Ci a ion: Z onko a, M.; Adamek, M.;
Skow onko a, N.; Dlabaja, S.; Ma yas,
J.; Jasso, M.; Adamko a, A.; Mlcek, J.;
Salek, R.N.; Bu an, M. Compac
3D-P in ed Uni o Sepa a ion o
Simple Gas Mix u es Combined wi h
Chemi esis i e Senso s. Senso s 2024,
24, 4391. h ps://doi.o g/10.3390/
s24134391
Academic Edi o : Jesus Lozano
Recei ed: 17 May 2024
Re ised: 27 June 2024
Accep ed: 4 July 2024
Published: 6 July 2024
Copy igh : © 2024 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
senso s
A icle
Compac 3D-P in ed Uni o Sepa a ion o Simple Gas Mix u es
Combined wi h Chemi esis i e Senso s
Magdalena Z onko a 1, Ma in Adamek 2, Nela Skow onko a 1, S epan Dlabaja 2, Ji i Ma yas 3,
Mi osla Jasso 1, Anna Adamko a 1,* , Ji i Mlcek 1,* , Richa dos Nikolaos Salek 4and Ma in Bu an 5
1Depa men o Food Analysis and Chemis y, Facul y o Technology, Tomas Ba a Uni e si y in Zlin,
Va ecko a 5669, 760 01 Zlin, Czech Republic; [email p o ec ed] (M.Z.); [email p o ec ed] (N.S.);
[email p o ec ed] (M.J.)
2
Depa men o Au oma ion and Con ol Enginee ing, Facul y o Applied In o ma ics, Tomas Ba a Uni e si y
in Zlin, Nad S anemi 4511, 760 05 Zlin, Czech Republic; [email p o ec ed] (M.A.); [email p o ec ed] (S.D.)
3Cen e o Polyme Sys ems, Uni e si y Ins i u e, Tomas Ba a Uni e si y in Zlin, T ida Tomase Ba i 5678,
760 01 Zlin, Czech Republic; [email p o ec ed]
4Depa men o Food Technology, Facul y o Technology, Tomas Ba a Uni e si y in Zlin, Va ecko a 5669,
760 01 Zlin, Czech Republic; [email p o ec ed]
5Depa men o Mic oelec onics, Facul y o Elec ical Enginee ing and Communica ion, B no Uni e si y o
Technology, Technicka 3058/10, 616 00 B no, Czech Republic; ma in.bu an@ u b .cz
*Co espondence: [email p o ec ed] (A.A.); [email p o ec ed] (J.M.)
Abs ac : Inexpensi e chemi esis i e senso s a e o en insu icien ly selec i e as hey a e sensi i e o
mul iple componen s o he gas mix u e a he same ime. One solu ion would be o inse a de ice
in on o he senso ha sepa a es he measu ed gas mix u e and possibly isola es he unwan ed
componen s. This s udy ocused on he ab ica ion and cha ac e iza ion o a compac uni , which
was ab ica ed by 3D p in ing, o he sepa a ion and de ec ion o simple gas mix u es. The capilla y,
he basic pa o he compac uni , was 4.689 m long and had a diame e o 0.7 mm. The compac
uni also con ained a mixing chambe on he inle side and a measu ing chambe wi h a MiCS-6814
senso on he ou le side. Mix u es o e hanol and wa e a di e en concen a ions we e chosen
o cha ac e iza ion. The measu ed calib a ion cu e was ound o ha e a eliabili y o R
2
= 0.9941.
The s udy u he add essed he elemen s o en i onmen al iendliness o he ma e ials used and
hei sus ainabili y.
Keywo ds: chemi esis i e gas senso s; 3D p in ing; polylac ic acid; capilla y; sus ainabili y
1. In oduc ion
Al hough he e a e s ill challenges o o e come, 3D p in ing has become a a o ed
app oach cu en ly employed in he ield o gas senso analysis [
1
]. One o he bigges
ad an ages o di e se 3D p in ing echniques is hei modi iabili y based on po en ial
applica ions and uses; hus, 3D p in ing o gas senso s and a ious componen s connec ed
o hem pa es he way o u he esea ch while o e ing a wide ange o applicabili y [
2
,
3
].
As desc ibed by Zhou e al. [
2
], 3D p in ing can be employed o he manu ac u ing o
addi ional componen s including he cells, channels, ci cui s, elec odes, chambe s used
o di e se pu poses such as gas p ep ocessing o he imp o emen in senso s’ sensing
pe o mance [
2
]. The s uc u al componen s in ol ed in he cons uc ion o he inal de ice
can also be 3D p in ed, as e iewed by he a o emen ioned au ho s. They can unc ion no
only as cus omized holde s o comme cial senso s [
4
] bu also as p o ec ion o he senso s
om mois u e [5] o dus [6].
