By Io­niza­ti­on Only: De­tec­ting Ni­tros­ami­nes with Mass Spec­tro­me­try

In pre­vious ar­tic­les, you have al­re­a­dy lear­ned that mass spec­tro­me­try is an im­pres­si­ve tech­no­lo­gy with the po­ten­ti­al to si­gni­fi­cant­ly im­pact re­se­arch, la­bo­ra­to­ries, and in­dus­try. Ho­we­ver, for a mass spec­tro­me­ter to de­li­ver re­sults, io­niza­ti­on or “char­ging” is cru­cial. Only when the sub­s­tance to be ana­ly­zed is „char­ged“, the mass spec­tro­me­ter work its mi­ra­cles. In this ar­tic­le, you will dis­co­ver which io­niza­ti­on me­thods are ty­pi­cal­ly used for the ana­ly­sis of ni­tros­ami­nes, the chal­lenges that may ari­se, and a pro­mi­sing al­ter­na­ti­ve.

Ni­tros­ami­nes in Phar­maceu­ti­cals

Ni­tros­ami­nes are po­ten­ti­al­ly car­ci­no­ge­nic sub­s­tances that went un­no­ti­ced for an ex­ten­ded pe­ri­od in me­di­ca­ti­ons for hy­per­ten­si­on. They were found in both Vals­ar­tan and Ra­nit­i­di­ne, lea­ding to ex­ten­si­ve re­call ac­tions. The fact that the­se sub­s­tances went un­no­ti­ced can be at­tri­bu­ted to their emer­gence du­ring the pro­duc­tion pro­cess, re­sul­ting from re­ac­tions bet­ween va­rious com­pon­ents. Ad­di­tio­nal­ly, the lack of ap­pro­pria­te test­ing me­thods for the­se sub­s­tances in phar­maceu­ti­cal com­pa­nies con­tri­bu­tes to their over­sight. The re­ve­la­ti­on po­sed si­gni­fi­cant chal­lenges for aut­ho­ri­ties, promp­ting the de­ve­lo­p­ment of new stan­dards for ma­nu­fac­tu­ring fa­ci­li­ties to pre­vent ni­tros­ami­ne-con­ta­mi­na­ted me­di­ca­ti­ons from rea­ching con­su­mers.

Io­niza­ti­on of Ni­tros­ami­nes: An In­ter­ac­tion of Che­mis­try and Phy­sics

Io­niza­ti­on in­vol­ves ad­ding or re­mo­ving an elec­tron or pro­ton from a mole­cu­le, gi­ving it a re­co­gnizable char­ge. This re­qui­res a type of en­er­gy jolt whe­re mole­cu­les break apart, and free elec­trons or pro­tons at­tach to others, put­ting them in an io­ni­zed sta­te. Only then, the mass spec­tro­me­ter can de­tect the ana­lytes. When it co­mes to phar­maceu­ti­cal test­ing, Li­quid-Chro­ma­to­gra­phy Mass Spec­tro­me­try (LC-MS) with Elec­t­rospray Ioniza­ti­on (ESI) is most com­mon­ly the me­thod of choice. This me­thod is espe­ci­al­ly sui­ta­ble for io­ni­zing sol­va­ble, po­lar sub­s­tances (e.g. ac­ti­ve in­gre­di­ents in me­di­ca­ti­ons for hy­per­ten­si­on). Ho­we­ver, many che­mi­cal com­pounds, such as the vo­la­ti­le ni­tros­ami­ne NDMA, can­not be io­ni­zed by ESI due to their vo­la­ti­le na­tu­re. The Atmo­sphe­ric Pres­su­re Che­mi­cal Ioniza­ti­on (APCI) is ty­pi­cal­ly used to io­ni­ze the­se sub­s­tances, as it is well-sui­ted for the task.

