tion of the sep­a­ra­tion and mea­sure­ment event.

Rel­a­tive prob­a­bil­ity: In mass spec­trom­e­try, the prob­a­bil­ity value for a hit is derived assum­ing that the com­pound is rep­re­sented by a spec­trum in the libraries searched. It only employs the dif­fer­ence between adja­cent hits in the hit list to get the rel­a­tive prob­a­bil­ity that any hit in the hit list is correct.

Rel­a­tive Reten­tion Time: The ratio of the adjusted or net reten­tion vol­ume (time) or reten­tion fac­tor of a com­po­nent rel­a­tive to that of a stan­dard, obtained under iden­ti­cal con­di­tions. It is cal­cu­lated by divid­ing the reten­tion time of the peak of inter­est by the reten­tion time of the main peak or selected peak. Any peak with an RRT <1 elutes before the selected or main peak, and any peak with an RRT >1 elutes after the main or selected peak.

Reli­able: Inversely related to ran­dom error. It is the con­sis­tency of a set of mea­sure­ments or of a mea­sur­ing instrument.

Repeat­able: Day-in and day-out the test using the same method on the same instru­men­ta­tion on the same unknown arrives at the same result.

Repli­cate Mea­sure­ment: Are mul­ti­ple mea­sure­ments made upon the same sam­ple. Repli­cate mea­sure­ments allow sta­tis­ti­cal treat­ment of data – this allows, for exam­ple, the spread of data and rel­a­tive stan­dard devi­a­tions to be cal­cu­lated. Repli­cate mea­sure­ments also allow some sources of error (espe­cially inde­ter­mi­nate) to be identified.

Repro­ducible: Refers to the abil­ity of a test or exper­i­ment to be accu­rately repro­duced, or repli­cated, by some­one else work­ing independently.

Res­o­lu­tion: A char­ac­ter­is­tic of the sep­a­ra­tion of two adja­cent peaks.

Reten­tion Time: The absolute time taken by a com­pound to travel from the injec­tor through the col­umn to the detec­tor. This is very depen­dent on oper­a­tional con­di­tions, so it is use­ful only to com­pare reten­tion times for var­i­ous com­po­nents on one instru­ment for exper­i­ments per­formed with the same con­di­tions. It is not mean­ing­ful to com­pare reten­tion times for dif­fer­ent instru­ments or the same instru­ment under dif­fer­ent conditions.

Salting-out: Can occur with “too much” salt, for exam­ple NaF, is present in the sam­ple. “Too much” NaF means too high a ratio of blood to the inor­ganic salt (usu­ally in excess of 10%-20% of total vol­ume). It is not as a mea­sure of an absolute, but the pro­por­tion. How­ever, the most com­pre­hen­sive answer is that when inor­ganic salts are added (e.g., NaF, sodium chlo­ride) there is a “salt­ing out effect.” By adding these salts to an aque­ous or liq­uid matrix, some ana­lytes such as ETOH can be forced to enter the gaseous phase above that which would hap­pen if no salts were present. If there is not the same amount of inor­ganic salt added con­sis­tently through­out the ver­i­fiers, stan­dards, the cal­i­bra­tors, the n-propanol blanks and the unknowns, then there is the a change in the con­di­tions. Doing so, results in the change of the val­i­dated the method. In isother­mal sta­tic head­space gas chro­matog­ra­phy, Henry’s Law is vio­lated. Quan­tifi­ca­tion is in jeop­ardy. As the stan­dards, the cal­i­bra­tors, the n-propanol blanks and the ver­i­fiers are made as to one vol­ume and pro­por­tion of salt and hence have one K value. n-propanol has a dif­fer­ent polar­ity than ETOH. So they have dif­fer­ent K val­ues at dif­fer­ent temperatures.

Robust: The method and instru­ment com­bine to have a low per­cent false pos­i­tive and low per­cent false neg­a­tive through­out all designed ana­lyt­i­cal con­di­tions; and most importantly.

Sam­ple: A spec­i­men or small quan­tity of something.

Sam­ple Prepa­ra­tion: Is an essen­tial stage in the analy­sis process. It takes place between sam­ple tak­ing and ana­lyt­i­cal mea­sur­ing of the pre­pared sample.

