direct inter-comparison of datasets obtained by different ptr-ms: a

Nestlé Research Center

PTR-MS Conference 2005

Direct inter-comparison of datasets obtained by different PTR-MS:

A novel approach to optimize and adapt the fragmentation pattern using a standardization

procedure

Title

Christian Lindinger, Philippe Pollien, Santo Ali, Julia Märk, and Imre Blank, Tilmann Märk


Agenda

Overview about PTR-MS application at Nestle NRC

On-line coffee headspaceOn-line monitoring of Maillard reactionsOff-line identification using GC-MS/PTR-MS

Outstanding problems using PTR-MS for these applications

Quantification: transmission, fragmentation-pattern

Standardization procedure

Characterizing the fragmentation-energy for reproducible measurementsEasy measurement of the transmission



Hot Liquid Headspace Measurement

TimeTime--resolved analysis of hot liquid headresolved analysis of hot liquid head--spacespace

Air, N2

PTR-MS

VOC + H3O+ ⌦ VOC·H+ + H2OVOC + H3O+ ⌦ VOC·H+ + H2O

H3O+

0

20

40

coun

ts-p

er-s

econ

ds

Espressox103

headspacesampling

on-line analysisby PTR-MS time-intensity profiles



Features:Features:

Experimental Setup

• Sample gas at high temperature• Very high VOC concentration• Water vapor saturated sample


humidity control 1

humidity control 2


0

20

40

coun

ts-p

er-s

econ

ds

Ristrettox103

Arpeggio

0

20

40

0 5 10 15 20 25 30

Time [min]

coun

ts-p

er-s

econ

ds

x103

Volluto

Cosi

0 5 10 15 20 25 30

Time [min]

m/z 41: 3-Methylbutanal (79%)2-Methylbutanal (21%)

m/z 61: Acetic acid (49%)Methyl formate (40%)2,3-Pentanedione (11%)

m/z 68: Pyrrole (100%)

m/z 73: 2-Butanone (100%)

m/z 75: Methyl acetate (99%)

m/z 82: 1-Methylpyrrole (100%)

m/z 87: 2-Methyl butanal (50%)Diacetyl (43%)3-Methylbutanal (7%)

m/z 97: Furfural (100%)

m/z 101: 2,3-Pentanedione (79%)2-Methyl THF (21%)

Time-intensity profiles:

Some profiles arecommon to all types

Some profiles arecharacteristic

Differentiating the Espresso-types

Coffee 1

Coffee 4

Coffee 2

Coffee 3



0

1

2

3

4

5

6

7

8

M61/M75 M81/M97 M45/M75 M101/M68

Coffee 1Coffee 2Coffee 3Coffee 4Coffee 5Coffee 6Coffee 7Coffee 8Coffee 9Coffee 10

0

10

20

30

40

50

60

M68/M97

Mass-ratios to differentiatebetween Espressos



First try to find correlations between analytical data and sensory datasetsby using simple mass ratios

Sensory profiles ~ Analytical data

SensoryDescriptive:

Burnt

Woody

Cocoa

Roasted

Citrus

Winey

Flowery

Buttery

Cereal

m41/m61Cereal

0.00

0.20

0.40

0.60

0.80

1.00

1.20

COFFEE 1COFFEE 2COFFEE 3COFFEE 4COFFEE 5COFFEE 6COFFEE 7COFFEE 8COFFEE 9COFFEE 10COFFEE 11

SensorialAnalytical



Result - Predictions implemented in an Excel sheet



Result - Good correlation Analytic / Sensory profile

Global pattern is well preserved.

Sensory data

Analytic data


Coffee 12

Intense

Burnt

Woody

Roasted

Cocoa

Cereal

Butter

Winey

Citrus

Flowery


On-line monitoring of Maillard reactions


0

500

1000

1500

2000

0 50 100 150 200 250 300Time[min]

HS

Con

c [p

pbv]

010002000300040005000600070008000

mass 45 mass 47 mass 51mass 57 mass 59 mass 71mass 75 mass 87 mass 145mass 43 mass 61

HS

Con

c. [p

pbv]

, mas

ses

43 a

nd 6

1

Experimental set-upfor Maillard PTR-MS

On-line monitoring of volatilesgenerated upon heating


Acrylamide formation – Asparagine, Glucose, Fructose



Can we assignion tracesto VOCs?

