CS260524B1 - Method for determining the concentration of zinc in liquid and solid lubricants - Google Patents

Abstract

The purpose of the solution is a simple and inexpensive method for determining the concentration of zinc in lubricants. The stated purpose is achieved by burning a lubricant sample, dissolving the ash in hydrochloric acid, adjusting the ionic strength and pH of the aqueous solution to a suitable value and determining the sum of the zinc + calcium content by potentiometric titration using a new calcium ion-selective electrode, in combination with a suitable reference electrode, as an equivalence point indicator and subtracting the calcium concentration from the potentiometric titration result.

Description

The invention relates to a method for determining the concentration of zinc in liquid and solid lubricants by potentiometric titration.

Organic zinc compounds, ^e.g. zinc dialkyldithiophosphate, are used as additives to modify lubricants to improve their performance characteristics. Determination of zinc concentration is one of the parameters for assessing quality during production and during their operational use. So far, the zinc concentration in lubricants has been determined mainly by the atomic absorption spectrophotometry method, which requires oil-soluble standards and expensive imported instrumentation for rapid determination.

The above-mentioned shortcomings are eliminated by the determination of zinc according to the invention, the essence of which consists in the chelatometric titration of an ash solution obtained by burning a lubricant sample, dissolving the ash in hydrochloric acid and adjusting the ionic strength and pH with diethanolamine to a value of 8.1 to 9.3, using a calcium ion-selective electrode. The electrode used has a plastic membrane based on a neutral carrier. The membrane has a composition of 35 to 36 wt. % of high molecular weight polyvinyl chloride, 62 to 63 wt. % of 2,4-dinitrophenyl-n-octyl ether, 0.5 to 1.0 wt. % of sodium tetraphenylborate and 1 to 2 wt. % of the neutral carrier N,N'-dimethyl-N,N'-di-/ll-ethoxycarbonylundecyl/diamide of 4,4,5,5-tetramethyl-3,6-dioxaoctanedioic acid.

A calcium ion-selective electrode in combination with a suitable regenerant electrode is used as an indicator of the equivalence point of potentiometric titration. A solution of ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid, or their diethanolammonium salts in an aqueous solution of diethanolamine /c = 1 mol/1/, is used for titration. Under the specified conditions, the concentration of zinc + calcium is determined by titration. After subtracting the calcium concentration, determined by another suitable method, e.g. direct potentiometric determination with a calcium ion-selective electrode /cz. AO 250 797/, the value of the zinc concentration is obtained.

The concentration of zinc + calcium is calculated from the relationship ^tltr.no. * ^In titr.no.

Ca+Zn ^In the model. where ^c titer no. is concentration of titrant [mol/l] ^title no. is titration reagent consumption LU ^In the is volume of titrated sample [lj

The zinc concentration is obtained by subtracting the calcium concentration value ^C ZN ^{= c} Ca+Zn ^c Ca

From the value of the zinc concentration in the ash solution, the zinc concentration in the lubricant is calculated from the relationship where V is the total volume of the ash solution [l] ^c Zn ^ ^no The previous solution [mol/lj nav. is the weight of the lubricant to be ashed [gj [ g/raoj.j at. wt. is the atomic weight of zinc

Example 1

For potentiometric titration, a cell consisting of a saturated calomel electrode and a calcium ion-selective electrode with a plastic membrane composed of 35.40 wt.% CaCl was used. high molecular weight polyvinyl chloride (Mevil III /prepared in the Macromolecular Chemistry Department of the Czechoslovak Academy of Sciences/], 62.92 wt. % 2,4-dinitrophenyl-n-octyl ether, 0.56 wt. % sodium tetraphenylborate and 1.12 wt. % neutral carrier, N,N'-dimethyl-N,N'-di-/ll-ethoxycarbonylundecyl/diamide of 4,4,5,5-tetramethyl-3,6-dioxaoctanedioic acid. The titration was carried out with intensive+ ¹ stirring at a temperature of 295 - 2 К. To stabilize the equilibrium, 0.5 to 1 minute was waited after each addition of the titrant. A solution of ~2 ethylenediaminetetraacetic acid, c = 10 mol/1 and diethanolamine, c ~ 1 mol/1, was used as the titrant. Solutions of 10.0 ml of diethanolamine, c - 2.44 mol/1 + 10 ml ZnCl, c = 2 x 10~ ⁴ mol/1 - 5 χ 10" ³ mol/1; -4 -3

