Method for detecting total iron content of lubricating oil
By treating lubricating oil samples through evaporation, ashing, and acid leaching, combined with colorimetry, the problem of rapid and accurate detection of total iron content in lubricating oil was solved. This method is suitable for both field and laboratory use, enabling real-time monitoring of the lubricating oil's condition.
Patent Information
- Application Number
- CN202610021671.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-08
- Publication Date
- 2026-03-20
AI Technical Summary
Existing technologies lack methods for quickly and accurately detecting the content of various forms of iron impurities in lubricating oil on-site, resulting in delayed equipment condition monitoring and an inability to take timely and effective maintenance measures.
A combination of evaporation, ashing, acid leaching, and colorimetric methods was used. The base oil was removed by evaporation, the organic additives were decomposed by ashing, the iron was converted into soluble ions by acid leaching, and quantitative detection was performed using a spectrophotometer.
It enables accurate and rapid detection of total iron content in lubricating oil, is suitable for field environments, ensures the reliability and sensitivity of test results, and is compatible with common small spectrophotometers, making it suitable for both field and laboratory use.
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Figure CN121703031A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lubricating oil quality testing technology, specifically relating to a method for detecting the total iron content of lubricating oil. Background Technology
[0002] Lubricating oil plays a vital role in the operation of mechanical equipment, including lubrication, cooling, cleaning, sealing, and rust prevention. However, during equipment operation, due to wear and corrosion of parts and the intrusion of external contaminants, metallic impurities gradually accumulate in the lubricating oil, among which iron impurities are one of the most significant and indicative wear metals. These iron impurities exist primarily in two forms: metallic wear iron particles and compounds such as sulfides and oxides.
[0003] Regardless of the form in which iron impurities exist, they pose a serious threat to lubricating oil and equipment systems. First, iron particles themselves are catalytically active, accelerating the oxidative cracking and deterioration of hydrocarbon base oils, and promoting the formation of sludge and varnish. Second, as equipment operating time increases, the acidic substances produced by lubricating oil oxidation corrode iron components in the equipment, and the corrosion products (iron compounds) further catalyze oil deterioration, creating a vicious cycle. Oil deterioration ultimately leads to a decline in the lubricating performance of the lubricating oil, affecting the normal lubrication and heat dissipation of the equipment assembly, and potentially causing serious equipment failures such as pitting, abnormal wear, and even tooth breakage. Therefore, accurate monitoring of the total iron content of lubricating oil during operation is a crucial step in assessing equipment wear conditions, predicting equipment lifespan, and guiding oil regeneration treatment.
[0004] Currently, the standard laboratory methods for detecting metal content in lubricating oils typically rely on large, sophisticated instruments such as atomic absorption spectrometry (AAS) or inductively coupled plasma optical emission spectrometry (ICP-OES). While these methods offer high accuracy, they also have significant limitations: (1) The equipment is expensive, bulky, and has high requirements for the operating environment, making it impossible to deploy it to the production site; (2) The sample pretreatment is complicated and the analysis cycle is long, which cannot meet the needs of rapid on-site decision-making; (3) High skill requirements for operators. This results in a serious lag in test results, making it impossible to provide real-time and effective data support for on-site equipment status monitoring and maintenance.
[0005] To meet the need for rapid on-site testing, some explorations have been conducted in this field. For example, a simple colorimetric method has been attempted. The principle is based on the reaction of iron ions (usually divalent or trivalent) in lubricating oil with a specific colorimetric agent (such as potassium thiocyanate) to form a colored complex, with quantification based on the intensity of the color. However, this type of method has encountered insurmountable obstacles in practical applications: (1) Lubricating oil is a complex organic matrix in which a large amount of iron is encapsulated in the form of metal particles or stable compounds. Simple dilution or extraction cannot effectively release it and convert it into an ionic state that can react with the colorimetric agent. (2) The color of the lubricating oil base oil itself, the interference of additives and other coexisting metal ions can seriously affect the accuracy and specificity of colorimetric determination. Therefore, directly applying the traditional colorimetric method often leads to severely low or completely failed test results, which cannot truly reflect the "total iron" content in the lubricating oil.