Can we assignion tracesto VOCs?

Espresso coffee:dynamic above-the-cup volatile profile

0

200

400

600

800

1000

1200

1400

1600

1800

2000

-4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

Time [min]

Con

cent

ratio

n [p

pbv ]

mass 61

mass 68

mass 69

mass 73

mass 75

mass 81

mass 83

mass 87

mass 89

mass 97

mass 101

Assigning Ion Trace to VOC



Coupling GC – EI-MS / PTR-MS(simplified scheme)

Coupling Setup



assi

gnm

ent o

fdy

nam

ic P

TR-M

S(fr

agm

. pat

tern

)

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

1.0E+06

1.2E+06

1.4E+06

0 5 10 15 20 25 30 35 40 45

Time [min]

Abu

ndan

ce

TIC GC-PTR-MS

0.0E+00

1.0E+06

2.0E+06

3.0E+06

4.0E+06

5.0E+06

6.0E+06 TIC GC-EI-MS

Ace

tald

ehyd

e

Met

hyl f

orm

ate

Fura

n

Furfu

ryla

lcoh

ol

1-M

ethy

lpyr

role

Furfu

ral

Ace

tic a

cid

2-TH

F-3-

one

2,3-

Pen

tane

dion

e

2,3-

But

aned

ione

3-M

ethy

lbut

anal

2-M

ethy

lbut

anal

2-B

utan

one

2-M

ethy

lfura

n

Met

hyla

ceta

techem

ical

id

entif

icat

ion

Chemical Identification



0.0E+00

1.0E+06

2.0E+06

3.0E+06

4.0E+06

5.0E+06

6.0E+06 TIC GC-EI-MS

Ace

tald

ehyd

e

Met

hyl f

orm

ate

Fura

n

Furfu

ryla

lcoh

ol

1-M

ethy

lpyr

role

Furfu

ral

Ace

tic a

cid

2-TH

F-3-

one

2,3-

Pen

tane

dion

e

2,3-

But

aned

ione

3-M

ethy

lbut

anal

2-M

ethy

lbut

anal

2-B

utan

one

2-M

ethy

lfura

n

Met

hyla

ceta

te

0.E+00

1.E+05

2.E+05

3.E+05

4.E+05

5.E+05

6.E+05

0 5 10 15 20 25 30 35 40 45Time [min]

Inte

nsity

[cps

]

m/z 73

Compounds yieldingPTR-MS ion intensityat m/z 73

2-Methyl propanal2-Butanone

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

1.0E+06

1.2E+06

1.4E+06

0 5 10 15 20 25 30 35 40 45

Time [min]

Abu

ndan

ce

TIC GC-PTR-MS

Example for mass 73


Identification changes with time


0 5 10 15 20 25 300

200

400

600

800

1000

1200

conc

entr

atio

n [p

pb]

time [min]

95 m/z 80 m/z 75 m/z 68 m/z

0

1000

2000

3000

4000

5000#5#4#3#2#1

120s trapped on Tenax

conc

entr

atio

n [p

pb]

111 m/z 101 m/z 87 m/z 73 m/z 45 m/z

5 traps during the release process Full identification of each trap


Some examples


0 5 10 15 20 25 30 35 400

2x104

4x104

2% furan 2% N-ethylpyrrol96%

retention time [min]