This s udy ocuses on he idea o using a simple capilla y ch oma og aphic column
made om biodeg adable ma e ials ia common 3D p in ing o he sepa a ion o a sam-
ple in o indi idual componen s be o e hei measu emen using low-cos chemi esis i e
senso s. The eason o doing his pe ains o he sensi i i y o hese senso s o se e al
Senso s 2024,24, 4391. h ps://doi.o g/10.3390/s24134391 h ps://www.mdpi.com/jou nal/senso s
Senso s 2024,24, 4391 2 o 14
gases simul aneously. Wi hou addi ional de ices o in o ma ion abou he sample, a single
senso (senso y elemen ) canno p o ide de ailed in o ma ion abou he unknown sample
being measu ed. I can only de e mine a esponse o he en i e g oup o gases speci ied
by he manu ac u e [
7
]. The e o e, he imp o emen s desc ibed u he in his a icle a e
aimed a modi ying he esolu ion capabili y o he sys em and de eloping a de ice ha
would no only be able o sepa a e and subsequen ly de ec componen s o simple gas
mix u es, bu also possibly semi-quan i y di e en analy es. The aim was o inco po a e
no only he capilla y column bu also o he pa s o he measu ing chain, including he
mixing chambe and he de ec o ’s measu ing chambe , in o one compac uni . This is one
o he key aspec s cha ac e izing he no el y o his s udy.
Wi h bo h he a o emen ioned objec i es in mind, g ea emphasis was also placed
on inding a sus ainable solu ion, i.e., all he chosen componen s o he manu ac u ed
de ice we e ei he biodeg adable o ecyclable. The e o e, polylac ic acid (PLA) was cho-
sen o he 3D p in ing o he capilla y and o he componen s, such as he holde s and
he mixing chambe . In he global sea ch o sus ainable ma e ials, PLA has eme ged
as a sui able al e na i e o o he polyme s in selec ed applica ions, mainly because o
i s biodeg adabili y, a ailabili y, and con enien mechanical and he mal p ope ies [
8
].
Fu he mo e, lac ic acid (LA) monome s can be ob ained om enewable sou ces such as
po a o, suga cane o co n by mic obial e men a ion, and hen PLA can be p oduced using
a simple, cos - and ene gy-e icien syn hesis [
9
]. E en hough PLA syn hesis is conside ed
ene gy-e icien , he mos demanding p ocess in e ms o CO
2
eleasing in o he a mosphe e
is he ac ual con e sion o he ag icul u al p oduc s o PLA. By he op imiza ion o he
syn hesis eac ions, PLA could also become a low-ca bon ma e ial [
10
]. Cu en ly, he e
a e se e al PLA deg ada ion s a egies, such as land illing, compos ing, anae obic diges-
ion, incine a ion o he mal ea men , and chemical and mechanical ecycling [
11
]. The
en i onmen al oo p in o PLA’s deg ada ion can be minimized by chemical (molecula )
ecycling—depolyme iza ion—and he epea ed use o LA monome s o syn hesize new
ma e ial [
12
]. Rega ding ene gy consump ion, his app oach is p e e able o he epea ed
p oduc ion o LA om s a chy ag icul u al was e [
13
]. Resea che s ha e also sugges ed he
possibili y o he di ec ep ocessing o 3D-p in ed PLA p oduc s back in o he ilamen s
used o 3D p in ing wi hou signi ican deg ada ion o he ma e ial [14].
In addi ion o he a o emen ioned componen s made om PLA, o he ma e ials used
o he cons uc ion o he de ice included plas ic, ca dboa d, and me al, which a e ully
ecyclable o ep ocessable in he Czech Republic. Plas ic sy inges se ed as a dispensing
de ice o he ca ie gas, while me al pa s we e employed o ensu e he mechanical
unc ionali y o he de ice, and all he componen s we e subsequen ly moun ed on a
ca dboa d box, which p o ided he basic s uc u al backbone o he whole se up.
The only non-biodeg adable o non- ecyclable pa s used we e he elec onic compo-
nen s such as elec ical cables o gas senso s, which a e eusable and can ei he be emo ed
and used in o he expe imen al con igu a ions o eplaced, i necessa y, and he emaining
pa s o he de ice can be used un il any mechanical de ec s occu . In gene al, he ope a ing
li e ime o he senso s a ies acco ding o he equency o use o he gas concen a ions
ha a e applied o he senso s, bu i is also based on hei s o age and usage condi ions
such as empe a u e o humidi y [15–17].
2. Ma e ials and Me hods
The p inciple o he en i e de ice is based on he idea o u ilizing a simple capilla y
ch oma og aphic column manu ac u ed by 3D p in ing o he sepa a ion o samples in o
componen s p io o hei measu emen using inexpensi e chemi esis i e senso s.
The sample is dispensed om a sy inge in o a s eam o clean ai lowing h ough he
capilla y column. Wi hin his column, he mix u e is sepa a ed in o indi idual componen s
ha a i e a he de ec o (chemi esis i e senso ) a di e en imes. The de ec o is housed
in a closed chambe a he end o he column, and upon he a i al o molecula componen s
om he sample, i eac s by educing he elec ical esis ance o he sensi i e laye . This
Senso s 2024,24, 4391 3 o 14
dec ease in elec ical esis ance would be eco ded as a dec ease in elec ical ol age a
he speci ic sensi i e elemen and hen con e ed in o an equi alen digi al alue by an
A/D con e e , which would hen be eco ded and u he p ocessed by a mic ocon olle .
F om he alues ob ained om he A/D con e e , i was possible o de e mine he a io
o he esis ance o he sensi i e laye du ing analy e de ec ion o he esis ance when he
sensi i e laye is placed in clean ai . F om his a io, he concen a ion o he analy e could
be calcula ed. Howe e , his applies only unde he condi ion ha he moni o ed gas is
known and ha he e a e no o he gases in he obse ed gas mix u e o which he senso
eac s. These condi ions canno be me by unknown analy es. The e o e, a sepa a ion
capilla y ch oma og aphic column was used in he s udy o sample p ocessing.
