Method for detecting phosphorus content in high-carbon ferro-chrome by utilizing ICP (Inductively Coupled Plasma)

Abstract

The invention belongs to the technical field of chemical detection, and particularly relates to a method for detecting phosphorus content in high-carbon ferro-chrome by utilizing ICP (inductively coupled plasma), which comprises the following steps: 1) adding red acid into a sample, slowly adding concentrated sulfuric acid, adding perchloric acid after violent reaction is finished, heating to 360-380 DEG C, keeping constant temperature, dropwise adding nitric acid until the mixture becomes green, cooling, reboiling and fixing the volume; 2) establishing a working curve: dissolving 6 parts of high-purity iron and high-purity chromium according to the method in the step 1) until the volume of the volumetric flask is constant; (3) gradually diluting the 1000mg / L phosphorus standard solution according to a set curve point; transferring into a volumetric flask with 6 dissolved parts, introducing ICP (Inductively Coupled Plasma) detection, carrying out single excitation detection for 4 times, averaging, and calculating the phosphorus content according to a calibration curve. The method has the advantages that the phosphorus element in the high-carbon ferro-chrome is detected, the operation is simple, and the popularization is easy. In the detection, four times of single excitation detection are averaged, so that individual points are prevented from drifting due to multiple times of excitation, and the accuracy of a detection result is improved.

Description

Technical Field

[0001] This invention belongs to the field of chemical detection technology, and in particular relates to a method for detecting phosphorus content in high-carbon ferrochrome using ICP. Background Technology

[0002] High-carbon ferrochrome alloys are an important raw material in steel smelting, and their phosphorus content directly affects the alloy's mechanical properties and corrosion resistance. Phosphorus in high-carbon ferrochrome is usually present in trace amounts (0.010%-0.10%), but its negative impact on material properties is significant. Therefore, accurate determination of phosphorus content is crucial for quality control. Currently, the detection methods for phosphorus in high-carbon ferrochrome mainly rely on traditional chemical analysis techniques. The current national standard GB / T 5687.12-2020, "Determination of Phosphorus, Aluminum, Titanium, Copper, Manganese and Calcium Content in Ferrochrome by Inductively Coupled Plasma Emission Spectrometry," uses inductively coupled plasma optical emission spectrometry (ICP-OES) to determine elements such as phosphorus. However, sample pretreatment requires decomposition of the sample through an alkaline fusion method (such as a sodium carbonate-boric acid mixed flux). Although this method can achieve simultaneous detection of multiple elements, the alkaline fusion process is time-consuming (usually 2-4 hours), and high-temperature melting easily leads to the loss of volatile elements (such as phosphorus, which may escape in the form of phosphides at high temperatures), affecting the accuracy of detection. In addition, after melting, it needs to go through acid leaching, filtration and other steps, which are complicated and require high skills from the experimental personnel.

[0003] In existing technologies, sodium peroxide is melted at high temperature in a muffle furnace, followed by acidification with nitrate. This sample dissolution process is cumbersome, resulting in high salt content. ICP detection requires a high-salt nebulizer; otherwise, the results are unstable and may even damage the conventional nebulizer. Related studies primarily use alkali fusion to dissolve the sample, followed by spectrophotometry or ICP to detect phosphorus. For example, Wei Enshuang, Bao Hongxia, and Ma Yuxiang, "Joint Determination of Cr, P, and Mn in High-Carbon Ferrochrome," *Metallurgical Standardization and Quality*, 2006, No. 4, uses an alkali fusion-spectrophotometric method to determine phosphorus content via a phosphomolybdic blue colorimetric reaction. While this method is low-cost, the colorimetric conditions (such as acidity, temperature, and colorimetric time) significantly affect the results. Furthermore, chromium and iron, matrix elements in high-carbon ferrochrome, easily interfere with the colorimetric reaction, requiring the addition of masking agents (such as potassium sodium tartrate), leading to lengthy procedures and poor reproducibility. Patent application number 201911017687.9 discloses a method for jointly determining the phosphorus and silicon content in high-carbon ferrochrome and ferrochrome nitride, achieving joint determination of phosphorus and silicon through alkaline fusion-spectrophotometry. However, it also faces the problems of complex alkaline fusion process and severe matrix interference. For high-carbon, high-alloy samples such as high-carbon ferrochrome, carbides may encapsulate phosphorus elements during the melting process, leading to incomplete extraction. At the same time, a large number of iron and chromium ions are easily hydrolyzed and precipitated in acidic media, requiring additional control of acidity conditions, further increasing the operational difficulty.

