He­li­um Shorta­ge: Hy­dro­gen as an Al­ter­na­ti­ve Car­ri­er Gas with Be­ne­fits on Top

The use of he­li­um as a car­ri­er gas in gas chro­ma­to­gra­phy (GC) has been the go-to op­ti­on for many ye­ars. It has been a po­pu­lar choice due to its in­ert­ness, ex­cel­lent se­pa­ra­ti­on per­for­mance, low safe­ty risk, and fast ana­ly­sis times. Ho­we­ver, the world­wi­de re­ser­ves of he­li­um are li­mi­t­ed, and this has led to a shorta­ge, re­sul­ting in de­li­very is­sues and high pri­ces. The­r­e­fo­re, la­bo­ra­to­ries might be fa­cing se­ve­re down­ti­mes and, in some ca­ses, even in­sol­ven­cy. De­spi­te the­se di­s­ad­van­ta­ges, it re­mains the pre­fer­red car­ri­er gas. This ar­tic­le will de­mons­tra­te that hy­dro­gen as an al­ter­na­ti­ve to he­li­um even co­mes with ad­van­ta­ges like high se­pa­ra­ti­on ef­fi­ci­en­cy and re­du­ced ana­ly­sis time up to 40%.

Al­ter­na­ti­ves to He­li­um: Ni­tro­gen and Hy­dro­gen

Re­gar­ding the th­ree most com­mon­ly used car­ri­er ga­ses in GC, the Van-De­em­ter plot can pro­vi­de va­luable in­sights. This plot il­lus­tra­tes the height equi­va­lent of a theo­re­ti­cal pla­te (HETP) in re­la­ti­on to the li­ne­ar ve­lo­ci­ty of the gas. A smal­ler HETP va­lue in­di­ca­tes a hig­her se­pa­ra­ti­on ef­fi­ci­en­cy of the sys­tem.

Figure 1: Van-Deemter-Plot of different carrier gases (Shimadzu Corporation, Kyoto, Japan: https://www.shimadzu-webapp.eu/de/magazine/ausgabe-2022-2_de/heliumknappheit-alternative-tragergase)
Fi­gu­re 1: Van-De­em­ter-Plot of dif­fe­rent car­ri­er ga­ses (Shi­madzu Cor­po­ra­ti­on, Kyo­to, Ja­pan: https://www.shimadzu-webapp.eu/de/magazine/ausgabe-2022–2_de/heliumknappheit-alternative-tragergase)

Ni­tro­gen ex­hi­bits the lo­west HETP. Ho­we­ver, its se­pa­ra­ti­on ef­fi­ci­en­cy si­gni­fi­cant­ly de­cli­nes at hig­her or lower flow ve­lo­ci­ties than the op­ti­mum. Ni­tro­gen re­qui­res a lon­ger time to achie­ve sa­tis­fac­to­ry se­pa­ra­ti­on re­sults. Mo­reo­ver, its low dif­fu­si­on co­ef­fi­ci­ent li­mits its ap­pli­ca­bi­li­ty for time ef­fi­ci­ent rou­ti­ne ana­ly­sis.

In con­trast, he­li­um has a slight­ly hig­her mi­ni­mal HETP and at­ta­ins op­ti­mum se­pa­ra­ti­on ef­fi­ci­en­cy at a hig­her flow rate com­pared to ni­tro­gen. Tog­e­ther with its in­ert­ness, this cha­rac­te­ristic is of­ten why he­li­um is pre­fer­red in la­bo­ra­to­ry and rou­ti­ne set­tings.

Hy­dro­gen, on the other hand, is com­pa­ra­ble in terms of HETP with he­li­um, but its uni­que pro­per­ties make it an at­trac­ti­ve al­ter­na­ti­ve to he­li­um. With its low vis­co­si­ty and high dif­fu­si­on co­ef­fi­ci­ent, hy­dro­gen can achie­ve much hig­her li­ne­ar ve­lo­ci­ties main­tai­ning ex­cel­lent se­pa­ra­ti­on per­for­mance. Mo­reo­ver, an­o­ther ad­van­ta­ge of hy­dro­gen lies in its avai­la­bi­li­ty and the pos­si­bi­li­ty of on-site ge­ne­ra­ti­on using gas ge­ne­ra­tors, re­du­cing de­pen­dence on ex­ter­nal sup­pli­ers.