2.1. Design and De elopmen o he Capilla y and he De ice
The measu ing de ice consis s o se e al in e connec ed blocks. The co e block o he
measu ing de ice is a compac uni made by 3D p in ing echnology, in eg a ing a capilla y
o he sepa a ion o he componen s o he mix u e, a mixing chambe o mixing he gas
sample wi h he ca ie gas, and a measu ing chambe equipped wi h a chemi esis i e
senso . The appa a us u he includes a sample dispensing de ice and a ca ie gas
dispensing de ice wi h a mo o and a gea box. E e y hing is con olled and scanned by a
con ol and measu emen uni , which is con olled by an ESP-32 mic ocon olle .
The main pa is a compac block wi h a capilla y, he design o which was based on
ea lie esea ch desc ibed in Adámek e al. [
7
]. As pa o he de elopmen , se e al a ious
ypes o hese blocks had been designed and p in ed (Figu e 1) du ing he s udy. The g ey
block (1) ep esen s he o iginal p o o ype om he p e ious s udy by Adámek e al. [
7
],
while he g een (2) and o ange (3) blocks a e p o o ypes o he imp o ed ype. The whi e
block (4) is u ilized wi hin his pape .
Senso s 2024, 24, x FOR PEER REVIEW 3 o 14
componen s ha a i e a he de ec o (chemi esis i e senso ) a diffe en imes. The
de ec o is housed in a closed chambe a he end o he column, and upon he a i al o
molecula componen s om he sample, i eac s by educing he elec ical esis ance o
he sensi i e laye . This dec ease in elec ical esis ance would be eco ded as a dec ease
in elec ical ol age a he speci ic sensi i e elemen and hen con e ed in o an equi alen
digi al alue by an A/D con e e , which would hen be eco ded and u he p ocessed
by a mic ocon olle . F om he alues ob ained om he A/D con e e , i was possible o
de e mine he a io o he esis ance o he sensi i e laye du ing analy e de ec ion o he
esis ance when he sensi i e laye is placed in clean ai . F om his a io, he concen a ion
o he analy e could be calcula ed. Howe e , his applies only unde he condi ion ha he
moni o ed gas is known and ha he e a e no o he gases in he obse ed gas mix u e o
which he senso eac s. These condi ions canno be me by unknown analy es. The e o e,
a sepa a ion capilla y ch oma og aphic column was used in he s udy o sample
p ocessing.
2.1. Design and De elopmen o he Capilla y and he De ice
The measu ing de ice consis s o se e al in e connec ed blocks. The co e block o he
measu ing de ice is a compac uni made by 3D p in ing echnology, in eg a ing a
capilla y o he sepa a ion o he componen s o he mix u e, a mixing chambe o
mixing he gas sample wi h he ca ie gas, and a measu ing chambe equipped wi h a
chemi esis i e senso . The appa a us u he includes a sample dispensing de ice and a
ca ie gas dispensing de ice wi h a mo o and a gea box. E e y hing is con olled and
scanned by a con ol and measu emen uni , which is con olled by an ESP-32
mic ocon olle .
The main pa is a compac block wi h a capilla y, he design o which was based on
ea lie esea ch desc ibed in Adámek e al. [7]. As pa o he de elopmen , se e al a ious
ypes o hese blocks had been designed and p in ed (Figu e 1) du ing he s udy. The g ey
block (1) ep esen s he o iginal p o o ype om he p e ious s udy by Adámek e al. [7],
while he g een (2) and o ange (3) blocks a e p o o ypes o he imp o ed ype. The whi e
block (4) is u ilized wi hin his pape .
Emphasis was placed on he app op ia e in eg a ion o he mixing and measu ing
chambe s in o a compac uni wi h he capilla y (Figu es 2 and 3). The diame e o he
capilla y was educed o d = 0.7 mm. O e all, he capilla y diame e was educed by
nea ly 42% compa ed o he model p esen ed in he p e ious pape [7].
Figu e 1. Diffe en capilla y blocks wi h mixing and measu ing chambe du ing de elopmen . The
g ey block (1) is he o iginal p o o ype om he p e ious s udy by Adámek e al. [7], he g een (2)
and o ange (3) blocks a e imp o ed p o o ypes, and he whi e block (4) is used wi hin his a icle.
Figu e 1. Di e en capilla y blocks wi h mixing and measu ing chambe du ing de elopmen . The
g ey block (1) is he o iginal p o o ype om he p e ious s udy by Adámek e al. [
7
], he g een (2)
and o ange (3) blocks a e imp o ed p o o ypes, and he whi e block (4) is used wi hin his a icle.
Emphasis was placed on he app op ia e in eg a ion o he mixing and measu ing
chambe s in o a compac uni wi h he capilla y (Figu es 2and 3). The diame e o he
capilla y was educed o d = 0.7 mm. O e all, he capilla y diame e was educed by nea ly
42% compa ed o he model p esen ed in he p e ious pape [7].
Senso s 2024,24, 4391 4 o 14
Senso s 2024, 24, x FOR PEER REVIEW 4 o 14
The wo- ie capilla y’s leng h was 4.689 m, which is compa able o he p e iously
desc ibed h ee- ie capilla y wi h a leng h o 4.692 m. I s design ea u ed wo mi o ed
helices in e connec ed by a con inuous cu e, ensu ing ha he e we e no excessi e
ac u es ha could hinde he p in ing p ocess. The capilla y was success ully p in ed
using a comme cially a ailable Bambu Lab PS1 p in e (Bambu Lab, Shenzhen, China)
equipped wi h a s anda d 0.4 mm nozzle. Figu e 3 illus a es he ex e nal dimensions o
he compac block and he squa e measu ing chambe .