[0006] In summary, a significant gap exists in the existing technology: to date, there is a lack of a rapid, accurate, and dedicated method for detecting the total iron content of lubricating oil that can effectively break down the organic matrix of lubricating oil, completely extract iron impurities in various forms, and is applicable to field environments. This technological bottleneck prevents field personnel from promptly ascertaining the true iron contamination level of lubricating oil, making it difficult to take reasonable and effective preventive maintenance or oil regeneration measures, thus posing potential risks to the safe and stable operation of equipment. Summary of the Invention
[0007] The technical problem to be solved by the present invention is to provide a method for detecting the total iron content of lubricating oil, which addresses the shortcomings of the prior art. This method can detect the total iron content of lubricating oil in both on-site and laboratory settings. It solves the technical problem in the prior art that the lack of a detection method specifically designed for the matrix characteristics of lubricating oil makes it impossible to quickly and accurately determine the total iron content in all forms (including metal particles and compounds) of iron impurities in lubricating oil in an on-site environment.
[0008] The present invention adopts the following technical solution: A method for detecting the total iron content in lubricating oil includes the following steps: S1. Evaporate the lubricating oil sample to be tested until the oil is completely evaporated; S2. Ash the remaining material after evaporation until no carbon residue remains; S3. The ashing product is treated with acid leaching to obtain a solution containing soluble iron ions; S4. Add reagents to the acid-soaked solution and make up to volume, shake well and let stand; S5. The total iron content of the lubricating oil sample was obtained by colorimetric detection of the solution after it was brought to a constant volume using a spectrophotometer.
[0009] Preferably, in step S1, 0.1-1.0g of the lubricating oil sample to be tested is weighed and placed in a quartz beaker with a volume of 40-60ml for the evaporation treatment.
[0010] Preferably, the evaporation treatment temperature is 250-350℃; in step S2, the ashing treatment temperature is 600-800℃.
[0011] Preferably, in step S3, the specific operation of the acid leaching treatment is as follows: first, rinse the inner wall of the container holding the ashing product with ultrapure water, then add 1.5-2.5 ml of concentrated hydrochloric acid to the container, cover it with a watch glass, and boil for 8-12 minutes.
[0012] Preferably, in step S4, the acid-soaked solution is transferred to a stoppered graduated glass test tube with a volume of 8-12 ml, and then reagents are added to perform a volume adjustment operation, wherein the volume adjustment operation is to adjust the solution to 8-12 ml.
[0013] Preferably, the added reagents include potassium persulfate solution and potassium thiocyanate solution, wherein the mass concentration of the potassium persulfate solution is 1.5%-2.5% and the amount added is 0.15-0.25 ml; the mass concentration of the potassium thiocyanate solution is 18%-22% and the amount added is 1.8-2.2 ml.
[0014] Preferably, in step S4, the time for letting the mixture stand after shaking is 4-6 minutes.
[0015] Preferably, in step S5, the detection wavelength of the spectrophotometer is 480-490 nm.
[0016] Preferably, in step S1, the mass of the lubricating oil sample to be tested is 0.2-0.8g, and the volume of the quartz beaker is 45-55ml.
[0017] Preferably, in step S1, the temperature of the evaporation treatment is 280-320℃; in step S2, the temperature of the ashing treatment is 650-750℃.
[0018] Compared with the prior art, the present invention has at least the following beneficial effects: A method for detecting the total iron content in lubricating oil systematically solves the challenge of accurately detecting the target element (iron) in complex matrices (lubricating oil). The method involves removing the base oil through evaporation, thoroughly decomposing organic additives and impurities through ashing, ensuring that all forms of iron are converted into soluble ions through acid leaching, and finally using colorimetry for quantification. This method ensures the accuracy and reliability of the detection results and is particularly suitable for rapid on-site testing scenarios.
[0019] Furthermore, an optimal balance between detection sensitivity and operational feasibility was achieved. A lower limit of 0.1g ensures high sensitivity for samples with low iron content, while an upper limit of 1.0g prevents high-iron-content samples from exceeding the spectrophotometer's linear range during subsequent color development. The 40-60ml quartz beaker volume allows for safe evaporation and ashing of 1.0g of oil sample without spillage, while also facilitating subsequent rinsing and acid leaching, demonstrating the method's versatility and safety.
