Method of determining zinc dithiophosphates in engine oil

FIELD: chemistry.

SUBSTANCE: method includes preparing a 1% solution of engine oil in hexane for full extraction of zinc dithiophosphates from engine oil and purity of the obtained samples; adding the obtained solution to an extraction cartridge filled with hydroxylated silica gel in amount of not more than 2 ml of the 1% solution of the oil in hexane per 1 g sorbent; successively passing a hexane:acetone mixture taken in volume ratio of 9:1, respectively; passing an isopropanol:water:phosphoric acid:acetonitrile mixture, taken in ratio of 4:2:0.4:1, respectively. Each mixture is taken in amount of not less than 1.5 times the volume of the oil solution in hexane. An aliquot of the obtained solution is analysed by RP HPLC.

EFFECT: high accuracy and reliability of determination.

1 tbl, 7 dwg

 

The invention relates to the field of analytical chemistry for the determination of additives in motor oils and may find application in analytical laboratories, manufacturing and technology labs, oil refineries, forensic practice.

In the modern system of quality control engine oils controlled the main characteristics of engine oils are their physico-chemical properties, and the establishment of their component composition is not provided. On the other hand, identification and quantification of the components of the additive package is necessary not only for determining the quality of oils and prediction of performance properties, but also the falsification detection products, as well as to address some of the forensic challenges. Various manufacturers of engine oils, and transmission & hydraulic is widely used multifunctional additive zinc dithiophosphates characterizing largely anti-oxidation, antiwear and antifriction properties of these oils (Fuels, lubricants, technical liquids. Range and application: Guide / G. I. Anisimov, K. M. Badyshtova, S. A. Blatov, etc.; Under the editorship of V. M. Shkolnikov. Ed. 2nd revised and enlarged extra - M.: Publishing center ")", 1999. - 596 p.).

The known method of determining presado� by flame atomic absorption spectroscopy, comprising dissolving in kerosene samples of oils with subsequent burning in the flame of a gas burner and the determination of spectral absorption at a wavelength of 213.9 nm (GOST R 52666-2006. The lubricating oil. The concentrations of barium, calcium, magnesium and zinc by atomic absorption spectrometry. - Introductio. 2008-01-01. - M.: Publishing house of standards, 2007. - 16 (C). This method allows to determine only the active elements are the metals included in the composition of additives, but does not allow to set the type of chemical compounds and identify the components of the additive.

Known IR-spectroscopic method of detecting dialkyl(aryl)dithiophosphates of zinc on the most intense bands of the stretching vibrations of the P=S in the 650-670 cm-1and R-O-s in the 970-1020 cm-1(I. Zolotarevsky A. Forensic investigation of petroleum products and fuels & lubricants / I. A. Zolotarevsky, M. L. Karabach, V. A. Kiselev and others - M.: VNOISE. - 1989. - Vol. 2. - 178). Identification and quantification of additives is complicated significantly impede the influence of similar functional groups of the various components of the oils.

The known method of determination of zinc dithiophosphates by gas chromatography, but its ability is limited by the need for prior derivatization of zinc dithiophosphates. (Becchi, M. Structural determination of zinc dithiophosphates in lubricating oilsby gas chromatography-mass spectrometry with electron impact and electron capture negative ion chemical ionization / M. Becchi, F. Perret, B. Carraze, J. F. Beziau, J. P. Michel // Journal of Chromatography A. 2001. - Vol. 905. - P. 207-222).

The closest method to the determination of additives, which represents a salt of the ester of dithiophosphoric acid, is the method by reversed-phase high-performance liquid chromatography (reverse phase HPLC) consisting of sample preparation extraction of the additive methanol. The oil sample is mixed with methanol in a ratio of 1:2 respectively, then the resulting extract chromatographic column on CAC-4. Mobile phase - acetonitrile:water (80:20), detector - UV, 254 nm (Kamaev V. A. Application of liquid chromatography in the study of forensic objects: methodical recommendations / V. A. Kamaev. - M.: forensic science center of the Ministry of internal Affairs, 1994. 20).