Figu e 2. In e nal a angemen o he compac block comp ising o wo mi o ed helices.
Figu e 3. Ex e nal dimensions o he compac block and squa e measu ing chambe .
Sample and ca ie ai dispense s we e also posi ioned on he ecyclable pape
subs a e (Figu e 4). The p inciple and basic use we e he same as he sys em desc ibed in
he p e ious a icle [7]. The 2 mL sy inge holde s o he sample and he wo 150 mL
sy inges o he ca ie gas we e new (pu e ai was used; he ull sy inge olume is 165
mL). Bo h he ca ie gas and sample we e d awn in o sy inges by he equipmen ope a o .
No mal oom ai se ed as he ca ie gas, il e ed h ough a NY 0.22 µm sy inge il e
(Ch omse is s. .o., P ague, Czech Republic). Immedia ely be o e gas measu emen , a
sample was d awn in o he sy inge h ough he needle, posi ioning he ip jus abo e o
ligh ly ouching he liquid su ace, ensu ing he needle lumen mou h was no subme ged
Figu e 2. In e nal a angemen o he compac block comp ising o wo mi o ed helices.
Senso s 2024, 24, x FOR PEER REVIEW 4 o 14
The wo- ie capilla y’s leng h was 4.689 m, which is compa able o he p e iously
desc ibed h ee- ie capilla y wi h a leng h o 4.692 m. I s design ea u ed wo mi o ed
helices in e connec ed by a con inuous cu e, ensu ing ha he e we e no excessi e
ac u es ha could hinde he p in ing p ocess. The capilla y was success ully p in ed
using a comme cially a ailable Bambu Lab PS1 p in e (Bambu Lab, Shenzhen, China)
equipped wi h a s anda d 0.4 mm nozzle. Figu e 3 illus a es he ex e nal dimensions o
he compac block and he squa e measu ing chambe .
Figu e 2. In e nal a angemen o he compac block comp ising o wo mi o ed helices.
Figu e 3. Ex e nal dimensions o he compac block and squa e measu ing chambe .
Sample and ca ie ai dispense s we e also posi ioned on he ecyclable pape
subs a e (Figu e 4). The p inciple and basic use we e he same as he sys em desc ibed in
he p e ious a icle [7]. The 2 mL sy inge holde s o he sample and he wo 150 mL
sy inges o he ca ie gas we e new (pu e ai was used; he ull sy inge olume is 165
mL). Bo h he ca ie gas and sample we e d awn in o sy inges by he equipmen ope a o .
No mal oom ai se ed as he ca ie gas, il e ed h ough a NY 0.22 µm sy inge il e
(Ch omse is s. .o., P ague, Czech Republic). Immedia ely be o e gas measu emen , a
sample was d awn in o he sy inge h ough he needle, posi ioning he ip jus abo e o
ligh ly ouching he liquid su ace, ensu ing he needle lumen mou h was no subme ged
Figu e 3. Ex e nal dimensions o he compac block and squa e measu ing chambe .
The wo- ie capilla y’s leng h was 4.689 m, which is compa able o he p e iously
desc ibed h ee- ie capilla y wi h a leng h o 4.692 m. I s design ea u ed wo mi o ed
helices in e connec ed by a con inuous cu e, ensu ing ha he e we e no excessi e ac-
u es ha could hinde he p in ing p ocess. The capilla y was success ully p in ed using a
comme cially a ailable Bambu Lab PS1 p in e (Bambu Lab, Shenzhen, China) equipped
wi h a s anda d 0.4 mm nozzle. Figu e 3illus a es he ex e nal dimensions o he compac
block and he squa e measu ing chambe .
Sample and ca ie ai dispense s we e also posi ioned on he ecyclable pape sub-
s a e (Figu e 4). The p inciple and basic use we e he same as he sys em desc ibed in
he p e ious a icle [
7
]. The 2 mL sy inge holde s o he sample and he wo 150 mL
sy inges o he ca ie gas we e new (pu e ai was used; he ull sy inge olume is 165 mL).
Bo h he ca ie gas and sample we e d awn in o sy inges by he equipmen ope a o .
No mal oom ai se ed as he ca ie gas, il e ed h ough a NY 0.22
µ
m sy inge il e
(Ch omse is s. .o., P ague, Czech Republic). Immedia ely be o e gas measu emen , a
sample was d awn in o he sy inge h ough he needle, posi ioning he ip jus abo e o
ligh ly ouching he liquid su ace, ensu ing he needle lumen mou h was no subme ged in
he liquid. The sy inge con aining he sample was hen inse ed in o he measu ing sys em,
Senso s 2024,24, 4391 5 o 14
and he measu emen commenced. The ca ie gas was expelled om he sy inges by a
pushing mechanism wi h a newly designed cons uc ion and a gea box. This allowed he
pushing mechanism o mo e o wa d and backwa d, and i was adap ed o wo k in slow
and as modes du ing eposi ioning. The mode change was possible when he ope a o
mechanically adjus ed he posi ion o one o he gea wheels. The new sy inge holde s and
new pushing mechanism ensu ed be e s abili y o he sy inge posi ion, highe s abili y
o he ou pu olume a e, and educed isk o he sy inge pis on s alling o c ossing. The
basic pa s o he sys em we e 3D p in ed om PLA ma e ial, inc easing he po abili y o
he sys em (weigh educ ion) and inc easing i s ecyclabili y.
