Method and apparatus

Abstract

An aspect of the disclosure provides a method of reducing electrical measurement noise in a detection apparatus configured to detect the arrival of ions at a collector electrode, wherein the detection apparatus comprises an air mover to provide a flow of air in the apparatus, the method comprising: operating the air mover, at an operating level, to provide the flow of air; reducing operation of the air mover for a quiet period; and operating the detection apparatus to allow ions to travel to be detected by a collector electrode during the quiet period.

Description

[0001] Method and Apparatus

[0002] Field, of Invention

[0003] The pres e nt inventi o n rel ate s to me thods and apparatus, and i n pa rti cu l ar method s and app a ratus for de tecti ng i ons, which may be us ed in s ystems for de tecti ng s ub stance s of i nte r es t and / or ana lys i ng s ub stance s. St il l more parti cul ar ly the pr es ent di s cl os ure rel ate s to methods and app aratus fo r reduc ing me a surement noi s e i n the d e te cti on of io ns a t a c ol l ecto r el e ctrode.

[0004] Background

[0005] A var i ety of sys tems, such a s phys i ca l me as ureme nt apparatus and trace de te ct i on apparatus, spe c trome te r s and othe r types o f physi ca l ins trume nts rel y on the dete ct i on o f el ectri c al charge to se ns e the arr iva l of ions at an el ect rode of a det ector. Such an el ectrod e may be refe rre d to as a co l le ctor e le ctrode.

[0006] Examp le s of s uch sys tems i nclude ion mob il i ty spe ct r ome te rs, and ma s s spe c trome te r s. One examp le o f a type o f ma ss spe ctr ome te r i s a s o -cal led " time o f f l ight" ma s s spe c trome te r, TOE -MS. A vari ety of such sys tems exi st.

[0007] Ion mob il i ty spec trome ter s ( IMS ) c an id entify mater i al from a sampl e of i nte res t by i oni s i ng the mater i a l ( e. g., mo le cul es, atoms, and so forth ) and me a sur ing the time i t take s the re s ul ti ng i ons to tr ave l a known dis tance through a counte rf low of dr i ft gas under a known e l ectri c f i eld. T yp i ca l l y this t ime i s me a sured fr om the time an i on gate (whi ch may a ls o be re ferred to as a n ion shutter ) i s opened, to the time that i on a rr ive s at a de t ector s uch a s a Faraday cup.

[0008] Each i on ' s time o f f l ight i s a ss oci ated with the i on ' s mob i li ty. An ion ' s mob il i ty r el ate s to i ts ma ss and ge ome try. Ther efo re, by me a suri ng the time of f li ght o f an ion it i s pos s ib l e to infe r its i d entity. The s e t ime s o f f l ight may be d i sp layed numer i ca ll y and / or graphi ca l ly as a spe ctrum.

[0009] Some IMS ce l ls i nc lud e dete ctor s wh ic h co ll e ct ion s to me as ure the ir t ime of f l ight so the y can be ide n ti f ied, thi s ma y be d one in the pre s ence of a dr i ft ga s s o that mob i li ty ef fects can separate the i ons. Ion mob il i ty s pectrome ter s typ ica ll y compr is e at l e as t s ome el e ctromechani ca l actua tor s and othe r types o f actua to r s, inc lud ing motors. Thes e may be us ed for th ing s l ike ope rati ng f ans a nd bl owe rs and o the r type s o f a ir move r s. Thes e can be u sed to pro vide the f low of dri f t g a s through the dr ift chamber and to ope rat e pres sure pul s er s, whi ch ar e use d to take sampl es u si ng a p inhol e or othe r type s of s amp l i ng i nl e t. A var ie ty of type s o f IMS devi ce s exi st - inc ludi ng some types o f di f fe re nti a l mob il ity s pe ctrome te r s ( DMS ) and fi e ld a s ymmetri c IMS d evi ces FAIMS, i n wh ic h the me chani sm o f res o lvi ng mob il ity cha racte ri s ti cs i s di ffe re nt. Many of the se a ls o have me chani ca l compone nts fo r rea s ons s imi lar to tho se outli ned above.

[0010] Time-of- fl i ght mas s sp ectromet er s ( TOF -MS ) may use tr ave l time th rough a ch ambe r under e l ec tri c f ie ld in the ab s ence of dr ift ga s to mea sur e ma ss to charge r ati o. T yp ica ll y, mas s spe ctromet e rs comp r is e at l ea st some el e ctromechani ca l actuator s and othe r type s o f actua tors, i ncludi ng mot or s for a i r moving functions s uch as the ope ration of vacuum pump s, providi ng s ampl e f l o ws; a nd othe r appl icati o ns.

[0011] Summary

[0012] Aspects and exampl e s o f the pre se nt invent ion are se t out i n the cl a ims and a im to addres s the pr ob lem of me a surement no is e due t o me chani cal vibrat ion i n de te cti on de vi ce s, s uch a s ion mob il ity spe ctromete rs and mas s spe c trome te r s. In an aspect there is provided a method of reducing electrical measurement noise in a detection apparatus configured to detect the arrival of ions at a collector electrode, where in the detection apparatus comprises an air mover to provide a flow of air in the apparatus, the method compris ing:

[0013] operating the air mover, at an operating level, to provide the flow of air;

[0014] reducing operation of the air mover for a quiet period; and

[0015] operating the detection apparatus to allow ions to travel to be detected by a collector electrode dur ing the quiet period.

