Converting Helium Carrier Gas GC

Methods Nitrogen and Hydrogen

Jim McCurry Agilent Technologies Wilmington, DE 18951 USA

October 12, 2012 1

Market Situation The world of He supply is not reliable, prices are increasing and

customers are seeking alternative carrier gases

Agilent Restricted

Page 2 October 12, 2012 2

The Carrier Gas Decision

Agilent Restricted

Page 3

Consider migration to H2 Consider migration to N2 He Conservation

GC/MS specific H2 considerations

Is the chemist willing to convert to alternative gasses?

Is the Application based on GC or GC/MS?

Does the current GC method have too much resolution?

No

No

Yes

Yes

GC/MS GC

October 12, 2012 3

Migration to H2: Considerations for GC & GC/MS

Agilent Restricted

Page 4

Consider migration to H2 Consider migration to N2 He Conservation

GC/MS specific H2 considerations

Is the chemist willing to convert to alternative gasses?

Is the Application based on GC or GC/MS?

Does the current GC method have too much resolution?

No

No

Yes

Yes

GC/MS GC

October 12, 2012 4

H2: Considerations for GC & GC/MS Application

Agilent Restricted

Page 5

H2 safety

Sources of hydrogen

Plumbing modifications

Chromatographic method migration

Method revalidation

October 12, 2012 5

H2 Safety

Agilent Restricted

Page 6

GC, GC/MS: Both offer H2 enabled features • Agilent H2 safety letter and safety manuals available • GC four levels of safety design

• Safety Shutdown • Flow Limiting Frit • Oven ON/OFF Sequence • Explosion Test

• Newer version 6890, 7890 GC and 5773, 5975 MSD offer greater safety than older versions of GC and GC/MSD.

October 12, 2012 6

H2 Generator – preferred • Very clean H2, >99.9999% available • More consistent purity • Built-in safety considerations • Make sure to buy a good one with a low spec for water and oxygen • Parker’s H-MD are used in LFS and SCS

H2 Cylinder • Consider gas clean filter • Possible to add safety device

Source of Hydrogen

Agilent Restricted

Page 7 October 12, 2012 7

H2: Plumbing Modification Considerations

Agilent Restricted

Page 8

Tubing: • Use chromatographic quality stainless steel tubing • Do not use old tuning (H2 is known as scrubbing agent) • Especially don’t use old copper tubing (brittleness is a safety concern)

Venting: • Connect split vent and septum purge vent to exhaust

Leak checking: • Recommend G3388B leak detector

October 12, 2012 8

Migration to N2 for GC Application

Agilent Restricted

Page 9

Consider migration to H2 Consider migration to N2 He Conservation

GC/MS specific H2 considerations

Is the chemist willing to convert to alternative gasses?

Is the Application based on GC or GC/MS?

Does the current GC method have too much resolution?

No

No

Yes

Yes

GC/MS GC

October 12, 2012 9

Use N2 as carrier gas

Agilent Restricted

Page 10

Many HPI methods suited to nitrogen • Readily available and less expensive gas • No safety concern • Suitable for simple routine analysis (w. enough resolution) • 2-D GC ideally suited to nitrogen

– Resolution issues solved by using 2 different columns

Potential issues • Reduced separation resolution • Not suitable for GC/MSD and certain GC detector applications

October 12, 2012 10

Helium Carrier Gas Alternatives • Hydrogen, nitrogen, argon, argon/methane • Detector considerations can influence choice • Hydrogen and nitrogen are the most common alternatives

October 12, 2012 11

Helium Carrier Gas Alternatives Important Theoretical Considerations Relating To Peak Efficiency

12

Solute

Time

Start

Inert Gas

t m t R

' t R

We would like to know the actual time the component spends in the stationary phase.

Let's relate “n” to the length of the column.

or Plates per meter (N) = n L

Height equivalent to a theoretical plate (HETP) = n L

Thus, the more efficient the column, the bigger the "N" the smaller the "HETP“.

n = 5.545

t R '

W h

2 t R - t m = t R ' t R ' t R '

Calculating Efficiency

R t '

= Corrected Retention Time.

n = effective theoretical plates.

