Method for determining trace impurity elements in triphenyl antimony

Abstract

The application discloses a method for determining trace impurity elements in triphenyl antimony, which comprises the following steps: (1) selecting a sample to be measured, and adopting a nuclear magnetic resonance method to confirm whether the sample to be measured is triphenyl antimony; (2) placing the sample to be measured confirmed as triphenyl antimony on a high-purity indium sheet, and adopting a direct current glow discharge mass spectrometry (GD-MS) to determine impurity elements in the triphenyl antimony. The method directly samples a solid, does not need complex pretreatment, effectively avoids sample hydrolysis and pollution risks, has the advantages of high sensitivity, efficient testing and simultaneous determination of multiple elements, can meet the accurate detection requirements of trace impurities in triphenyl antimony for food-grade polyester production, and provides reliable technical support for purity control.

Description

Technical Field

[0001] This invention belongs to the field of chemical analysis technology, specifically relating to a method for determining trace impurity elements in triphenylantimony. Background Technology

[0002] Triphenylantimony is a widely used and highly efficient catalyst in polyester production, characterized by high catalytic activity, fast reaction rate, and low cost. However, its purity directly affects the molecular weight distribution and color of polyester products. When the content of metallic impurities exceeds 0.1 ppm, it leads to a decrease in the polycondensation reaction rate and an increase in the yellowing index (YI) of the final product by 3-5 units. Furthermore, triphenylantimony readily absorbs water and decomposes into antimony trioxide and triphenylantimony when exposed to air. Therefore, it is necessary to minimize the exposure time at room temperature and pressure during sample pretreatment to reduce the hydrolysis of triphenylantimony and ensure the accuracy of the results.

[0003] The industry standard YS / T 972-2014, used for testing the purity of triphenylantimony, references the national standards GB / T 3253.1, GB / T 3253.2, and GB / T 3253.3 for measuring arsenic, iron, and lead impurities in triphenylantimony, respectively. The minimum detection range of these national standard methods is 2 ppm. Traditional atomic absorption spectrometry (AAS), limited by flame atomization efficiency, has a detection limit of only 1 ppm for elements such as calcium, iron, arsenic, and lead, which cannot meet the purity requirements of triphenylantimony used in food-grade polyester production.

[0004] Inductively coupled plasma mass spectrometry (ICP-MS), commonly used for trace component detection, requires complex sample pretreatment. The complete digestion of triphenylantimony takes about 4 hours. The pretreatment for digestion requires weighing and other operations. During this process, triphenylantimony will rapidly absorb moisture and decompose, resulting in the final result not matching the actual value. Furthermore, the acid or alkali digestion method can introduce impurities, making it impossible to detect the content of all elements in the sample.

[0005] Currently, the core standards for triphenylantimony only cover the determination of the antimony content of the main component, limits of key impurities, and physical performance indicators (appearance, melting point, solubility). There are few reports on the identification of triphenylantimony and the detection of its various impurities. Summary of the Invention

[0006] The purpose of this invention is to provide a method for determining trace impurity elements in triphenylantimony.

[0007] The method of this invention uses direct solid injection, which eliminates the need for complex pretreatment and effectively avoids the risks of sample hydrolysis and contamination. It also has the advantages of high sensitivity, high testing efficiency, and simultaneous determination of multiple elements. It can meet the requirements for accurate detection of trace impurities in triphenyl antimony used in food-grade polyester production and provides reliable technical support for its purity control.

[0008] The above-mentioned objective of this invention can be achieved through the following technical solution: a method for determining trace impurity elements in triphenylantimony, comprising the following steps:

[0009] (1) Select the sample to be tested and use nuclear magnetic resonance to confirm whether the sample to be tested is triphenylantimony;

[0010] (2) The sample to be tested, which is confirmed to be triphenyl antimony, is placed on a high-purity indium sheet. The diameter of the triphenyl antimony is 4-5 mm. The impurity elements in the triphenyl antimony are determined by DC glow discharge mass spectrometry (GD-MS). The discharge current of the DC glow discharge mass spectrometer is 1.8 mA-2 mA, the discharge voltage is 850 V-950 V, and the pre-sputtering time is 10 min-15 min.

[0011] In the above method for determining trace impurity elements in triphenylantimony:

[0012] Preferably, in step (1), when using nuclear magnetic resonance to confirm whether the sample to be tested is triphenyl antimony, a vacuum glove box is used to complete the vacuum dissolution and sealing preservation of the sample to be tested. Specifically, the following steps are taken: the glove box is evacuated to a pressure below 0.1 MPa, and high-purity argon gas with a purity of 99.999%-99.9999% (more preferably 99.9999%) is introduced to atmospheric pressure. This operation is repeated 3 times to completely replace the air and water vapor in the box. Under the protection of dry argon gas, the sample to be tested is weighed, transferred to the NMR tube, deuterated chloroform is added, and the sample is completely dissolved by ultrasonic oscillation. The tube is sealed with an alcohol lamp flame in the glove box. After confirming that the seal is intact, the glove box is depressurized to atmospheric pressure, the sealed NMR tube is taken out, and it is left to stand at room temperature for testing.

