JP4738253B2 - Method for analysis of salicylates in lubricants - Google Patents

Description

  The present invention relates to a method for analyzing salicylate contained as an additive in a lubricant, and a method for determining deterioration of a lubricant based on the method for analyzing salicylate.

  Salicylate is an important additive that is frequently used in lubricants, particularly in engine oils for automobiles and ships. Salicylate disperses insoluble sludge, soot, solid impurities and the like produced by using a lubricant as a cleaning dispersant in oil. Other actions of salicylate include solubilizing action in sludge precursors, water, etc., and neutralizing action of acidic substances such as organic acids, sulfuric acid, and nitrogen oxides.

  Conventional methods for analyzing salicylates in lubricants include infrared spectroscopy, pyrolysis gas chromatography, thin layer chromatography, distribution paper chromatography, nuclear magnetic resonance spectroscopy, and liquid chromatography. It has been. For example, JP-A-11-051918 discloses an analytical method in which salicylate in a lubricant is acid-decomposed and used for liquid chromatography.

However, the salicylate content that is generally used in lubricants is extremely low, and because it is easily disturbed by components such as coexisting base oils and various additives, accurate and reproducible quantification is not possible. was difficult.
JP-A-11-051918

  In view of the above-described conventional circumstances, an object of the present invention is to provide a method for analyzing salicylate in a lubricant that is easy to operate, has high sensitivity, good reproducibility, and excellent quantification.

  As a result of repeated investigations on the analysis of salicylates in lubricants, the inventors have found out methods that can be directly analyzed by gas chromatography without being affected by coexisting base oils and additives. And found that salicylate can be made into a highly sensitive and highly separable form by gas chromatography by methyl esterifying the carboxyl group of salicylate contained in or by acetylating the hydroxyl group of salicylate. Has been reached.

  That is, in the first method for analyzing salicylate in a lubricant according to the present invention, methanol or diazomethane in which boron trifluoride is dissolved is added to a lubricant containing salicylate, and the carboxyl group of salicylate is methyl esterified. The obtained reaction product is subjected to gas chromatography.

  The second method for analyzing salicylate in a lubricant according to the present invention is to add pyridine and acetic anhydride to a lubricant containing salicylate, acetylate the hydroxyl group of the salicylate, and then subject the resulting reaction product to gas chromatography. It is characterized by serving.

Furthermore, the present invention relates to the peak area before degradation of the peak area of methyl esterified or acetylated salicylate after degradation from the chromatogram obtained by the first and second salicylate analysis methods according to the present invention. Thus, the present invention provides a method for judging the deterioration of a lubricant, characterized by evaluating the degree of salicylate reduction .

  According to the present invention, boron trifluoride and methanol or diazomethane, or pyridine and acetic anhydride are highly reactive with salicylate, and the reaction product can be well separated by gas chromatography. The salicylate can be quantified accurately and reproducibly, and the structure and quantity ratio of the salicylate can also be analyzed. In addition, the operation is easy, rapid and simple analysis is possible, and the system can be used as it is without improving the gas chromatography apparatus.

  In addition, according to the present invention, salicylate is measured in a form suitable for gas chromatography with high sensitivity and high resolution, and therefore analysis is possible even for a very small sample of about 1 mg. Therefore, a sample can be sampled from a small amount of lubricant actually used to analyze salicylate. Further, the degree of deterioration of the lubricant can be grasped by analyzing the salicylate contained in the deteriorated lubricant in use and comparing it with that which has not deteriorated before use.

  The lubricant that can be analyzed by the analysis method of the present invention is not particularly limited as long as it contains salicylate, and examples thereof include mineral oil-based lubricants, semi-synthetic oil-based lubricants, and synthetic oil-based lubricants. In addition, grease and lubricating paints can be analyzed. The salicylate contained in the lubricant is a compound that has been conventionally used as an additive, and is a neutral alkaline earth metal salicylate, basic alkaline earth metal salicylate, carbonate overbased alkaline earth. There are similar metal salicylates.