HET

P C RESISTANCE TO MASS TRANSFER

A EDDY DIFFUSION

MOLECULAR DIFFUSION

µ ( opt µ)

}

} B {

HETP = A +

+ C µ B µ

Efficiency & Carrier Gas Linear Velocity

Efficiency is a function of the carrier gas linear velocity or flow rate. The minimum of the curve represents the smallest HETP (or largest plates per meter) and thus the best efficiency. "A" term is not present for capillary columns.

• Plot of HETP versus linear velocity is know as the Van Deemter plot.

• The linear velocity value at the minimum of the curve is the optimum value for achieving the best efficiency.

Helium Carrier Gas Alternatives Let’s Make This Easy

13

Solute

Time

Start

Inert Gas

t m t R

' t R

We would like to know the actual time the component spends in the stationary phase.

Let's relate “n” to the length of the column.

or Plates per meter (N) = n L

Height equivalent to a theoretical plate (HETP) = n L

Thus, the more efficient the column, the bigger the "N" the smaller the "HETP“.

n = 5.545

t R '

W h

2 t R - t m = t R ' t R ' t R '

Calculating Efficiency

R t '

= Corrected Retention Time.

n = effective theoretical plates.

HET

P C RESISTANCE TO MASS TRANSFER

A EDDY DIFFUSION

MOLECULAR DIFFUSION

µ ( opt µ)

}

} B {

HETP = A +

+ C µ B µ

Efficiency & Carrier Gas Linear Velocity

Efficiency is a function of the carrier gas linear velocity or flow rate. The minimum of the curve represents the smallest HETP (or largest plates per meter) and thus the best efficiency. "A" term is not present for capillary columns.

• Plot of HETP versus linear velocity is know as the Van Deemter plot.

• The linear velocity value at the minimum of the curve is the optimum value for achieving the best efficiency.

Helium Carrier Gas Alternatives Let’s Make This Easy • Goal: change carrier gas while keeping other method conditions the same

– use the same column – use the same oven program – adjust column flow or holdup time velocity to:

• same peak elution order • same peak retention times

• For N2, test resolution of key components

• adjust GC conditions (temp, flow) if needed

• Easier method revalidation – minimal changes to timed integration events – minimal changes to peak identification table

• Use tools built into the Agilent Chemstation to guide us through the process

14 October 12, 2012

The Tyranny of Van Deemter Why Nitrogen Gets a Bad Rap for Capillary GC

• N2 actually provides the best efficiency, but at a slower speed • Most helium methods have too much resolution

– Lower N2 efficiency at higher flows can still provide “good enough” resolution • Most GC methods now use constant flow

– N2 efficiency losses with temp programming are not as severe

October 12, 2012 15

Average Linear Velocity (cm/sec)

HETP (mm)

1.2

1.0

.8

.6

.4

.2

10 20 30 40 50 60 70 80 90

C17 at 175º C k' = 4.95

OV-101 25m x 0.25 mm x 0.4µ

N2

He

H2

Helium 58 cm/s

2.5 mL/min

R = 1.17

Nitrogen 58 cm/s

2.4 mL/min

Hydrogen 58 cm/s

1.7 mL/min

R = 1.37

Helium Carrier Gas Alternative Test Case: ASTM D6584 for Free and Total Glycerin in Biodiesel

16

COC Inlet: Oven Track ModePre-column: Ultimetal 2m x 0.53mm ID

Column: Ultimetal DB5HT, 15m x 0.32mm ID x 0.1 df Column Flow: Helium at 3.0 mL/min (50 deg C)

Column Pressure: 7.63 psi constant pressure modeInitial Column Temp: 50 oC for 1 min.

Oven Ramp 1: 15 oC/min to 180 oCOven Ramp 2: 7 oC/min to 230 oCOven Ramp 3: 30 oC/min to 380 oC, hold 10 min.

