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View/Open - ARAN - National University of Ireland, Galway

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Introduction<br />

Figure 1.5: HPLC Chromatogram from a typical SARA analysis. The bold line represents<br />

the RI signal, while the thin line represents the UV signal at 254nm.<br />

The maxima <strong>of</strong> the aromatic and resin peaks are cut for better visualisation.<br />

Reproduced from [35].<br />

In the case <strong>of</strong> complex mixtures covering a broad range <strong>of</strong> molecular weights and<br />

polarity, currently available chromatographic methods <strong>of</strong>ten have some limitations.<br />

Problems can arise from inadequate resolving power, low volatility, low solubility <strong>of</strong><br />

the components in the chromatographic mobile phase, strong adsorption <strong>of</strong> sample<br />

components on the stationary phase, or low detector sensitivity. Thus, no sin-<br />

gle HPLC method can be utilised for all types <strong>of</strong> crude oils so specific methods<br />

must be developed. A particular crude oil may need specific solvents, detectors and<br />

columns [16]. Because <strong>of</strong> these limitations <strong>of</strong> HPLC, the OCLC method is still<br />

used regularly for the analysis <strong>of</strong> crude oils, particularly when separations <strong>of</strong> large<br />

quantities are required [33].<br />

12

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