  Although the production method of these salicylates is arbitrary, for example, neutral alkaline earth metal salicylates are alkyl salicylic acid having 1 to 2 linear or branched alkyl groups having about 0 to 15 carbon atoms. And an alkaline earth metal salt or an alkaline earth metal base (such as an alkaline earth metal hydroxide or oxide). In addition, the basic alkaline earth metal salicylate includes, for example, an alkyl salicylic acid having 1 to 2 linear or branched alkyl groups having about 0 to 15 carbon atoms, an excessive amount of alkaline earth metal salt, It is produced by reacting an alkaline earth metal base (such as a hydroxide or oxide of an alkaline earth metal) by heating in the presence of water. Further, carbonate overbased alkaline earth metal salicylates are dispersed in, for example, alkaline earth metal bases (hydroxides or oxides of alkaline earth metals) in the above neutral (normal salt) alkaline earth metal salicylates. And carbon dioxide gas is blown to react with an alkaline earth metal base to produce an alkaline earth metal carbonate dispersion in the system.

  For the production of salicylate, as described above, alkyl salicylic acid having 1 to 2 linear or branched alkyl groups having about 0 to 15 carbon atoms is used as a preferred raw material, but alkyl salicylic acid has an alkyl group. When two are present, these alkyl groups may be the same or different. Specific examples of the alkyl group of the alkyl salicylic acid include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, linear or branched chain Pentyl group, linear or branched hexyl group, linear or branched heptyl group, and the like.

  In the first method according to the present invention, methanol or diazomethane in which boron trifluoride is dissolved is added to the lubricant containing salicylate to methyl esterify the carboxyl group of salicylate. Specifically, boron trifluoride solution diluted with methanol to 5 to 20% is added to 10 to 1000 parts by weight, preferably 50 to 500 parts by weight, based on 1 part by weight of the lubricant sample, and methyl esterified. . The reaction temperature is 70 to 100 ° C. for refluxing methanol, and the reaction time is preferably 0.5 to 4 hours, more preferably 1 to 2 hours.

  In the second method according to the present invention, pyridine and acetic anhydride are added to the lubricant containing salicylate to acetylate the hydroxyl group of salicylate. Specifically, pyridine is 5 to 500 parts by weight, preferably 20 to 200 parts by weight, based on 1 part by weight of the lubricant sample, and acetic anhydride is 5 to 500 parts by weight, preferably 20 to 200 parts by weight, based on 1 part by weight of the sample. 200 parts by weight are added for acetylation. The reaction temperature is 70 to 100 ° C., and the reaction time is preferably 0.5 to 4 hours, and more preferably 1 to 2 hours.

  In the analysis method of the present invention, the reaction product from each of the above reactions is used as a sample for gas chromatography. That is, the reaction product obtained by the first method is 20 to 500 parts by weight of hexane, preferably 50 to 200 parts by weight, and 50 to 1000 parts by weight of 10% by weight saline, preferably 100 to 500 parts by weight. A part by weight is added and the solvent extracted with hexane is subjected to gas chromatography. Further, the reaction product obtained by the second method is diluted by adding 10 to 100 parts by weight of a diluent solvent such as acetone, hexane, and toluene, and subjected to gas chromatography. It is not necessary to dilute when it is desired to detect with higher sensitivity.

  In general, gas chromatography is chromatography using a gas such as helium or nitrogen as a mobile phase. The stationary phase consists of a stainless steel or glass hollow column having an inner diameter of about 3 mm and a length of about 1 to 5 m, a powder carrier in which silicone or the like is modified with silica gel called a filler, or a styrene-divinylbenzene copolymer. A packed column filled with polymer powder or the like, or a capillary column in which silicone or the like is bonded inside polyimide or stainless steel having an inner diameter of about 0.2 to 1 mm and a length of about 10 to 100 m is used.