Detector: FID with 25 mL/min N2 makeup

5 10 15 20 25 30 35

Istd 1

1

2

3

4

Istd 2

1. Glycerol 2. Monoglycerides 3. Diglycerides 4. triglycerides

Configure Inlet for Carrier Gas in Chemstation

17

Set the Control Mode: Flow or Holdup Time

October 12, 2012 18

Wider Retention Time Variation Using the Same Flow

October 12, 2012 19

18 19 20 21 22 23 24

Helium Flow: 3.00 mL/min P: 7.63 psi Tr: 0.472 min. µ: 52.97 cm/s

Hydrogen Flow: 3.00 mL/min P: 3.85 psi Tr: 0.420 min. µ: 59.50 cm/s

Nitrogen Flow: 3.00 mL/min P: 7.09 psi Tr: 0.464 min. µ: 53.84 cm/s

23.818 min

23.469 min

23.705 min

Same Holdup Time (Tr) Gives Consistent Retention Times

October 12, 2012 20

18 19 20 21 22 23 24

Helium Flow: 3.00 mL/min P: 7.63 psi Tr: 0.472 min. µ: 52.97 cm/s

Hydrogen Flow: 2.64 mL/min P: 3.43 psi Tr: 0.472 min. µ: 52.97 cm/s

Nitrogen Flow: 2.94 mL/min P: 6.98 psi Tr: 0.472 min. µ: 52.97 cm/s

23.818 min

23.862 min

23.776 min

Monoglyceride Resolution “Good Enough” Using Nitrogen Carrier

October 12, 2012 21

16.5 17 17.5 18 18.5 19 19.5

Mono2 area: 1049

Mono2 area: 1050

Mono2 area: 1049

Mono1 Mono3

Mono1

Mono1

Mono3

Mono3

Helium Flow: 3.00 mL/min Tr: 0.472 min.

Hydrogen Flow: 2.64 mL/min Tr: 0.472 min.

Nitrogen Flow: 2.94 mL/min Tr: 0.472 min.

ASTM D6584 - Quantitative Results For Alternative Carrier Gas

October 12, 2012 22

Helium Hydrogen NitrogenGlycerin 0.015 0.014 0.013Monoglycerides 0.226 0.216 0.223Diglycerides 0.114 0.115 0.110Triglycerides 0.071 0.085 0.098Total Glycerin 0.097 0.095 0.098

Weight Percent

Analysis of Oxygenates and Aromatics in Gasoline Using 2-D Gas Chromatography

ASTM Method D4815 – Oxygenated Additives – Ethers and alcohols from 0.1 wt% to 15 wt% – Usually only one or two additives in a sample

ASTM Method D5580 – Aromatics in Gasoline – Measures benzene, toluene, C8 aromatics and C9 plus aromatics – Two injections per sample for complete analysis

Preliminary separation removes light hydrocarbons from sample

– Polar TCEP micro-packed columns retains polars and aromatics – Back flush TCEP column to non-polar capillary column (HP-1) to

complete analysis

October 12, 2012 23

GC System for D4815 and D5580

Similarities between each method – Same GC hardware requirements

• Inlets, detectors, plumbing and valve configuration – Same separation scheme

• 2-D separation using polar TCEP micro-packed primary column • 20% TCEP on 80/100 Chromosorb PAW, 22“ x 1/16“ stainless

• Only one difference in instrument requirements – non-polar capillary column – D4815 – 2.65 µm methyl silicone, 30m x 0.53mm – D5580 – 5 µm methyl silicone, 30m x 0.53mm

October 12, 2012 24

Configuration and Operation for D4815 and D5580

1 2 3

4 5 6 7

8

9 10

S/S EPC

PCM EPC

TCEP column

HP-1 capillary column

FID

split/splitless inlet

variable restrictor

Primary flow

Secondary flow

TCD

October 12, 2012 25

Instrument Conditions D4815 Method D5580 Method

carrier gas nitrogen nitrogenInlet Split/Splitless Split/Splitlessinlet temperature 200 Deg C 200 Deg Cinlet presuure 9 psi (constant P) 25 psi (constant P)TCEP column flow 5 mL/min 10 mL/minsplit vent flow 70 mL/min 100 mL/minsplit ratio 15:1 100:1PCM pressure program 13 psi for 14 min 23 psi for 12.1 min

99 psi/min to 40 psi 99 psi/min to 40 psiHP-1 column flow 3 mL/min 10 mL/minFID temperature 250 deg C 250 deg Coven temperature 80 deg C isothermal 60 C for 6 min