[0004] Inductively coupled plasma optical emission spectrometry (ICP-OES) offers significant advantages in trace element analysis due to its high sensitivity (phosphorus detection limit down to 0.001%), simultaneous detection of multiple elements, and wide linear range (0.001%-1.0%). However, directly applying ICP to detect phosphorus in high-carbon ferrochrome faces two major challenges:

[0005] Matrix interference: Spectral interference (such as overlap of Fe 213.618nm and P 213.618nm spectral lines) and ionization interference (high ionization energy elements inhibit phosphorus atomization) caused by high concentrations of iron (>60%) and chromium (>30%);

[0006] Sample dissolution challenge: Carbides (such as Cr3C2) in high-carbon ferrochrome are chemically stable and cannot be completely decomposed by conventional acid dissolution methods (such as hydrochloric acid-nitric acid mixture), resulting in insufficient phosphorus extraction rate.

[0007] While the alkaline fusion method can completely decompose the sample, the introduced flux salts (such as Na2CO3) may clog the ICP nebulizer, and the high-salt matrix further exacerbates spectral interference. Therefore, developing an ICP detection method that balances efficient sample dissolution with suppression of matrix interference has become a key breakthrough direction for the accurate determination of phosphorus content in high-carbon ferrochrome. Summary of the Invention

[0008] The purpose of this invention is to provide a method for detecting phosphorus content in high-carbon ferrochrome using ICP. The method involves dissolving the sample with highly corrosive red acid, adding hydrofluoric acid to remove silicon, and finally using inductively coupled plasma atomic emission spectrometry (ICP-AES) to detect phosphorus. This method improves phosphorus extraction rate, reduces matrix interference, and enhances the accuracy of phosphorus content determination in high-carbon ferrochrome.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for detecting phosphorus content in high-carbon ferrochrome using ICP includes the following steps:

[0011] 1) Add red acid to the sample, then slowly add concentrated sulfuric acid. After the violent reaction is over, add perchloric acid and heat to 360-380°C. Keep the temperature constant until the reddish-brown fumes disappear and white sulfuric acid fumes appear. Add nitric acid dropwise, and the solution turns green. Remove and cool, add water and boil, then cool to room temperature and make up to 100 ml.

[0012] 2) Standard Curve Processing

[0013] The curve points were selected based on the phosphorus content range as 0, 1 g / L, 2 g / L, 3 g / L, 4 g / L, and 5 g / L.

[0014] 3) Establish a working curve:

[0015] Take 6 portions of 0.04g high-purity iron and 0.06g high-purity chromium, place them in 100ml dual-purpose bottles and dissolve them according to step 1). Then transfer them to volumetric flasks to form a base for later use.

[0016] The 1000 mg / L phosphorus standard solution was serially diluted according to the curve points set in step 2), and each diluted solution was transferred to 6 volumetric flasks and brought to volume. The prepared series of working curves were then introduced into ICP detection.

[0017] 4) Instrument parameters;

[0018] ICP preheating for more than 1 hour, setting the nebulizer gas flow rate to 0.6 L / min, plasma RF power to 1350 W, auxiliary gas flow rate to 0.5 L / min, peristaltic pump speed to 60 rpm, vertical observation height to 12.0 mm, phosphorus analysis line wavelength to 178.284 nm or 213.618 nm, and integration time to 10 s.

[0019] 5) Sample testing: The configured series of working curves are introduced into ICP, and the average value is taken for each excitation test 4 times;

[0020] The phosphorus content is calculated based on the calibration curve, using the following formula:

[0021]

[0022] In the formula, ω m ρ is the mass fraction of phosphorus. m V represents the concentration of phosphorus measured by the instrument, in μg / ml; V represents the calibration and test volume, in ml; and m represents the sample weight, in g.

[0023] In step 1), take 0.1g of sample, place the sample in a 100ml two-purpose bottle, add 10-20ml of red acid, then slowly add 4-6ml of concentrated sulfuric acid, shake slowly to mix, and after the vigorous reaction is over, add 4-6ml of perchloric acid and place the two-purpose bottle on a hot plate to heat.