trap #50

2x1044x104 99%

trap #40

2x1044x1046x104

100%

m/z

68

GC

-PTR

-MS

inte

nsity

trap #30

2x1044x1046x104

100%

trap #2

02x1044x1046x104

100% pyrrole

trap #1

0 5 10 15 20 25 30 35 400

5x1031x104

20%

50%21%


trap #50

1x104

9%

2%3%

43%52%

trap #40

2x104

3%13%

47%

m/z

73

GC

-PTR

-MS

inte

nsity

trap #30

2x1044x104

5%16%

45%

trap #20

4x104

8x104

2% 2-methyl tetrahydrofuran-3-one2% 4-methyl-2-pentanone

39% 2-butanone

36%

34%

57%isobutanal

trap #1

0 5 10 15 20 25 30 35 400

1x105

2x105100%

99% pyridine


trap #50

1x105

2x105 100%

trap #40

1x105

2x105 100%

m/z

80

GC

-PTR

-MS

inte

nsity

trap #30

1x1052x1053x105

100%

trap #20

1x1052x1053x105

trap #1

0 5 10 15 20 25 30 35 400

5x1031x1042x104

30% 2-methylbutanal

9%3-methylbutanal

67%

63%

27%


trap #50

1x104

2x104

26%7%

13%

trap #40

1x104

2x104

5%16%

61%18%

m/z

87

GC

-PTR

-MS

inte

nsity

trap #30

1x104

2x104

14%2%

54%21%

trap #20

1x1042x1043x104

6%

67% 2,3-butanedione

9% gamma-butyrolactone

trap #1


Trapping efficiencyExperimental setup

0 50 100 150 200

0.0

0.2

0.4

0.6

0.8

1.0

1.2120 s

33 m/z 45 m/z 59 m/z 61 m/z 80 m/z

norm

aliz

ed c

once

ntra

tion

trapping time [s]

preferably used trapping time

About 30% of the methanol and 50% of acetaldehyde are trapped

using a trapping time window of 2 min.



Degradation using Tenax traps


A well known problem of using Tenax traps is the degradation of thermo-sensible molecules. Mercaptane i.e. is an important flavor compound in coffee and suffers under thermal degradation.

The measured trapping efficiency using the above mentioned method is 70%. Injecting a well defined amount of mercaptane, a degradation of 70% was observed. Concluding: The whole setup from sampling to GC detection, 21% of the headspace concentration reaches the PTR-MS detector at the end of the GC column.


AgendaOverview about PTR-MS application at Nestle NRC

On-line coffee headspaceOn-line monitoring of maillard reactionsOff-line identification using GC-MS/PTR-MS


Quantification: transmission, fragment-pattern





Problems in Quantification


Application: Quantifying toxic compounds generated upon heating (Maillard reactions)

++

++ +=

'******

*****'

15,27323022.6

)15,273(22400013,191][

3

3

RdriftdriftOH

OHdriftR

TransEPtkInt

TransTEIntR

Needed information: IntR’+ : counts-per-seconds of ion mass corresponding to compound RIntH3O+ : counts-per-seconds of the primary ion H3O+

Trans H3O+ : transmission of quadrupole MS at the mass of the primary ion H3O+

TransR'+ : transmission of quadrupole MS at mass R’Pdrift : pressure in drift tube [bar]Tdrift : temperature in drift-tube [°C]k : reaction rate constant (2*10-9cm3/s)tdrift : reaction time (105 μs)frag : fraction of compound R at m/z R’+ (fragmentation ratio)(R’+ being any ion signal related to the protonated and eventually fragmented compound R)



IntR’+ : counts-per-seconds of ion mass corresponding to compound RIntH3O+ : counts-per-seconds of the primary ion H3O+

P-drift : pressure in drift tube [bar]T-drift : temperature in drift-tube [°C]

Measured data:

Literature, measured or calculated data:k : reaction rate constant (~2*10-9cm3/s)

Trans H3O+ : transmission of quadrupole MS at the mass of H3O+

TransR'+ : transmission of quadrupole MS at mass R’tdrift : reaction time (105 μs)frag : fraction of compound R at m/z R’+ (fragmentation ratio)

Influenced parameters (influenced by the settings of PTR-MS):

Where to get these values from?