[0013] Preferably, the nuclear magnetic resonance test conditions in step (1) are: ¹H spectrum, single pulse mode, pulse angle 30°, delay time 1s, number of scans 32, and sampling bandwidth 20ppm.

[0014] Preferably, in step (2), the test sample identified as triphenyl antimony is placed on a high-purity indium sheet, including: weighing the triphenyl antimony sample onto the high-purity indium sheet, covering it with weighing paper, pressing it firmly, and removing any powder sample that is not pressed firmly on the surface, so as to ensure that the diameter of the triphenyl antimony powder sample on the indium sheet is 4-5 mm.

[0015] Preferably, the high-purity indium sheet in step (2) is pretreated before use. The pretreatment includes: adding nitric acid to the high-purity indium sample for cleaning, then cleaning with pure water, and finally cleaning with ethanol. After drying, it is pressed into a high-purity indium sheet with a diameter of 14-25 mm.

[0016] Preferably, the purity of the high-purity indium sheet in step (2) is not less than 99.999995%.

[0017] Preferably, the impurity elements mentioned in step (2) are nine types, namely Na, Mg, Al, Ca, Fe, As, Sn, Pb and Bi.

[0018] Preferably, in step (2), the isotopes used for testing the elements Na, Mg, Al, Ca, Fe, As, Sn, Pb, and Bi in the DC glow discharge mass spectrometry (GD-MS) method are as follows: 23 Na、 24 Mg 27 Al、 44 Ca, 56 Fe、 75 As、 119 Sn、 208 Pb and 209 Bi; uses a resolution of 3000-4000.

[0019] More preferably, in step (2), the discharge current of the DC glow discharge mass spectrometer is 1.8mA, the discharge voltage is 850V, and the pre-sputtering time is 10min.

[0020] Glow discharge mass spectrometry (GD-MS) allows for direct solid-state sample introduction, eliminating the need for pretreatment of powder samples. Only a small amount of sample needs to be pressed onto a high-purity indium plate, avoiding the risk of contamination during digestion. It also offers advantages such as high sensitivity, a wide testing range, and the ability to determine multiple elements simultaneously. For organometallic compounds with molecular weights greater than 200 Daltons, GD-MS exhibits 10-100 times higher sensitivity than inductively coupled plasma mass spectrometry (ICP-MS) in continuous operation mode. This is attributed to its higher ion extraction efficiency and lower matrix inhibition effect.

[0021] The present invention has the following advantages:

[0022] (1) This invention establishes an analytical method for the direct determination of nine impurity elements, namely Na, Mg, Al, Ca, Fe, As, Sn, Pb and Bi, in triphenyl antimony by direct current glow discharge mass spectrometry (GD-MS), and optimizes the sample preparation method and instrument operating parameters (discharge current, voltage and pre-sputtering time, etc.).

[0023] (2) The relative standard deviation (RSD) of the seven parallel determinations of the method of the present invention is ≤5.71%, which shows good precision; the accuracy and reliability of the method are verified by comparison with the ICP-MS test results.

[0024] (3) The method of the present invention uses solid direct injection, which does not require complicated pretreatment, effectively avoiding the risk of sample hydrolysis and contamination. It has the advantages of high sensitivity, high testing efficiency and simultaneous determination of multiple elements, which can meet the accurate detection requirements of trace impurities in triphenyl antimony used in food-grade polyester production, and provide reliable technical support for its purity control. Attached Figure Description

[0025] Figure 1 The NMR spectrum and chemical shift of triphenylantimony in Example 1 are shown below.

[0026] Figure 2 The triphenylantimony pressed onto indium in Example 1 is shown in the figure. The black disc is an indium sheet, and the white powder in the middle is triphenylantimony. Detailed Implementation

[0027] The present invention will be further described below through specific embodiments, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the scope of the present invention.

[0028] Unless otherwise mentioned, all reagents listed below are commercially available raw materials.

[0029] Example 1

[0030] 1. Experimental Section

[0031] 1.1 Reagents and Materials

[0032] Recommended, but not limited to: deuterated chloroform or deuterated toluene; high-purity indium (purity not less than 99.999995%, Pioneer Thin Film Materials (Guangdong) Co., Ltd.); 28 ICP-MS calibration standard solutions mixed standard-2A (commercial product number: 8500-6940.L1, CPAchem): 100 mg / L; 10 element calibration standards (commercial product number: 8500-6948.L1, CPAchem): 10 μg / mL; nitric acid, hydrofluoric acid, ethanol (UP grade, Suzhou Jingrui Chemical Co., Ltd.); the experimental water is ultrapure water (resistivity 18.2 MΩ·cm).

[0033] 1.2 Instruments and operating parameters

[0034] Recommended, but not limited to: Nuclear magnetic resonance spectrometer: AdvanceNeo 500MHz, Bruker GmbH, Germany; 1H spectrum, mode: single pulse; test temperature: room temperature; pulse angle: 30°; delay time: 1 s; number of scans (NS): 32; sampling bandwidth (SW): 20 ppm.

