“ . . . back to THE basics“ >

. . . forgotten ?

 re Theoretical Plates”
& a perrenial problem !

  • > Chronic & prolonged GC “performance” Errors over decades
    from ‘60s  > to even current times !
    & by many “GC Gurus”
    negligible for packed columns
    BUT highly deceiving for naive or exploitive column Manufacturers and/or for R&D “purposes” ! ?
  • where huge N(T) results were often ambiguously being promoted

> from the first “days” of Capillary column development and OUR R&D Initiation !

N(T)=N(Eff)x(k/(k+1)
where k= RetentionTime / DeadVol time)

Confusion and exploitation of capillary column “education”

The deliberate confusion > conflation of Theoretical Plates

Total N(T) and “Effective”Theoretical Plates > N(Eff)
N(Eff)
and the dependence on inflated Column Peak Resolution . . .  > by ignoring column Dead Volume Effects of Partition Coefficients for “unresolved” at k=1 up to k=4-6 where k=Tr/(Tr-Td)
T
are the “relevant” peak retention times

ALL is NOT “Rocket” Science but deceptive IF Ignored > exploited

Perpetuated by many pioneers of capillary column technology and still less by naive ”beginners” in
Capillary GC !

to . . . “Those” that SIMPLY don’t want
to know” !

> the deluded > naive ! “pseudo sales”

Translations Between Differing Liquid Chromatography Formats: Advantages, Principles, and Possible Pitfalls”
from LC/GC Mag
Volume 18 Number 1 p6-16

reprinted here in FlipHTML5 copyrite?
BUT in the “education” Interests of “Mankind” !

Un-beknown or perhaps exploitation by Column OEMs > ignorance ( or just the usual  marketing practice ? )
Errors induced( internal ) friction heating

coarse > fine particles ( 1.8um vs 5um); Solid core > “New” Porous-Shell column material
 & similar consideration of Neff vs NT ( as above)
effect of extra- column ( Injector &
post-column dead volume (Td) inc Detector volume effects eg UV Cell 

> all necessitates  the practical determination
( experimentally ) by injecting a non-adsorbed sample ( often Uracil is used for C10 > non-polar T(d)


ALL at Non-Gradient & Isothermal Column Temp. !

HPLC > micro-HPLC ( uHPLC )
and exploitive > extreme high Cost of the latter !
-    often with the need for renewed “Method Certification ( Regulatory ! )

GC  Column Oven Temperature
> ACCURACY ?
PDF pdfGC Ovens LCGCAsiaPacific_March2015-022-026 GC Ovens

for those actually ”Smart Enough(?)”
to Use Retention Index(RI) to help U identify GC peaks
Isothermal > more-so PTGC
( ALL are under-rated re Power
(Watts) required  ?

  • at least Be-A-WARE !

    > makes IT Very DIFFICULT for ANY  GC Method transfer from > that published
    and /or between
    GC
    Instruments and OEM Brands/Models

> a neglect / oversight of ALL GC OEMs
unless U prove otherwise !

  • but THIS Does help protect their GC/MS(MS) Sales > extreme costs ! etc. . . of course !

NO GC OEM bothers to calibrate
or even try to linearise Oven Temperatures “ramps”
> SHAME !

THIS Is essential as RI does depend
on temperature particularly-so for Polar Liquid Phases

  • ALL  OEM GCs Oven Temperature during PTGC is wildly inaccurate (?) at temperatures > 120C and high rates >10C/ min > worse at higher temps and high rates
    Accuracy of FAST GC Column Heating is even more suspect
     
  • very few GC Ovens will control at All ! at Column ambient Temp or below 40degC
    ( +5-10degC above A )

 Listen to THE Data PDF pdf Listen to Data
LCGCAsiaPacific_March2015-017-021 Listen to the Data.pdf

re . . . >

  • Systematic errors > re-Data System . Integration unresolved peaks etc
  • Drift in retention time & “Integration Window” > accuracy ?

NOT Optimising Column Flow Rates

> Operate at the MIN of the VanDeemter Curve

for Capillary Columns

  • N2 “linear velocity” u 15-20cm/sec, Helium 20-30, H2 20 to 40

THE QC “Syndrome”

  • methology” to meet “tight” specs
  • under pressure > time deadlines etc
                   >  just an “inclination” ! ? > maybe ?
    SIMILARLY ? >
    NOT carefully optimising choice of column type or Liquid Phase “Selectivity” > expediency > lack of suitable column stock ! even lack of Method “Validation” !

Often to meet QC specs analysts mave have a tendency to allow column instrument performance to deteriorate >by simple attrition OR Not even monitor
( thru’ Column Efficiency )

Column Effeciency

Core-shell vs uHPLC ?

GC Oven Temp ?

Follow The Data

Optimised Flow ?

QC “Syndrome”

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