[0020] Furthermore, the completeness and safety of the pretreatment process are precisely controlled. The evaporation temperature of 250-350℃ can effectively evaporate the lubricating oil without causing it to burn or splash rapidly; the ashing temperature of 600-800℃ can ensure that the organic matter is completely oxidized and decomposed into CO2 and water (without residual carbon), while avoiding excessively high temperatures that would cause iron to form insoluble inert oxides, thus ensuring the complete dissolution of iron in the subsequent acid leaching step.
[0021] Furthermore, to maximize iron dissolution efficiency and eliminate interference, ultrapure water rinsing ensures complete ash transfer; 1.5-2.5 ml of concentrated hydrochloric acid provides sufficient H₂. + This process dissolves iron oxides and metallic iron, creating the acidic environment required for subsequent color development. The 8-12 minute boiling process accelerates the reaction through heating, ensuring that the iron encased in the residual carbon is also fully dissolved, thus accurately reflecting the "total iron" content.
[0022] Furthermore, this method ensures both accuracy and convenience in the detection process. Using stoppered, graduated test tubes allows for precise control of the final volume and prevents spillage during mixing. Maintaining a consistent volume range of 8-12 ml makes this method compatible with common small spectrophotometer cuvettes, ideal for on-site testing, and facilitates the plotting and calculation of standard curves.
[0023] Furthermore, this ensures the completeness, stability, and specificity of the colorimetric reaction. At this concentration and dosage, potassium persulfate ensures the complete oxidation of dissolved ferrous ions to ferric ions; potassium thiocyanate provides sufficient thiocyanate ions to form a stable blood-red complex with ferric ions. The colorimetric reaction at this ratio is rapid, the color is stable, and the absorbance values are highly reproducible, laying a solid foundation for accurate quantification.
[0024] Furthermore, this ensures the complete establishment of reaction equilibrium. This time range guarantees that both oxidation and complexation reactions reach equilibrium, resulting in stable and maximum color intensity. It avoids low detection values due to insufficient settling time or solution instability due to excessive settling time, thereby improving data reproducibility and accuracy.
[0025] Furthermore, maximum absorption was achieved for the target chromogenic analyte. The ferric iron-thiocyanate complex exhibits a maximum absorption peak in this wavelength range, resulting in the highest detection sensitivity at this wavelength. This effectively lowers the detection limit and reduces interference from other potential coexisting substances, leading to more accurate detection results.
[0026] Furthermore, the operating window and safety of the method have been optimized. This range represents the ideal sample size for most lubricating oil samples, being both representative of the overall sample and easy to handle. The 45-55 ml beaker provides ample space for this sample volume, greatly reducing the risk of boiling or splashing during evaporation and ashing, making the operation safer and the results more reliable.
[0027] Furthermore, energy efficiency and operational controllability are improved while ensuring treatment effectiveness. This temperature range is the most economical and controllable interval for achieving complete evaporation and ashing of oil samples, which helps to shorten analysis time, reduce energy consumption, and reduce experimental errors caused by temperature fluctuations. It represents the optimal process window for achieving efficient and stable operation of the method.
[0028] In summary, this invention, through optimized evaporation, ashing, acid leaching, volume adjustment, and colorimetric steps, can completely release and detect various forms of iron in lubricating oil, overcoming the difficulty of accurate on-site detection in existing technologies. It features high sensitivity and good reproducibility, making it suitable for both field and laboratory use, and providing key technical support for equipment lubrication status monitoring and early warning.
[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the following description of the relative embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0031] Figure 1 A line graph showing the detection error comparison. Detailed Implementation
[0032] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0033] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.
[0034] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.
[0035] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.
[0036] In this invention, unless otherwise specified, the components involved or their preferred components can be combined to form new technical solutions.
[0037] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation of these numerical combinations.
[0038] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.
[0039] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.
[0040] In this invention, unless otherwise stated, the various reaction or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.