Senso s 2024, 24, x FOR PEER REVIEW 5 o 14
in he liquid. The sy inge con aining he sample was hen inse ed in o he measu ing
sys em, and he measu emen commenced. The ca ie gas was expelled om he sy inges
by a pushing mechanism wi h a newly designed cons uc ion and a gea box. This allowed
he pushing mechanism o mo e o wa d and backwa d, and i was adap ed o wo k in
slow and as modes du ing eposi ioning. The mode change was possible when he
ope a o mechanically adjus ed he posi ion o one o he gea wheels. The new sy inge
holde s and new pushing mechanism ensu ed be e s abili y o he sy inge posi ion,
highe s abili y o he ou pu olume a e, and educed isk o he sy inge pis on s alling
o c ossing. The basic pa s o he sys em we e 3D p in ed om PLA ma e ial, inc easing
he po abili y o he sys em (weigh educ ion) and inc easing i s ecyclabili y.
Figu e 4. Comple e eal a angemen o he expe imen al measu ing sys em (1—sy inges o he
ca ie gas, 2— wo-speed gea box, 3—powe supply o mo o s, 4—sample dispense , 5—
capilla y block, 6—measu ing chambe , 7—con ol boa d wi h ESP-32 mic ocon olle , 8—
compu e o da a acquisi ion, 9—mo o d i e ).
The las pa , moun ed on he subs a e, is he con ol and measu emen uni (Figu e
5). The cen al pa o his sec ion is he ESP-WROM-32 mic ocon olle (Esp essi
Sys ems, Shanghai, China) on he boa d Wemos LoLin 32 ESP-WROOM-32, con olling
he use in e ace (display, pushbu on), ope a ing he H-b idges o mo o con ol based
on he L298N ci cui , sensing signals om he MiCS-6814 senso (SGX Senso ech,
Neuchâ el, Swi ze land) and communica ing wi h a PC-class compu e using a common
USB/COM in e ace wi h a communica ion speed o 115,200 Bd.
The MiCS-6814 is a compac MOS senso con aining h ee ully independen sensing
elemen s (RED, OX and NH3) on one package [18]. The mic ocon olle is also connec ed
o he RTC DS 3231 eal- ime clock and SD memo y ca d. This solu ion allowed he de ice
o wo k wi hou a connec ed compu e and compu e communica ion in as uc u e and
allowed o easie da a ans e and backup. In addi ion o highe p ocessing powe ,
g ea e communica ion capabili ies, and he abili y o s o e mo e da a, one o he main
ad an ages o his mic ocon olle was he highe esolu ion o he A/D con e e (12 b
ins ead o he o iginal 10 b). This allowed o a u he inc ease in accu acy o he sensed
signal.
Figu e 4. Comple e eal a angemen o he expe imen al measu ing sys em (1—sy inges o he
ca ie gas, 2— wo-speed gea box, 3—powe supply o mo o s, 4—sample dispense , 5—capilla y
block, 6—measu ing chambe , 7—con ol boa d wi h ESP-32 mic ocon olle , 8—compu e o da a
acquisi ion, 9—mo o d i e ).
The las pa , moun ed on he subs a e, is he con ol and measu emen uni (Figu e 5).
The cen al pa o his sec ion is he ESP-WROM-32 mic ocon olle (Esp essi Sys ems,
Shanghai, China) on he boa d Wemos LoLin 32 ESP-WROOM-32, con olling he use
in e ace (display, pushbu on), ope a ing he H-b idges o mo o con ol based on he
L298N ci cui , sensing signals om he MiCS-6814 senso (SGX Senso ech, Neuchâ el,
Swi ze land) and communica ing wi h a PC-class compu e using a common USB/COM
in e ace wi h a communica ion speed o 115,200 Bd.
The MiCS-6814 is a compac MOS senso con aining h ee ully independen sensing
elemen s (RED, OX and NH3) on one package [
18
]. The mic ocon olle is also connec ed
o he RTC DS 3231 eal- ime clock and SD memo y ca d. This solu ion allowed he de ice
o wo k wi hou a connec ed compu e and compu e communica ion in as uc u e and
allowed o easie da a ans e and backup. In addi ion o highe p ocessing powe , g ea e
communica ion capabili ies, and he abili y o s o e mo e da a, one o he main ad an ages
o his mic ocon olle was he highe esolu ion o he A/D con e e (12 b ins ead o he
o iginal 10 b). This allowed o a u he inc ease in accu acy o he sensed signal.
Senso s 2024,24, 4391 6 o 14
Senso s 2024, 24, x FOR PEER REVIEW 6 o 14
Figu e 5. Expe imen al measu ing sys em—Connec ion o main componen s.
2.2. Measu emen Me hodology
The measu emen me hodology was simila o he one desc ibed in [7] and modi ied
as ollows. A e s a ing he measu emen , he mixing chambe , he capilla y, and he
measu ing chambe unde go cleaning wi h he ca ie gas (clean ai ) o a du a ion o =
30 s. Subsequen ly, he sample is injec ed in o he measu ing chambe , and he ca ie gas
is g adually displaced om he sy inges a a cons an a e. The measu emen is e mina ed
once he ca ie gas is ully expelled om he sy inges.