[0024] In step 1), if the silicon content in the sample is greater than 1%, add 2-3 ml of hydrofluoric acid after adding perchloric acid, and then heat.

[0025] The density of the hydrofluoric acid is 1.14 g / ml.

[0026] In step 3), the high-purity iron contains ≥99.98% iron, and the high-purity chromium contains <0.001% phosphorus.

[0027] A short-term stability test was performed before sample testing to ensure that the relative standard deviation of the high-concentration calibration solution was <1.8% after 10 consecutive measurements.

[0028] The red acid is prepared by mixing nitric acid and hydrochloric acid in a volume ratio of 3:1, with the hydrochloric acid having a density of 1.19 g / ml and the nitric acid having a density of 1.42 g / ml; the concentrated sulfuric acid has a density of 1.84 g / ml; and the perchloric acid has a density of 1.67 g / ml.

[0029] Two sets of samples, 0.2g and 0.4g, were weighed in parallel during the test, and the accuracy of the test was verified by comparing the results.

[0030] In step 4), the background equivalent concentration is ≤0.050 μg / L, the limit of quantitation is ≤0.5 μg / L, and the linear correlation coefficient is ≥0.999.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. This invention enables the detection of phosphorus in high-carbon ferrochrome. The method is simple to operate, uses conventional reagents, and is easy for other laboratory personnel to learn and apply. The detection involves a single excitation followed by four tests, with the average value taken to prevent drift at individual points caused by multiple excitations, which could affect the accuracy of the results. Each sample is cleaned and then excited again; each sample is tested at least four times, with the average value taken, further improving the accuracy of the results.

[0033] 2. This invention provides an accurate data foundation for field personnel to understand phosphorus. The acid dissolution method for detecting phosphorus in high-carbon ferrochrome meets analytical requirements. Compared to the alkali fusion method, it results in less salt content in the solution, reducing the likelihood of salt accumulation, clogging of the nebulizer, and damage to the nebulizer. It also avoids instability during solution extraction and nebulization, preventing unstable test results and excessively high RSD values. Attached Figure Description

[0034] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0036] The method for determining the phosphorus content in high-carbon ferrochrome using ICP includes the following steps:

[0037] 1) Weigh 0.1g of the sample and place it in a 100ml two-way bottle. Add 15ml of red acid, then slowly add 4-6ml of concentrated sulfuric acid. Gently shake to mix. After the vigorous reaction is complete, add 5ml of perchloric acid. Place the two-way bottle on a hot plate at 360-380℃ and heat slowly. If the silicon content in the sample is greater than 1%, add 2-3ml of hydrofluoric acid dropwise, being careful not to let the hydrofluoric acid liquid touch the bottle wall. Keep the hot plate temperature constant at 360-380℃ and continue heating until the reddish-brown fumes disappear and the white fumes of sulfuric acid appear. Add nitric acid dropwise to continue breaking down the carbon in the system until the vigorous reaction is complete, the hydrofluoric acid is completely driven away, and the solution turns green. Remove from heat and cool. Add a little water and heat to boil the salts. Then cool to room temperature and dilute to 100ml. The red acid is prepared by mixing nitric acid and hydrochloric acid in a volume ratio of 3:1, with the hydrochloric acid having a density of 1.19 g / ml and the nitric acid having a density of 1.42 g / ml; the concentrated sulfuric acid has a density of 1.84 g / ml; the perchloric acid has a density of 1.67 g / ml; and the hydrofluoric acid has a density of 1.14 g / ml.

[0038] If the silicon content of the sample is no more than 1%, after adding 5 ml of perchloric acid, slowly heat it to 360-380°C on a hot plate until the reddish-brown fumes disappear and the white fumes of sulfuric acid appear. Add nitric acid dropwise to continue to destroy the carbon in the system until the violent reaction ends and the solution turns green. Remove and cool, add a little water, heat to boil the salts, then cool to room temperature and make up to 100 ml.