[0041] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.
[0042] This invention provides a method for detecting the total iron content in lubricating oil. The method involves sequentially treating the lubricating oil sample with evaporation, ashing, acid leaching, volume adjustment, and colorimetric analysis. First, an appropriate amount of oil sample is weighed into a quartz beaker, evaporated to dryness at a specific temperature, and then ashed at high temperature to thoroughly remove organic matter. Subsequently, the ash is rinsed with ultrapure water, and a measured amount of concentrated hydrochloric acid is added and boiled to convert all forms of iron into soluble iron ions. The acid leaching solution is transferred to a stoppered test tube, and measured amounts of potassium persulfate and potassium thiocyanate solutions are added for oxidation and colorimetric reactions. After volume adjustment, the solution is allowed to stand. Finally, the absorbance of the solution is measured at a specific wavelength using a spectrophotometer, and the total iron content of the lubricating oil is calculated using a standard curve method. This invention features rigorous steps and clearly defined parameters, enabling accurate and rapid detection of the total iron content in lubricating oil, making it particularly suitable for field applications.
[0043] This invention discloses a method for detecting the total iron content in lubricating oil, comprising the following steps: S1. Weigh the sample of the lubricating oil to be tested into a quartz beaker, then evaporate the oil completely, and then ashing it until there is no residual carbon. Weigh 0.1g-1g of the lubricating oil sample to be tested into a 50ml quartz beaker, then evaporate the oil completely at 250-350℃, and then ashing it at 600-800℃ until no carbon residue remains.
[0044] S2. Rinse the inner wall of the quartz beaker with ultrapure water, then add concentrated hydrochloric acid, cover with a watch glass and boil. Rinse the inner wall of the quartz beaker with ultrapure water, then add 2 ml of concentrated hydrochloric acid, cover with a watch glass, and boil for 10 minutes.
[0045] S3. Transfer the solution in the quartz beaker to a stoppered graduated glass test tube, then add potassium persulfate solution and potassium thiocyanate solution, then make up to volume, shake well and let stand. Transfer the solution in the quartz beaker to a 10ml stoppered graduated glass test tube, then add 0.2ml of 2% potassium persulfate solution and 2ml of 20% potassium thiocyanate solution, and then make up to 10ml. Shake well and let stand for 5 minutes.
[0046] S4. The total iron content of the solution in the stoppered graduated glass test tube was detected by a spectrophotometer at a wavelength of 485 nm, and the detection result was used as the total iron content of the lubricating oil sample to be tested.
[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0048] Example 1 The method for detecting the total iron content of lubricating oil according to the present invention includes the following steps: 1) Weigh 0.1g of the lubricating oil sample to be tested into a 50ml quartz beaker, then evaporate the oil completely at 250℃, and then ashed it at 600℃ until no carbon residue remains. 2) Rinse the inner wall of the quartz beaker with ultrapure water, then add 2ml of concentrated hydrochloric acid, cover with a watch glass and boil for 10 minutes. 3) Transfer the solution in the quartz beaker to a 10ml stoppered graduated glass test tube, add 0.2ml of 2% potassium persulfate solution and 2ml of 20% potassium thiocyanate solution, then make up to 10ml, shake well and let stand for 5min. 4) The total iron content of the solution in the stoppered graduated glass test tube was detected by a spectrophotometer at a wavelength of 485 nm, and the detection result was used as the total iron content of the lubricating oil sample to be tested.
[0049] Example 2 The method for detecting the total iron content of lubricating oil according to the present invention includes the following steps: 1) Weigh 0.2g of the lubricating oil sample to be tested into a 50ml quartz beaker, then evaporate the oil completely at 350℃, and then ashed it at 800℃ until no carbon residue remains. 2) Rinse the inner wall of the quartz beaker with ultrapure water, then add 2ml of concentrated hydrochloric acid, cover with a watch glass and boil for 10 minutes. 3) Transfer the solution in the quartz beaker to a 10ml stoppered graduated glass test tube, add 0.2ml of 2% potassium persulfate solution and 2ml of 20% potassium thiocyanate solution, then make up to 10ml, shake well and let stand for 5min. 4) The total iron content of the solution in the stoppered graduated glass test tube was detected by a spectrophotometer at a wavelength of 485 nm, and the detection result was used as the total iron content of the lubricating oil sample to be tested.
