ADV06-15_1-412

383 / 413

2006.03
the Restek Advantage
IN THIS ISSUE
Editorial
Comprehensive 2D Gas Chromatography­
Making GCSeparations Work Harder ..... 2
Clinical/Forensics
Fast Screening and Confirmation for
Gamma-Hydroxybutyrate (GHB) 3
Drugs of Abuse Analytical
Reference Materials 6
Rapid Analysis of Steroid
Hormones by GClMS 7
Environmental
Enhanced Resolution of Endocrine
Disrupting Hormones 8
New Rxi'"-1ms Capillary GCColumn 10
GClMS for Low-Level Semivolatiles
in Drinking Water 12
Fast, Sensitive LCiMS/MS Analysis
of Paraquat and Diqu at. 14
Analytical Reference Materials
for Semivolatile Pollutants 16
Pharmaceutical
Assaying Local Anesthetics by GC/FID ... 17
Optimized RP-HPLCMethod for
Hydroxybenzoic Acid s 18
Chemical/Petrochemical
GC Analysis ofTotal Reduced
Sulfurs at ppbv Levels 20
Sulflnerts-Treated Sample Cylinders 21
How Good is Your PONA Column? 22
Foods, Flavors &Fragrances
Rapid, Reproducible HPLC
Analysis for Flavonoids in Cocoa 24
HPLC Accessories
Krornasil " HPLCBulk Packing Materials.. 26
GCAccessories
Cool Tools for Thermo Instruments 27
Peak Performers:
Inject ion Port Maintenance 28
General Information
Commonly Asked Quest ions 30
Restek Trademar1<s
Allure, Carbofrit, Crossbond, FastPack, Hycroquard,MegaMix,
Press-Tight, Resprep, Rtx, Rxi,SilcoCan, Siltek, Sulfinert, Thermolite,
Trident,Turning VisionsintoReality, Uniliner, Restek logo.
OtherTrademarks
API 3200, CurtainGas, IonSpray(Applied Biosysterns), AutoSYS
(PerkinElmer), Carbowax(UnionCarbideCorp.), Decthal (Amvac
ChemicalCorp.),Devrinol (United PhosphorusLtn.), Dursban(Dow
ChemicalCo.), Kel·F(3MCo.), Kromasil (EkaChemicals AB), Mylar,
Velpar, Viton(E.!. duPont deNemours & Co., Inc.), Sonar(Sepro
Corp.),Swagelok (SwagelokCompany),Terrazole(Uniroyal
Chemical Co., Inc.),Trace (ThermQuest Corp.), Unique (LecoCorp.).
Comprehensive 20 GasChromatography ­
Making GCSeparations Work Harder
By Dr. Philip Marriott, Professor of Chemistry,RMIT University, Melbourne, Australia,
We are entering a period in its development where the expectations
of comp rehens ive two-dimension al gas chromatography (GCx GC)
sho uld - justifiably - match the rhetoric. Since its inception about
15 years ago, researchers who have made it their (life) goal to devel­
op and promote GCxGC have waxed lyrical about the advantages
of GCxGC to the GC community. If we were to list the three pr i­
mary contr ibutions that are often ascribed to GCxGC, these would
be: (i) greater separation capacity; (ii) greater sensitivity; and (iii)
retention structure in the 20 data presentation that permits the
analyst to identify, or predict the identity of, related compounds
based on the molecular properties that contro l retent ion . At this
point, I should admit that I count myself guilty of being amo ngst those who have promul­
gated these advantages! Further, I also stro ngly support the position of GCxGC, and the
benefits it holds for volatile and semi-volatile chemical analysis. And if these benefits are
indeed general ou tcomes of GCxGC, then it is only logical that, sooner or later, this coupled
column techn ique will supplant the single-column method that has served us so well for
many years. But we might query whether single column GC has really served us so well.
Admittedly, it has been just about all we had, so we have had to learn to live with its inher­
ent limitations. Just as we might have recognised, and been frustrated by, the limited sepa­
ration capacity of single column GC (i.e., as we searched for more complete understanding
of th e molecular composi tion of complex samples), analysts turned their attention to
GC/MS which became routinely available. Considerable effort was devoted to implement
solutions based on mass-detection to provide the necessary uniqu e identification of indi­
vidual compo unds in (grossly) overlapping chromatograms. The mantra that MS can solve
(all) our overlap problems probably became a crutch that somewhat numbed our realisa­
tion, accord ing to my Research Group's philosoph y, that often "the only Solution is better
Resolut ion':
So, now that we have this new tool, what does it mean to the analyst?Well, in a simple answer
- everythin g! With extra separation, the rationale for having to rely on MS for comp ound
measurement (as opposed to ident ification ) might now be negotiable. This is a considerable
conceptual departure from the classical reliance on GC/MS. Extra sensitivity is a useful
propert y to analysts, but this may be a lesser advantage of GCxGc. The ability to remove
column bleed from solute elution does have benefits (when doing GCxGC /MS). The most
significant advantage is separation power. To be able to resolve many more compounds
immediately enables a mu ch more complete 'picture' of the comp osition of a sample.
Picture is used deliberately here, since the 20 GC presentation is very much akin to a pic­
ture. The comparison of 10 GC results is via a conventional GC trace - a one-dimensional
time-response plot. The comparison is limited by the extent to which peaks coincide, or give
mul tiple compo und respo nses at one point. In GCxGC, the greater separa tion and picture­
style GC plot means that we can simply compare two 20 pictur es. Each compound now
resides in its own 20 location which is determined by, or depends upon , the specific chem­
ical-physical properties of a molecule which generate the peak position thoug h specific
interaction s with the column stationary phases. The 20 plot has been called a chemical
propert y retention map, which has axes contro lled by retention mechanisms on each of the
two columns. Choice of column phases is crucial to the effectiveness with which compounds
are located within the available 20 space. Here, we will not consider how we genera te the
GCxGC experiment (i.e., the modul ation methods used), however a few comments on the
column selection are warra nted in th is text.
In GCxGC we usually couple a long 10 column directly to a short 20 column (or a regular
elution column to a fast elution column) . The second column has to work hard ! We ask it
to resolve peaks that are overlapping on the 10 column. Being abo ut 1 m in length, with a
need to complete continual, on-the- fly analyses of effluent from the 10 column within
about 4-5 s, perfor mance is everything. We use high carrier flow and nar row bore columns,
but actual conditions are flexible. We now commo nly find some regions of 10 GC analyses
where up to 5 - 10 or more compo unds co-elute. This is clearly beyond the scope of MS
Con tin ued on page 31.
Website : E-mail : TelNo : 03 9762 2034 . . . in AUSTRALIA