Analytical Instrumentation

Total Sulfur at Ultra Trace Level with Nitrogen Oxide Elimination Technology (NO-ET)

Jan 06 2017 Comments 0

When analysing Total Sulphur in Petroleum Products and Derivatives at trace level (<1ppm), interference of high Nitrogen concentrations becomes significant. TE Instruments developed Nitrogen Oxide Elimination Technology (NO-ET) in order to analyse the true amount of Total Sulphur at trace level in samples that contain high quantities of Nitrogen.

During combustion, the amount of Nitrogen present in the sample is converted into Nitrogen Oxide molecules (NO2). The NO-molecules interfere by emitting light at the same wavelength as SO2 during the absorption and excitation stage of UV-Fluorescence detection technique. Resulting in a false (positive) contribution of 0.4% Nitrogen to the measured amount of Total Sulphur.

The innovative XPLORER-S and, in particular, its UV-Fluorescence detector has reduced sensitivity to the false contribution of NO. When absolute elimination is required, the XPLORER-S will be tailored with NO-ET. The NO-molecules are destructed which prevents incorrect measuring of ultra-low (<1 ppm) Total Sulfur concentrations.

Cumene is the common name for Isopropyl benzene, an organic compound which is an aromatic hydrocarbon present in Crude Oil and Refinery Fuels. During the production process wherein Benzene is converted to Cumene, expensive zeolite-based catalysts are used. The catalyst material is affected by Sulphur compounds present in Benzene. By measuring Total Sulphur in the final product, determination whether and when the catalyst require replacement can be achieved more accurately.

To demonstrate the effect of TE Instruments’ solution against Nitrogen Oxide interference, a Cumene sample was measured on a XPLORER-NS and a XPLORER-S equipped with NO-ET, introduced by the ARCHIE liquids auto sampler:

Sample

Concentration S  (µg/L or ppb)

RSD (%) n=4

Concentration N (mg/L or ppm)

RSD (%)

n=4

 

Dilution

Cumene XPLORER-S NO-ET

199.87

0.65

-

-

-

Cumene XPLORER-NS

295.52

2.32

22.79

0.97

-


The mathematical approach containing typical correction of 0.4% for NO matches.

The results with interference are 295.52 μg/L for Total Sulphur and 22.79 mg/L for Total Nitrogen.

- 22.79 : 100 x 0.4 = 91.16 μg/L
- 295.52 – 91.16 = 204.36 μg/L Sulphur as corrected concentration

The XPLORER-S equipped with NO-ET provides 199.87 μg/L as a result which demonstrates that the interference is almost completely eliminated.

To demonstrate the ultimate sensitivity of the XPLORER-S equipped with NO-ET, the Cumene sample was diluted and measured under the same conditions:

Sample

Concentration S  (µg/L or ppb)

RSD (%) n=4

Dilution

Cumene  XPLORER-S NO-ET

101.11

0.73

2

Cumene  XPLORER-S NO-ET

29.09

3.99

6.02


The XPLORER-S provides a repeatability (%) lower than 5% at trace level in a high Nitrogen containing Cumene sample. The above shown data clearly proves the effectiveness of the NO-ET for this application.

Note: All solvents and gases (Ar/O2) must be of high purity to accurately measure Total Sulphur at trace level.

For more information regarding TE Instruments’ solution against Nitrogen Oxide Interference, contact our Sales Team (sales@teinstruments.com).

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