JP4907377B2 - Trace metal analysis method - Google Patents

Description

  The present invention relates to a method for quantitatively analyzing trace metals contained in hydrocarbon oils with high sensitivity and high accuracy, and more particularly to a method for quantitatively determining trace metals of 1 ppm or less.

  There are two major techniques for quantifying trace metals in conventional hydrocarbon oils. The first technique is a technique of quantifying by inductively coupled plasma (ICP) emission analysis or ICP mass spectrometry after burning hydrocarbon oil into an inorganic aqueous solution (see Patent Document 1 below). However, this method has a complicated procedure, and is susceptible to environmental pollution in the pretreatment process and the like, and has a drawback that an accurate value cannot be obtained by quantifying trace metals of 1 ppm or less.

  The second technique is a technique in which a hydrocarbon oil is directly or diluted with another hydrocarbon oil and quantified by ICP emission analysis or ICP mass spectrometry (see Non-Patent Document 1 below). As this method, as a test method for metal content in lubricating oil, JPI-5S-44-95: test method for Fe, Cu, Al, Pb, Cr and Sn content in used lubricating oil (solvent dilution-ICP emission analysis method) ) And JPI-5S-38-03: Lubricating oil-added element test method-inductively coupled plasma emission spectroscopic analysis method, etc. are known, but all can only determine 1 ppm or more.

  In order to achieve the determination of a metal content of 1 ppm or less, it is necessary not only to make the determination system highly sensitive but also to have the test component uniformly present in the actual sample and the standard sample. Detailed investigations by the present inventor have revealed that there are many cases in which trace metals of 1 ppm or less in hydrocarbon oil do not exist uniformly. Therefore, conventionally, an accurate quantitative value could not be obtained for trace metals of 1 ppm or less in hydrocarbon oil.

  When quantifying metals in hydrocarbon oil, the handling differs depending on whether the content is 1 ppm or less. Assuming that the specific gravity of the test component is 1 particle, if the content is 1 ppm, there are 1 million per mL, and when this 1 mL of solution is sprayed into an ICP emission spectrometer, it is generally 99% Is removed as a drain, so a signal with 1% or 10,000 grains is obtained. However, when the content is 1 ppb, there are only 1000 per mL. When this 1 mL of solution is sprayed on the analyzer, only about 1% of the signal, that is, signals from 10 grains can be obtained, so that the measurement accuracy becomes low. If it is 1 ppm or more, it can be quantitatively analyzed by shaking sufficiently even if it is present in the form of grains, but at the ppb level, it is accurate if the test component does not exist in a homogeneously dissolved state in the measurement sample. Cannot perform good quantitative analysis.

JP-A-11-344440 AKBAR MONTASER, “Inductively coupled plasma mass spectrometry”, p. 741-758, Chemical Industry Daily, 2000

  As described above, the trace metals in the hydrocarbon oil are present unevenly as gel-like substances and suspended particulate substances due to hydrolysis. Even if shaken violently, sedimentation, vessel wall adsorption, etc. occur, so a uniform state cannot be created. Even if a non-uniform solution is sprayed and quantification is performed by ICP emission analysis or ICP mass spectrometry, only inaccurate and low-accuracy results are obtained.

  The present invention solves the above-described drawbacks, and it is an object of the present invention to provide an analysis method for accurately and highly accurately measuring trace metals in hydrocarbon oils by ICP emission spectrometry or ICP mass spectrometry. And

  As a result of diligent research, the present inventors have uniformly dissolved trace metals in hydrocarbon oils by adding and mixing acids when analyzing trace metals of 1 ppm or less contained in hydrocarbon oils. As a result, it was found that it can be accurately and accurately quantified by ICP emission analysis or ICP mass spectrometry, and the present invention has been conceived.

That is, the present invention
(1) A method for analyzing a trace metal in which an acid is mixed with a hydrocarbon oil when quantifying a trace metal of 1 ppm or less contained in a hydrocarbon oil by ICP emission analysis or ICP mass spectrometry;
(2) The trace metal analysis method according to (1), wherein the acid is at least one selected from nitric acid, hydrochloric acid, sulfuric acid, hydrofluoric acid, phosphoric acid, perchloric acid, acetic acid, and formic acid;
(3) The trace metal according to (1) or (2), wherein one or more selected from 2-propanol, ethanol, methanol, 2-ethoxyethanol, and 2-butoxyethanol are mixed with the hydrocarbon oil as an auxiliary solvent. analysis method; and (4) (1) with an assay of trace metals as described in any one of the - (3) was analyzed for metal content in the hydrocarbon oil, in the quality control method of a quality control There is .