The disadvantage of this method is that extraction of the additive methanol has a low (32%) the degree of extraction and the methanol sextrailer well as a number of components of the oil are deposited on a chromatographic column and significantly affect the analysis results.

The technical result of the invention is the completeness of extraction of dithiophosphates of zinc from motor oil and the purity of the resulting samples.

Said technical result is achieved by preparing a 1% solution of motor oil in hexane. In an extraction cartridge filled with hydroxylated silica gel, bring the solution up to 2 m� 1% solution of oil in hexane per 1 g of sorbent, then passed successively a mixture of hexane:acetone, taken in a volume ratio of 9:1 respectively; then the mixture was passed isopropanol:water:phosphoric acid:acetonitrile in the ratio 4:2:0.4:1, respectively; wherein each mixture take not less than 1.5 times the volume of the solution of oil in hexane. An aliquot of the resulting solution was analyzed by reverse phase HPLC method.

The distinctive features of the claimed method:

- the use of solid-phase extraction gidrauxilirovanne silica gel to separate the oily bases;

- separation of components of engine oil using optimal extraction of mixtures composition and volume;

the transmission sequence of formulas.

Fig. 1 - Thin-layer (TLC) chromatograms comparing the mobility of zinc dithiophosphates in mixture No. 1 (1. a); in mixture No. 2 (1. b). Aliquots of a solution of oil Mobil 1 New Life in hexane - 1; oil Mobil 1 New Life - 2; oil Mobil Super M - 3; oil Shell Helix - 4; additive DF-11 - 5.

Fig. 2 - illustration by TLC-the mobility of zinc dithiophosphates in the presence of phosphate (2. a) and acetic acid (2. b). Aliquots of a solution of oil Mobil 1 in hexane mixed in a ratio of 1:10 to 1; Mobil oil 1-2; acetonitrile extract from Mobil oil 1-3; additive DF-11-4.

Fig. 3 - chromatogram of engine oil Mobil 1 New Life. Conditions of chromatography: Quadrex column (30 m, 0.25 mm); temperature program: 150°C 5 min), heating up to 280°C (15 min), 280°C (50 min); carrier gas - nitrogen; detector flame ionization.

Fig. 4 - chromatogram of the extract from engine oil Mobil 1 New Life, the extractant - acetone mixed with oil at a ratio of 10 to 1, respectively; when the chromatography conditions described above.

Fig. 5 is the chromatogram of the extract from engine oil Mobil 1 New Life, the extractant - acetonitrile, mixed with oil at a ratio of 10:1, respectively; when the chromatography conditions described above.

Fig. 6 is the chromatogram of the extract from engine oil Mobil 1 New Life, the extractant is methanol, mixed with oil at a ratio of 10:1, respectively; when the chromatography conditions described above.

Fig. 7 is a chromatogram of the extract from engine oil Mobil 1 New Life, the extractant - ethanol, mixed with oil at a ratio of 10:1, respectively; when the chromatography conditions described above.

The authors evaluated the possibility of applying the elution systems, which are used for separation of additives on the plate for thin-layer chromatography (TLC), in an embodiment, the solid-phase extraction (Tagirov, because a Comprehensive study of lubricants based on synthetic, and mixed petroleum oils / T. Tagirov K., Polyakov D. Y. - M.: Federal center of forensic expertise, 2009. - 203). We adopted a mixture of the following composition:

- No. 1 - hexane:acetone in the ratio 9:1;

- No. 2 - ethanol:water:acetic acid:acetone in the ratio 8:2:2:1.

The dithiophosphates of zinc in the mixture No. 1 does not have mobility, separated base oil base, and mixture No. 2 additive moves on the plate and detected by dithizone in the form of pink patches with Rf=0.5-0.6 (Fig. 1).