[0016] The collector electrode may have a capacitance which is affected by mechanical vibration caused by the air mover. For example, one or more capacitive elements (e. g., conductive and / or charge carrying elements ) may be as sembled with the collector electrode. Mechanical vibration of this as sembly may cause corresponding variations in a capacitance of the collector e lectrode. The flow of air may be as sociated with operation of the detection apparatus, for example it may perform a function upon which the detection method used by the apparatus depends. As an example it may provide a f low of air through a pneumatic system of the apparatus such as may be used in providing a f low of drift gas in an IMS system. As another example it may operate a pump to provide a reduced pres sure region, such as a vacuum chamber of a TOF-IMS sys tem.

[0017] The start of the quiet period may precede the operating of the detection apparatus by a wait period. The wait peri od may be selected to allow variations in a capacitance of the collector due to vibration of the collector by the air mover to be reduced below a threshold level. A pres sure pulser may be used to move a sample of gaseous fluid through a sampling inlet, such as a pi nhole, into the detector. The amplitude of operation of the pres sure pulser may be reduced during the quiet period as compared to its operation when the air mover is operating at its usual operating level.

[0018] After the end of the quiet period the air mover may be increased to return to the operating level.

[0019] The method may comprise performing a series of cycles of operation of the detection apparatus dur ing the quiet period. For example, a sample of gaseous fluid may be obtained via a sampl ing inlet ( e. g. by operation of a pres sure pulser) prior to the serie s of cycles. An ioniser may be operated to generate ions from the s ample at the start of each cycle. The method may comprise maintaining the air mover in reduced operation throughout the series of cycles and operating the a ir mover at the operating level be fore any s ubsequent sample i s obtained through the sampling inlet.

[0020] The method may compris e performing only a s ingle cycle of operating the detection apparatus during the quiet period and then operating the air mover at the operating level before a subsequent cycle of operation of the detection apparatus.

[0021] This may comprise obtaining a sample of gaseous fluid through the sampling inlet prior to a series of cycles of operating the ion mobility spectrometer, and providing a series of quiet periods corresponding to the series of cycles of operation of the ion mobility spectrometer. The air mover may be returned to operating at the operating level between each cycle of operation. The air mover at the operating level before any subsequent s ample is obtained through the sampl i ng inlet. In an a spe ct the re i s provided a contro ll e r o f a dete ction appar atus, the contro l le r compr i si n g: a contro l i nter face for contr ol l ing a n a i r mover of the de te c ti on appar atus and for ope rati ng the de te cti o n app aratus to a ll ow i ons to travel to be de tected b y a co l le ctor e le c trode. The contro ll er may be confi gured to pe rf orm any one or mor e o f the methods des c ribed he rei n.

[0022] An aspect o f the di s cl o sure compr i se s conf iguri ng such a contr ol l er of a de te cti on appa ratus to per fo rm any one or mor e o f the methods des cr ibed here in. Embodime nts o f the di sc l os ure provide a computer prog ram pr oduct conf i gured to prog ram a programmab l e pro ces s or, s uch as a control l er o f dete ction appar atus to per f orm any o f the me thods d es cr ibed or c l aimed he rei n. S uch compute r programs may be e ncode d i n tang ib l e non - trans itory compute r readab l e stora ge media.

[0023]

[0024] a s pe ct the dis c lo s ure provides a detect ion appa ratus compr is i ng such a c ontro ll e r.

[0025] The d is c lo s ur e a ls o provid e s a dete ction apparatus comp r is i ng: a co ll e ctor el ectrode a s sembl y fo r detecting i on s, wherei n the col le ctor e le ctrode a ss emb ly is s ubj ect to var ia tions i n capac itance due to me chani c al vibr ati on;

[0026] a chambe r a long 'wh i ch i ons trave l to re ach the col l ec tor el e ctrode for de te c ti on;

[0027] a contr ol l er c onf igured to operate the dete cti on apparatus to pr ovide i ons to be de te cte d by the c ol l ector appa r atus dur ing a qui et pe r iod,

[0028] whe re in me chani ca l vibrat ion of the co ll e ctor el ectrode i s reduced dur ing the quie t pe ri od. The c ontrol le r may be confi gured to i nhibi t opera ti on o f at le as t one vibrati on s ource of the de tecti on appa ratus to p rovid e s aid reduced me chani c al vibrati on. The vibrati on s ource compri s es a n ai r move r, such as a fan, pump, or bl owe r.

[0029] The a ir mover ma y ope ra te to provi de ai r f l ow i nto and / or out o f the chambe r.

[0030] The de te c ti o n apparatus may compr i se an i on mob i li t y spe ctrome te r ( IMS ) ce ll, the fl ow of ai r i s provid ed a l ong a dr i ft chamb er o f the IMS ce ll, and the ions tr ave l i n the dri ft chambe r to b e de tected by the co l le ctor e le ctrod e.