[0050] Example 3 The method for detecting the total iron content of lubricating oil according to the present invention includes the following steps: 1) Weigh 0.4g of the lubricating oil sample to be tested into a 50ml quartz beaker, then evaporate the oil completely at 300℃, and then ashed it at 700℃ until no carbon residue remains. 2) Rinse the inner wall of the quartz beaker with ultrapure water, then add 2ml of concentrated hydrochloric acid, cover with a watch glass and boil for 10 minutes. 3) Transfer the solution in the quartz beaker to a 10ml stoppered graduated glass test tube, add 0.2ml of 2% potassium persulfate solution and 2ml of 20% potassium thiocyanate solution, then make up to 10ml, shake well and let stand for 5min. 4) The total iron content of the solution in the stoppered graduated glass test tube was detected by a spectrophotometer at a wavelength of 485 nm, and the detection result was used as the total iron content of the lubricating oil sample to be tested.
[0051] Example 4 The method for detecting the total iron content of lubricating oil according to the present invention includes the following steps: 1) Weigh 0.6g of the lubricating oil sample to be tested into a 50ml quartz beaker, then evaporate the oil completely at 280℃, and then ashed it at 650℃ until no carbon residue remains. 2) Rinse the inner wall of the quartz beaker with ultrapure water, then add 2ml of concentrated hydrochloric acid, cover with a watch glass and boil for 10 minutes. 3) Transfer the solution in the quartz beaker to a 10ml stoppered graduated glass test tube, add 0.2ml of 2% potassium persulfate solution and 2ml of 20% potassium thiocyanate solution, then make up to 10ml, shake well and let stand for 5min. 4) The total iron content of the solution in the stoppered graduated glass test tube was detected by a spectrophotometer at a wavelength of 485 nm, and the detection result was used as the total iron content of the lubricating oil sample to be tested.
[0052] Example 5 The method for detecting the total iron content of lubricating oil according to the present invention includes the following steps: 1) Weigh 0.8g of the lubricating oil sample to be tested into a 50ml quartz beaker, then evaporate the oil completely at 320℃, and then ashed it at 750℃ until no carbon residue remains. 2) Rinse the inner wall of the quartz beaker with ultrapure water, then add 2ml of concentrated hydrochloric acid, cover with a watch glass and boil for 10 minutes. 3) Transfer the solution in the quartz beaker to a 10ml stoppered graduated glass test tube, add 0.2ml of 2% potassium persulfate solution and 2ml of 20% potassium thiocyanate solution, then make up to 10ml, shake well and let stand for 5min. 4) The total iron content of the solution in the stoppered graduated glass test tube was detected by a spectrophotometer at a wavelength of 485 nm, and the detection result was used as the total iron content of the lubricating oil sample to be tested.
[0053] Example 6 The method for detecting the total iron content of lubricating oil according to the present invention includes the following steps: 1) Weigh 1.0g of the lubricating oil sample to be tested into a 50ml quartz beaker, then evaporate the oil completely at 290℃, and then ashed it at 790℃ until no carbon residue remains. 2) Rinse the inner wall of the quartz beaker with ultrapure water, then add 2ml of concentrated hydrochloric acid, cover with a watch glass and boil for 10 minutes. 3) Transfer the solution in the quartz beaker to a 10ml stoppered graduated glass test tube, add 0.2ml of 2% potassium persulfate solution and 2ml of 20% potassium thiocyanate solution, then make up to 10ml, shake well and let stand for 5min. 4) The total iron content of the solution in the stoppered graduated glass test tube was detected by a spectrophotometer at a wavelength of 485 nm, and the detection result was used as the total iron content of the lubricating oil sample to be tested.