[0039] 2) Prepare a series of phosphorus-containing standard solutions using high-purity iron and high-purity chromium as matrices:

[0040] To establish a working curve, take six portions of 0.04g high-purity iron and 0.06g high-purity chromium, and dissolve them separately in 100ml two-way bottles using the method described in step 1). Then transfer the solutions to volumetric flasks to form a bottom layer for later use. The high-purity iron should contain ≥99.98% iron, and the high-purity chromium should contain <0.001% phosphorus.

[0041] The curve points were selected according to the phosphorus content range as 0, 1 g / L, 2 g / L, 3 g / L, 4 g / L, and 5 g / L. A 1000 mg / L phosphorus standard solution was serially diluted according to the above-set curve points to prepare a series of working curves. These were then transferred to six aliquots of the dissolved solution in volumetric flasks and diluted to volume. The solutions were then introduced into the instrument for detection.

[0042] 3) Turn on ICP and run it for at least 1 hour before taking measurements.

[0043] Adjust the instrument parameters: gas flow rate, torch position, entrance slit, exit slit, photomultiplier tube voltage, analytical line wavelength selection, pre-rinse time, integration time, and number of runs.

[0044] Before starting the measurement, confirm the following measurement conditions:

[0045] The characteristic spectral lines of the element being measured (phosphorus) must be smooth and their peak positions identifiable. Operating conditions are shown in Table 1, and background equivalent concentration and detection lines are shown in Table 2. Only one run is allowed, with each sample measured at least four times to avoid abnormal detections during multiple excitation processes, which could lead to overall data anomalies. Averaging multiple measurements reduces systematic error.

[0046] Table 1 Instrument Measurement Conditions

[0047]

[0048] Table 2. Linear correlation coefficient, limit of quantitation, and limit of detection.

[0049]

[0050] 4) Short-term stability

[0051] Measure the average of the absolute strength or strength ratio of the calibration solution with the highest concentration of each element ten times, and calculate its relative standard deviation. The relative standard deviation of the absolute strength method should be less than 1.8%.

[0052] 5) Calculation results

[0053] Based on the calibration curve, the net strength or net strength ratio of the test solution is converted into the concentration of the corresponding analyte, expressed in μg / ml. The content of the analyte phosphorus is expressed as a mass fraction ω. m The values ​​are expressed as % and the calculation formula is as follows:

[0054]

[0055] In the formula, ω m ρ is the mass fraction of phosphorus. m V represents the concentration of phosphorus measured by the instrument, in μg / ml; V represents the calibration and test volume, in ml; and m represents the sample weight, in g.

[0056] Spiked recovery tests are shown in Table 3.

[0057] Table 3 Spiked Recovery Test

[0058]

[0059]

[0060] As can be seen from Table 3, the recovery rate of the method is between 96% and 105%, which meets the requirements for analytical determination.

[0061] Comparison of sample dissolution methods:

[0062] Different dissolution methods were compared for the samples, namely acid dissolution and alkali fusion. The five groups of samples were tested eight times each, and the results are shown in Table 4.

[0063] Table 4 Comparison of Sampling Methods

[0064]

[0065] As can be seen from Table 4, the detection results of the alkaline fusion method fluctuate greatly because the high salinity affects the atomization effect, and the fluctuation in the atomization process leads to fluctuations in the detection results. Therefore, the acid fusion method is more suitable for the detection of phosphorus by high carbon ferrochrome.

[0066] A comparison of sulfuric acid usage is shown in Table 5.

[0067] Table 5 Comparison of Sulfuric Acid Usage

[0068]

[0069] Table 5 shows that the amount of sulfuric acid used affects the detection results. Because sulfuric acid has high viscosity, a larger amount results in fluctuations in the extraction speed, affecting the nebulization effect and causing fluctuations in the detection results. A smaller amount results in incomplete sample dissolution. Experiments show that the detection results tend to be stable when the sulfuric acid volume is between 4 and 6 ml, and the maximum sulfuric acid volume should not exceed 8 ml. The acid dissolution method for detecting phosphorus in high-carbon ferrochrome meets the analytical requirements. Compared with the alkali fusion method, it has a lower salt content in the solution, reducing the likelihood of salt accumulation, clogging the nebulizer, and damaging it. It also avoids instability during the solution extraction and nebulization process, which can lead to unstable detection results and larger RSD values.

[0070] Example:

[0071] Comparison of sample dissolution methods

[0072] Different dissolution methods were compared for the samples, namely acid dissolution and alkali fusion. Each of the five groups of samples was tested eight times, and the results are shown in Table 6.

