Two-dimensional chromatography of gasoline by on-line coupled HPLC-HRGC, as described in this paper, allows separarate GC analysis of paraffins and aromatics. The GC system contains a retention gap of only 10 rn length for introducing HPLC fractions of 100 pl volume. This becomes possible through evaporation of part of the solvent during introduction of the HPLC eluent. This "partially concurrent solvent evaporation" technique allows transfer of large volumes of HPLC eluent into relatively short retention gaps, maintaining the full efficiency of the solvent effects in reconcentrating the bands of the early eluted solutes.

The characterization of heavy petroleum fractions is essential for the design and improvement of cracking plants converting heavy feedstock into valuable "white" products. Conventional simulated distillation methods using packed columns are unsuitablefor this purposes, being limited to boiling points up to about 600OC. The method presented is able to cover a boiling points interval ranging from about 150°C up to around 800OC. It employs a short, nonpolar, highly thermostable capillary column routinely operated at temperatures around 430OC. The analytical system is based on a high temperatureversionof a fullyautoma-Dedicated to Professor Kurt Grob on his 65th birthday. tic, capillary dedicated gas chromatograph. The experimental data demonstrate that cold on-column injection is the sole sampling system suitable for such heavy compounds. The conversionof theretentiontimesinto boilingpoints, basedontheuseof low molecular weight polyethylenes, is extremely reliable, as demonstrated by the excellent retention time reproducibilities. The lower part (up to 550-600°C TBP) of the boiling point distribution curves of heavy petroleum fractionsobtained on capillary columns fits well with the corresponding distribution curves based on packed column data. For the petroleum fractionsfully eluted from the column the quantitative results obtained either using internal standards or by direct processing of the elution curves are in excellent agreement (less than 0.3 weight YO differences). The method has been applied to the determination of the true boiling points corresponding to short path vacuum distillation (DISTACT) cut points over 300OC. 0

Citrus essential oil analysis is characterized by the complexity of the separation of all the components which may belong to different classes of compounds and be present in a wide range of concentrations. Capillary GC is the best technique for characterizing the volatile fraction of citrus essential oil. In many cases, however, this technique does not achieve complete separation of all the components. A combination of LC and HRGC in off‐line methods is necessary to achieve complete resolution of the minor components present in the oil and in general to facilitate the identification of the components belonging to different classes. Very recently we have demonstrated the possibility of using on‐line HPLC‐HRGC coupling for fractionation and identification of alcohols in lemon oils. In the present work, a fully automatic HPLC‐HRGC instrument was used for the pre‐separation of the essential oils into the various classes of compounds, using gradient elution and multiple fraction transfer into the capillary column. This method allowed a pre‐separation of the components into four major classes of compounds: hydrocarbons, aldehydes, esters, and alcohols before their transfer into the GC. A good correlation with the existing off‐line methods was found. The ability of the Instrument to perform, In a fully automatic way, HPLC pre‐separation with gradient elution and GC transfer of more than one fraction from a single HPLC injection, was found to be very useful for routine characterization of various essential oils.

Modification of the Carlo-Erba cold on-column injector for (automated) analysis of high molecular compounds at high oven temperatures is described. The secondary cooling tube of the cold on-column injector is replaced by a lengthened tube through which a high air flow is directed. The injection site is maintained at 65-70°C while the oven is at high temperature (Z 3OOOC). For automated injection, a short deactivated precolumn of 22 to 30 cm X 0.53 mm i.d. is coupled to the analytical column via a butt connector with make-up gas supply. For a triglyceride mixture, automatically injected at 300°C, the mean %deviation forall peakareaswas 1.8%and themean%deviation for all retention times was 0.09% for five consecutive runs.

SummaryCharacterization of fuels by LC-GC is possible by use of automatic successive transfer (multiple transfer) of HPLC fractions to a GC via an on-column interface. This paper describes the instrumentation and the methodology for the HPLC separation of the hydrocarbons (aliphatic and aromatic) into separate groups and the on-line transfer of these groups to a capillary GC column. Two HPLC methods were used with the same valve configuration: single column (silica) with column back-flush to detector; and double column (silica and amino-bonded silica) with multiple fraction transfer and back-flush. The first method was used for the analysis of total saturated compounds and total aromatic compounds; the second was used for the separation of the one-, two-, three-, and four-ring aromatic compounds present in diesel fuels. Examples are shown of the characterization of diesel fuels, and the repeatability of the data.