[0054] Example 7 The method for detecting the total iron content of lubricating oil according to the present invention includes the following steps: 1) Weigh 1.0g of the lubricating oil sample to be tested into a 50ml quartz beaker, then evaporate the oil completely at 270℃, and then ashed it at 650℃ until no carbon residue remains. 2) Rinse the inner wall of the quartz beaker with ultrapure water, then add 2ml of concentrated hydrochloric acid, cover with a watch glass and boil for 10 minutes. 3) Transfer the solution in the quartz beaker to a 10ml stoppered graduated glass test tube, add 0.2ml of 2% potassium persulfate solution and 2ml of 20% potassium thiocyanate solution, then make up to 10ml, shake well and let stand for 5min. 4) The total iron content of the solution in the stoppered graduated glass test tube was detected by a spectrophotometer at a wavelength of 485 nm, and the detection result was used as the total iron content of the lubricating oil sample to be tested.
[0055] Comparative Example 1 (Detection Method for Deviations from the Parameter Range of Claims) Weigh 0.5g of the lubricating oil sample to be tested and place it in a 50ml quartz beaker. Evaporate at 200℃ for 30min (the oil was not completely evaporated and a small amount of high-boiling-point hydrocarbons remained). Skip the ashing step and directly add 3.0 ml of concentrated hydrochloric acid to the beaker and boil for 15 minutes; Transfer the solution to a 10ml stoppered test tube, add 0.3ml of 3.0% potassium persulfate solution and 2.5ml of 25% potassium thiocyanate solution, and make up to 10ml. Let stand for 3min. The total iron content was measured at a wavelength of 470 nm using a spectrophotometer, yielding a result of 5.2 mg / kg, with a detection error of ±1.2 mg / kg.
[0056] Comparative analysis Detection accuracy: The present invention completely converts iron, and the error is much lower than that of the seven comparative examples. The detection values are concentrated in 8.0-8.6 mg / kg (the actual total iron content of the oil sample is 8.3 mg / kg), with an error of only ±0.1-0.3 mg / kg. The comparative example detection value is 5.2 mg / kg, which deviates from the actual value by 37.3%, with an error of ±1.2 mg / kg.
[0057] This invention utilizes the "evaporation-ashing" steps of claim 1. Evaporation at 250-350℃ ensures complete removal of hydrocarbons, while ashing at 600-800℃ destroys the structure of iron compounds, converting all forms of iron into acid-leached ash. In contrast, the comparative example's evaporation at 200℃ is incomplete, leaving residual hydrocarbons encapsulating iron impurities. Furthermore, the omitted ashing step prevents iron compounds (such as FeS) from being completely dissolved by hydrochloric acid, resulting in significantly lower detection values. Additionally, the comparative example's reagent dosage and wavelength deviate from the range, further exacerbating the error.
[0058] Operational Stability: The present invention has a reasonable parameter range and strong repeatability. Seven embodiments cover different parameter combinations, including the lower limit, upper limit, and preferred range of the claims, but the fluctuation in detection values is only ±0.6 mg / kg, with errors all ≤ ±0.3 mg / kg, indicating stable operation within the parameter range. In contrast, the comparative examples, lacking reasonable parameter constraints, exhibited significant deviations in a single test and could not be repeated. Practical Significance: On-site testing is affected by equipment accuracy (e.g., temperature controller ±5℃) and operating techniques, leading to slight parameter fluctuations. The parameter range of the present invention is compatible with these fluctuations, ensuring consistency between on-site and laboratory results, and solving the problem of "unstable on-site testing" in existing technologies.
[0059] Economy and Convenience: This invention optimizes parameters, reducing costs and time. The reagent dosage is small (e.g., 1.5-2.5 ml concentrated hydrochloric acid, 0.15-0.25 ml potassium persulfate), with a single test taking approximately 30 minutes. In contrast, the comparative method uses over 20% concentrated hydrochloric acid, and due to incomplete evaporation and excessive boiling time, the total time reaches 50 minutes, increasing reagent costs and reducing efficiency. In summary, this invention, through standardized procedures and a reasonable parameter range, achieves "accurate, stable, and convenient" total iron detection, filling a gap in on-site testing and providing reliable data support for equipment maintenance and oil regeneration.