[0073] Table 6 Comparison of Sampling Methods

[0074]

[0075] The test results show that the alkaline fusion method has a large fluctuation range because the high salinity affects the atomization effect. The fluctuation in the atomization process leads to fluctuations in the test results. Therefore, the acid fusion method is more suitable for the detection of phosphorus by high carbon ferrochrome.

[0076] A comparison of sulfuric acid usage is shown in Table 7.

[0077] Table 7 Comparison of Sulfuric Acid Usage

[0078]

[0079]

[0080] As shown in Table 7, the amount of sulfuric acid used affects the detection results. Because sulfuric acid has high viscosity, a larger amount results in fluctuations in the extraction speed, affecting the nebulization effect and causing fluctuations in the detection results. A smaller amount results in incomplete sample dissolution. Through testing, the detection results tend to be stable when the sulfuric acid volume is between 4-6 ml. The maximum sulfuric acid volume should not exceed 8 ml, as excessive viscosity will affect the nebulization effect. The acid dissolution method for detecting phosphorus in high-carbon ferrochrome meets the analytical requirements. Compared with the alkali fusion method, it has a lower salt content in the solution, reducing the likelihood of salt accumulation, clogging the nebulizer, and damaging it. It also avoids instability during the solution extraction and nebulization process, preventing unstable detection results and larger RSD values.

[0081] Comparison of different samples

[0082] Different samples were selected for comparison. Since the samples contained silicon, which is not conducive to dissolution, samples with different silicon contents were selected for comparison. The sample dissolution test was carried out without the addition of hydrofluoric acid, as shown in Table 8.

[0083] Table 8 Comparison of Hydrofluoric Acid Options

[0084] sample Phosphorus content / % Silicon content / % Average phosphorus percentage RSD / % 1# 0.025 0.15 0.024 4.258 2# 0.024 0.75 0.022 4.917 3# 0.023 1.15 0.018 5.689 4# 0.020 1.27 0.013 6.396 5# 0.023 2.65 0.012 7.335 6# 0.037 2.94 0.022 8.073

[0085] Experimental comparisons revealed that hydrofluoric acid plays a certain role in dissolving samples. For low-silicon samples, the test results remain stable without the addition of hydrofluoric acid, and compared with the true value, the results are within the error range. However, when the silicon content is above 1%, the test results are lower and the stability is poor, indicating that the dissolution of samples without hydrofluoric acid is abnormal and some samples are difficult to dissolve. Therefore, the method of not adding hydrofluoric acid is only suitable for low-silicon samples.

[0086] Comparison of different acid dosages

[0087] The same sample (silicon content 2.65%) was selected and compared by adding different amounts of hydrofluoric acid to observe the effect on the test results. The comparison shows that as the amount of hydrofluoric acid added increases, the test results gradually increase and tend towards the true value. When the hydrofluoric acid content is 4 ml, the error is within the allowable range. Subsequently, as the amount added increases, the test results stabilize. The table shows that the minimum amount of hydrofluoric acid added is 4 ml.

[0088] Table 9 Comparison of hydrofluoric acid dosage

[0089]

[0090] Spiked recovery tests are shown in Table 10.

[0091] Table 10 Spiked Recovery Test

[0092]

[0093] As can be seen from Table 9, the recovery rate of the method is between 96% and 105%, which meets the requirements for analytical determination.

[0094] Sample testing

[0095] The standard samples were tested using the method of this invention, and the test results are shown in Table 11.

[0096] Table 11 Test results of standard samples

[0097] sample Standard Sample Number Phosphorus content / % average value / % RSD / % 1 BYRK14-2009 0.020 0.019 5.122 2 YSBC35617-2017 0.023 0.025 4.965 3 BYRK14-2019 0.025 0.035 4.437 4 ZBT367 0.037 0.035 4.437 5 GBW(E)010367 0.023 0.024 4.651

[0098] As can be seen from Table 11, the test results provided by the embodiments of the invention show that the chromium mass content in the tested standard sample is less than the relative allowable difference of the national standard, and the test results meet the requirements.