APCI for Ni­tros­ami­ne Ana­ly­sis

In at­mo­sphe­ric pres­su­re che­mi­cal io­niza­ti­on, the ana­ly­te is con­ver­ted into a gas­eous sta­te (e.g., by hea­ting). An elec­tri­cal­ly char­ged co­ro­na need­le ge­ne­ra­tes elec­trons and io­ni­zes sol­vent and car­ri­er gas. Sub­se­quent­ly, a che­mi­cal re­ac­tion bet­ween the­se re­ac­tant ions and the ana­lytes ta­kes place, re­mo­ving elec­trons from the ana­ly­te or trans­fer­ring pro­tons to it. This pro­cess oc­curs in a cham­ber at at­mo­sphe­ric pres­su­re, moun­ted be­fo­re the ent­rance of the mass spec­tro­me­ter. Con­se­quent­ly, a va­rie­ty of io­ni­zed ana­lytes may be lost, as they might not be drawn into the mass spec­tro­me­ter.

Cou­pled with high-pres­su­re li­quid chro­ma­to­gra­phy, whe­re the sam­ple is se­pa­ra­ted into its in­di­vi­du­al com­pon­ents, APCI ge­ne­ral­ly pro­vi­des meaningful evi­dence for ni­tros­ami­nes. Ho­we­ver, it is not sui­ta­ble to pro­vi­de evi­dence for the ac­ti­ve in­gre­di­ents of hy­per­ten­si­on me­di­ca­ti­on due to its li­mi­ta­ti­on re­gar­ding po­la­ri­ty. This me­ans that to com­ply with the new stan­dards po­sed by aut­ho­ri­ties, ma­nu­fac­tu­ring fa­ci­li­ties usual­ly need to run two ana­ly­ses with dif­fe­rent io­niza­ti­on me­thods.
Ma­nu­fac­tu­r­ers are the­r­e­fo­re still sear­ching for a re­lia­ble and easy me­ans to com­ply with aut­ho­ri­ty stan­dards by using one io­niza­ti­on tech­no­lo­gy only.

SICRIT as an Al­ter­na­ti­ve

The SICRIT (Soft Ioniza­ti­on by Che­mi­cal Reac­tion in Trans­fer) io­niza­ti­on source fea­tures th­ree io­niza­ti­on me­cha­nisms hap­pe­ning at the same time. One of the­se is si­mi­lar to APCI; it oc­curs both che­mi­cal­ly th­rough a car­ri­er gas and elec­tri­cal­ly th­rough a pul­se. Ho­we­ver, the main dif­fe­rence lies in the de­sign of the source. The elec­tri­cal pul­se is not trans­mit­ted by a co­ro­na need­le but by a plas­ma ring wi­t­hout di­rect cont­act to the ana­ly­te, re­sul­ting in a gent­ler io­niza­ti­on, hence the term „soft“ io­niza­ti­on. This mi­ni­mi­zes frag­men­ta­ti­on, re­fer­ring to mole­cu­les brea­king apart du­ring io­niza­ti­on, ma­king their sub­se­quent ana­ly­sis ea­sier. An­o­ther struc­tu­ral dif­fe­rence is that the SICRIT source can be di­rect­ly moun­ted at the in­let of the mass spec­tro­me­ter. As a re­sult, al­most all ana­lytes en­te­ring the source are also trans­fer­red into the mass spec­tro­me­ter, lea­ding to an in­creased sen­si­ti­vi­ty com­pared to APCI, whe­re a si­gni­fi­cant por­ti­on may be lost.

Com­pa­ring APCI and SICRIT in Ni­tros­ami­ne Ana­ly­sis

A re­cent com­pa­ri­son of APCI and SICRIT in­clu­ding iden­ti­cal li­quid chro­ma­to­gra­phic se­pa­ra­ti­on and op­ti­miza­ti­on for the hig­hest sen­si­ti­vi­ty shows: SICRIT is also ca­pa­ble to io­ni­ze Ni­tros­ami­nes and pro­vi­des on avera­ge a 247% hig­her peak area than APCI for the se­ven Ni­tros­ami­nes that have been in­ves­ti­ga­ted. SICRIT, due to the dif­fe­rent io­niza­ti­on me­cha­nisms, en­ables a broa­der co­vera­ge and is the­r­e­fo­re usual­ly also able to io­ni­ze the ac­ti­ve in­gre­di­ents of me­di­ca­ti­ons. Ac­cor­din­gly it pres­ents a via­ble al­ter­na­ti­ve for ni­tros­ami­ne ana­ly­sis with in­creased sen­si­ti­vi­ty.

Fur­ther in­for­ma­ti­on about the source and its ad­van­ta­ges can be found on our TECHNOLOGY page or th­rough per­so­nal CONTACT.