Upon comple ion o he sample measu emen , he sys em is lushed wi h 330 mL o
ca ie gas ( he measu emen is pe o med wi hou he injec ion o he sample). The a e
o ca ie gas displacemen and consequen ly he o al measu emen ime a e con olled
by he mo o ol age.
Fo ins ance, wi h a slow gea box speed and a ol age o U = 12 V a he mo o , along
wi h a ull ca ie gas sy inge olume se , he o al gas displacemen ime amoun s o =
830 s, achie ing a gas displacemen a e o Q = 0.397 mL/s. When u ilizing a as gea box
speed and a ol age o U = 6 V on he mo o , alongside a ull ca ie gas sy inge olume
se , he o al gas displacemen ime is educed o = 240 s, esul ing in a highe gas
displacemen a e o Q = 1375 mL/s. This con igu a ion was employed o he
measu emen s. In he inal pa , he pis on was able o push agains he sy inge wall,
he e o e only he i s 235 samples we e conside ed in he p ocessing.
No ably, 96% e hanol (Ing. Pe Š ec-PENTA s. .o., P ague, Czech Republic, CAS: 64-
17-5, EINECS: 200-578-6) was used as a base ma e ial o p epa ing he measu ing
solu ions. F om he s ock solu ion, solu ions o 6%, 12%, 24%, and 48% we e mixed by
sequen ial dilu ion. Demine alized wa e was used o he dilu ion. Sampling om he
sample bo le was pe o med using a needle sy inge, wi h he needle posi ioned jus abo e
he sample le el.
2.3. E alua ion Me hodology
The e alua ion me hodology mi o s he one ou lined in he pape by Adámek e al.
[7], wi h a sligh modi ica ion conce ning he inc ease in he maximum numbe o ou pu
Figu e 5. Expe imen al measu ing sys em—Connec ion o main componen s.
2.2. Measu emen Me hodology
The measu emen me hodology was simila o he one desc ibed in [
7
] and modi ied
as ollows. A e s a ing he measu emen , he mixing chambe , he capilla y, and he
measu ing chambe unde go cleaning wi h he ca ie gas (clean ai ) o a du a ion o
= 30 s. Subsequen ly, he sample is injec ed in o he measu ing chambe , and he ca ie
gas is g adually displaced om he sy inges a a cons an a e. The measu emen is
e mina ed once he ca ie gas is ully expelled om he sy inges.
Upon comple ion o he sample measu emen , he sys em is lushed wi h 330 mL o
ca ie gas ( he measu emen is pe o med wi hou he injec ion o he sample). The a e o
ca ie gas displacemen and consequen ly he o al measu emen ime a e con olled by
he mo o ol age.
Fo ins ance, wi h a slow gea box speed and a ol age o U = 12 V a he mo o ,
along wi h a ull ca ie gas sy inge olume se , he o al gas displacemen ime amoun s o
= 830 s, achie ing a gas displacemen a e o Q = 0.397 mL/s. When u ilizing a as gea box
speed and a ol age o U = 6 V on he mo o , alongside a ull ca ie gas sy inge olume se ,
he o al gas displacemen ime is educed o = 240 s, esul ing in a highe gas displacemen
a e o Q = 1375 mL/s. This con igu a ion was employed o he measu emen s. In he
inal pa , he pis on was able o push agains he sy inge wall, he e o e only he i s
235 samples we e conside ed in he p ocessing.
No ably, 96% e hanol (Ing. Pe Š ec-PENTA s. .o., P ague, Czech Republic, CAS:
64-17-5, EINECS: 200-578-6) was used as a base ma e ial o p epa ing he measu ing
solu ions. F om he s ock solu ion, solu ions o 6%, 12%, 24%, and 48% we e mixed by
sequen ial dilu ion. Demine alized wa e was used o he dilu ion. Sampling om he
sample bo le was pe o med using a needle sy inge, wi h he needle posi ioned jus abo e
he sample le el.
2.3. E alua ion Me hodology
The e alua ion me hodology mi o s he one ou lined in he pape by Adámek e al. [
7
],
wi h a sligh modi ica ion conce ning he inc ease in he maximum numbe o ou pu signal
le els om he A/D con e e . Speci ically, he ange ex ended om 0 o 4095 ins ead o
Senso s 2024,24, 4391 7 o 14
he p e ious ange om 0 o 1023, accommoda ing smalle inpu ol age a ia ions wi hin
he ange o 0 o 3.3 V as opposed o 0 o 5 V. No ably, hese adjus men s we e compa ed
ollowing no maliza ion, ela i e o he ini ia ion o he measu emen a ime = 30 s.
Fo da a p ocessing and g aphical ep esen a ion o he measu emen ou comes,
Mic oso Excel 2019 (Mic oso Co po a ion, Redmond, WA, USA) was used.
3. Resul s and Discussion
3.1. Rep oducibili y o he Measu emen s
Pu e ai was measu ed as a i s se o samples, se ing as a ca ie gas. These esul s
we e used o de e mine he backg ound alues o he unsampled measu emen s and
u he used o s anda diza ion in o de o elimina e he backg ound e ec caused by he
ca ie gas. Successi e measu emen s o e hanol samples o 6%, 12%, 24%, 48%, and 96%
concen a ion we e hen aken.
Since he OX elemen in he combined senso MiCS-6814 eac s mainly o NO
2
and NO,
and i does no espond o e hanol, he esul s om his senso will only be b ie ly desc ibed.