[0035] Astrum glow discharge mass spectrometer (Nu Instruments, UK), ULTIMA 2 inductively coupled plasma atomic emission spectrometer (HORIBA JY, France), Class 100 clean bench (Guangdong Kunling Purification Equipment Co., Ltd.), hand-operated press, Milli-Q ultrapure water system (Millipore, USA), BSA224S electronic balance (0.0001 g, Satorius): accuracy 0.0001 g, high-purity Ar gas (purity 99.9999%).

[0036] 1.3 Experimental Methods

[0037] 1.3.1 NMR tube sample determination

[0038] Triphenylantimony is sensitive to air and moisture. Its decomposition rate can be slowed down under light-proof and low-temperature conditions (usually below 4°C), thereby extending its storage time. However, even in light-proof and low-temperature environments, the substance will still undergo slow oxidation with residual oxygen in the air. Therefore, to ensure the accuracy of nuclear magnetic resonance (NMR) structure confirmation, the dissolution and encapsulation of the sample must be carried out under oxygen-free and water-free conditions.

[0039] Based on the above considerations, this embodiment uses a vacuum glove box to complete the vacuum dissolution and sealing preservation of the sample.

[0040] First, evacuate the glove box to a pressure below 0.1 MPa, then fill it with high-purity argon gas to atmospheric pressure. Repeat this operation three times to completely replace the air and moisture inside the box.

[0041] Under dry argon protection, accurately weigh approximately 10 mg of sample and transfer it to a clean 5 mm NMR tube. Add 0.6 mL of deuterated chloroform (CDCl3) using a microsyringe, quickly cap the tube, and sonicate for 2 min to completely dissolve the sample.

[0042] Subsequently, the tube was sealed inside the glove box using an alcohol lamp flame (the sealing length was about 3-4 cm). After confirming that the seal was intact, the glove box was slowly depressurized to atmospheric pressure. The sealed NMR tube was then removed and left to stand at room temperature for testing.

[0043] The nuclear magnetic resonance testing conditions were: ¹H spectrum, single pulse mode, pulse angle 30°, delay time 1s, number of scans 32, and sampling bandwidth 20ppm.

[0044] The NMR spectrum, chemical shift, and structural formula of the triphenylantimony standard reference are shown below. Figure 1 .

[0045] According to the dual-use item control catalog, the first step is to determine whether the sample is an organoantimony compound. The test results must then be consistent with... Figure 1The standard substances in the sample are consistent, which indicates that the main component of the sample is triphenylantimony (an organic antimony substance). Then, the metal impurities in the sample are quantified. If the concentration of triphenylantimony after removing impurities is greater than or equal to 99.999%, it belongs to the dual-use item control list.

[0046] 1.3.2 Fabrication of Indium Auxiliary Electrode

[0047] Approximately 2g of high-purity indium sample was placed in a 100mL polytetrafluoroethylene (PFA) bottle. After washing with 10-15mL of nitric acid for 10-20s, it was rinsed several times with pure water, then once with ethanol. After drying, it was pressed into indium sheets with a diameter of approximately 15mm using a hand press. The cleaning process was repeated once more, and the sheets were dried in a clean bench. The impurity content was determined using DC-GDMS (Direct Current Glow Discharge Mass Spectrometry). Except for Na, Mg, S, Ti, Cr, Fe, Zn, and Bi, whose impurity mass fractions were 0.2-3ng / g, the mass fractions of all other impurities were less than 1ng / g (see Table 1 below).

[0048] Table 1. Determination results of impurity elements in indium (In) sheets (n=5)

[0049]

[0050] 1.3.3 Sample Preparation

[0051] Select an appropriate amount of triphenylantimony sample and place it on the indium sheet. Cover it with several layers of weighing paper and manually press it firmly with a polytetrafluoroethylene (PFA) rod. Then, use tweezers to hold the edge of the indium and gently tap it to remove any loose powder sample. At this point, the diameter of the triphenylantimony powder pressed onto the indium sheet should be approximately 4-5 mm. The prepared sample is shown below. Figure 2 As shown.

[0052] 1.4 Instrument Operating Conditions

[0053] Table 2 shows the parameters of the glow discharge mass spectrometer used in the experiment. Under these parameters, a stable matrix signal can be obtained.

[0054] Table 2 Instrument operating parameters

[0055]

[0056] 1.5 Experimental Data Processing

[0057] During the detection, Sb was set as the matrix, and the content of matrix Sb was defined as 34% based on the percentage of Sb in triphenylantimony. The content of impurity elements in triphenylantimony can be calculated by subtracting the contribution of that element from the indium sheet from the content of the element to be tested in the sample sheet. Since the purity of the high-purity indium used in the experiment has reached 99.99999%, the contribution of impurities in high-purity indium can be ignored. The formula for calculating the impurity elements in triphenylantimony is shown in (1):

[0058] (1)

[0059] In the formula: The content of element X in the triphenylantimony sample to be tested; I X I Sb The signal intensities of elements X and Sb are respectively; A X 、 A Sb These are the isotopic abundances of elements X and Sb, respectively; RSF X RSF Sb , respectively, are the relative sensitivity factors of elements X and Sb, and 0.34 is the proportion of Sb in triphenylantimony.