0

0.5

1

Tran

s M

x

Compound 1 Compound 2

Tran

s M

y

PTR-MS analysis

0

5

10fra

gmen

t M

xCompound 1

Compound 2

fragm

ent

My

0.0

1.0

2.0

3.0 Ratio My / Mx

Change in fragmentation and in transmission

Inte

nsity

0

5

10

fragm

ent

Mx

Compound 1 Compound 2

fragm

ent

My

Inte

nsity

0.0

1.0

2.0

3.0 Ratio My / Mx

Inte

nsity

0.0

1.0

2.0

3.0 Ratio My / Mx

Wrongprediction

sensory profile

Problems with changing transmission of MS and changings in fragmentation.

predictionsensory profile



AgendaOverview about PTR-MS application at Nestle NRC

On-line coffee headspaceOn-line monitoring of maillard reactionsOff-line identification using GC-MS/PTR-MS


Quantification: transmission, fragment-pattern






50 50Inlet He ating Drift Tube Heating

+

_CL

U

LNT200-10

+

_CL

LNT200-10

CL

LNT200-10

CL

U

LNT200-10

CL

U

LNT200-10

CL

LNT200-10

CL

U

LNT200-10

CL

U

LNT200-10

CL

U

LNT200-10

CL

LNT200-10

4

10U

I

SNT600-1012V/2A± 15V/2AISO-AI ISO-AO

V1V2V3V4V5V6

VALVE-CTRL

powe rI

O

QMG 422

309: Act rotspd1200 Hz

DCU


DCU

CHPARA

1.955E-1 mBar

SP 4SP 3SP 1 SP 21 ON

2 ON

DualGauge

PTR-MS IONICON ANALYTIK


+

_CL

U

LNT200-10

+

_CL

LNT200-10

CL

LNT200-10

CL

U

LNT200-10

CL

U

LNT200-10

CL

LNT200-10

CL

U

LNT200-10

CL

U

LNT200-10

CL

U

LNT200-10

CL

LNT200-10

4

10U

I


V1V2V3V4V5V6

VALVE-CTRL

powe r I

O

QMG 422


DCU


DCU

CHPARA

1.955E-1 mBar


2 ON

DualGauge


Different PTR-MS obtaines same results





+

_CL

U

LNT200-10

+

_CL

LNT200-10

CL

LNT200-10

CL

U

LNT200-10

CL

U

LNT200-10

CL

LNT200-10

CL

U

LNT200-10

CL

U

LNT200-10

CL

U

LNT200-10

CL

LNT200-10

4

10U

I


V1V2V3V4V5V6

VALVE-CTRL

powe rI

O

QMG 422


DCU


DCU

CHPARA

1.955E-1 mBar


2 ON

DualGauge


Over time same results


time


0

1

0 2000

2.5

0

0

80

70100

SA=1.1

SB=1.8

SC=2.1

00

Primery Ion (m/z=21)

Compound (m/z= M+1)

Transmission measurement

MFC

Compound(e.g. Acetone)

PTR-MS

MFC

Purge gas

Dilution gasSetup for controlled VOS’s flow

Increasing concentration

to PTR-MS

Time

Inte

nsity

With variouscompoundsA, B, C….

Com

poun

ds in

tens

ity

Primery Ion intensitym/z

Slop

e

Relative transmission

m/z

Transmission



Fitting the transmission function

0 50 100 150 200 250

0.2

0.4

0.6

0.8

1.0

Equation: ((1-(1/(1+exp((x-P3)/P4))))*((1/(1+(P1^(x-P2))))^0.25)/P5) Chi^2/DoF = 0.00071 R^2 = 0.99118 P1 1.086 ±0 P2 126.19492 ±1.4018 P3 46.77031 ±1.50389 P4 37.26908 ±2.29123 P5 0.8 ±0

Tran

smis

sion

Mass [m/z]

PTR-MS 2



New way to measure the transmission

Compoundwith many fragments

PTR-MSdirect inlet

valve

Trans-2-dodecenylacetate


m/z

=227

[M

H]+

m/z

=167

m/z

=125m

/z=1

11m

/z=9

7m

/z=8

3m

/z=6

9m

/z=5

5m

/z=4

1


Measured fragmentation

0

5

10

15

20

1

41 (1

0%) 69

(15%

)

83 (5

%)

97 (6

%)