Emphasis will ins ead be placed on he RED elemen , which is he mos eac i e pa o
MiCS-6814 o e hanol. The o iginal esponses om he OX and NH
3
elemen s a e shown in
Figu e 6. While changes in he NH
3
elemen ’s dependence on e hanol concen a ion can be
obse ed, he pos -p ocessed signals ha e p o en unsui able o mo e p ecise analysis.
Senso s 2024, 24, x FOR PEER REVIEW 7 o 14
signal le els om he A/D con e e . Speci ically, he ange ex ended om 0 o 4095
ins ead o he p e ious ange om 0 o 1023, accommoda ing smalle inpu ol age
a ia ions wi hin he ange o 0 o 3.3 V as opposed o 0 o 5 V. No ably, hese adjus men s
we e compa ed ollowing no maliza ion, ela i e o he ini ia ion o he measu emen a
ime = 30 s.
Fo da a p ocessing and g aphical ep esen a ion o he measu emen ou comes,
Mic oso Excel 2019 (Mic oso Co po a ion, Redmond, WA, USA) was used.
3. Resul s and Discussion
3.1. Rep oducibili y o he Measu emen s
Pu e ai was measu ed as a i s se o samples, se ing as a ca ie gas. These esul s
we e used o de e mine he backg ound alues o he unsampled measu emen s and
u he used o s anda diza ion in o de o elimina e he backg ound effec caused by he
ca ie gas. Successi e measu emen s o e hanol samples o 6%, 12%, 24%, 48%, and 96%
concen a ion we e hen aken.
(a) The OX elemen . (b) The NH3 elemen .
Figu e 6. O iginal ou pu ime esponse on he ou pu o he A/D con e e connec ed o he
indi idual elemen s o he combined senso MiCS-6814: (a) The OX elemen ; (b) The NH3 elemen .
The RED elemen exhibi ed he s onges and mos consis en esponses o he
samples wi h a ying e hanol concen a ions. The esponses o each sample wi h diffe en
e hanol concen a ions a e depic ed in Figu e 7. The Y-axis scale (d [-]) emains consis en
ac oss all he plo s o acili a e he compa ison o measu emen ep oducibili y. Apa
om he sample wi h 96% e hanol, he esponse cu es a e ela i ely close o each o he ,
indica ing good ep oducibili y. This is u he suppo ed by he maximum alues o
s anda d de ia ion calcula ed om he measu ed alues o he h ee cha ac e is ics a he
speci ied e hanol concen a ion and ime, as shown in Table 1.
Table 1. Maximum s anda d de ia ion and maximum diffe ence alues o each cha ac e is ic se
ac oss diffe en e hanol concen a ions in he sample.
E hanol Concen a ion 0% 6% 12% 24% 48% 96%
Maximum SD 1.73 2.52 2.08 1.15 2.52 8.62
Maximum dmax − dmin 3 5 4 2 5 17
2070
2090
2110
2130
0 50 100 150 200 250
d [-]
T [s]
Ai Ai Ai
e hanol 6 % e hanol 6 % e hanol 6 %
e hanol 12 % e hanol 12 % e hanol 12 %
e hanol 24 % e hanol 24 % e hanol 24 %
e hanol 48% e hanol 48% e hanol 48%
e hanol 96 % e hanol 96 % e hanol 96 %
1820
1830
1840
1850
1860
1870
1880
1890
0 50 100 150 200 250
d [-]
T [s]
Ai Ai Ai
e hanol 6 % e hanol 6 % e hanol 6 %
e hanol 12 % e hanol 12 % e hanol 12 %
e hanol 24 % e hanol 24 % e hanol 24 %
e hanol 48% e hanol 48% e hanol 48%
e hanol 96 % e hanol 96 % e hanol 96 %
Figu e 6. O iginal ou pu ime esponse on he ou pu o he A/D con e e connec ed o he
indi idual elemen s o he combined senso MiCS-6814: (a) The OX elemen ; (b) The NH3elemen .
The RED elemen exhibi ed he s onges and mos consis en esponses o he samples
wi h a ying e hanol concen a ions. The esponses o each sample wi h di e en e hanol
concen a ions a e depic ed in Figu e 7. The Y-axis scale (d [-]) emains consis en ac oss
all he plo s o acili a e he compa ison o measu emen ep oducibili y. Apa om he
sample wi h 96% e hanol, he esponse cu es a e ela i ely close o each o he , indica ing
good ep oducibili y. This is u he suppo ed by he maximum alues o s anda d
de ia ion calcula ed om he measu ed alues o he h ee cha ac e is ics a he speci ied
e hanol concen a ion and ime, as shown in Table 1.
Senso s 2024,24, 4391 8 o 14
Senso s 2024, 24, x FOR PEER REVIEW 8 o 14
(a) The clean ai sample. (b) E hanol 6%.
(c) E hanol 12%. (d) E hanol 24%.
(e) E hanol 48%. ( ) E hanol 96%.
Figu e 7. O iginal ou pu ime esponse a he A/D con e e ou pu (d [-]) linked o he RED
elemen o he combined senso MiCS-6814 a a ious e hanol concen a ions. The Y-axis scale (d [-
]) is consis en ac oss all plo s o acili a e compa ison o measu ed alues’ ep oducibili y.
