Analysis of Sulfur in Oils according to ASTMD2622 MethodThermo Scientific ARL PERFORM'X Series Advanced X-Ray Fluorescence Spectrometers

IntroductionIn order to demonstrate the analysis of sulfur (S) in oil, acalibration curve has been prepared according to theASTM D2622 norm and repeatability tests done.

InstrumentThermo Scientific ARL PERFORM’X series spectrometerused in this analysis was a 4200 watt system. This systemis configured with 6primary beam filters, 4collimators, up to ninecrystals, two detectors,helium purge and our5GN+ Rh X-ray tube forbest performance fromultra-light to heaviestelements thanks to its 50micron Be window. Thisnew X-ray tube fitted witha low current filamentensures an unequalledanalytical stability monthafter month.

The ARL PERFORM'Xoffers the ultimate in performance and sample analysissafety. Its unique LoadSafe design includes a series offeatures that prevent any trouble during sample flushingand loading. Liquid cassette recognition prevents anyliquid sample to be exposed to vacuum by mistake. Overexposure safety automatically ejects a liquid sample ifX-ray exposure time is too long.

The Secutainer system protects the primary chamberby vacuum collecting any loose powders in a speciallydesigned container, easily removed and cleaned by anyoperator. For spectral chamber protection, the ARLPERFORM'X uses a helium shutter designed for absoluteprotection of your goniometer during liquid analysisunder helium operation. In the "LoadSafe Ultra" optionalconfiguration, a special X-ray tube shield provides totalprotection against sample breakage or liquid cell rupture.

Sulfur analysis in oils The ASTM D2622 norm hasbeen followed and six standardsamples have been prepared inorder to construct a calibrationcurve. The analytical conditionswere set according to the ASTMnorms.

The S net intensities have beendetermined with the followingformula:S net = (S Ka1, 2 – S background)

The intensity of each standard has been correlatedwith the S content in ppm, which resulted in thecalibration curve shown in Figure 1. Table 1 gives thenumerical results including the absolute differencebetween nominal and calculated concentrations, as well asthe Standard Error of Estimate.

Sample # S net Nom. Calcul. AbsoluteConc. % Conc.% diff. %

502 25.031 0.502 0.497 - 0.005998 48.647 0.998 1.009 0.0112045 92.567 2.045 2.042 - 0.0033009 129.271 3.009 2.995 - 0.0144027 166.437 4.027 4.045 0.0184986 196.284 4.986 4.979 - 0.007Standard error of estimate: 0.015%

Table 1: Calibration results

Figure 1: S calibration curve

Key Words

• ARL PERFORM'X4200 W

• Oil

• X-ray fluorescence

• XRF

• ASTM D2622

ApplicationNote: 41667

Stability test on a sample of oil residuecontaining sulfurA sulfur stability test has been made on an oil residuesample, loaded into three different liquid cells: A, B and C.

Each cell was analyzed three times; the results areshown in Table 2.

Run # Cell A Cell B Cell CS concentration in % S concentration in % S concentration in %

1 3.60 3.59 3.552 3.61 3.60 3.563 3.59 3.58 3.57Average 3.60 3.59 3.56St.Dev. 0.008 0.011 0.008

Table 2: Stability test on an oil residue sample

Examination of these results reveals the excellentrepeatability of analysis that can be achieved for S in oilwith the ARL PERFORM'X XRF.

Analysis of unknown oil samplesFour unknown samples were prepared and each wasloaded into three different cells: crude oil, heavy oil andtwo different oil residues.

Table 3 shows the repeatability results obtained aswell as a comparison with the certified sulfurconcentration.

Sample Certified Specimen Specimen Specimen Average St.Dev. RSDvalue % #1 % #2 % #3 % % % %

Crude oil 2.05 1.998 2.000 1.999 1.999 0.002 0.121Heavy oil 2.10 2.072 2.063 2.068 2.068 0.004 0.215Oil residue 1 4.6 4.785 4.772 4.771 4.776 0.008 0.169Oil residue 2 3.6 3.612 3.616 3.600 3.609 0.008 0.235

Table 3: Analytical results and comparisons for 4 unknown oil samples

ConclusionGood calibration curves can be obtained with the ARLPERFORM'X XRF for sulfur determination in oil whenapplying the appropriate ASTM standard method.

Thanks to the reproducibility of loading and to theinnovative helium shutter protecting the goniometerchamber from the helium environment, high repeatabilityof analysis can be demonstrated for S analysis.

The results obtained either for concentrations or forrepeatability show that very good accuracy and precisioncan be achieved with the ARL PERFORM'X XRFinstrument. This instrument is well suited for the analysisof S in petrochemical products.

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