To assess the applicability of these compounds in the cartridge for solid phase extraction, filled hydroxylated silica gel made with 0.5 ml hexane solution of motor oil, then passed successively the mixture is No. 1 in the amount of 10 ml and the mixture No. 2-5 ml. In the processing of the sorbent by dithizone in chloroform it was painted in pink color, which is typical of dithizonate zinc and points to the incompleteness of its extraction. Increasing the number of mixture No. 2 did not lead to a significant shift of the dithiophosphates of zinc on the sorbent, which confirms its pink color after treatment with dithizone.

In order to increase the mobility of zinc dithiophosphates mixture No. 2 was modified by replacing the ethanol to isopropanol and reducing the alcohol content is 2 times. Also, replaced the acetone in acetonitrile, as he used transparent in the UV region of the spectrum when analyzing by HPLC. Using a mixture of isopropanol:water:acetic acid:acetonitrile in the ratio 4:2:2:1 respectively, the mobility of zinc dithiophosphates on a plate for thin-layer� chromatography has not changed. To increase the mobility phase acetic acid was replaced by phosphoric. On two plates for thin-layer chromatography aliquots were applied:solution of Mobil 1 oil in hexane 1:10-1; Mobil oil 1-2; acetonitrile extract from Mobil oil 1-3; additive DF-11 - 4. First, both plates were placed in a mixture of No. 1, then dried and placed in a mixture of No. 2. The first plate was chromatographically in mixture No. 2 containing phosphorus (Fig. 2.a) acid, and the second - acetic acid (Fig. 2.b). Detection of zinc dithiophosphates conducted by dithizone in chloroform. As can be seen, the mobility of the additive in mixtures containing phosphoric acid (Fig. 2.a) higher than in eluent with acetic acid (Fig. 2.b).

Using the result, determined the appropriate acid content in the mixture provides the necessary mobility of the additive (Fig. 2.a) taking into account the viscosity of the resulting mixture. Plates for TLC was applied a solution of oil in hexane, after which he chromatographically in a mixture of No. 1, then No. 2, containing different amounts of phosphoric acid (1%, 5%, 10% and 20%). On the plate was observed promoting additives abroad solvent front. The high viscosity of the mixture containing 20% phosphoric acid, minimizes the velocity of the front of solvents in comparison with other options.

Optimized by TLC the mixture was applied to the SPE cartridge for filled �hydroxycarbonyl silica gel. The cartridge was introduced 0.5 ml of 1% solution of oil, skipped the mixture No. 1 in the amount of 10 ml, then the mixture No. 2-5 ml. Compared the results of elution using a mixture of No. 2, containing 1, 5 or 10% phosphoric acid. The sorbent was dried and treated with dithizone in chloroform to check on the content of zinc dithiophosphate. Pink color characteristic of dithizonate zinc, were observed in all cases. However, when the content of acid in an amount of 10% or higher, the viscosity is too high for him passing through the cartridge, therefore, the acid content in the mixture should not exceed 10%.

To determine the maximum possible amount of additive in which it is not desorbed with a mixture of No. 1, but quantitatively eluated with a mixture of No. 2, was studied dynamic sorption capacity of additives on silica gel. In oil additive is added with the content of zinc is not above 0.12-0.15%, therefore, for studies of the additive concentrate (50% solution DF-11 in oil) dissolved in pure mineral oil was prepared 2.5% solution, and from it prepared 1% solution in hexane (A. B. Vipper Foreign oil and additives / B. A. Wipper, A. V. Vilenkin, D. A. Geisner. - M.: Chemistry, 1981). By varying the noise volume of the resulting solution through a cartridge filled with silica gel, the solution was collected by the reaction with dithizone judged the �of idiotocracy of zinc. Thus found that the sorption capacity of the additive in the silica gel is 6 mg/g of sorbent in terms of zinc. However, this value of the sorption capacity of the additive is desorbed with a mixture of hexane:acetone 9:1 by passing its volume is 1 ml. So to set the content of the additive, in which the desorption of the oil occurs. To do this consistently reduced the number of passed 1% hexane solution of the additive in the oil through the cartridge based on the sorption capacity, and then passed the mixture No. 1 to check for possible desorption, which was monitored by passing the reaction solution with dithizone in chloroform. Found that desorption does not occur when the sorption capacity of 30 µg/g of sorbent in terms of zinc.

