Evaporative Light Scattering Detector (ELSD) ANALATYCAL CHEMISTRY 427 PHC Done by: Madawi AlUbied Areej Alsuwayyid

Objectives What is Evaporative Light Scattering Detector ? Capabilities how does it work? Characteristic properties Advantages Sensitivity Problems

1. What is Evaporative Light Scattering Detector ? Evaporative Light Scattering Detectors (ELS Detectors) are essentially universal detectors. primarily used in High Performance Liquid Chromatography (HPLC). ELS detectors are an ideal substitute, or supplement to, traditional HPLC detectors for liquid chromatography concentration detection.

2. Capabilities The detector responds to all compounds that are, relative to their mobile phase, sufficiently nonvolatile at the conditions of analysis. ELSD is suitable for all LC separated analyses that does not have light absorbing chromophores. So it dose not rely on optical properties . Ex: phospholipids, carbohydrates, amino acids , fatty acids and synthetic polymers.

3. how does it work? 3 key stages: 2 3 1

Nebulizer uses a stream of inert gas to transform eluent from LC into fine vapor of uniform size droplets

Stage 2: Evaporation  Evaporative tube temperature is controlled to remove solvent from less volatile analyte particles , also the tube has low volume to minimize heat dispersion

Detector has high-efficiency LED light (or short wave length high power laser) to maximize scattering of small analyte particles

4. Characteristic properties Low background noise (no solvent peaks) Reproducibility (in the 1μg range, STD ~ 1%) Low band broadening (short transit time) “Near” linear response (instrument and concentration dependent, smart choice of stand)

5. Advantages No sample preparation No drivatisation Universal - responds to all compounds in the mobile phase Not dependent on spectroscopic properties of analyte Not susceptible to baseline drift during gradient elution, temperature or solvent pump fluctuations ELSD compatible with a much wider range of solvents compared to Refractive Index detector No interference from solvent front peaks (enables fast analysis) Flow rates up to up to 5ml/min can be achieved with no affect on baseline stability Ideal for High Throughput Screening and quantification

The ELSD Improves Baseline Stability and Detection Sensitivity Compared to RI 10278 1. Fructose 2. Glucose 3. Sucrose 10277 Column: Prevail™ Carbohydrate ES, 5µm, 53 x 7mm (Part No. 35104) Mobile Phase: Acetonitrile:Water (75:25) Flowrate: 2.0mL/min RI ELSD

6. Sensitivity Sensitivity with ELSD is limited to 1–50 ng on-column in the best instances. the followings factors are considered to be affect ELSD sensitivity : Gas quality Solvent quality Column contributions Solvent modifiers

7. Problems: arising with an ELSD are usually manifest in a noisy baseline. This can have several causes: Evaporation Temperature too low: the solvent is not completely evaporated. Evaporation Temperature too high: the solvent is boiling in the nebuliser. Air or nitrogen not clean: remove traces of water or oil with a filter. Gas flow too low: poor nebulisation of the eluent. Involatile material in the eluent: replace any buffer salt with a volatile one (such as ammonium acetate) and ensure that the eluent is particle free.

References http://www.usedhplc.co.uk/UsedHPLC- IntroductiontoEvaporativeLightScatteringDetectorsELSD.htm http://www.separationsnow.com/details/ezine/sepspec10174e zine/Exploring-the-alluring-charms-of-a-charged-aerosol- detector-for-HPLC.html?tzcheck=1 http://www.laserchrom.com/LaserchromHPLC- TechnicalSupportCentre-TechnicalTips-IntrotoELSD.htm http://fxg-ent.com/downloads/SoftaELSDBrochure.pdf