|
“ . . . 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
 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
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 )
|
from ~31Mar24+