CaC^r c = 2 x 10 mol/1 - 5 x 10 mol/1; HCl, c = 0.76 mol/1. The titrated solutions had

pH 9.17 up to 9, 30. Fig. 1 shows the obtained titration curves for solutions ZnCl ₂ + CaCl ₂ · 1. ZnCl ₂ , c = 2 x 10 ⁴ mol/1; CaCl ₂ , c = 2 x 10 ⁴ mol/1 2. ZnCl ₂ f C = 5 x 10 ⁴ mol/1; CaCl ₂ , c = 5 χ 10 ^- · ⁴ mol/1 3. ZnCl ₂ , C = 5 χ 10~ ⁴ ; CaCl ₂ , c = 10' ³ mol/1 4. ZnCl ₂ , C -3 -3 * = 10 ^J mol/1? CaCl ₂ , c = 10 ^ύ mol/1 5. ZnCl ₂ , C = 2 x 10 ³ mol/1; CaC^rc = 2 x 10 ³ mol/1 6. ZnCl ₂ and C = 5 x 10 ³ ; CaCl ₂ / c = 5 x 10 ³ mol/1

In repeated titrations, the consumption of titrant was reproducible with an accuracy of 0.02 ml.

For a 4 g sample of lubricant, the ash dissolved in HCl and the solution made up to a volume of 100 ml, curve 1 corresponds to a concentration of 325 µg Zn/g lubricant and curve 2 to a concentration of 8 125 µg Zn/g lubricant? for a 2 g sample, the curves correspond to double the concentrations.

Example 2

A sample of M6 AD engine oil weighing 2.060 9 g was ashed. The ash was dissolved in hydrochloric acid and the solution was made up to 100 ml with distilled water. In the same arrangement as in ex. 1, the Zn+Ca concentration was determined. The titration curve is shown in Fig. 2; M6 AD curve. After subtracting the Ca concentration obtained by direct potentiometric measurement in the same sample, before starting the titration and calculating from the above relationship, a value of 880 µg Zn/g oil was obtained.

The results obtained were compared with the results of measuring Zn concentration using the direct atomic absorption method using standards (made by Conostan) and the polarographic method.

The differences found were less than 15%. ;

Example3

A sample of the development engine oil M6 W/20 D weighing 4.024 5 g was incinerated.

The ash was dissolved in hydrochloric acid and the solution was made up to 100 ml with distilled water. As in Example 2, the concentration of Zn+Ca was determined by titration. The titration curve is shown in Fig. 2; curve M6 W/20 D. Similarly, a value of 3,680 µg Zn/g oil was obtained.

Example 4

The same titration curves and values of Zn concentrations in oil samples were obtained using a solution of diethylenetriaminepentaacetic acid, c = 10 mol/1, and diethanolamine, c = 1 mol/1 as titrants in the same titration arrangement as in Examples 1, 2, and 3.

Claims (2)

SUBJECT OF THE INVENTION Method for determining the concentration of zinc in liquid and solid lubricants containing zinc and lime additives, characterized in that, after preparation of the sample by incineration, the ash is dissolved by dissolution in hydrochloric acid and made up to the desired volume with distilled water and after adjusting the ionic strength and pH of the solution to the zinc + calcium content was determined by titration with 9.1 to 9.3 using diethanolamine, using a calcium ion selective electrode with a plastic membrane of 35 to 36 wt. % high molecular weight polyvinyl chloride, 62-63 wt. % 2,4-dinitrophenyl-n-octyl ether, 0.5 to 1 wt. % sodium tetrafenylborate and 1 to 2 wt. neutral carrier, N, N'-dimethyl-N, N'-di- (11-ethoxycarbonylundecyl) diamide of 4,4,5,5-tetramethyl-3,6-dioxaoctanedioic acid, as an indicator of the equivalence point of titration with ethylenediaminotetraacetic acid solution or acid of diethylenetriaminopentaacetic acid in a solution of diethanolamine and, after subtraction of the calcium content, the zinc concentration is obtained.