ATOM’s Excimer technology is the principal technology used in our analyzers for total sulfur measurement. The benefits of using this technology are numerous allowing analyzers to be designed for ease-of-use, reduced maintenance, and increased reliability.
Excimer Technology :
- Higher Spectral Purity
- Higher Relative Sensitivity
- Highly Reduced Nitrogen Interference
- Longer Life Relative to Other Sources (Operational and Calibration Cost Savings)
Analyzer Design :
- Bottled O2 not needed for Analysis
- Bottled Carrier Gas not needed for Analysis (e.g.: Argon)
- High Speed Analysis (60-100s per cycle for majority of applications)
- Fast Response Time (99% of response in 1 cycle)
- Standard Operation does not require installation in a shelter
- Compact Footprint
- Low Utility Consumption (4-6 weeks on standard 300 ft3 compressed air bottle)
Principle of Operation
The UV Fluorescence method is the most simple and practical low-level sulfur analytical technique. It has been widely used and proven over many years of use in industrial settings. This method involves the injection of a sample into a high-temperature oxidation furnace, converting all hydrocarbons into water (H2O) and carbon dioxide (CO2). Total sulfur contained in molecular-bound hydrocarbon species is oxidized at temperatures in excess of 1000°C into sulfur dioxide (SO2) by the reaction:
R-SH + R-NH + O2 → SO2 + CO2 + H2O
The furnace effluent containing these combustion byproducts is directed into a detection chamber where it is excited by high-energy, short-wavelength emission from the EUVF of Excimer UVF source. The UV photons from the excitation source, transfer energy into the SO2 molecule and raise its energy level to create an excited singlet state. These excited molecules rapidly decay back to their lower energy ground state releasing the absorbed energy as a secondary emission known as fluorescence.
SO2 + hv → SO2* → SO2 + hv’
Fluorescence emission is optically filtered to remove undesired wavelengths from excitation source and background scatter within the detector chamber. Detection of filtered fluorescence emission is accomplished using a Photomultiplier Tube and amplified by proprietary high sensitivity electronics.
Excimer Technology Benefit
ATOM’s Excimer lamp emission has significantly higher spectral purity than other commercially available UV lamps such as Zinc and Xenon lamps.
The above graph reflects principle spectroscopic emission differences between a zinc lamp (blue trace) and ATOM’s Excimer UV lamp (red trace) across the UV and visible wavelength region. The 214 nm zinc emission line traditionally used in UV Fluorescence analysis represents less than 20% of its entire emission spectrum. By comparison, the quasi-monochromatic emission of ATOM’s Excimer UV lamp represents about 90% of its total emission spectrum. The 222 nm peak emission wavelength of ATOM’s Excimer UV lamp has been shown to be ideally suited and superior for the detection of total sulfur.
Unsurpassed Nitrogen Interference Reduction
The ATOM Excimer technology is much less sensitive to interference from molecular-bound nitrogen, which can significantly affect the accuracy of sulfur measurement depending on the composition of the analyzed samples.
The above 3 samples demonstrate the superior Nitrogen Rejection obtained with ATOM’s Excimer technology. The certified sulfur sample contains 1.453 ppm/wt sulfur as Dibutylsulfide whereas the nitrogen sample contains 8850 ppm/wt nitrogen as Pyridine. The Blank sample, as well as the balance of the two other samples, was HPLC-grade iso-octane. All samples were run in triplicate and the average of each sample was used to calculate nitrogen rejection according to the formula:
The molecular-bound nitrogen in the pyridine sample is nearly 0.9% by weight, but its response is less than half of the 1.453 ppm/wt. sulfur sample, resulting in a nitrogen rejection ratio greater than 5,000:1. Also note, that the Blank sample has almost no detectable response. This unsurpassed nitrogen rejection is highly beneficial in reducing measurement error when analyzing high nitrogen content samples for sulfur content.
The above graph shows achievable emission stability of ATOM’s Excimer UVF lamp over a period of 5,000 hours (about 7 months). After 7 months of operation, the lamp has only lost about 7% of intensity. Lamp lifetime far exceeds that obtained with other commercially available UF lamps.
ATOM Analyzers based on Excimer UV fluorescence technology meet or exceed all operational and performance requirements set forth in the following methods:
ASTM D 5453
Standard Test Method for Determination of Total Sulfur in Light Hydrocarbons, Spark Ignition Engine Fuel, Diesel Engine Fuel, and Engine Oil by Ultraviolet Fluorescence Scope: This test method covers the determination of total sulfur in liquid hydrocarbons, boiling in the range from approximately 25 to 400°C, with viscosities between approximately 0.2 and 20 cSt (mm2/S) at room temperature.
ASTM D 6667
Standard Test Method for Determination of Total Volatile Sulfur in Gaseous Hydrocarbons and Liquefied Petroleum Gases by Ultraviolet Fluorescence Scope: This test method covers the determination of total volatile sulfur in gaseous hydrocarbons and liquefied petroleum (LP) gases. It is applicable to analysis of natural, processed, and final product materials containing sulfur in the range of 1 to 100 mg/kg.