Table 1 also indica es he maximum diffe ence be ween hese cha ac e is ics a a
consis en e hanol concen a ion and ime. I shows ha a alue o 3 s eps pe A/D
con e e (app oxima ely 2.5 mV) ep esen s he maximum diffe ence be ween he
measu ed cu es o ai , which can be conside ed as he maximum noise le el. This alue
is compa able o he alues obse ed o he o he measu ed se s o cha ac e is ics ac oss
diffe en e hanol concen a ions (2–5 s eps). The sampling s anda d de ia ion is less han
1790
1800
1810
1820
1830
1840
1850
1860
1870
1880
0 50 100 150 200 250
d [-]
T [s]
Ai Ai Ai
1790
1800
1810
1820
1830
1840
1850
1860
1870
1880
0 50 100 150 200 250
d [-]
T [s]
e hanol 6 % e hanol 6 % e hanol 6 %
1790
1800
1810
1820
1830
1840
1850
1860
1870
1880
0 50 100 150 200 250
d [-]
T [s]
e hanol 12 % e hanol 12 % e hanol 12 %
1790
1800
1810
1820
1830
1840
1850
1860
1870
1880
0 50 100 150 200 250
d [-]
T [s]
e hanol 24 % e hanol 24 % e hanol 24 %
1790
1800
1810
1820
1830
1840
1850
1860
1870
1880
0 50 100 150 200 250
d [-]
T [s]
e hanol 48% e hanol 48% e hanol 48%
1790
1800
1810
1820
1830
1840
1850
1860
1870
1880
0 50 100 150 200 250
d [-]
T [s]
e hanol 96 % e hanol 96 % e hanol 96 %
Figu e 7. O iginal ou pu ime esponse a he A/D con e e ou pu (d [-]) linked o he RED
elemen o he combined senso MiCS-6814 a a ious e hanol concen a ions. The Y-axis scale (d [-])
is consis en ac oss all plo s o acili a e compa ison o measu ed alues’ ep oducibili y.
Table 1. Maximum s anda d de ia ion and maximum di e ence alues o each cha ac e is ic se
ac oss di e en e hanol concen a ions in he sample.
E hanol Concen a ion 0% 6% 12% 24% 48% 96%
Maximum SD 1.73 2.52 2.08 1.15 2.52 8.62
Maximum dmax −dmin 3 5 4 2 5 17
Senso s 2024,24, 4391 9 o 14
Table 1also indica es he maximum di e ence be ween hese cha ac e is ics a a con-
sis en e hanol concen a ion and ime. I shows ha a alue o 3 s eps pe A/D con e e
(app oxima ely 2.5 mV) ep esen s he maximum di e ence be ween he measu ed cu es
o ai , which can be conside ed as he maximum noise le el. This alue is compa able o
he alues obse ed o he o he measu ed se s o cha ac e is ics ac oss di e en e hanol
concen a ions (2–5 s eps). The sampling s anda d de ia ion is less han 3 A/D con e e
s eps o all concen a ions (lowe han he di e ence be ween he measu ed cu es o pu e
ai ). The e o e, he ep oducibili y o he measu emen s can be conside ed adequa e. The
excep ion is obse ed wi h 96% e hanol, whe e a maximum sampling s anda d de ia ion
o 8.62 s eps is de e mined.
3.2. S anda diza ion o Da a
The nex s ep in da a p ocessing in ol ed a e aging each se o cu es o e e y
e hanol concen a ion in o a single cu e ep esen ing he a e age alue. Subsequen ly,
hese a e age cu es we e smoo hed using a mean mo ing a e age (m = 11) and hen s an-
da dized acco ding o [
7
]. A la ge mo ing a e age ange esul ed in smoo he cu es and
educed noise. Howe e , smoo hing in his manne inc eased he likelihood o obscu ing
small ye signi ican changes on he cu e ha may be conside ed impo an . The esul ing
g aphs o he indi idual senso s a e displayed in Figu e 8.
Senso s 2024, 24, x FOR PEER REVIEW 9 o 14
3 A/D con e e s eps o all concen a ions (lowe han he diffe ence be ween he
measu ed cu es o pu e ai ). The e o e, he ep oducibili y o he measu emen s can be
conside ed adequa e. The excep ion is obse ed wi h 96% e hanol, whe e a maximum
sampling s anda d de ia ion o 8.62 s eps is de e mined.
3.2. S anda diza ion o Da a
The nex s ep in da a p ocessing in ol ed a e aging each se o cu es o e e y
e hanol concen a ion in o a single cu e ep esen ing he a e age alue. Subsequen ly,
hese a e age cu es we e smoo hed using a mean mo ing a e age (m = 11) and hen
s anda dized acco ding o [7]. A la ge mo ing a e age ange esul ed in smoo he cu es
and educed noise. Howe e , smoo hing in his manne inc eased he likelihood o
obscu ing small ye signi ican changes on he cu e ha may be conside ed impo an .
The esul ing g aphs o he indi idual senso s a e displayed in Figu e 8.
(a) The OX elemen . (b) The NH3 elemen .
(c) The RED elemen .
Figu e 8. A e age ou pu ime esponse o each elemen a e s anda diza ion o each concen a ion
se : (a) The OX elemen ; (b) he NH3 elemen ; and (c) he RED elemen .
The g aph o he OX elemen exhibi s no iceable wa iness in he cu es, small
ampli ude changes, and an une en dis ibu ion o he cu es. Consequen ly, he da a
Figu e 8. A e age ou pu ime esponse o each elemen a e s anda diza ion o each concen a ion
se : (a) The OX elemen ; (b) he NH3elemen ; and (c) he RED elemen .