2 C/min to 115 C115 C for 1.5 min

Run time 16 min 35 min

October 12, 2012 26

Analysis of MtBE and Ethanol in Gasoline using N2 Carrier Gas

MtBE

DME(IS) benzene

valve reset

2 4 6 8 10 12 14 16

DME(IS) benzene

ethanol

aromatic and heavy non-aromatic hydrocarbons

October 12, 2012 27

ASTM Precision Specifications

Compound Mass % Spec Observed Spec ObservedEthanol 0.99 0.06 0.01 0.23 0.01Ethanol 6.63 0.19 0.03 0.68 0.04MtBE 2.10 0.08 0.01 0.20 0.01MtBE 11.29 0.19 0.05 0.61 0.08

Repeatability Reproducibility

Sample known foundSRM2294 #1 10.97 10.61SRM2294 #2 10.97 10.60

AccuStd Check 12.00 11.81

MtBE mass %

D4815 Precision Measures

Accuracy Evaluation

October 12, 2012 28

D5580 Requires Two Runs per Sample for Complete Aromatic Analysis

1

2

3

T1 T3

4 1. benzene 2. toluene 3. 2-hexanone (IS) 4. C8 aromatics, C9 plus aromatics, and non-aromatic hydrocarbons

Method D5580A

1

5 10 15 20 25

4 2

3

T2

T4 5 1. 2-hexanone (IS) 2. ethylbenzene 3. m,p-xylene 4. o-xylene 5. C9 plus aromatics

Method D5580B

Good resolution with nitrogen carrier gas

October 12, 2012 29

Detector Response Precision for a Pump Gasoline Sample – 5 Runs Over 5 Days

FID Response (area counts) Run # Method MtBE Benzene Toluene Ethylbenzene m,p-Xylene o-Xylene

1 4815 24077 5580A 3306 19427 5580B 5402 21825 8069

2 4815 23384 5580A 3244 19436 5580B 5402 21956 8105

3 4815 22807 5580A 3178 19580 5580B 5422 22342 8232

4 4815 22915 5580A 3048 19344 5580B 5432 22263 8201

5 4815 23053 5580A 3099 19529 5580B 5422 22253 8199 Avg 23247 3175 19463 5416 22128 8161

Std. Dev 512 105 92 14 224 70 %RSD 2.2 3.3 0.5 0.2 1.0 0.9

October 12, 2012 30

Correcting Occasional Resolution Problems

– Some combinations of TCEP and HP-1 columns show less resolution using N2 carrier

– Fastest and easiest solution is to lower the initial oven temperature

T2 = 1.85 min.

Initial oven temp = 60 oC

ethylbenzene

m,p-xylene

5 10 15 20 25

T2 = 1.85 min.

Initial oven temp = 50 oC m,p-xylene

ethylbenzene

October 12, 2012 31

Using Nitrogen With High Resolution Capillary Columns

Test Case: EN14103 for Total FAME and Methyl Linolenate Content in B100 Biodiesel • Expand method to include animal fat derived biodiesel

– Replace C17 FAMEs ISTD with C19 FAME ISTD

• Expand method to include tropical oil (palm) derived FAMEs – Quantify C6 to C24 FAMEs and methyl linolenate (C18:3) – Requires column temperature program to resolve all FAMEs

• Method updated to provide better precision

– Verify C19:0 ISTD purity

October 12, 2012 32

EN14103:2011 GC Configuration and Operating Conditions

Standard 7890A GC Hardware G3440A Agilent 7890A Series GC

Option 112 100 psi split/splitless Inlet with EPC control Option 211 Capillary FID with EPC control

G4513A Agilent 7693 Autoinjector 19091N-133 HP-INNOWax Column, 30 m x 0.25 mm ID x 0.25 mm

Split/Splitless Inlet Temperature

Split flow

250 oC 100 mL/min.

Column Flow He or H2 at 1 mL/min. constant flow

Column temperature

60 oC for 2 min. 10 oC /min. to 200 oC 5 oC/min. to 240 oC Hold 240 oC for 7 min.