[0060] 2. Results and Discussion

[0061] 2.1 Selection of Sample Preparation Area

[0062] Triphenylantimony is a non-conductive sample, and the amount of sample directly affects the magnitude and stability of the matrix signal. This experiment investigated the effect of different sample sizes on the matrix signal intensity and stability. When the sample size was 9–10 mm, the signal remained unstable after half an hour of sputtering; when the sample size was 6–8 mm, half an hour of sputtering also failed to stabilize the signal, making it impossible to complete the sample test; when the sample size was 4–5 mm, the matrix signal stabilized within a few minutes. 121 The signal strength of Sb is 4.2 × 10⁻⁶. 8 cps.

[0063] 2.2 Discharge Parameters

[0064] When detecting insulator samples, conductors or semiconductors preferentially undergo sputtering. Some of the sputtered atoms deposit on the surface of the insulator sample, forming a conductive film, thus initiating sputtering of the insulator sample. The sputtering rate and signal intensity generally increase with increasing discharge current and voltage. For insulator samples, the discharge parameters cannot be too large; otherwise, the sputtering rate will be too fast, resulting in significant sample loss and a rapid decrease in the matrix signal, increasing the error in impurity element detection. Furthermore, large discharge parameters are also detrimental to the stability of the matrix signal. Considering all factors, the discharge parameters selected for the experiment were 1.8 mA / 850 V.

[0065] 2.2.1 Current

[0066] Discharge current is one of the key parameters affecting the analytical performance of glow discharge mass spectrometry (GD-MS), directly determining the cathode sputtering rate, sample atomization efficiency, and ionization degree. For non-conductive samples such as triphenylantimony, the choice of current is particularly sensitive: too low a current results in insufficient sputtering to form a stable conductive layer on the sample surface, leading to weak and volatile matrix signals; too high a current may cause sample overheating, deterioration of sputtering pit morphology, and even increase in molecular ion fragmentation or rapid sample consumption. To investigate the effect of current on signal intensity, experiments were conducted at a fixed discharge voltage of 850 V and an argon flow rate of 0.45 mL / min. -1 Under the given conditions, the current was set to 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0 mA respectively, and the signal strength (cps) of ¹²¹Sb was recorded. The results are shown in Table 3.

[0067] Table 3 Signal strength under different discharge currents

[0068]

[0069] The experimental data in Table 3 show that when the current is 1.0 mA, the signal strength is 9.3 × 10⁻⁶. 7 The signal strength was 1.2 cps, but at this point the discharge electrode was unstable, with signal fluctuations exceeding ±30%, which likely originated primarily from background noise or brief abnormal sputtering events. When the current rose to 1.2 mA, the signal strength plummeted to 1.3 × 10⁻⁶. 8 The low cps (centrifuge strength) is due to the fact that the sputtering process is just beginning and a uniform conductive film has not yet formed on the sample surface, resulting in extremely low ion extraction efficiency. As the current further increases to 1.4 mA and 1.6 mA, the signal strength increases to 2.5 × 10⁻⁶, respectively. 8 cps and 3.9×10 8 The increased cps indicates that the sputtering rate is accelerating, the conductive film is gradually stabilizing, and the ion yield is significantly increasing. The signal strength reaches its maximum value of 4.2 × 10⁻⁶ when the current reaches 1.8 mA. 8 The signal strength was measured at cps, and the relative standard deviation (RSD) was only 3.2% over 30 minutes of continuous monitoring, indicating that the discharge state was ideal. Increasing the current to 2.0 mA slightly reduced the signal strength to 4.1 × 10⁻⁶. 8 The sample consumption rate increased, and the matrix signal showed a slow decline in the later stages of the test.

[0070] The above phenomenon can be attributed to the following: within the medium current range (1.6-1.8 mA), sputtering and deposition reach a dynamic equilibrium, resulting in good conductivity on the sample surface; above 1.8 mA, the excessively high current density leads to localized overheating, causing partial thermal decomposition of triphenylantimony. The resulting insulating oxides (such as Sb₂O₃) disrupt the continuity of the conductive film, thus suppressing the signal. Considering signal strength, stability, and sample consumption, 1.8 mA was selected as the optimal discharge current for the experiment.

[0071] 2.2.2 Voltage

[0072] The discharge voltage determines the kinetic energy imparted to argon ions by the accelerating electric field, thus affecting sputtering yield and ion transport efficiency. For non-conductive samples, excessively high voltage exacerbates charge accumulation on the sample surface, leading to "micro-arc discharge" and signal jitter; excessively low voltage results in insufficient sputtering yield and difficulty in exciting impurity elements. To optimize the voltage parameters, a fixed discharge current of 1.8 mA and an argon flow rate of 0.45 mL / min were used. -1 Under these conditions, the voltage range of 600V to 1100V was investigated. 121 The signal intensity changes of Sb are shown in Table 4.

