Jim McCurry Chemical Solutions Business Unit September · PDF fileJim McCurry Chemical Solutions Business Unit September 5, 2000 ... •Advances in electronic pneumatics control (EPC)

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Jim McCurryChemical Solutions Business UnitSeptember 5, 2000

Qualitative GC - Can Retention Time NowReplace Retention Index?

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GC Retention Time Precision

• Advances in electronic pneumatics control (EPC)

• GC temperature control and pressurecompensation

• Advanced column manufacturing processes

You can achieve excellent retention time precision when you use the Agilent 6890 and 6850 with today’s capillary columns

Why?


RT Precision in a Single GC Setup

std dev = 0.0008 min

7.8 8 8.2 8.4 8.6 8.8 9 9.2

0

100

200

300

400

500

600

700

800

std dev = 0.0011 min

15 Runs Over 5 Days

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Fragrance Sample on 3 GC Systems

10 15 20 25 30

Inlet P = 14.11 psi


RT Reproducibility of Fragrance Sample

Retention Time (min)GC System 1 GC System 2 GC System 3 Std Dev (min) RSD Range (min)

7.343 7.803 7.971 0.325 4.219 0.6289.465 9.981 10.155 0.359 3.637 0.69012.361 12.929 13.113 0.392 3.062 0.75215.226 15.823 16.010 0.409 2.610 0.78420.212 20.837 21.027 0.426 2.061 0.81521.805 22.435 22.631 0.432 1.936 0.82624.431 25.093 25.302 0.455 1.823 0.87124.631 25.273 25.464 0.436 1.737 0.83324.814 25.460 25.650 0.438 1.732 0.83628.400 29.060 29.264 0.452 1.562 0.86430.514 31.163 31.366 0.445 1.435 0.852

Avg 0.415 2.347 0.796

Inlet P = 14.11 psi

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Traditional Approach - Retention Indices (RI)

• Enhances comparison of GC data collected on differentGC systems

• Uses a homologous series as a retention time reference

– n-alkanes or n-ethyl esters are a common indexreference standard

• Linear retention index calculations for temperature-programmed runs has special requirements:

– exact adherence to oven temperature, columndimensions, liquid-phase chemistry, and pneumaticscontrol

– slight variations in conditions can reduce effectivenessof linear RI calculations


Linear Retention Index Calculation

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RI Reference on 3 Different GCs

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Normal C1 - C18 ethyl estersInlet P = 14.11 psi


RT Reproducibility of RI Reference

Retention Time (min)Ethyl Ester GC System 1 GC System 2 GC System 3 Std Dev (min) RSDC1 1.731 1.881 1.991 0.131 6.988C2 1.882 2.045 2.162 0.141 6.929C3 2.192 2.381 2.511 0.160 6.793C4 2.736 2.996 3.118 0.195 6.614C5 3.806 4.111 4.270 0.236 5.804C6 5.529 5.932 6.096 0.292 4.986C7 7.957 8.449 8.619 0.344 4.122C8 10.902 11.454 11.631 0.380 3.356C9 14.097 14.683 14.863 0.401 2.753C10 17.342 17.945 18.127 0.411 2.308C11 20.518 21.127 21.310 0.415 1.976C12 23.587 24.197 24.382 0.416 1.729C13 26.505 27.121 27.309 0.421 1.559C14 29.330 29.942 30.124 0.416 1.396C15 32.009 32.620 32.803 0.416 1.280C16 34.592 35.198 35.376 0.411 1.172C17 37.005 37.622 37.811 0.422 1.125C18 39.558 40.313 40.544 0.516 1.285

Avg 0.340 3.454

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RI Improves Comparison of Data

Retention IndexGC System 1 GC System 2 GC System 3 Std Dev RSD Range

674.13 674.35 674.30 0.12 0.02 0.22750.65 750.98 750.98 0.19 0.03 0.33845.18 845.68 845.85 0.35 0.04 0.67934.27 934.93 935.14 0.45 0.05 0.87

1089.96 1090.89 1091.10 0.61 0.06 1.141141.60 1142.61 1142.99 0.72 0.06 1.391228.51 1230.63 1231.45 1.52 0.12 2.941235.42 1236.79 1237.00 0.86 0.07 1.581241.72 1243.19 1243.34 0.90 0.07 1.621366.74 1368.74 1369.45 1.41 0.10 2.711443.93 1445.58 1446.35 1.24 0.09 2.42

Avg 0.76 0.06 1.44

Break Number 1

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Optimizing the Method’s RT Precision

Column 1

Column 2

Column 3

Column 4

Retention times vary from GC to GC by as much as 0.5 min. ...

GC1

GC2

GC3

GC4


Retention Time Locking (RTL)

GC1 Column 1

GC2 Column 2

GC3 Column 3

GC4 Column 4

Retention time variation between GC systems now less than 0.03 min with RTL ...

