SIMULTANEOUS DETERMINATION OF SOLVENT YELLOW 124 AND SOLVENT RED 19

IN DIESEL OIL USING FLUORESCENCE SPECTROSCOPY AND CHEMOMETRICS

J. Orzeł, M. Daszykowski, and B. Walczak

Department of Analytical Chemistry, Chemometric Research Group, Institute of Chemistry, The University of Silesia,

9 Szkolna Street, 40-006 Katowice, Poland

Introduction

Diesel oil is commonly used for transport, heating and agricultural machinery.

Depending on the usage, the tax for diesel oil is different in most European

and American countries. A low-tax fuel (meant for heating, agricultural

machinery) is spiked with additives that change its physicochemical properties

(for instance changing the color).

Two additives are introduced into diesel oil in all countries: a marker and a dye,

however their type and concentration levels vary from country to country. In all

countries fuel for heating and agricultural machinery is dyed red whereas fuel

used for transport has no additional tax-component introduced thus it is yellow,

see Fig. 1.

References

[1] European Commission Decision 2003/900/EC

[2] Polish Finance Minister Decision, Polish Journal of Laws 157 (2010) 1054

[3] T. Lisinger, et.al., Energ. Fuels 18 (2004) 1851-1854

[4] DIN 51430

[5] T. Naes et al., A user-friendly guide to multivariate calibration and

classification, NIR Publications, Chichester, 2002. [6] R. Bro, J. Chemom., 10 (1996) 47-62.

Marker it is a compound described as a irremovable from the diesel oil

matrix. In European Union countries a diazo compound - Solvent Yellow 124

(SY124) has been introduced as a common marker for low-tax fuels [1]. The

concentration of SY124 in spiked fuel should be not less than 6.0 mg·L-1 and

not higher than 9.0 mg·L-1.

Dye it is a compound changing the color of fuel to red. As a dye different

diazo compound are used (the type and concentration depends on the law of

certain countries). Example of popular red dyes are Solvent Red 164 (SR164),

Solvent Red 19 (SR19), and Solvent Red 26 (SR26).

In Poland, the concentration of the marker in diesel oil is regulated by the

European Norm [1], and the concentration of dye cannot be lower than

6.6 mg·L-1 for SR164 and 6.3 mg·L-1 for SR19 [2].

Description of a problem

Substantial differences in tax encourage oil adulteration through removing the

marker and dye compounds. Thus, by changing the purpose of fuel, it has an

increased value on the market. Decreased levels of the marker and dye in oil

or their absence are an indication of a possible oil adulteration. Therefore fast

and low cost methods for evaluation concentration of both additives in diesel

oil are required.

Analytical methods for evaluation the level of concentration of these

compounds exist [3,4]. However, the chromatographic separation of tested

components from complex diesel oil matrix is necessary. The high

performance liquid chromatograph is used for that purpose in developed

methods. Further analysis is performed using UV-Vis detection and the

calibration models.

Proposed approach

An analytical procedure combined with a chemometric approach to determine

the content of SY124 and SR19 was proposed. Owing to the sensitivity of the

excitation-emission fluorescence technique and fluorescence properties of

tested compounds (the chemical structure is presented in Fig. 2) samples were

described by their excitation-emission spectra and multivariate calibration

techniques (e.g. partial least squares [5] and three-way partial least squares

[6]) were used to detect any possible adulteration process that may lead to

a partial or nearly complete removal of SY124 and SR19 from fuel.

Fig. 1 Diesel oil free of additives and spiked with tax-additives

Fig. 2 Chemical structure of SY124 (left) and SR19 (right)

Data set

A set of 20 calibration solutions of diesel oil simultaneously spiked with both

additives (the concentrations were kept in a range of 0 and 10 mg·L-1) was

prepared. Every sample was prepared three times (laboratory replicates). For

each of them excitation-emission fluorescence signals (EEM) were recorded

(emission spectra were registered in a 2 nm interval from 350 to 800 nm at 46

excitation wavelengths selected in a 10 nm interval in the range of 250 and

700 nm). Three technical replicates collected for a single sample gave in total 180

EEMs. An example of EEM of diesel oil sample spiked with both additives and not

spiked is shown in Fig. 3.

350 450 550 650450

550

650

750

0

100

200

300

400

Inte

nsity

Excitation [nm]Emission [nm] 350 450 550 650450

550

650

750

0

100

200

300

400

Inte

nsity

Excitation [nm]

Fig. 3 EEM of diesel oil free of additives (left) and spiked with tax-additives (right)

Results

The PLS model was constructed using unfolded EEM (the data size was

1801396 – samples (excitation wavelengths emission wavelengths)),

whereas the N-PLS model was constructed using the three dimensional data (the

data size was 18022646 – samples excitation wavelengths emission

wavelengths). For calibration models construction the model set of 120 spectra

(two out of three laboratory replicates) was used. The remaining 60 fluorescence

spectra formed the test set. Calibration models were constructed separately

according to the SY124 and SR19 concentration in samples.

Obtained results are presented in Fig. 4 (as y predicted vs. y observed for model

and test set samples) and in Table 1 (the complexity, fit, and prediction properties

of constructed model are given).

PLS

Additive f fit prediction

SR19 8 0.175 0.189

SY124 8 0.237 0.257

N-PLS

Additive f fit prediction

SR19 10 0.174 0.184

SY124 10 0.206 0.221

Fig. 4 PLS models for SY124 (a) and SR19 (b)

and N-PLS models for SY124 (c) and SR 19 (d)

Table 1 Complexity (f), fit and

prediction of developed models

Conclusions

Calibration results give a clear indication that the fluorescence spectroscopy,

which is fast and cost effective, combined with multivariate calibration techniques

can be applied successfully to examine the content of SY124 and SR19 in oil

samples and to trace their adulteration.