Sam­ple selec­tion: Seeks to answer the ques­tion, “How large should a sam­ple be from any given pop­u­la­tion?” or “What part of the sam­ple should be taken for sampling?”

Sam­pling: The phys­i­cal act of tak­ing a sample.

Scalars: Mea­sure­ments that have a mag­ni­tude but have no direction.

Selected Ion Mon­i­tor­ing: This term is used to describe the oper­a­tion of the mass spec­trom­e­ter in which the inten­si­ties of sev­eral spe­cific ion beams are recorded rather than the entire mass spectrum.

Selec­tive: Selec­tiv­ity refers to the extent to which the method can be used to deter­mine par­tic­u­lar ana­lytes in mix­tures or matri­ces with­out inter­fer­ences from other com­po­nents of sim­i­lar behav­ior. Selec­tiv­ity gives an indi­ca­tion of how strongly the result is affected by other com­po­nents in the sam­ple. A selec­tive test may be not a spe­cific test due to cross-reactivity, inter­fer­ence, or codetermination.

Sen­si­tive: The quan­ti­ta­tive mea­sure is within the demon­strated lin­ear dynamic range in that the unknown amount exceeds both the Limit of Detec­tion and the Limit of Quan­tifi­ca­tion but does not exceed the Limit of Linearity;

Sep­a­ra­tion Matrix: A mix of stan­dards in one sam­ple that is used to prove that the ana­lyt­i­cal device can indeed sep­a­rate with suf­fi­cient res­o­lu­tion like analytes.

Sep­tum: Septa main­tain the leak-free seal and exclude air from the inlet. They are also used in head­space vials to allow for pierc­ing so that a sam­ple may be extracted but not to allow any leak. They come in many dif­fer­ent sizes and are made from many dif­fer­ent types of mate­r­ial spe­cific to analy­sis needs. It is respon­si­ble, in part for main­tain­ing the sam­ple flow path from the out­side world. It must pro­vide a bar­rier that is read­ily pen­e­trated by the injec­tor nee­dle while main­tain­ing inter­nal pres­sure with­out con­t­a­m­i­nat­ing the analysis.

Sigma: Stan­dard devi­a­tion. (See the def­i­n­i­tion of Stan­dard Devi­a­tion below.)

Sim­i­lar­ity Search: A method of search algo­rithms pre­formed by the soft­ware typ­i­cally used to per­form pat­tern recog­ni­tion of a spec­tral library. An Iden­tity search is designed to find exact matches of the com­pound that pro­duced the sub­mit­ted spec­trum and there­fore pre­sumes that the unknown com­pound is rep­re­sented in he ref­er­ence library. Only exper­i­men­tal vari­abil­ity pre­vents a per­fect match. The “Sim­i­lar­ity” search is opti­mized to find sim­i­lar com­pounds and is intended for use when a com­pound can­not be iden­ti­fied by the “Iden­tity” search.

Spe­cific: A test that reacts only with the ana­lyte of inter­est and noth­ing else so that when there is a mea­sure it is unique to that which is exam­ined. It is not sim­ply selec­tive, which is an exhi­bi­tion of a degree of pref­er­ence for the sub­stance tested for, but not nec­es­sar­ily unique.

Stan­dard Devi­a­tion: Is a sta­tis­tic that tells us how tightly all the var­i­ous exam­ples are clus­tered around the mean in a set of data. When the exam­ples are pretty tightly bunched together and the bell-shaped curve is steep, the stan­dard devi­a­tion is small. When the exam­ples are spread apart and the bell curve is rel­a­tively flat, that tells us that we have a rel­a­tively large stan­dard devi­a­tion. Tech­ni­cally it is defined as the pos­i­tive square root of the sum of the squares of the devi­a­tions between the obser­va­tions and the mean of the series, divided by one less than the total num­ber in the series. The stan­dard devi­a­tion is the pos­i­tive square root of the vari­ance, a more fun­da­men­tal sta­tis­ti­cal quantity.

Sta­tic: Per­tain­ing to or char­ac­ter­ized by a fixed or sta­tion­ary condition.