[0073] Table 4 Signal strength under different discharge voltages

[0074]

[0075] The experimental data in Table 4 show that when the voltage is 600V, the signal strength is 7.1×10⁻⁶. 3 The signal strength was 8.9 × 10⁻⁶ cps, but the discharge was extremely weak at this point, and there were almost no obvious sputtering pits on the sample surface. When the voltage was increased to 700V, the signal strength increased to 8.9 × 10⁻⁶ cps. 6 The sample signal strength was 850V, but the signal intensity was still too low to meet the detection requirements. After the voltage reached 850V, the signal strength jumped to 4.2×10⁻⁶. 8 The cps indicates that the sputtering threshold has been crossed and the sample has begun to be sputtered stably. The signal strength reaches its maximum value of 5.2 × 10⁻⁶ at 1000 V. 8 At this point, the glow emission is bright and stable, and the sputtering craters are uniform. However, when the voltage is further increased to 1100V, the signal strength actually decreases to 1.1 × 10⁻⁶. 7 The sample consumption rate increased dramatically, with a large number of polyatomic ion interference peaks (such as SbAr⁺, C6H5⁺, etc.) detected at the same time, and the sample consumption time for a single sample was less than 10 minutes before it was exhausted.

[0076] It is worth noting that although the highest signal intensity was obtained at 1000V, the matrix signal decayed rapidly at this voltage (decreasing by about 15% every 10 minutes), which is detrimental to the data reproducibility during continuous multi-element measurements. In addition, excessively high voltage can exacerbate the redeposition and memory effect of trace impurities (such as As and Pb) in triphenylantimony.

[0077] Therefore, considering signal stability, interference level, and sample utilization, the experiment did not choose the strongest signal at 1000V, but instead used 850V (at which the signal strength is approximately 4.2 × 10⁻⁶). 8 (cps) in exchange for a longer steady-state sputtering window and lower multi-atom interference. Actual tests show that the matrix signal fluctuation is less than 5% within 60 minutes at 850V, fully meeting the requirements for trace analysis.

[0078] 2.2.3 Pre-sputtering time

[0079] Pre-sputtering is an indispensable step in GD-MS analysis. Its purpose is to remove adsorbed gases, moisture, and oxide layers from the sample surface, while simultaneously establishing stable sputtering pits and conductive films. For triphenylantimony, which is easily hygroscopic and decomposes in air, too short a pre-sputtering time can lead to interference from surface contaminants, while too long a time may cause excessive sample consumption or thermal decomposition. Experiments were conducted under discharge current conditions of 1.8 mA and voltage of 850 V to investigate the effects of different pre-sputtering times (5, 10, 15, 20, and 30 min). 121 The signal strength and stability of Sb are shown in Table 5.

[0080] Data shows that the signal strength was 3.4 × 10⁻⁶ after 5 minutes of pre-sputtering. 8 The signal intensity was low (cps), but the signal fluctuated significantly (RSD≈8.2%). This was because adsorbed water and oxygen on the sample surface were not completely removed, and the conductive film was not yet fully formed, leading to uneven sputtering due to localized charge accumulation. When the pre-sputtering time was extended to 10 min, the signal intensity increased to 4.2 × 10⁻⁶. 8 The signal intensity decreased significantly (RSD≈3.1%), indicating that surface impurities had been sufficiently removed and the conductive film had reached a stable state. Further pre-sputtering was performed for 15 min and 20 min, and the signal intensity stabilized at 4.2 × 10⁻⁶. 8 cps and 4.1×10 8 A change in cps of less than 3% indicates that sputtering has entered a steady state. The signal strength at 30 minutes was 4.2 × 10⁻⁶. 8 The cps result showed no significant difference from the 10min result, but approximately 30μg of sample had already been consumed, making it less than optimal for precious samples or small-sized sample preparation.

[0081] Mechanistically, during the initial pre-sputtering stage (0-5 min), the desorption of surface physical adsorbates and the removal of volatile impurities mainly occur. From 5-10 min, the conductivity provided by the indium substrate gradually emerges, and a mixed conductive layer composed of redeposited sputtered atoms forms on the triphenylantimony surface, with the ion yield steadily increasing. After 10 min, the sputtering rate and redeposition rate reach equilibrium, and the signal enters a plateau. It is noteworthy that after pre-sputtering exceeds 20 min, the edge of the indium auxiliary electrode begins to warp, potentially leading to poor contact in some areas and a slight signal decrease. Therefore, to ensure surface cleanliness while balancing testing efficiency and sample utilization, 10 min was selected as the optimal pre-sputtering time. Under these conditions, the signal intensity of all nine target impurity elements remained stable within the subsequent 30 min, and the precision experiment yielded satisfactory results (RSD ≤ 5.71%).