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What is Retention Time Locking?

The ability to precisely matchchromatographic retention times in anysystem to those in anotherchromatographic system with the samenominal column.


How is Retention Time Locking Done?

By Adjusting Column Head Pressure via

EPC

Interactive Agilent ChemStation RTL software

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RTL Method Development

• Perform ALL method development work first

– appropriate column(s)

– GC conditions

– required resolution

– required sensitivity

• Target Compound Requirements

– well resolved

– easily detected

– middle of run

– not close to oven temperature transitions

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RTL Method Development

5 10 15 20 25

Inlet Pressure = 20.00 psi

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Done Once for a Method - FOREVER

● Make five runs at five differentinlet pressures:

➨ target –20%

➨ target –10%

➨ target

➨ target +10%

➨ target +20%

● Determine RT of your targetcompound in each chromatogram

● Enter into RTL software


Locking a GC System

1. Make one (or two) runs at nominal method pressure. 2. Determine RT of target compound. 3. New locking pressure is calculated by software. 4. Make run to confirm locked RTs.

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RT Precision Between GCs with RTL


Can RTL Replace Retention Indices?

• RTL uses only one peak to calibrate RT vs. pressure

• RTL calibration only needs to be done once permethod

• No special calculations required

• Do not need to estimate if missing RI standard

• Time is an easier concept to grasp

• Graphically easier to compare data between systems

• Easier to review historic data

Some Advantages to Using RTL

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Locking a Fragrance Sample

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A Fragrance Sample After RTL

10 15 20 25 30

Inlet P = 14.11 psi

Inlet P = 13.73 psi

Inlet P = 13.21 psi

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10x Better RT Precision With RTL

Retention Times After RTLGC System 1 GC System 2 GC System 3 Std Dev RSD Range (Min)

7.909 7.971 7.975 0.037 0.465 0.06610.102 10.176 10.159 0.039 0.382 0.07413.065 13.148 13.118 0.042 0.321 0.08315.977 16.059 16.015 0.041 0.256 0.08221.008 21.082 21.033 0.038 0.179 0.07422.618 22.688 22.637 0.036 0.160 0.07025.298 25.359 25.309 0.033 0.128 0.06125.582 25.532 25.470 0.056 0.220 0.11225.650 25.719 25.658 0.038 0.147 0.06929.276 29.335 29.270 0.036 0.123 0.06531.388 31.447 31.374 0.039 0.123 0.073

Avg 0.039 0.228 0.075vs. 2.347

without RTL!


Build a Retention Time Table

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Master RTTableGC1 FID

Record retention times under RT-Lockedconditions...

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Use RT Tables Worldwide

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Master RTTable

GC1

GC4 GC5 GC6

GC3GC2

Lab 1, USA

GC1

GC4 GC5 GC6

GC3GC2

Lab 1, FRA

GC1

GC4 GC5 GC6

GC3GC2

Lab 1, JPN

GC1

GC4 GC5 GC6

GC3GC2

Lab 1, UK


Combining RTL with RI

• RTL uses only one peak in the reference standard tocalibrate RT vs. pressure

• After RTL, the RTs of all the reference peaks on all GCswill be the same

• RTL can improve the precision of linear retention indexcalculations

– reduces errors contributed by variations in columndimensions

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RI Reference After RTL

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Normal C1 - C18 ethyl esters


If You Still Need Retention Indices...

Retention Index After RTLGC System 1 GC System 2 GC System 3 Std Dev RSD Range

674.29 674.93 674.32 0.36 0.05 0.64751.01 751.63 750.99 0.36 0.05 0.64845.64 846.36 845.84 0.37 0.04 0.72935.01 935.65 935.12 0.34 0.04 0.64

1090.71 1091.14 1091.03 0.22 0.02 0.431142.56 1143.00 1142.92 0.23 0.02 0.441230.94 1231.26 1231.39 0.23 0.02 0.451236.49 1237.17 1236.88 0.34 0.03 0.681242.96 1243.55 1243.32 0.30 0.02 0.591368.85 1369.38 1369.38 0.31 0.02 0.531445.68 1446.00 1446.29 0.31 0.02 0.61

Avg 0.31 0.03 0.58

RTL Can Improve RI Precision

vs. 0.06without RTL!

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Summary

No RTL or RI RSD = 2.35%

RI Only: RSD = 0.06%

RTL Only: RSD = 0.23%

RTL, RI Combination: RSD = 0.03%

Wrap-up Questions

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Jim McCurry Chemical Solutions Business Unit September · PDF fileJim McCurry Chemical Solutions Business Unit September 5, 2000 ... •Advances in electronic pneumatics control (EPC)