Sta­tion­ary Phase: One of the two phases form­ing a chro­mato­graphic sys­tem (the other is the mobile phase). It may be a solid, a gel or a liq­uid. If a liq­uid, it may be dis­trib­uted on a solid. This solid may or may not con­tribute to the sep­a­ra­tion process. The liq­uid may also be chem­i­cally bonded to the solid (bonded phase) or immo­bi­lized onto it (immo­bi­lized phase). The expres­sion chro­mato­graphic bed or sor­bent may be used as a gen­eral term to denote any of the dif­fer­ent forms in which the sta­tion­ary phase is used.

Sys­temic Error: Remains fixed when the mea­sure­ment is repeated under the same conditions.

Total Ion Cur­rent Chro­matogram: Rep­re­sents the summed inten­sity across the entire range of masses being detected at every point in the analy­sis. The range is typ­i­cally sev­eral hun­dred mass-to-charge units or more. In com­plex sam­ples, the TIC chro­matogram often pro­vides lim­ited infor­ma­tion as mul­ti­ple ana­lytes elute simul­ta­ne­ously, obscur­ing indi­vid­ual species.

Trace­able: The com­plete­ness of the infor­ma­tion about every step in a process chain.

True Blank: A true blank is a sam­ple that is pre­pared free of any detectable ana­lyte. It can be used to check for ana­lyt­i­cal carry-over.

True: The value that char­ac­ter­izes a quan­tity per­fectly in the con­di­tions that exist when that quan­tity is con­sid­ered. It is an ideal value, which could be arrived at only if all causes of uncer­tainty (error) are eliminated.

Type A error: A method of eval­u­a­tion by sta­tis­ti­cal analy­sis of a series of observations.

Type B error: Any­thing that is not Type A error; a method of eval­u­a­tion by any means other than sta­tis­ti­cal analy­sis of a series of observations.

Type I error: Also known as an “error of the first kind,” an α error, or a “false pos­i­tive”: the error of reject­ing a null hypoth­e­sis when it is actu­ally true. Plainly speak­ing, it occurs when we are observ­ing a dif­fer­ence when in truth there is none, thus indi­cat­ing a test of poor speci­ficity. An exam­ple of this would be if a test shows that a woman is preg­nant when in real­ity she is not. Type I error can be viewed as the error of exces­sive credulity.

Type II error: Also known as an “error of the sec­ond kind,” a β error, or a “false neg­a­tive”: the error of fail­ing to reject a null hypoth­e­sis when it is in fact not true. In other words, this is the error of fail­ing to observe a dif­fer­ence when in truth there is one, thus indi­cat­ing a test of poor sen­si­tiv­ity. An exam­ple of this would be if a test shows that a woman is not preg­nant, when in real­ity, she is. Type II error can be viewed as the error of exces­sive skepticism.

Uncer­tainty Mea­sure­ment (UM): A metro­log­i­cal prin­ci­ple that is a com­bi­na­tion of both qual­i­ta­tive and quan­ti­ta­tive uncer­tainty in the mea­sure­ment itself.

Valid: Doc­u­mented proof that the process under­taken is suit­able for its intended use and achieves the intended reported result cor­rectly and uniquely.

Vec­tors: A mea­sure­ment that has a mag­ni­tude (an amount) and a direction.

Ver­i­fi­able: The abil­ity to take all infor­ma­tion pro­vided and arrive at the same con­clu­sions as the orig­i­nal ana­lyst with­out the need to inde­pen­dently test.

Ver­i­fier: It is the known amount of ana­lyte of inter­est that is placed within the batch of the run to insure that the ana­lyt­i­cal instru­ment is detect­ing the known within an estab­lished tol­er­ance. It is called a cal­i­bra­tor if it is placed before the unknowns are tested and a ver­i­fier if placed after the unknowns are tested.

Volatil­ity: A mea­sure of the ten­dency of a sub­stance to vapor­ize. It has also been defined as a mea­sure of how read­ily a sub­stance vaporizes.

Weighted mean: Sim­i­lar to a mean, supra, where instead of each of the data points con­tribut­ing equally to the final aver­age, some data points con­tribute more than oth­ers. This can occur when out­liers are elim­i­nated with­out rea­son. Unless the weights can be assigned objec­tively, the use of the weighted mean is not nor­mally recommended.