[0031] The de te cti on app aratus ma y compr is e a mas s spec trometer s uch a s a time of f li ght ma s s spe ctr ome te r (TOF -MS ) compr is i ng a r educed pre ss ure chamber, the a i r move r ope rat e s to reduce a ir pr e ss ure in the chambe r, and the i ons trave l in the reduced pr e ss ur e chamber to the col l ector e l ectrode.

[0032] The contro l le r may be confi gur ed to reduce ope ration o f the ai r mover to provide the qui et pe r iod. For examp l e, the contr ol le r ma y b e con f igured s o that the s ta rt of the quie t pe ri od pr e cede s the op er ati ng o f the dete ction apparatu s to p rovide the i o ns by a wa i t pe r iod. The c ontro ll e r may b e c onf igure d s o that the wai t pe r iod i s long e nough to al l ow var ia tions i n a capacitance of the co l le ctor due to vibra tion o f the col l ector by the a i r mover to be re duced be low a thre s ho ld level.

[0033] The c ontrol le r ma y be confi gur ed to i nc rea s e ope r ati on of the ai r mover a fte r the qui et pe ri od. Fo r examp l e, it may r eturn ope rati on o f the a i r mover to the ope rating l eve l at whi ch it i s us ual ly ope ra ted to provide functi on of the dete cti on appar atus. The dete ction appara tus ma y compr i se one or mo re capa c itive elements, for e xampl e co nducti ve or char ge carryi ng e lements. Such el eme nt s may be capac it ive l y coupl e d to the c ol l ector el e ctrode. For examp l e the s e e l ements may be a s sembl ed around the co l le ctor e le ctrode s uf f ic i ent ly c l os e ly a s to ma ke an appre ci abl e contr i bu ti on to the c apaci tance o f the col l ector el e ctrode. One e xampl e o f s uch a n e l ement i s a sc ree n e le ctrode arranged to s hie ld the co l le cto r el ectrode from e lectr ic fi eld from the i on s and the var i ation in capac i tance is a ss oci ate d with vibra ti ona l changes i n a spaci ng betwee n the s cre e n e le ctrode and the c ol l ector e l ectrode.

[0034] The quie t p e ri od des cr ibed he re i n may be pr ovided by re duc ing ope ra ti on o f the a i r mover, thi s may be do ne by reduc in g a powe r or spe e d o f ope rat ion of the a i r move r. Th is may be done b y swi tchi ng the a i r mover of f or otherwis e ce as ing operat i on.

[0035] Brief Description of Drawings

[0036] Embodime nts o f the dis c lo s ure wi ll now be de sc r ibed i n d etai l wi th re fer e nc e to the accompanyi ng drawi ng s, in whi ch:

[0037] Fi gure 1 shows a cut awa y vi ew of an ion mob il ity spe ctromete r;

[0038] Fi gure 2 s hows a f low cha r t of a me thod o f reduc ing me a surement no is e i n a de tect io n apparat us such a s that il l us tra ted i n Figure 1 or Fi gure 5;

[0039] Fi gure 3 s hows a furthe r f low cha rt of a me thod o f reduc ing me a surement no is e i n a de tectio n apparatus such a s that il lus trated i n Figure 1 or Fi gure 5;

[0040] Fi gure 4 s hows ye t a furthe r flow cha rt o f a me thod o f reduc ing me as urement no is e in a d e te ct i on appara tus such a s that il lus trated i n Figure 1 or Fi gur e 5; Figure 5 shows very schematic. view of a different detection apparatus.

[0041] In the drawings li ke reference numerals are us ed to indicate like elements.

[0042] Specific Description

[0043] The embodiments described below present di fferent types of detection apparatus in which the methods of the present disclosure can be implemented. These methods of fer particular advantages in detection devices which include ion mobil ity spectrometry capability, where a collector electrode maybe used to detect the arr ival of ions and mechanica l vibrati on of the collector e lectrode may create a particular problem of vibration induced capacitance fluctuation. This may arise particularl y in systems where the assembly around the collector electrode comprises conductive elements. Embodiments als o offer signi f icant advantages in mass spectrometry devices, where comparable structures may be present and may be subj ect to comparable mechanical vibration.

[0044] Accordingly, embodiments of the disclosure provide a quiet period, during which mechanical vibration of the col lector electrode as sembly is reduced and operate the detection apparatus to al low ions to travel to be detected by the coll ector electrode during the quiet period. A variety of implementations are contemplated, as will become apparent from the dis closure which follows.

[0045] The ion mobility spectrometer of Figure 1 comprises a reaction region 102, an ionis ation source 104 for ionis ing gaseous fluid in the reaction region 102, an ion shutter 105, a collector electrode 118 such as a Faraday cup, and a controller 120. The ion mobility spectrometer also compri ses a drift region 103, dr i ft el e ct rodes 103 a, 103 b, a scre e n gr id 117, an a i r move r 122, a dri ft ga s inlet 1 19, and a dr i ft ga s outl et 12 1.