[0082] Table 5 Signal strength at different pre-sputtering times

[0083]

[0084] 2.3 Isotope and Resolution Selection

[0085] In glow discharge mass spectrometry, the appropriate selection of isotopes and resolution is crucial for ensuring the accuracy and reliability of measurement results. For organometallic compounds with complex matrices, such as triphenylantimony, the discharge process generates numerous mass spectrometric interferences, including polyatomic ions, isotopes, and multicharged ions. In severe cases, these interferences can cause the measured values ​​of impurity elements to deviate from the true values ​​by orders of magnitude. Therefore, this embodiment systematically evaluated the isotopic abundance, potential interference sources, and required resolution of nine target impurity elements. The screening results are summarized in Table 6.

[0086] Because the matrix of triphenylantimony contains a large amount of carbon, hydrogen, oxygen, and antimony elements, it readily generates various polyions in glow discharge power sources. For example, 24 Mg may be affected 12 C 12 Severe interference from C-dimer ions, 28 Si will be affected 12 C 16 Interference from O molecular ions, and 48 Ti cannot avoid 12 C 36 Ar polyatomic ion superposition. Spectroscopic analysis showed that the aforementioned interference was difficult to separate effectively in low-resolution mode (approximately 400 nm), resulting in complete overlap between the target element signal and the interference peak. Experiments demonstrated that increasing the resolution to 4000 nm (medium-resolution mode) significantly reduced the full width at half maximum (FWHM) of the interference peak, allowing for clear separation of the target element and the interfering ions. Experimental data showed that at a resolution of 4000 nm, 24 Mg and12 C 12 The mass-to-charge ratio difference between the C peaks can be fully resolved, and the background signal of Mg is reduced by about three orders of magnitude.

[0087] However, for some ion pairs where the interference peaks have a very close mass-to-charge ratio to the target element, a resolution of 4000 ppm is still insufficient for separation. Take calcium as an example. 40 Ar is an unavoidable abundance species when using argon as a glow discharge gas. 40 Ar + Ion peaks and 40 Ca + The target peaks almost completely overlapped and could not be effectively separated using the medium-resolution mode. Therefore, in this embodiment, an abundance of approximately 2.1% was selected. 44 Ca was used as the isotope to be tested, thus effectively avoiding 40 Severe interference from Ar. Similarly, for tin, due to... 120 Sn and multiple 40 Ar polyatomic polymer ions (such as Ar polyatomic polymer ions, such as Ar polyatomic polymer ions) 40 Ar 40 Ar 40 Ar) has overlapping mass numbers, therefore this embodiment selects 119 Although sn is used for isotope determination due to its low natural abundance, it avoids the superposition interference of isotopes. For the analysis of arsenic, 75 As is a monoisotope element, it can be effectively eliminated in high-resolution mode. 40 Ar 35 The influence of impurity ions such as Cl was investigated. The experiment ultimately determined that all nine target elements were sampled and quantified using a 4000-resolution mode, based on the isotopes listed in Table 6, ensuring the independence of mass spectrometry peaks and the reliability of the measurement data.

[0088] Table 6 Selection of Isotopes and Resolution for Test Elements

[0089]

[0090] 2.4 Mass Spectrometry Interference and Elimination

[0091] Interference in glow discharge mass spectrometry generally falls into three main types: isotope interference, polyatomic ion interference, and multiply charged ion interference. In experiments, isotope analysis typically selects the element with the highest abundance and no interference. For most elements, a standard resolution of 4000 nm is sufficient to separate the vast majority of polyatomic ion interference peaks, such as... 12 C 12 C 24 Mg, 12 C 16 O pair 28 Si, 12 C36 Ar to 48 Ti, 16 O 40 Ar to 56 Interference from Fe. And interference from some elements is difficult to separate even at high resolution, such as... 40 Ar to 40 Ca, 40 Ar 40 Ar to 80 Se, 40 Ar 40 Ar 40 Ar to 120 To avoid interference from Sn, only measurements of isotopes with lower abundance can be performed, such as Ca. 44 Ca, Se selection 78 Se, Sn selection 119 Sn.

[0092] 2.5 Detection Limit and Precision

[0093] The main parameters affecting the detection limit include the matrix signal intensity, integration time, and the presence of interference. Since the sample preparation area and discharge parameters significantly affect the signal stability of the matrix, it is difficult to optimize the detection limit by increasing the matrix signal intensity using these two parameters. Therefore, in the absence of interference, the element with the highest abundance is preferentially selected, while the detection limit is lowered by increasing the integration time. Eleven sets of data were collected from the sample, and the standard deviation was calculated. The method detection limit was defined as three times the standard deviation. The detection limits and integration times for each element are shown in Table 7.

[0094] Table 7 Detection limits and integration times for elements

[0095]

[0096] To examine the stability and reproducibility of the established method under repeated determination conditions, this embodiment performed seven parallel sample preparations and independent analyses on the same batch of triphenylantimony samples, covering nine representative impurity elements: Na, Mg, Al, Ca, Fe, As, Sn, Pb, and Bi. The determination results and related statistical parameters are detailed in Table 8.

[0097] Table 8. Precision experiment results (n=7)

[0098]

[0099] The analysis results in Table 8 show that the relative standard deviation (RSD) of all elements ranges from 0.84% ​​to 5.71%, indicating that the method has good internal precision and repeatability.