111

(12%

)12

5 (4

%)

167

(7%

)

227

(4%

)

Frag

men

tatio

n %

m/z

Example for the fragmentation pattern of Trans-2-dodecenylacetate



Result for Transmission

0.4

0.6

0.8

1

1

But problem….– Fragmentation is not constant

41 X

100

% /

10%

Tran

smis

sion

227

X 1

00%

/ 4%

m/z



Fragmentation changesPTR-MS1

05

101520253035

400 450 500 550 600drift voltage [V]

rela

tive

ambu

ndan

ce [%

] m/z 41m/z 55 m/z 69m/z 83m/z 97m/z 111m/z 125m/z 167m/z 227

PTR-MS2

05

101520253035

400 450 500 550 600drift voltage [V]

rela

tive

ambu

ndan

ce [%

] m/z 41m/z 55 m/z 69m/z 83m/z 97m/z 111m/z 125m/z 167m/z 227

Δ ~ 30V


PTR-MS

changing drift voltage during the measurement

400V – 600V



How to measure the fragmentation energy

1. Compound:

Ratio of fragments independent on [H3O+] but depended on

transmission

[MY]C1* TMy

[MX]C1* TMx

2. Compound:

Compound 1 and 2 has fragments on the same masses

[MY]C2* TMy

[MX]C2* TMx

Eliminating the transmission factor

[MY]C1

[MX]C1[MY]C2

[MX]C2

FC1=

FC2=

FC1

FC2=



Measuring the fragment-pattern

1. Compound: Trans-2-dodecenylacetate2. Compound: 3-methylbutanal

Same fragments: m/z 41 and m/z 69

cps m/z 69 / cps m/z 41

0

100

200

300

400

500

600

300 350 400 450 500 550 600drift voltage [V]

inte

nsity

3-methylbutanal




Fragments of Trans-2-dodecenylacetate

O

O

HO

O

+

OH

O

+

+

+

H3O+

m/z 69m/z 41

m/z 167

m/z 227


acetic acid


Fragments of 3-Methylbutanal

O OH+

+

+H3O+

- H2O - C2H4

m/z 69 m/z 41m/z 87



Eliminating the transmission

PTR-MS2 U9=6V H=2°C P=1.9mbar

00.20.40.60.8

11.21.41.6

300 350 400 450 500 550 600drift voltage [V]

inte

nsity

[MY]C1

[MX]C1[MY]C2

[MX]C2

FC1

FC2=

1.27

397 V

• Peak amplitude• Drift voltage at peak Independent from transmission



Peak amplitude and voltage depending on U9, P-drift, humidity

1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4

360

380

400

420

440

460

480

500

Voltage at peak depending on drift pressure

PTR-MS 1 PTR-MS 2

drift

vol

tage

[V]

drift pressure [mbar]1.8 1.9 2.0 2.1 2.2 2.3

1.10

1.15

1.20

1.25

1.30

1.35

1.40

Dependence on drift pressure (P-drift):

Peak amplitude depending on drift pressure

PTR-MS 1 PTR-MS 2

inte

nsity

drift pressure [mbar]



Peak amplitude and voltage depending on U9, P-drift, humidity

Dependence on U9 (noscone):

4 5 6 7 8 9 10 11 12 13

360

380

400

420

Voltage of peak depending on U9

PTR-MS 1 PTR-MS 2

drift

vol

tage

[V]

U9 [V]4 5 6 7 8 9 10 11 12 13

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

Peak amplitude depending on U9

PTR-MS 1 PTR-MS 2

ampl

itude

U9 [V]



Conclusion


Automatic standardization procedure:• Setting the U9 to optimum fragmentation pattern• Set U-drift or P-drift to defined fragmentation pattern of

Trans-2-dodecenylacetate• Measuring the transmission using the fitting function

Transfer of a characteristic value to optimize different PTR-MS (normal, HS, compact) to same fragmentation pattern

Compound 2

PTR-MSdirect inlet

valve

Compound 1 Auto optimization software

+capillaries

direct inter-comparison of datasets obtained by different ptr-ms: a

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