[0046] The spe ct rome te r compr i se s a housi ng, s uch a s a tube 101. The re action r eg ion 102 i s at o ne e nd inside th is hous i ng 101, and separated from the co ll e ctor e le c trode 118 by a dr if t re gi o n 103. The r e act io n re gi o n 102 i s s epa rated from the dri ft reg ion 10 3 by the i on s hutter 105. The housi ng 10 1 compr i se s a n inl et 10 8 for enabl ing a sampl e o f gas e ous f luid ( such as vapour, and / or g as, and / or an aer os o l ) to be i ntroduce d i nto the re a cti on r e gi on 102.

[0047] The i oni sa tion s ource 10 4 i s di spo s ed i n the housi ng for ge nerati ng i ons to i oni s e the sampl e of ga se ous f luid i n the re act ion re gi on 102. I n the e xampl e i l lu s trate d i n Figure 1, the ionis ati on s our ce 1 04 compr is es a c orona po int. Embodiments o f the dis c lo s ur e may us e a dual po int coro na ioni s ati on s ource.

[0048] A vol tage pr of i le may be provided in the dr ift re g io n 103 u si ng a se r ie s o f dri ft e le ctrode s 103 a, 1 03b space d apart a long the dr i ft re gi o n 103. Although no t i l lu strate d in Fi g ure 1, a repel le r pl ate or other el e ctrod e may be arranged fo r exte nd ing thi s vo l tag e pro fi l e i nto the re acti on r e gi on 102. Be twe e n the re action re gi o n 102 and the dete ctor 118 the p ro f il e vo ltage var ie s sp atia l ly (e. g. as a function o f di sp l aceme nt al o ng the ce l l in the dri ft di re cti on) to provid e a n e le ct r ic fi eld that moves i ons al ong the ce ll 100 towards the col l ec tor 118. The el e ctri c fi el d may be uni form and / or known a lo ng the dri ft reg ion 103 and / or the reac ti on re g ion 102.

[0049] The s cre en gr i d 117 is di spo sed betwee n the dri ft re g io n and the co l le ctor e le ctr ode and typ ical l y c l os el y adj acent

[0050]

[0051] the co l le ctor e le ctrode. I t is conne cted to the contro l le r 12 0. The con trol l er is conf i gured to ho ld the vol tage o f the sc ree n grid 117 a t a po te nti al s el ected to s hi e ld the col l ec tor e l ec trode 118 from image charge effects as sociated with ions approaching the collector e lectrode from the drift region 103. To help prevent peak broadening the screen grid 117 is generally positioned close ly adj acent to the collector electrode 118, and typically it is pos itioned paral lel to the collector electrode. The screen grid may extend across a portion of the centre of the collector electrode on the axis of the drift chamber. For example, the screen grid may cover substantially all of the collector electrode to shield it from image charge effects from approaching ions.

[0052] As a result the screen grid is one of the large st contributions to the capacitance of the col lector electrode. However, there may be other contributions to this capacitance such as those as sociated 'with any other conductive and / or charge carrying elements in the as sembly around the collector electrode but which are not at the same DC potential. This assembly may be referred to herein as the collector electrode a ssembly. The capacitance of the collector e lectrode as sembly may arise from the screen grid and / or such other other conductive and / or charge carrying elements as are as sembled sufficiently close ly to the collector electrode assembly that the contr ibute appreciably to the apparent capacitance of the collector electrode.

[0053] The controller 120 i s also connected to control the air mover 122. The air mover 122 typically compri ses a fan, pump, or blower or other appropriate air movement means. It is connected by an air circulation system, such as appropriate conduits, to the drift gas inlet. Typically, the air mover is mounted in or to the detector such that mechanica l vibration produced by operation of the air mover ca be communicated to the collector as sembly through the detection apparatus itself. The contro ll e r 12 0 ope rate s the a ir move r 122 to provide a f low of dri ft ga s i nto the dri ft re gi on vi a the dri f t ga s inl et. The dr i ft ga s then fl ows down the dr i ft re g ion 10 3 away from the co l le ctor 118 towards the re acti o n re gi on 102. I t ex i ts the dr ift re g ion vi a the dri ft ga s out le t, from where it may be re c ircul ated to the ai r move r. T he dr i ft ga s may a ls o be pas sed through c l eani ng and / or drying stage s such as mol e cula r s ieve s and s o i orth.

[0054] The operati on of the a i r move r 122 may be o ne s ource o f me chani cal vibr ations, whi ch may be tr ansmi tted through the body of the io n mobi l ity spec tr ome ter to the co l le c tor e l ec trode 118 and / o r the s urroundi ng a ss emb ly comp r is ing conductive or cha rg e ca rrying el eme nts. Thes e vibra ti ons ma y caus e re l ative di spl aceme nt o f s uch el eme nts and the c o ll e ctor e l ectr ode f rom one a nothe r. As a re sult, the c apac i ta nce of the col l ector el e ctrode ma y e xh ibi t co rre spo nd i ng va r iat ions becaus e of the depende nce of c apac itance o n spa ci ng.