Flame ionization detector 250 oC

October 12, 2012 33

Peak # RT (min.) Peak # RT (min.)1 methyl hexanoate C6:0 6.031 11 methyl arachidate C20:0 22.8572 methyl myristate C14:0 15.878 12 methyl eicosonate C20:1 23.1663 methyl myristoleate C14:1 16.275 13 methyl eicosadienoate C20:2 23.8084 methyl palmitate C16:0 17.996 14 methyl arachidonate C20:4 24.5515 methyl palmitoleate C16:1 18.311 15 methyl eicosatrienoate C20:3 24.7306 methyl stearate C18:0 20.332 16 methyl behenate & C22:0 25.5827 methyl oleate (9) C18:1 20.617 methyl eicosapentaenoate C20:58 methyl oleate (11) C18:1 20.697 17 methyl erucate C22:1 26.0319 methyl linoleate C18:2 21.205 18 methyl lignocerate C24:0 29.574

10 methyl linolenate C18:3 22.052 19 methyl nervonate C24:1 30.20320 methyl docosahexaenoate C22:6 30.365

Name Name

0 5 10 15 20 25 30

1

2

3

4

5

7

6

9 10 11

12

13 14

16 17 20

8

15

18

19

EN14103 – FAME Identification Standard Helium at 1 mL/min Constant Flow

October 12, 2012 34

EN14103 – FAME Retention Time Standard Comparison of He and N2 Carrier Gas

min 16 18 20 22 24 26 28 30

pA

20 40 60 80

100 120 140 160

min 16 18 20 22 24 26 28 30

20

40

60

80

100

120

140

Helium at 1 mL/min Constant Flow

Nitrogen at 1 mL/min Constant Flow

October 12, 2012 35

EN14103 – Soya B100 Biodiesel Comparison of Helium and N2 Carrier Gas

October 12, 2012 36

min 16 18 20 22 24 26 28 30

min 16 18 20 22 24 26 28 30

C19:0 (IS)

Helium at 1 mL/min Constant Flow

Nitrogen at 1 mL/min Constant Flow

EN14103 – FAME Content in Biodiesel Comparison of He and N2 Carrier Gas

October 12, 2012 37

Sample Run 1 Run 2 r Run 1 Run 2 r r (spec)SRM 2772 96.9 96.7 0.2 97.2 97.2 0.0 1.01Rapeseed 96.7 96.0 0.7 95.5 95.7 0.2 1.01Coconut 87.4 86.9 0.5 86.6 86.9 0.3 1.01Rape/Coco (50/50) 91.2 91.2 0.0 91.4 91.0 0.4 1.01

Sample Run 1 Run 2 r Run 1 Run 2 r r (spec)SRM 2772 7.3 7.3 0.0 7.3 7.3 0.0 0.2Rapeseed 8.5 8.4 0.1 8.3 8.3 0.0 0.2Coconut 0.0 0.0 0.0 0.0 0.0 0.0 0.0Rape/Coco (50/50) 4.2 4.2 0.0 4.2 4.1 0.1 0.1

Helium NitrogenFAME Content (wt%)

C18:3 (wt%)Helium Nitrogen

If You MUST Use Helium – Consider Conservation

Agilent Restricted

Page 38

Consider migration to H2 Consider migration to N2 He Conservation

GC/MS specific H2 considerations

Is the chemist willing to convert to alternative gasses?

Is the Application based on GC or GC/MS?

Does the current GC method have too much resolution?

No

No

Yes

Yes

GC/MS GC

October 12, 2012 38

Reduce Helium Consumption

• 7890 GC Gas Saver – reduces split flow to conserve helium consumption

• Leak checking • Turn off the system to avoid long term idle

– Not always recommended for some GC columns or traps

Agilent Restricted

Page 39

Agilent Little Falls Site was able to reduce

consumption by 50%

October 12, 2012 39

Summary Migrating your GC method from helium carrier gas can be easily done • For resolution critical methods, H2 offer the best alternative

– Agilent GC and GC/MS systems have many built-in safety features

• For many GC applications, N2 offers a cheap, easy alternative without any safety worries – Most existing helium methods have too much resolution – N2 can be used without changing any of the existing GC conditions

• keep the holdup time the same as the original method – 2-D methods have high resolution built-in, so N2 is ideally suited as a carrier

gas • Valve-based or Deans switch, not GCxGC

• If helium alternative is not an option, consider conservation

October 12, 2012 40