Using the result, set the volumes of mixtures No. 1 and No. 2, are needed to separate the components of the oil. In the cartridge filled with silica gel was introduced 2 ml of 1% hexane solution of motor oil, then missed a blend No. 1 by volume to 10 ml, collecting fractions of 1 ml. Aliquot of each fraction were applied to a TLC plate placed, and treated with 0.05% aqueous-alcoholic solution of encriptada yellow and were inspected in the rays of the UV lamp. The illumination characteristic of the components of the base oil base, was observed in the first fraction (intensively) in Deut�second and third fractions visible trace amounts of base oil base. Processing plate by dithizone in chloroform showed that the pink spots, characteristic of zinc dithiophosphates, no.Thus, the optimal volume of the mixture No. 1 is 3 ml, i.e. 1.5 times more than the amount of 1% hexane solution of motor oil. Volume of the mixture No. 2 is set as follows: in some cartridges were introduced 2 ml of 1% hexane solution of motor oil, and then passed the mixture No. 1 in the amount of not less than 3 ml, and then run different volumes of the mixture No. 2 (from 10 ml to 1 ml). Then the sorbent was dried and treated with dithizone in chloroform. When a volume of 3 ml and above of the colour typical of dithizonate zinc and indicating the presence of zinc dithiophosphates, was not observed.

Thus, at first the cartridge make a solution of oil in hexane, then hexane:acetone 9:1 is desorbed basic carrier oil, then a mixture of isopropanol:water:phosphoric acid:acetonitrile 4:2:0.4:1 extract zinc dithiophosphates. Their presence in solution (red staining) and absence (no coloring) on the sorbent identified by dithizone. The zinc dithiophosphates are extracted using solid phase extraction quantitatively, whereas the liquid-liquid extraction with methanol from the oil in the ratio 2:1 the degree of extraction is at the level of 32%. The use of other extragent� in different proportions with oil (tab.1) gives the maximum degree of extraction of not more than 50-60%. Data on the degree of extraction of zinc dithiophosphates in different solvents obtained by a direct input of the extracts in the flame atomic absorption spectrometer, the criterion was the degree of extraction of zinc.

Fig.3 shows the chromatogram of the engine oil. On the chromatogram (Fig. 4-7) shows a large number of peaks corresponding to the base oil base and a number of additives, which shows their coextraction when using liquid - liquid extraction. The content of these components in the extracts complicates the procedure of analysis by HPLC, influences on the accuracy of determination of additives and contaminates the chromatographic column.

The data of research suggests that the use of solid-phase extraction gidrauxilirovanne silica gel allows the separation of the base oil base, which affects the conditions determining the desired additives. And on compositions of the mixtures and their volumes have enabled us to achieve the completeness of extraction of zinc dithiophosphates and purity of the resulting samples for subsequent analysis by reverse phase HPLC. Thus, we can conclude that the proposed method has novelty, inventive step and industrial applicability, i.e., satisfies the requirements of inventions.

Method defined�termination of dithiophosphates of zinc in motor oils by the method of reversed-phase high-performance liquid chromatography (reverse phase HPLC), including sample preparation, providing for the separation of a base oil, characterized in that the sample preparation is performed in the following sequence, namely, in an extraction cartridge filled with hydroxylated silica gel, make up to 2 ml of a 1% solution of oil in hexane per 1 g of sorbent, then passed sequentially to 1.5-fold excess of a mixture of hexane : acetone in a volume ratio of 9:1 respectively, and then pass a 1.5-fold excess of a mixture of isopropanol: water: phosphoric acid: acetonitrile in the ratio 4:2:0.4:1, respectively, then analyze an aliquot of the resulting solution.



 

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