Ho­we­ver, the use of hy­dro­gen does pre­sent chal­lenges. First­ly, hy­dro­gen is high­ly re­ac­ti­ve and flamma­ble, de­man­ding spe­cia­li­zed safe­ty pre­cau­ti­ons in the la­bo­ra­to­ry. Se­cond­ly, the com­bi­na­ti­on of hy­dro­gen with GC-MS (mass spec­tro­me­ter) can be pro­ble­ma­tic, as ol­der GC-MS pumps may not be ca­pa­ble of hand­ling the high flow ra­tes re­qui­red for hy­dro­gen. Alt­hough new GC-MS sys­tem can ma­na­ge the­se hy­dro­gen flow ra­tes, the­re is a si­gni­fi­cant loss of sen­si­ti­vi­ty (ty­pi­cal­ly a fac­tor of 3–10) when using hy­dro­gen as a car­ri­er gas in GC-MS.

Be­ne­fits by Using Hy­dro­gen

The choice of car­ri­er gas in gas chro­ma­to­gra­phy de­pends on the spe­ci­fic ap­pli­ca­ti­on and ana­ly­sis re­qui­re­ments. Ho­we­ver, as men­tio­ned ear­lier, hy­dro­gen of­fers num­e­rous ad­van­ta­ges, in­clu­ding more than 40% re­du­ced ana­ly­sis time. Fur­ther­mo­re, the­re are straight­for­ward so­lu­ti­ons to ad­dress the chal­lenges men­tio­ned.

The risk of achie­ving an ex­plo­si­ve hy­dro­gen con­cen­tra­ti­on in a la­bo­ra­to­ry is al­most non-exis­tent due to stan­dard ven­ting sys­tems. Ad­di­tio­nal­ly, GC ven­dors such as Shi­madzu pro­vi­de mul­ti­ple safe­ty fea­tures in their in­stru­ments, such as a le­aka­ge de­tec­tion sen­sor in­si­de the GC that au­to­ma­ti­cal­ly shuts down hy­dro­gen sup­p­ly in the event of an an­oma­ly. When com­bi­ned with a hy­dro­gen ge­ne­ra­tor, the risk of rea­ching an ex­plo­si­ve con­cen­tra­ti­on of hy­dro­gen in the GC or la­bo­ra­to­ry is es­sen­ti­al­ly eli­mi­na­ted.

The big­gest draw­back of hy­dro­gen, a ge­ne­ral­ly re­du­ced sen­si­ti­vi­ty in clas­si­cal GC-MS sys­tems, can be over­co­me by swit­ching from GC-MS to LC-MS in­stru­ments. The pumps in LC-MS sys­tems are powerful en­ough to hand­le even much hig­her flow ra­tes of hy­dro­gen en­ab­ling a fur­ther spee­dup of the ana­ly­sis. The uni­que plug-and-play SICRIT® Ion Source en­ables the cou­pling of a GC with an LC-MS, harnes­sing the ad­van­ta­ges of both tech­ni­ques for your me­a­su­re­ments. Fur­ther­mo­re, when hy­dro­gen is used in com­bi­na­ti­on with the SICRIT® Ion Source and an LC-MS sys­tem, the­re is no loss, but even a gain in sen­si­ti­vi­ty.

Our re­cent App Note „GC-SICRIT®-MS: Fast and sen­si­ti­ve ana­ly­sis of 6 ni­tros­ami­nes by re­pla­cing he­li­um with hy­dro­gen as car­ri­er gas“ shows that hy­dro­gen can be used as a car­ri­er gas wi­t­hout a loss of sen­si­ti­vi­ty and ad­di­tio­nal­ly can speed up your ana­ly­sis time by al­most 50%.

Rethink your Lab

La­bo­ra­to­ries will need to find al­ter­na­ti­ves to he­li­um as its world­wi­de re­ser­ves are li­mi­t­ed, lea­ding to de­li­very is­sues and high pri­ces. Ad­di­tio­nal­ly, in the in­te­rest of sus­taina­bi­li­ty, it is cru­cial to rethink la­bo­ra­to­ry work­flows and ex­plo­re sui­ta­ble al­ter­na­ti­ves in GC. This is espe­ci­al­ly im­portant as the re­mai­ning sup­p­ly of he­li­um is also es­sen­ti­al for me­di­cal ap­pli­ca­ti­ons like MRI whe­re no via­ble sub­sti­tu­tes have been found thus far.

Are you re­a­dy to rethink your lab? Cont­act us for more in­for­ma­ti­on!