[0055] The i on s hutte r 1 05 compr i se s two e le ctrode s 106, 107, ’whi ch are coupl ed to the control l er 12 0 to enab l e a barri e r vo l tage to be pr ovi ded be twee n the two el ectrod es 10 6, 10 7. When the s hutte r 105 i s "c l os e d" this b arr i er vo ltage acts to prevent i on s from trave ll i ng from the react i on re gi on into a dri ft re g ion o f the IMS, and an open s tate i n wh ich ions c an travel i nto the dr ift re g ion towa rds the de tector. The ion s hutte r 10 5 may compr is e a Tynda ll - Powel l, Bradbury-Nie ls e n shutter, or othe r type o f shutter. The shutter el e ctrodes 10 6, 107 may each compr is e el ongate conduc tor s, and the el ong a te conductor s of the fi rs t shutter el e ctrode 10 6 may be al i gne d i n the dr i ft di r ection with the e l ongat e conductor s of the se cond s hutter el e ctrode 1 07. The el ongate conductors of each s hutte r e le ctrode 10 6, 107 may be arr anged as a gr id, s uch as a me sh, fo r examp le a tr i angul ar, re ctangular, hexa gonal, or othe r re gul ar or irregul a r me sh. The shutter el ectrod es 10 6, 1 07 need not be s eparated i n the dr ift di recti on. For examp l e the y may be c op l ana r, i n whi ch ca s e the el ongate conducto rs may be interdig i tated, for examp le the y may be inte r le ave d or i nterwove n.

[0056] The contro l le r 12 0 may compr i se a contro l i nte r face for control l ing the a i r move r and othe r part s of the IMS ce ll. Examp le s o f contr ol i nte r face s may i nclude s er i al or pa ral le l inter faces a nd s ynchronous and as ynchro nous i nte rface s. By thes e or other mean s, the co ntrol l er 120 i s connected to the ion shutter 105 and to the co l le ctor e l ectrode for se n si ng a rr iva l o f ions at the co ll ector el e ctrode. The contro l le r 120 may a l so be conne cted for opera ti ng the i oni sa tion s ource 10 4.

[0057] The ope r ati on of th is app aratus wil l now be des cr ibe d with re ference to Fi gure 2. A sampl e of ga s eous f luid ( such a s vapour ) is pr ovi ded into the re a cti on re g ion. Thi s may be done b y ope rati on o f a pre s s ure pul se r or other me ans or tak i ng a s amp le, the contro ll er 12 0 provide s a pul se o r se r ie s of puls es o f the ionis ati on source 10 4 t o ge nerate ions. The se ion s are mixed with the s amp le to generate sampl e i ons. Dur i ng th i s proc es s, the contr ol l er 12 0 ope rate s 20 0 the a i r move r, at a n oper ati ng l evel, to provide the f low o f a i r a long the dri ft chambe r 103. Thi s f low of a ir may act to ke ep the dr ift chambe r 'clean' for examp l e to inhib it the f low or di f fus io n o f ne utra l sampl e i nto the dr ift chamb er fr om the re acti on r eg ion.

[0058] The contr o ll e r 12 0 the n provi des 2 02 a quie t per i od, i n ’which me chani cal vibr ati on of the co l le ctor el e ctr ode ( and / o r any sur round ing components whi ch co ntr ibute to i ts apparent capac itance ) i s reduce d. Thi s may be done by reduci ng ope r ation of the ai r move r and / or other s ource s o f me chani ca l vibrati on. One way to do thi s i s to r educ e th e spee d or powe r of ope r at io n of the a ir mover. Thi s may be achi e ved by s impl y swi tching i t off, but mere reduction in speed / power of operat ion may be enough to reduce vibration, so the air mover need not always be completely switched off. This reduced operation of the air mover provides a quiet period.

[0059] During this quiet pe riod, the control le r 120 can operate 204 the detection apparatus to allow ions to travel to be detected by the collector electrode 118.

[0060] In a typical cycle of operation, after a gate de lay ( fol lowing operation of the ioniser ) the controller 120 opens the ion shutter for a gate width, which allows a cloud of ions to enter the drift region 103 where they travel, against the flow of drift gas to the collector electrode 118. As the ions travel along the drift chamber they become separated due to their differing mobilities so that they arrive at the collector e lectrode 118 at different times. The collector electrode 118 is connected to the controller so that the control l er can detect 206 the charge as sociated ’with the arrival of ions at the collector electrode 118. This s ignal i s used to provide an ion spectrum which characterises that cycle of operation of the IMS device. The controller 120 may operate the IMS device to provide a series of such cycles, for example a number of cycles of operation, for each sample. The resultant spectra may be combined, for example by averaging.

[0061] The start of the quiet period may precede the operating of the detection apparatus by a wait period. Typically, the wait period is s elected to be long enough for vibration of the collector by the vibration sources, such as the air mover, to be reduced below a threshold level. The relevant thre shold may be selected based on the speci fic details of the device and / or the desired accuracy of measurement. After the cycle (or s eries of cycles) of operation have been completed, the controller 120 may return 208 the ope ration o f the a i r mover 122 to the op e rating l evel. Thi s ma y a s s i st in pre ve nti ng dif fus io n or f l ow of neu tra l s ampl e vapour i nto the dr i ft r e gi o n.