[0100] Among the nine elements, bismuth (Bi) had the lowest RSD at only 0.84%, with seven repeated measurements showing values ​​of 12.46, 12.42, 12.43, 12.44, 12.72, 12.54, and 12.50 μg·g⁻¹. -1 The average value was 12.50 μg·g. -1 This excellent precision can be attributed to three factors: firstly, the relatively high Bi content in the sample (average 12.50 μg·g⁻¹). -1 First, the signal strength is sufficient and the statistical noise is relatively low. Second, the glow discharge behavior of Bi is relatively stable, and the sputtering efficiency and ionization efficiency fluctuate little. Third, when 209 is selected as the analytical isotope, there is no significant polyatomic ion interference from Ar or matrix elements.

[0101] In contrast, magnesium (Mg) exhibited the highest relative standard deviation (5.71%), with seven measurements of 0.31, 0.30, 0.31, 0.35, 0.31, 0.34, and 0.32 μg·g⁻¹. -1 The average value is 0.32 μg·g -1 This result is significantly higher than the precision levels of other elements. Further analysis shows that Mg has the lowest signal intensity among all target elements, resulting in a poor signal-to-noise ratio; even small fluctuations in the background signal can have a relatively large impact on the final results. The RSDs for tin (Sn) and aluminum (Al) are 3.88% and 2.82%, respectively, which are at a moderate level. The measured values ​​for tin range from 4.33 to 4.76 μg·g⁻¹. -1 The fluctuations between these values ​​may be related to the local deposition of tin on the sputtering pit surface during glow discharge; the signal strength of aluminum is also at a moderate level, and its RSD performance is also at a moderate level.

[0102] For elements such as sodium (Na), calcium (Ca), iron (Fe), arsenic (As), and lead (Pb), the RSDs were all controlled within a low range of 1.12% to 2.44%, further verifying the good repeatability of this method in determining trace impurities. The above results collectively demonstrate that the method of this invention has satisfactory precision in determining the nine target impurity elements in triphenylantimony, and can fully meet the batch detection and quality control requirements for trace impurities in triphenylantimony used in food-grade polyester production.

[0103] 2.6 Comparison of Results

[0104] To further verify the accuracy and reliability of this method in determining trace impurity elements in triphenylantimony, the established dc-GD-MS method was used to test the same batch of samples, and the results were compared with those obtained by inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS method used in this study followed the trace element determination procedure in the GB / T 18115 series of standards. Samples were analyzed after sealed microwave digestion. The determination results of the nine impurity elements by both methods are detailed in Table 9.

[0105] Table 9 Comparison of results for determining various impurity elements in triphenylantimony using different methods

[0106]

[0107] Overall, the results show that the values ​​measured by the GD-MS method and the ICP-MS method of this invention are highly consistent.

[0108] Taking sodium as an example, the content measured by GD-MS was 0.97 μg·g. -1 The value was measured to be 0.95 μg·g by ICP-MS. -1 The relative deviation was approximately 2.1%. The performance of the three light metals, magnesium, aluminum, and calcium, was also ideal: the GD-MS result for Mg was 0.054 μg·g⁻¹. -1 The ICP-MS result was 0.057 μg·g⁻¹. -1 Al was 0.22 μg·g -1 and 0.21 μg·g -1 The Ca concentrations were 0.86 μg·g⁻¹. -1 and 0.85 μg·g -1 The iron content was 1.39 μg·g. -1 (GD-MS) and 1.41 μg·g -1 (ICP-MS), deviation controlled within 1.4%.

[0109] For heavy metal impurities such as arsenic, tin, lead, and bismuth, both methods also showed good consistency. The GD-MS result for As was 0.96 μg·g⁻¹. -1 The ICP-MS result was 0.94 μg·g⁻¹. -1 The results for Sn were 5.30 μg·g. -1 and 5.29 μg·g -1 Pb was 12.75 μg·g -1 and 12.74 μg·g -1 Bi was 20.25 μg·g -1 and 20.29 μg·g -1The relative deviations of the measured values ​​of the above nine elements by both methods were controlled within 3%, indicating that the method has reliable accuracy.

[0110] It is worth noting that while ICP-MS offers advantages such as low detection limits and simultaneous multi-element analysis, its pretreatment process is time-consuming, requiring approximately 4 hours for complete digestion. Furthermore, steps such as weighing and dilution carry the risk of lower results due to the hygroscopic hydrolysis of triphenylantimony. In contrast, GD-MS uses direct solid injection, effectively avoiding errors introduced by the aforementioned pretreatment steps. The good agreement between the two methods indirectly confirms the feasibility of the high-purity indium-assisted electrode method for the quantitative analysis of triphenylantimony. Moreover, this method successfully extends the detection range to as low as 0.05 μg·g⁻¹. -1 The following levels overcome the limitation of atomic absorption spectrometry, whose detection limit is only at the ppm level. In summary, the method of this invention is suitable for the rapid, accurate, and simultaneous determination of trace impurity elements in triphenylantimony, and can provide reliable technical support for the purity evaluation and quality control of this dual-purpose controlled substance.