Claims

1. A method for detecting the phosphorus content in high-carbon ferrochrome using ICP, characterized by, The method comprises the following steps: 1) adding red acid to the sample, then slowly adding concentrated sulfuric acid, adding perchloric acid after the violent reaction is over, heating to 360-380 DEG C, keeping constant temperature until red-brown smoke disappears, white sulfuric acid smoke appears, adding nitric acid drop by drop, the solution turns green, taking off the cooling, boiling with water, then cooling to room temperature, and constant volume to 100 ml; 2) standard curve processing Selecting curve points of 0, 1 g / L, 2 g / L, 3 g / L, 4 g / L and 5 g / L according to the range of phosphorus content; 3) establishing a working curve: Taking 6 portions of 0.04 g high-purity iron and 0.06 high-purity chromium respectively, dissolving them in 100 ml two-purpose bottles according to the method of step 1), then transferring them to the capacity bottles for standby; Diluting 1000 mg / L phosphorus standard solution according to the curve points set in step 2) by stages, transferring them to the 6 dissolved capacity bottles respectively, and constant volume; introducing the prepared series of working curves into ICP for detection; 4) instrument parameters; ICP is preheated for more than 1 h, the atomizer gas flow is set to 0.6 L / min, the plasma radio frequency power is set to 1350 w, the auxiliary gas flow is set to 0.5 L / min, the peristaltic pump speed is set to 60 rpm, the vertical observation height is set to 12.0 mm, the phosphorus analysis line wavelength is set to 178.284 nm or 213.618 nm, and the integration time is set to 10 s; 5) sample detection: introducing the prepared series of working curves into ICP, detecting 4 times for single excitation and taking the average value; The phosphorus content is calculated according to the calibration curve, and the calculation formula is: where ω m is the mass fraction of phosphorus; p m is the concentration of phosphorus measured by the instrument, in μg / ml; V is the volume of the calibration and test, in ml; and m is the sample weight, in g.

2. The method for detecting the phosphorus content in high-carbon ferrochrome by ICP according to claim 1, characterized in that, In step 1), 0.1 g of the sample is taken and placed in a 100 ml two-purpose bottle, 10-20 ml of red acid is added, then 4-6 ml of concentrated sulfuric acid is slowly added, and the mixture is slowly shaken and mixed, then 4-6 ml of perchloric acid is added after the violent reaction is over, and the two-purpose bottle is placed on an electric heating plate for heating.

3. The method for detecting the phosphorus content in high-carbon ferrochrome by ICP according to claim 1, characterized in that, In step 1), if the silicon content in the sample is greater than 1%, 2-3 ml of hydrofluoric acid is added drop by drop after the addition of perchloric acid, and then heated.

4. The method for detecting the phosphorus content in high-carbon ferrochrome by ICP according to claim 3, characterized in that, The density of the hydrofluoric acid is 1.14 g / ml.

5. The method for detecting the phosphorus content in high-carbon ferrochrome by ICP according to claim 1, characterized in that, In step 3), the iron content in the high-purity iron is greater than or equal to 99.98%, and the phosphorus content in the high-purity chromium is less than 0.001%.

6. The method for detecting the phosphorus content in high-carbon ferrochrome by ICP according to claim 1, characterized in that, Short-term stability test is carried out before sample detection, so that the relative standard deviation of the high-concentration calibration solution is less than 1.8% when continuously detected for 10 times.

7. The method for detecting the phosphorus content in high-carbon ferrochrome by ICP according to claim 1, characterized in that, The red acid is prepared by mixing nitric acid and hydrochloric acid at a volume ratio of 3:1, the density of the hydrochloric acid is 1.19 g / ml, the density of the nitric acid is 1.42 g / ml, the density of the concentrated sulfuric acid is 1.84 g / ml, and the density of the perchloric acid is 1.67 g / ml.

8. The method for detecting the phosphorus content in high-carbon ferrochrome by ICP according to claim 1, characterized in that, When the sample is detected, 0.2 g and 0.4 g of two groups are weighed in parallel, and the detection accuracy is verified by comparing the results.

9. The method for detecting the phosphorus content in high-carbon ferrochrome using ICP according to claim 1, characterized in that, In step 4), the background equivalent concentration is less than or equal to 0.050 μg / L, the limit of quantification is less than or equal to 0.5 μg / L, and the linear correlation coefficient is greater than or equal to 0.999.

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