[0062] Fi gure 3 i l lustra tes a scheme of oper a ti on for a devi ce s uch a s tha t i llustra ted i n Figure 1. I n th is me thod, the pre s sure pul se r is ope rat ed 3 00 to obta in a sampl e, a nd to io ni s e the s mp le. Ope rati on o f any vibrati on source ( s uch as the ai r move r ) i s the n reduced 302 to provide a quie t pe ri od. The spe c tr ome te r i s the n contr ol l ed to per f orm a s er i es of cyc le s 305 of ope ration, befor e the vibrat i on source ( s ) are re tur ne d 3 0 8 to the i r norma l ope rati ng l evel. As they are a l l ta ken fr om a s i ng le sampl e, the spe ctra obtai ned fr om th is se r ie s o f cycles of operati on may be combi ned by s ummin g them, f or example to provid e an ave rag e.

[0063] Fi gure 4 il lus tra te s a further me thod o f ope rat i on. I n thi s me thod, the pres sure pul se r i s opera te d 400 to obta i n a s amp le, and the n the op era ti on of any vib rati o n source ( such as the ai r mover ) i s r educed 40 2. The spec trometer i s the n control led to pe r form 405 one cycl e o f operati o n before the vibra ti on s ource ( s uch a s the a i r mover ) i s re tur ned 40 8 to i ts ope rat ing l evel. The contro l le r may the n reduce ope r ation 402 o f the vib ration sourc e agai n, per form anothe r cycl e o f operati on 405, a nd the n re tur n 408 the vibra ti on s ource to its opera ti ng l eve l before each subs e que nt cycl e of oper ati on. I n the i nte rva ls be twee n cyc le s, furthe r neutra l s amp le may be ta ken into the re action re g ion to be ioni s ed. Whe n the pres s ure pul s er i s us ed be twee n succe s s ive qu ie t per i ods, the powe r app li ed to the pr e ss ure pul se r may be reduc ed a s compa red to its u se when the a i r move r is wo r ki ng at i t s oper ati ng le vel. Embodime nts o f the di sc l os ure may the re fore rel ate to sys tems in which ope ra tion o f the ai r mover whi ch provide s f low o f dr i ft g a s is reduced f or c e rtai n pe r iods, and dur i ng the se qui et pe r iods, the powe r l eve l o f e ach ope rati on o f the pres s ure p ul s er is al so re duced as compared to the l eve l use d whe n the ai r move r i s ope ra ting norma l ly.

[0064] Figure 5 illustrates a further detection apparatus. The detection apparatus 500 illustrated in Figure 5 is a time of flight mass spectrometer (TOF-MS) The appa ratus compri se s a r educed pr e ss ure chamb er 503, an a ir move r b 22, a col le ctor el e ct rode 518, a contr ol l er 52 0, ion source 506, and an inlet 508. The apparatus 50 0 a ls o compr i se s an a s sembl y of co nductive and / or ch arge car ryi ng el eme nts 517 ad j acent to t he co l le ctor e le ctrode.

[0065] The i on source 506 comp r is e s a s our ce o f i ons to be a na l ys e d and is coup l ed to the reduced pr es s ure chambe r 503 by the i nle t 508, whi ch may compr i se a cap il l ary inl et or i on funnel or othe r appropr i ate means of c onve yi ng io ns to th e reduc ed pre ss ur e chamb er 503.

[0066] The air mover 522 is connected to the controller 520 and is arranged in fluid communication with the reduced pressure chamber 503. The air mover 522 is operable to reduce the air pressure in the reduced pressure chamber 503, fo r exampl e i n the manne r o f a va cuum pump.

[0067] The col l ector e l ectr ode 518 i s arr anged a t the oppo s it e e nd o f the chamber 5 03 from the i nl e t 50 8 for dete ct ing io ns. The co l le ctor e le ctrode and a s semb l y 518, 5 17 i s s ubj ect to me chani cal vibra ti on due to ope rat ion o f the a ir mover 522. Thi s may caus e var iation s in cap ac itanc e.

[0068] The chamb er 503 may compri se a vacuum chamber a nd one or more el e ctrodes may be provided al ong the chamber to c aus e ions to trave l from the i nl et to re ach the c ol l ector el ectrode for de tecti on. The se a nd other c omponent s, such a s a s cr e en gr id, may pr ovide the a ss emb l y 51 The controller 520 is connected to operate the ion source 506 and / or the inlet 508 fo r control li ng the i nl e t. The co ntrol le r is thus ope rab le to al l ow or preve nt i ons to enter the re duced pr e ss ure ch amber to pr ovi de i ons to be de te cte d by the col l ector el e ctrod e. The co ntrol le r is al so c onne cted to the a ir mover and is ope rabl e to contr ol ope rat ion o f the a i r move r - e. g., to reduce or i ncrea s e the power / speed of ope rati on o f the a ir move r and / or to swi tch i t on and of f.