  According to the present invention, by performing simple preprocessing, a more accurate quantitative value can be obtained using a conventional apparatus. Further, by performing quality control by quantifying the metal content in the hydrocarbon oil by the analysis method of the present invention, it becomes possible not only to guarantee product quality but also to find problems in the manufacturing process. Therefore, the analysis method of the present invention can be effectively used for quality assurance of products, discovery of problems in the manufacturing process, and the like.

  The present invention is described in detail below. The trace metal analysis method of the present invention is characterized by mixing an acid with a hydrocarbon oil when quantifying a trace metal of 1 ppm or less contained in the hydrocarbon oil by ICP emission analysis or ICP mass spectrometry.

  By mixing acid in hydrocarbon oil, trace metal elements in hydrocarbon oil are hydrolyzed and dissolved in gel form, and dissolved as metal ions. Since it also dissolves as metal ions, it comes to exist uniformly in the solution.

  The acid can be used regardless of whether it is an inorganic acid or an organic acid, but is selected from nitric acid, hydrochloric acid, sulfuric acid, hydrofluoric acid, phosphoric acid, perchloric acid, acetic acid, and formic acid, based on the results of studies by the present inventors. It has been found that one or more are preferred.

  Moreover, the amount of the acid added is preferably in the range of 0.001 to 50% by volume, more preferably in the range of 0.01 to 5% by volume with respect to the hydrocarbon oil. An acid addition amount of less than 0.001% by volume is not preferable because there is no effect of acid addition, and heavy metals cannot be dissolved uniformly. Moreover, it is not preferable to add an acid exceeding 50% by volume because the collection ratio of hydrocarbon oil becomes small and trace analysis becomes difficult. In addition, although the concentration of the acid to be used is preferably a concentrated commercial reagent, it may be diluted 1.1 to 10 times with water. Concentrated products of commercially available reagents are 66.0 to 62.0 wt% in nitric acid, 35.0 to 37.0 wt% in hydrochloric acid, 95.0 wt% or more in sulfuric acid, and 46.0 in hydrofluoric acid. ~ 48.0 wt%, phosphoric acid content 85.0% wt or more, perchloric acid content 60.0-62.0 wt%, acetic acid content 99.5 wt% or more, formic acid content 88.0-92.0 wt% % Or 98 wt% or more. Use of a diluted acid is not preferable because it increases the possibility of phase separation with the hydrocarbon oil by the water used for dilution.

  In another embodiment of the present invention, there is a method of further using a co-solvent when mixing the acid with the hydrocarbon oil. When an acid is mixed with a hydrocarbon oil, the hydrocarbon oil and the acid may be phase-separated depending on the amount of acid added. The phase separation is not preferable because the sample cannot be sprayed uniformly in the analyzer, that is, cannot be uniformly introduced into the detector. Therefore, it is necessary to add a solvent compatible with both hydrocarbon oil and acid as an auxiliary solvent to make the entire sample uniform. As an auxiliary solvent, 1 type (s) or 2 or more types can be used. As this auxiliary solvent, it is preferable to use at least one selected from 2-propanol, ethanol, methanol, 2-ethoxyethanol and 2-butoxyethanol, and among these, 2-butoxyethanol is particularly preferably used. The amount of the auxiliary solvent added may be adjusted as appropriate, but is preferably in the range of 0.1 to 80% by volume, more preferably in the range of 5 to 30% by volume, and 5 to 20% by volume with respect to the hydrocarbon oil. % Range is particularly preferred.

  The hydrocarbon oil in the present invention is a hydrocarbon oil comprising an aromatic hydrocarbon, an aliphatic hydrocarbon, an alicyclic hydrocarbon, and a mixture thereof, and the hydrocarbon oil is obtained in a petroleum refining process. Also included are organic solvents such as benzene, xylene, toluene and cyclohexane as petrochemical raw materials, fuel oils such as gasoline and kerosene, especially fuel cells. The analysis method of the present invention can also be applied to a mixed solvent in which a polar solvent is added to these hydrocarbon oils.

  In the practice of the present invention, when mixing the acid with the hydrocarbon oil, the hydrocarbon oil can be used for analysis as it is, but since ICP mass spectrometry is extremely sensitive, the hydrocarbon oil is diluted with another hydrocarbon solvent. Can also be used for analysis. The hydrocarbon solvent used as the dilution solvent is preferably one that does not contain the detection target element as much as possible, has close properties to the dilution target hydrocarbon oil, and is compatible.

