THE NEW STANDARD IN SPECIATING SULFUR AND NITROGEN BY GAS CHROMATOGRAPHY
SeNse is a new detector that has been developed by AC Analytical Controls (PAC) for Gas Chromatography applications aiming to determine Sulfur species in hydrocarbon type matrices. While still based on the Chemiluminescence principle that was employed fi rst in the Antek 7090NS model, the detector has undergone a signifi cant redesign to provide unsurpassed sensitivity resulting in lower detection limits, excellent equimolar response, dynamic range and selectivity. A fast cold start-up, unrivalled signal stability, the sturdy but compact design, and the touchscreen interface makes it the easiest to work with.
The SeNse Sulfur Chemiluminescence Detector (SCD) and/or Nitrogen Chemiluminescence Detector (NCD) is a detector used in GC applications. The effl uent of the GC application is led to the base of the SeNse furnace. The components are mixed with air and hydrogen and oxidized in the furnace on top of the GC. The effl uent of the furnace is directed into the reaction cell under infl uence of an oil free vacuum pump. In the reaction cell, a Chemiluminescence reaction of Sulfur or Nitrogen containing molecules takes place under infl uence of ozone. The emitted light passes an optical fi lter and enters the PhotoMultiplier Tube (PMT) where a small current is generated.
INTRODUCTION:
The principle of operation for sulfur detection begins with the complete, high temperature oxidation of the entire sample matrix.
As each component elutes from the GC column, the component reacts with oxygen at oven temperatures ranging from 700- to 900°C. Oxidation products include CO2
, H2 O, SO2 of chemically bound sulfur to SO2
oxidized gases react with hydrogen (reduction), generating reduced sulfur species. The reduced sulfur species are then passed through the reaction chamber where they react with ozone. The reduced sulfur species react with O3
(under ideal conditions). The conversion (sulfur dioxide) is quantitative. The
Figure 1: Sense Stability over a timeperiod of 72 hours. 72 hours. The obtained response for each individual compound were found to be within 1.5% RSD. (ozone), produced by
* (sulfur dioxide in the excited state). As the excited species decays to the ground state, light is emitted and detected, at specifi c wavelengths, by a photomultiplier tube. This Chemiluminescent emission is selective for sulfur and is proportional to the amount of sulfur in the original sample.
an on-board ozone generator to form SO2
DEVELOPMENT:
In the development process of the new SCD unit all aspects of the Chemiluminescence phenomenon were considered and optimized to create a detector with unsurpassed signal stability over longer periods of time. Extensive studies on ceramic tube material, together with the optimization of the oxidation and reduction reaction conditions, has resulted in a unit performing with best in market stability over longer periods of time. Figure 1 represents a stability run of 30 injections over a period of
EQUIMOLARITY:
The SCD is an equimolar detector; therefore, all sulfur compounds are assumed to produce an equivalent response as sulfur. The response factors for all calibration components in the calibration gas are calculated and listed in Table 1. The response factor of each single sulfur compound are within 5% of the response factor for hydrogen sulfi de.
The optimized Chemiluminescence process together with improved electronics and digital fl ow control has resulted in a unit with surpassed sensitivity, excellent equimolar response, dynamic range and selectivity.
The performance specifi cations of the new SeNse SCD Chemiluminescence detector were cross- checked against ASTM D5504 (Sulfur compounds in Natural gas) based on the GC confi guration shown in Figure 2.
SENSITIVITY:
The Detection limit is calculated based on a ~ 50 ppb dilution (using a Mass Flow Controller) from a calibration standard containing Hydrogen Sulfi de (H2
S), Carbonyl Sulfi de (COS), Methyl Mercaptane
(MeSH), Ethyl Mercaptane (EtSH) and Dimethylsulfi de (DMS), presented in Figure 3. The calculated limit of the detector for each individual compound is below <5 ppb (LDL 3*N).
ANNUAL BUYERS GUIDE 2017 •
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