[0069] In operation, the ai r mover 522 is op e rated at an ope rating leve l to pr ovide a reduced ai r pres sure i n the chambe r. The contr ol le r the n reduc es the op erati on o f the a ir move r a s comp ared to the ope ra ti ng level, for exampl e b y swi tchi n g it o f f to pr ovide a qui et pe r iod. Duri ng the qui et p er i od, whil e me chanical vib ration of the co ll ector e l ectrode i s reduc ed, the contro l le r ope rate s the i nl e t to a ll ow i ons to e nte r the reduced pr e ss ur e chamber s o tha t the y can travel a l ong the reduc ed pres s ur e chambe r to the co l le ctor e le ctrode. As the chambe r i s evacuated, or a t le as t at reduced p res s ur e, the time of f l ight of i ons to the col l ector provide s an indicati on o f the i r mas s to charg e rati o. A se r ie s o f such c yc l es of ope ra tion may b e pe rf ormed before the cont rol le r re turns the a ir mover to i t s ope ra ting l eve l.

[0070] It wi l l be appre ci a ted i n the co ntext of the for ego ing di sc l os ur e that a var ie ty o f embodiment s ar e cont emp late d. The pri ncip le s o f the di sc l os ure have be en exp la i ne d wi th refere nce to ion mob il ity spe ctromete rs and time o f f l ight mas s spe ctromete rs, but they may fi nd app l ic ati on in othe r type s o f de te cti on apparatus, s uch a s di f fe re nti a l mobi li ty spec trometer s, fi eld as ymme tr ic IM S ( FAIMS ) devices and a ny o the r devi ce i n whi ch a col l ector e l ectrode i s us ed to de te ct the arr iva l o f i ons. It i s par t icular l y advantageous whe re time of arr iva l o f ions needs to be me a sured sensitively. The use of pressure pul sers and pinhole inlets has been described, but other kinds of inlet may also be used such as membrane inlets. The quiet period has been described as being achieved through reducing operation of a vibration source but in some embodiments, vibration of the collector electrode may be reduced by applying a counteracting vibrati on to the collector electrode as sembly. For example, the controller may be connected to a vibration provider and configured to detect vibration of the collector as sembly and further configured to control the vibration provider to apply a compensating vibration, such as a vibration in antiphase with the detected vibration. Such embodiments may employ the principles of active noise cancellation and other active methods to reduce vibration of the collector electrode and / or any surrounding conductive or charge carrying elements with which it is as sembled.

[0071] A variety of other embodiments will be apparent to the s kil led addressee in the context of the pres ent disclosure. Any feature of any one of the examples disclosed herein may be combined ’with any selected features of any of the other examples des cribed herein. For example, features of methods may be implemented in suitably conf i gured hardware, and the conf iguration of the specific hardware described here in may be employed in methods implemented using other hardware.

[0072] It will be appreciated from the discus sion above that the embodiments shown in the Figures are merely exemplary, and include features which may be generalis ed, removed or replaced as described her e in and as set out in the claims. With reference to the drawings in general, it will be appreciated that schemati c functional block diagrams are used to indicate functionality of systems and apparatus described herein. I t will be appreciated however that the functiona lity need not be divided in thi s way, and should not be ta ken to imply any particular structure of hardware othe r than that de s cr ib ed and cl aimed be l ow. The function of one or more o f the e lemen ts s hown i n the d rawi ngs may be fur the r s ubdivided, and / o r di stributed throughout apparatu s o f the dis c lo s ure. In some embodime nts the functi on of one or more elements s hown i n the drawing s may be i ntegr ated into a s ingl e functional un it.

[0073] In some examp l es the functi o na l ity o f the co ntro ll er may be provided by a ge ne ral purpo s e proces sor, which may be conf i gured to per f orm a me thod acc o rd i ng to any one o f tho se des c ribe d he r ei n. I n s ome exampl es the c ontr o ll e r may compr i se di gi ta l log ic, such a s fi eld pr ogrammab l e ga te arr ays, FPGA, app li c ation spe ci fi c i nte grated c ircui ts, AS IC, a dig i ta l s ignal pr oce ss or, DS P, or by any other approp ri ate hardware. I n s ome ex amp le s, one or more memory e lements can s tore data and / o r program ins tructions us e d to imp leme nt the op erati ons des cribed he re in. Embodime nts o f the dis c lo s ure provi de tangib le, non -trans itory storage medi a comp r is ing program i ns tructi ons ope rab le to p rogram a pr oce s sor to pe r form any one or more o f the methods des cribed and / or c l aimed her ei n and / or to provide data proce s si ng apparatus as de s cr ibe d and / or c la imed he re i n. The control l er may compr is e an anal ogue con trol ci rcuit which provid es a t l ea st a pa rt o f thi s contr o l func ti ona li ty. An embodime nt provides an ana logue control circuit c onfi gur ed to per form any one or more o f the me thods de s cr ibed herei n.

[0074] The above embodiments are to be understood as illustrative examples. Further embodiments are envisaged.

[0075]

[0076] to be under stood tha t any fe a tu re de s cr ibed i n re lati on to a ny one embod ime nt ma y be used a l one, or in combi nat ion wi th othe r fe ature s de scr ibed, and may a ls o be us ed in combi natio n ’wi th one or more fe atures of any othe r o f the embodime nt s, or any combi nation o f any othe r o f the embodime nts. Furthe rmore, equival e nts and modi fi cations not des cr ibed above may al s o be employed without departing from the scope of the invention, which is defined in the accompanying cla ims.