  The trace metal analysis method of the present invention is used for the determination of trace metals of 1 ppm or less contained in hydrocarbon oil. The lower limit of detection of the analysis method of the present invention is not particularly limited depending on the type of metal to be measured, but is preferably 1 ppb, more preferably 0.1 ppb, and particularly 0.01 ppb. It is.

  The metals to be measured in the present invention include lithium, beryllium, sodium, magnesium, aluminum, potassium, calcium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, and rubidium. Strontium, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, barium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead , Bismuth, thorium, uranium, lanthanum, cerium, praseodymium, neodymium, europium, gadolinium, terbium, dysprosium, erbium, thulium, ytterbium and Techiumu and the like.

  The quantification method by the ICP emission spectrometer or the ICP mass spectrometer may be performed by the same method as the conventional method. For example, first, a standard sample is measured to create a calibration curve, and then a test sample is measured. What is necessary is just to obtain | require a quantitative value. Therefore, the detection target element may be selected as appropriate, and a standard solution necessary for analysis may be prepared to create a calibration curve.

  The quality control method of the present invention is a quality control method for analyzing the metal content in the hydrocarbon oil by using the trace metal analysis method described above to manage the metal content in the hydrocarbon oil. Specifically, the quality control method of the present invention has an analysis step by the trace metal analysis method of the present invention between the production process and the product shipment process of the hydrocarbon oil. By comparing the analysis result with a predetermined specified value, judging that a hydrocarbon oil having a property below the specified value is a product, and determining that a hydrocarbon oil having a property above the specified value is not a product The metal content in the hydrocarbon of the product can be kept below a certain level. For hydrocarbon oils that deviate from the specified value, loss of production can be prevented by performing a separate processing step, for example, reprocessing by recycling to the distillation step, or processing step using an adsorbent, separation membrane, etc. be able to. The quality control method of the present invention can also be applied as means for detecting an abnormality in the manufacturing process.

  The hydrocarbon composition managed by the quality control method described above, because the heavy metal contained as an impure component is a fixed standard value, fuel for fuel cells, a solvent for semiconductor cleaning, for which a truly clean property is required, It is extremely useful in fields where emphasis is placed on trace metals, such as solvents for pharmaceutical production and high-purity plastic raw materials.

  An example of the acid addition effect of the present invention will be described below. Table 1 shows detection signal intensities when measuring with a ICP mass spectrometer with respect to toluene diluted solutions (concentration: 5 ng / mL) of cobalt, indium, and bismuth standard solutions (measurement apparatus and measurement conditions will be described later). Same as condition).

  From Table 1, it can be seen that by adding 0.02% by volume or more of nitric acid (concentration 70%) to the sample, the detection signal intensity is increased two to three times for all of cobalt, indium and bismuth.

  In addition, each standard solution of magnesium, aluminum, manganese, iron, nickel, copper, zinc, and cadmium was adjusted to 5 ng / mL with a sample prepared by adjusting the concentration of each element to 5 ng / mL using toluene / 2-butoxyethanol = 900 mL / 100 mL. Table 2 shows the relative signal intensity (signal intensity of the nitric acid-added sample ÷ signal intensity of the non-added sample) when 0.1 vol% is added.

  From the results shown in Table 2, it can be seen that the signal intensity increases by adding an acid even though the concentrations of various trace metal elements contained in the hydrocarbon oil are the same. In other words, by adding acid, various trace metal elements contained in hydrocarbon oils are dissolved into gel ions and suspended particulates from the presence of hydrolyzed gels and suspended particulates. It is inferred that trace metals were uniformly dispersed in the sample solution. Therefore, even if it is a trace amount of metal elements, the detection intensity will be increased if it is in a uniform state that does not cause adsorption to the inner wall of a container or sampling instrument, or sedimentation of the measured component. Is possible.

  Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.

(Preparation of standard solution)
(1) Preparation of indium solution for internal standard 1.00 g of CONOSTAN single element standard (indium: 5000 ppm) manufactured by Conoco Corporation is precisely weighed and dissolved in a solution of toluene / 2-butoxyethanol / nitric acid (900 mL: 100 mL: 1 mL). The indium standard stock solution (50 μg / mL) was made up to 100 mL. Next, the indium internal standard stock solution (50 μg / mL) was diluted 10,000 times with a toluene-2-butoxyethanol-nitric acid (900 mL: 100 mL: 1 mL) solution to prepare an indium solution for internal standard (50 ng / mL).