  The gas chromatography apparatus to be used is not particularly limited and may be a normal one. Basically, an apparatus including a sample injection unit, a separation unit (separation column), a detection unit (detector), and the like can be used. As the sample injection part, a syringe method in which a sample is taken in a microsyringe and injected through a septum, or a flow injection method in which a sample can be continuously injected can be used. As the separation column, since the sample contains a high boiling point lubricating oil, the stationary phase is preferably one that can withstand a temperature of 300 ° C. or higher. For example, in the case of a packed column, OV-1 and OV-101 manufactured by GL Sciences Inc. In the case of a capillary column, DB-1, DB-5, DB-17, DB-35, etc. manufactured by J & W are desirable. The detector is preferably a flame ionization detector (FID) or a mass spectrometer (MS) that can detect salicylate with high sensitivity.

  Gas chromatography may remove the high-boiling point lubricating oil component contained in the sample in advance, but usually the high-boiling point lubricating oil component is removed simultaneously with the analytical operation by gas chromatography without removing the high-boiling point lubricating oil component. The lubricating oil component can be separated. Therefore, since the methyl esterified or acetylated reactant can be used as it is as a sample for gas chromatography without complicated operations, the analytical operation can be performed quickly and easily. In addition, the gas chromatography can be analyzed with a very small amount of sample injection of about 0.1 to 2 μl, and the amount of reagent used may be very small.

  Further, unlike high-performance liquid chromatography and liquid chromatography, gas chromatography uses a gas as a mobile phase and does not use a solvent, so that waste can be reduced as much as possible. If a column having an acidic surface, for example, DB-FFAP manufactured by J & W, is used as a separation column for gas chromatography, there is a possibility that alkyl salicylic acid obtained by adding an acid to salicylate can be measured. However, this separation column can only be used up to about 250 ° C., and a sample containing lubricating oil with a high boiling point remains in the column and promotes deterioration of the column. In this case, an operation for removing the lubricating oil may be performed, but it is not preferable because complicated operations such as solid phase extraction and column chromatography are required.

  In the chromatogram obtained by gas chromatography, the peak of methyl salicylate produced by methyl esterification of salicylate usually appears in the first method, and the peak of acetylalkyl salicylic acid produced by acetylation appears in the second method. . Therefore, the salicylate in the lubricant can be quantified by comparing this peak with the chromatogram of the standard substance. In addition, when two or more kinds of methyl salicylate or acetylalkylsalicylic acid to be produced are present, respective separated peaks can be obtained, and the amount ratio of each salicylate can be analyzed therefrom.

  Furthermore, the degree of deterioration of the lubricant can be determined using the first and second salicylate analysis methods according to the present invention. That is, after salicylate contained in a deteriorated lubricant in use is methyl esterified or acetylated, the reaction product is analyzed by gas chromatography, and the resulting chromatogram is subjected to methyl esterification or acetylation after degradation. The degree of deterioration of the lubricant can be grasped by obtaining the salicylate peak area and comparing it with the salicylate peak area of the lubricant that has not been used and has not deteriorated.

[Example 1]
To 10 mg (0.01 g) of lubricating oil A containing salicylate, 0.1 g of boron trifluoride solution diluted to 7% with methanol was added, heated to 80 ° C., and reacted for 1 hour. After allowing to cool, 0.15 g of hexane and 0.5 g of 10 wt% brine were added, and the solvent was extracted with hexane.

  1 μl of this hexane phase was sampled as sample 1 and subjected to a gas chromatograph (gas chromatograph mass spectrometer: GCMS) equipped with a mass spectrometer (MS). The gas chromatograph was a 5973N GCMS system manufactured by Agilent, and the separation column used was DB-5ms (30 m × 0.25 mm) manufactured by J & W.

  Analysis of the sample 1 yielded the chromatogram shown in FIG. When peak 1 detected in FIG. 1 is analyzed for the mass spectrum of the peak, it is found that salicylic acid is methyl salicylate having the structural formula shown in FIG. The esterified product could be detected.