[0111] Therefore, this invention successfully established an analytical method for the direct determination of nine impurity elements (Na, Mg, Al, Ca, Fe, As, Sn, Pb, and Bi) in triphenylantimony using direct current glow discharge mass spectrometry (GD-MS). By systematically optimizing the sample preparation method and instrument operating parameters, accurate detection of trace impurities was achieved. The sample preparation process employs a solid-state direct injection mode, where the sample is placed on a pretreated high-purity indium sheet and pressed firmly before loading onto the instrument, effectively avoiding the problems of sample moisture absorption and hydrolysis, as well as contamination introduced during pretreatment, that occur in traditional methods. Optimized instrument parameters show that, under conditions of a discharge current of 1.8 mA, a voltage of 850 V, and a pre-sputtering time of 10 min, the signal intensity of the target elements reaches the ideal level.

[0112] Comparison of test results with those from inductively coupled plasma mass spectrometry (ICP-MS) showed a high degree of agreement, confirming the accuracy and reliability of the method. Furthermore, this method eliminates the need for complex sample pretreatment, significantly shortening the analysis cycle, and offers the advantage of simultaneous multi-element determination, overcoming the limitations of existing industry standards and detection methods.

[0113] The above examples illustrate specific embodiments of the present invention. It is important to note that these specific embodiments are only for further explanation and do not constitute a limitation on the scope of protection of the present invention. Non-essential modifications and adjustments made by others based on the present invention still fall within the scope of protection of the present invention.

Claims

1. A method for determining trace impurity elements in triphenylantimony, characterized in that, Includes the following steps: (1) Select the sample to be tested and use nuclear magnetic resonance to confirm whether the sample to be tested is triphenylantimony; (2) The sample to be tested, which is confirmed to be triphenyl antimony, is placed on a high-purity indium sheet. The diameter of the triphenyl antimony is 4-5 mm. The impurity elements in the triphenyl antimony are determined by DC glow discharge mass spectrometry (GD-MS). The discharge current of the DC glow discharge mass spectrometer is 1.8 mA-2 mA, the discharge voltage is 850 V-950 V, and the pre-sputtering time is 10 min-15 min.

2. The method for determining trace impurity elements in triphenylantimony according to claim 1, characterized in that, In step (1), when using nuclear magnetic resonance to confirm whether the sample to be tested is triphenyl antimony, a vacuum glove box is used to complete the vacuum dissolution and sealing preservation of the sample to be tested. Specifically, the following steps are taken: the glove box is evacuated to a pressure below 0.1 MPa, and high-purity argon gas with a purity of 99.999%-99.9999% is introduced to atmospheric pressure. This operation is repeated 3 times to completely replace the air and water vapor in the box. Under the protection of dry argon gas, the sample to be tested is weighed, transferred to the NMR tube, deuterated chloroform is added, and the sample is completely dissolved by ultrasonic vibration. The tube is sealed with an alcohol lamp flame in the glove box. After confirming that the seal is intact, the glove box is depressurized to atmospheric pressure, the sealed NMR tube is taken out, and it is left to stand at room temperature for testing.

3. The method for determining trace impurity elements in triphenylantimony according to claim 1, characterized in that, The nuclear magnetic resonance test conditions in step (1) are: ¹H spectrum, single pulse mode, pulse angle 30°, delay time 1s, number of scans 32, and sampling bandwidth 20ppm.

4. The method for determining trace impurity elements in triphenylantimony according to claim 1, characterized in that, In step (2), the test sample, which is confirmed to be triphenyl antimony, is placed on a high-purity indium sheet, including: weighing the triphenyl antimony sample onto the high-purity indium sheet, covering it with weighing paper, pressing it firmly, and removing any powder sample that is not pressed firmly on the surface, so as to ensure that the diameter of the triphenyl antimony powder sample on the indium sheet is 4-5 mm.

5. The method for determining trace impurity elements in triphenylantimony according to claim 1, characterized in that, The high-purity indium sheet described in step (2) is pretreated before use. The pretreatment includes: adding nitric acid to the high-purity indium sample for cleaning, then cleaning with pure water, and finally cleaning with ethanol. After drying, it is pressed into a high-purity indium sheet with a diameter of 14-25 mm.

6. The method for determining trace impurity elements in triphenylantimony according to claim 1, characterized in that, The purity of the high-purity indium sheet mentioned in step (2) is not less than 99.999995%.

7. The method for determining trace impurity elements in triphenylantimony according to claim 1, characterized in that, The impurity elements mentioned in step (2) are nine in number: Na, Mg, Al, Ca, Fe, As, Sn, Pb and Bi.

8. The method for determining trace impurity elements in triphenylantimony according to claim 6, characterized in that, In step (2), the isotopes used for the DC glow discharge mass spectrometry (GD-MS) tests of the elements Na, Mg, Al, Ca, Fe, As, Sn, Pb, and Bi are as follows: 23 Na、 24 Mg 27 Al、 44 Ca, 56 Fe、 75 As、 119 Sn、 208 Pb and 209 Bi; uses a resolution of 3000-4000.

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