(2) Preparation of 21 element standard solution CONOSTAN multi-element standard S-21 (Ag, Al, B, Ba, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Mo, Na, Ni, P, manufactured by Conoco Corporation 1.00 g of Pb, Si, Sn, Ti, V, and Zn (each 900 ppm) are precisely weighed and dissolved in a toluene / 2-butoxyethanol / nitric acid (900 mL: 100 mL: 1 mL) solution to make exactly 100 mL and 21 elements. A standard stock solution (9 μg / mL) was used. A 21-element standard stock solution (9 μg / mL) was diluted 100-fold with a toluene / 2-butoxyethanol / nitric acid (900 mL: 100 mL: 1 mL) solution to prepare a 21-element standard secondary stock solution (90 ng / mL). Take 10 mL of the 21 element secondary stock solution (90 ng / mL), add 10 mL of the indium solution for internal standard (50 ng / mL), and add 100 mL with toluene / 2-butoxyethanol / nitric acid (900 mL: 100 mL: 1 mL). A 21 element standard solution (9 ng / mL) was prepared as a constant volume.

Example 1
10 mL of commercially available kerosene A was collected, 10 mL of indium solution for internal standard (50 ng / mL) was added, and the volume was adjusted to 100 mL with toluene / 2-butoxyethanol / nitric acid / hydrochloric acid (900 mL: 100 mL: 1 mL: 1 mL), A sample solution was prepared. This was measured with an ICP mass spectrometer.

(Comparative Example 1)
10 mL of commercial kerosene A was sampled and made up to a constant volume of 100 mL with toluene to prepare a sample solution. This was measured with an ICP mass spectrometer.

(Example 2)
A sample solution was prepared in the same manner as in Example 1 except that the commercial kerosene A was changed to the commercial kerosene B, and measurement was performed.

(Comparative Example 2)
A sample solution was prepared in the same manner as in Comparative Example 1 except that the commercial kerosene A was changed to the commercial kerosene B, and the measurement was performed.

Example 3
Collect 10 mL of commercially available kerosene C, add 10 mL of indium solution for internal standard (50 ng / mL), adjust to 100 mL with toluene / 2-butoxyethanol / hydrochloric acid (200 mL: 100 mL: 1 mL), and prepare sample solution did. This was measured with an ICP mass spectrometer.

(Comparative Example 3)
A sample solution was prepared in the same manner as in Comparative Example 1 except that the commercial kerosene A was changed to the commercial kerosene C, and measurement was performed.

Example 4
A sample solution was prepared in the same manner as in Example 3 except that commercial kerosene C was changed to commercial kerosene D, and measurement was performed.

(Comparative Example 4)
A sample solution was prepared in the same manner as in Comparative Example 3 except that the commercial kerosene C was changed to the commercial kerosene D, and the measurement was performed.

The acid, solvent, etc. used above are as follows.
1) Toluene: manufactured by Kanto Chemical, for electronics industry 2) 2-butoxyethanol: manufactured by Junsei Chemical, genuine grade 1) Nitric acid: manufactured by Wako Pure Chemicals, for electronics industry, concentration 70%
4) Hydrochloric acid: Wako Pure Chemicals, electronics industry, concentration 35%

The sample solution and the analytical standard solution prepared as described above were measured by ICP mass spectrometry.
ICP mass spectrometer: 7500cs manufactured by Agilent Technologies
High frequency output: 1.6kW
Reflected wave output: 5 W or less Plasma gas (argon) flow rate: 15 L / min Carrier gas (argon) flow rate: 1.0 L / min Sampling depth (position of sampling orifice with respect to plasma): 10 mm
Dwell time: 20 ms Number of sweeps: 400

  Table 3 shows the results of the analysis performed under the above conditions.

Claims (4)

  A method for analyzing a trace metal, which comprises mixing an acid with a hydrocarbon oil when quantifying a trace metal of 1 ppm or less contained in a hydrocarbon oil by ICP emission analysis or ICP mass spectrometry.   The trace metal analysis method according to claim 1, wherein the acid is at least one selected from nitric acid, hydrochloric acid, sulfuric acid, hydrofluoric acid, phosphoric acid, perchloric acid, acetic acid, and formic acid.   The trace metal analysis method according to claim 1 or 2, wherein one or more selected from 2-propanol, ethanol, methanol, 2-ethoxyethanol, and 2-butoxyethanol are mixed with the hydrocarbon oil as an auxiliary solvent.   A quality control method for performing quality control by analyzing a metal content in a hydrocarbon oil using the trace metal analysis method according to claim 1.