{"id":5141,"date":"2020-04-30T11:26:58","date_gmt":"2020-04-30T15:26:58","guid":{"rendered":"https:\/\/phytochemia.com\/?p=5141"},"modified":"2020-04-30T11:26:58","modified_gmt":"2020-04-30T15:26:58","slug":"pretreatments-gc-fid-ms-analyzes-hydrosols","status":"publish","type":"articles-de-blogue","link":"https:\/\/phytochemia.com\/en\/articles-de-blogue\/pretreatments-gc-fid-ms-analyzes-hydrosols\/","title":{"rendered":"Pre-Treatments for GC-FID \/ MS Analyzes – The Example of Hydrosols"},"content":{"rendered":"\n\n\n\n
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Hydrosol obtained with Explorer (an Alchemia Solution Still)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Corine Lormel, PhD<\/p>\n

Samples often contain very different molecules. In analytical laboratories, finding the instrument which will identify and quantify them is the first step. For this purpose, the chemist must ensure that the chosen method can “separate” the compounds of interest but also makes them “visible” to the detectors.<\/p>\n

Which Molecules can be Analyzed by GC-FID?<\/span><\/h2>\n

To be \u201cseparated\u201d in gas chromatography (GC) (principle here<\/a>), molecules must be volatile and thermally stable. That means they can pass into a gaseous state for temperatures typically below 325 \u00b0C without decomposing themselves. To be \u201cseen\u201d by the Flame Ionization Detector (FID), molecules must be oxidizable to the contact of the flame to emit ions that can be counted by the detector. Organic compounds such as hydrocarbons and partially oxygenated compounds are detectable. Water, which is an inorganic molecule, is undetectable, like some small highly oxygenated compounds.<\/p>\n

This introduction helps to explain why essential oils that contain exclusively volatile organic compounds are \u201cideal\u201d candidates for GC-FID analyzes. Without any pretreatment, all the molecules of the sample may show on the chromatogram.<\/p>\n

How to Deal With Hydrosols ?<\/span><\/h2>\n

Hydrosols also contain volatile organic compounds, but they are diluted in a huge amount of water. Since water is undetectable by the FID detector, no indication can be obtained on the volatile molecules\u2019 concentration. Moreover, this low concentration also generates such a low intensity signal that it can be hardly analyzable. Finally, the massive injection of water in the chromatographic columns we use routinely may damage them.<\/p>\n

A pretreatment step is therefore necessary to get rid of the water and concentrate the sample.<\/p>\n

Liquid-liquid extraction to concentrate the sample and suppress water<\/h3>\n\n\n\n
\"\"Separating Funnel\u00a0 Liquid-Liquid Extraction<\/em><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

To concentrate dilute solutions, liquid-liquid extraction is a commonly used process. The compounds to analyze (analytes) are extracted from their initial solvent and transferred into another solvent with more favorable chemical or physical properties in view of a subsequent treatment.<\/p>\n

In the case of hydrosols, the solvent must be:<\/p>\n