Claims

1. Claims:

1. A method of reducing electrical measurement noise in a detection apparatus configured to detect the arrival of ions at a collector electrode, wherein the detection apparatus comprises an air mover to provide a flow of air in the apparatus, the method comprising:3.operating the air mover, at an operating level, to provide the flow of air;4.reducing operation of the air mover for a quiet period; and5.operating the detection apparatus to allow ions to travel to be detected by a collector electrode during the quiet period.

2. The method of claim 1 wherein the start of the quiet period precedes the operating of the detection apparatus by a wait period.

3. The method of claim 2 wherein the wait period is selected to allow variations in a capacitance of the collector due to vibration of the collector by the air mover to be reduced below a threshold level.

4. The method of claim 2 or 3 wherein during the quiet period a pressure pulser, used to move sample into the detector, is operated at reduced amplitude.

5. The method of any preceding claim comprising increasing operation of the air mover to the operating level after the quiet period.

6. The method of any of claims 1 to 5 wherein the detection apparatus comprises an ion mobility spectrometer ( IMS ) cell, the flow of air is provided along a drift chamber of the ion mobilityspectrometer, and the ions travel in the drift chamber to be detected by the collector electrode.

7. The method of any of claims 1 to 5 wherein the detection apparatus comprises a mass spectrometer, such as a time of flight mass spectrometer (TOF-MS) comprising a reduced pressure chamber, the air mover operates to reduce air pressure in the chamber, and the ions travel in the reduced pressure chamber to the collector electrode.

8. The method of any of claims 1 to 7 comprising performing a series of cycles of operating the detection apparatus during the quiet period.

9. The method of claim 8 comprising operating a sampling inlet to obtain a sample of gaseous fluid to be ionised to provide the ions prior to the series of cycles.

10. The method of claim 9 comprising maintaining the air mover in reduced operation throughout the series of cycles and operating the air mover at the operating level before any subsequent operation of the sampling inlet.

11. The method of any of claims 1 to 7 comprising performing only a single cycle of operating the detection apparatus during the quiet period and operating the air mover at the operating level before a subsequent cycle of operation of the detection apparatus.

12. The method of claim 11 comprising operating a sampling inlet to obtain a sample of gaseous fluid to be ionised to provide the ions prior to a series of cycles of operating the ion mobility spectrometer, andproviding a series of quiet periods corresponding to the series of cycles of operation of the ion mobility spectrometer, and optionally operating the air mover at the operating level between each cycle of operation.

13. The method of claim 9, 10, 11 or 12 comprising operating the air mover at the operating level before any subsequent operation of the sampling inlet.

14. A controller of a detection apparatus, the controller comprising:19.a control interface for controlling an air mover of the detection apparatus and an IMS cell of the spectrometer and for operating the detection apparatus to allow ions to travel to be detected by a collector electrode; and20.control logic configured to perform the method of any preceding claim.

15. A detection apparatus comprising the controller of claim 14.

16. A detection apparatus comprising:23.a collector electrode assembly for detecting ions, wherein the collector electrode assembly is subject to variations in capacitance due to mechanical vibration;24.a chamber along which ions travel to reach the collector electrode for detection;25.a controller configured to operate the detection apparatus to provide ions to be detected by the collector apparatus during a quiet period,26.wherein mechanical vibration of the collector electrode is reduced during the quiet period.

17. The detection apparatus of claim 16 wherein the controller is configured to inhibit operation of at least one vibrationsource of the detection apparatus to provide said reduced mechanical vibration for example wherein the vibration source comprises an air mover, such as a fan.

18. The detection apparatus of claim 17 wherein the air mover operates to provide air flow into and / or out of the chamber.

19. The detection apparatus of claim 18 wherein the detection apparatus comprises an ion mobility spectrometer ( IMS ) cell, the flow of air is provided along a drift chamber of the IMS cell, and the ions travel in the drift chamber to be detected by the collector electrode.

20. The detection apparatus of claim 19 wherein the detection apparatus comprises a mass spectrometer such as a time of flight mass spectrometer (TOF-MS) comprising a reduced pressure chamber, the air mover operates to reduce air pressure in the chamber, and the ions travel in the reduced pressure chamber to the collector electrode.

21. The detection apparatus of claim 19 or 20 wherein the controller is configured to reduce operation of the air mover to provide the quiet period.

22. The detection apparatus of claim 21 wherein the start of the quiet period precedes the operating of the detection apparatus to provide the ions by a wait period, for example wherein the wait period is selected to allow variations in a capacitance of the collector due to vibration of the collector by the air mover to be reduced below a threshold level for example wherein the controller is configured to increase operation of the air mover to an operating level after the quiet period.

23. The detection apparatus of any of claims 16 to 22 comprising a screen electrode arranged to shield the collector electrode from electric field from the ions and the variation in capacitance is associated with vibrational changes in a spacing between the screen electrode and the collector electrode.

24. The method of any of claims 1 to 13, or the detection apparatus of any of claims 14 to 23 wherein reducing operation of the air mover comprises ceasing operation.

25. A computer program product, configured to program a programmable controller of detection apparatus to perform the method of any of claims 1 to 13 or 23.

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