[0060] Please see Figure 1 The detection error (±mg / kg) of each sample was quantified in the form of a line graph. The X-axis represents the sample number, the Y-axis represents the error value, and the error level is marked on the right (excellent: ≤±0.3mg / kg, poor: >±1.0mg / kg).
[0061] The blue broken line shows that the errors of Examples 1-7 fluctuated in the range of ±0.1-±0.3 mg / kg, all of which were at the "excellent" level. Among them, Example 3 (intermediate parameter) had the lowest error (±0.1 mg / kg), indicating that parameter optimization can further improve accuracy.
[0062] The red dashed line indicates that the comparative error reached ±1.2 mg / kg, far exceeding the threshold of the "poor" level. This was due to deviations in parameters such as excessive reagents and insufficient reaction time, resulting in poor repeatability and a sharp increase in error.
[0063] The charts, through error quantification and comparison, verify the rationality of the parameter range of the present invention and highlight its significant advantages in detection accuracy and stability.
[0064] In summary, this invention provides a method for detecting the total iron content in lubricating oil, filling the gap in on-site detection of total iron in lubricating oil. It ensures complete iron conversion through "evaporation-ashing-acid leaching," with a reasonable parameter range covering key steps. It balances detection accuracy (error ±0.1-0.3 mg / kg) with ease of operation, is suitable for both on-site and laboratory use, requires less reagent and is quick to implement, and provides reliable data support for equipment maintenance and oil regeneration.
[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for detecting the total iron content in lubricating oil, characterized in that, Includes the following steps: S1. Evaporate the lubricating oil sample to be tested until the oil is completely evaporated; S2. Ash the remaining material after evaporation until no carbon residue remains; S3. The ashing product is treated with acid leaching to obtain a solution containing soluble iron ions; S4. Add reagents to the acid-soaked solution and make up to volume, shake well and let stand; S5. The total iron content of the lubricating oil sample was obtained by colorimetric detection of the solution after it was brought to a constant volume using a spectrophotometer.
2. The method for detecting the total iron content of lubricating oil according to claim 1, characterized in that, In step S1, 0.1-1.0g of the lubricating oil sample to be tested is weighed and placed in a quartz beaker with a volume of 40-60ml for the evaporation treatment.
3. The method for detecting the total iron content of lubricating oil according to claim 2, characterized in that, The evaporation treatment temperature is 250-350℃; in step S2, the ashing treatment temperature is 600-800℃.
4. The method for detecting the total iron content of lubricating oil according to claim 1, characterized in that, In step S3, the specific operation of the acid leaching treatment is as follows: first, rinse the inner wall of the container holding the ashing product with ultrapure water, then add 1.5-2.5 ml of concentrated hydrochloric acid to the container, cover it with a watch glass, and boil for 8-12 minutes.
5. The method for detecting the total iron content of lubricating oil according to claim 1, characterized in that, In step S4, the acid-soaked solution is transferred to a stoppered graduated glass test tube with a volume of 8-12 ml, and then reagents are added to perform a volume adjustment operation, which involves adjusting the solution to 8-12 ml.
6. The method for detecting the total iron content of lubricating oil according to claim 5, characterized in that, The added reagents include potassium persulfate solution and potassium thiocyanate solution, wherein the mass concentration of the potassium persulfate solution is 1.5%-2.5% and the amount added is 0.15-0.25 ml; the mass concentration of the potassium thiocyanate solution is 18%-22% and the amount added is 1.8-2.2 ml.
7. The method for detecting the total iron content of lubricating oil according to claim 1, characterized in that, In step S4, the time for letting the mixture stand after shaking is 4-6 minutes.
8. The method for detecting the total iron content of lubricating oil according to claim 1, characterized in that, In step S5, the detection wavelength of the spectrophotometer is 480-490 nm.
9. The method for detecting the total iron content of lubricating oil according to claim 1, characterized in that, In step S1, the mass of the lubricating oil sample to be tested is 0.2-0.8g, and the volume of the quartz beaker is 45-55ml.
10. The method for detecting the total iron content of lubricating oil according to claim 1, characterized in that, In step S1, the evaporation temperature is 280-320℃; in step S2, the ashing temperature is 650-750℃.