[Example 2]
To 5 mg (0.005 g) of lubricating oil A containing the same salicylate as in Example 1 above, 0.03 g of pyridine and 0.03 g of acetic anhydride were added, and the mixture was reacted at 80 ° C. for 1 hour. . After allowing to cool, 0.1 g of acetone was added for dilution, and 1 μl of this was sampled as sample 2 and subjected to a gas chromatograph (gas chromatograph mass spectrometer: GCMS) equipped with MS. The same gas chromatograph apparatus and separation column as those used in Example 1 were used.

  As a result of the analysis of Sample 2, the chromatogram shown in FIG. 3 was obtained. When peak 2 detected in FIG. 3 is analyzed for the mass spectrum of the peak, it is found that salicylic acid is acetylated and has the structural formula shown in FIG. 4, and acetylates salicylate in the lubricant. Was able to be detected.

  A sample obtained by adding 0.15 g of hexane to 1 mg (0.001 g) of the same lubricating oil A as described above was measured by gas chromatography under the same conditions as in Example 1 or Example 2. In any case, no peak was detected, and salicylate could not be identified.

[Example 3]
Lubricating oil B (new oil) containing salicylate, and lubricating oils B-1 (usage period 60 days) and B-2 (usage period 120 days) in use with the same lubricating oil B and having different usage times To 1 mg (0.001 g), 0.1 g of a boron trifluoride solution diluted to 7% with methanol was added, and the mixture was heated to 80 ° C. and reacted for 1 hour. After allowing to cool, 0.15 g of hexane and 0.5 g of 10% by weight saline were added, and the solvent was extracted with hexane.

  1 μl each of these hexane phases was sampled, Lubricant B (new oil) as sample 3, Lubricant B-1 (use period 60 days) as sample 4, and Lubricant B-2 (use period 120 days) as sample No. 5 was subjected to a gas chromatograph (gas chromatograph mass spectrometer: GCMS) equipped with MS. The same gas chromatograph apparatus and separation column as those used in Example 1 were used.

  The chromatogram shown in FIGS. 5-7 was obtained by the analysis of the said samples 3-5. Fig. 5 shows the chromatogram of lubricating oil B (new oil), Fig. 6 shows the chromatogram of lubricating oil B-1 (use period 60 days), and Fig. 7 shows the chromatogram of lubricant B-2 (use period 120 days). Show. When comparing the peak area of the peak detected from the lubricating oil B (new oil) with the peak area of the peak detected from the lubricating oil B-1 and the lubricating oil B-2 in use, the lubricating oil B-1 is the new oil. It was found that about 70% of the lubricating oil B and the lubricating oil B-2 were reduced to about 30%.

2 is a chromatogram obtained by analysis of a lubricating oil obtained by methyl esterifying salicylic acid in Example 1. 3 is a structural formula of methyl salicylate obtained by analyzing a mass spectrum from the chromatogram peak of Example 1. FIG. 2 is a chromatogram obtained by analysis of a lubricating oil obtained by acetylating salicylic acid in Example 2. 2 is a structural formula of acetylsalicylic acid obtained by analyzing a mass spectrum from the chromatogram peak of Example 2. It is the chromatogram obtained by the analysis of lubricating oil (new oil) in Example 3. 4 is a chromatogram obtained by analysis of lubricating oil in use in Example 3. 4 is a chromatogram obtained by analysis of another lubricating oil in use in Example 3. FIG.

Claims (2)

A method for analyzing salicylate in a lubricant, comprising adding pyridine and acetic anhydride to a lubricant containing salicylate, acetylating the hydroxyl group of the salicylate, and then subjecting the resultant reaction product to gas chromatography . A method for determining deterioration of a lubricant containing salicylate, wherein the peak area of acetylated salicylate after deterioration is compared with the peak area before deterioration from the chromatogram obtained by the method for analyzing salicylate according to claim 1. A method for judging deterioration of a lubricant, characterized in that the degree of salicylate reduction is evaluated .

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