Method for determining trace heavy metal elements in seawater by ICP-MS direct injection

Abstract

The application discloses a method for determining trace heavy metal elements in seawater by ICP-MS direct sampling, which comprises the following steps: acidifying seawater samples with nitric acid; mixing the acidified seawater samples with an internal standard dilute hydrochloric acid solution containing Ge, Te and Re online; determining by ICP-MS configured with a multi-pole rod collision reaction cell, and the operation parameters are as follows: RF power is 1500-1600 W, sampling depth is 10-12 mm, helium flow is 5-6 mL / min, atomization chamber refrigeration temperature is 2-4 DEG C, dilution gas flow is 0.2-0.3 L / min, and atomizer flow is 0.7-0.8 L / min; and the standard addition method with multiple internal standard corrections is adopted for quantification. The method effectively controls the deposition rate of the high salt base in the cone, and differentiates and efficiently suppresses the mass spectrum interference of multiple elements by the KED principle of the multi-pole rod through Delta H, so that long-time direct, stable and accurate analysis of elements such as Cr, Ni, Cu, Zn, As, Cd and Pb in seawater is realized.

Description

Technical Field

[0001] This invention relates to the field of environmental analysis and mass spectrometry detection technology, specifically to a method for direct sample determination of trace heavy metal elements in seawater using inductively coupled plasma mass spectrometry. Background Technology

[0002] Monitoring heavy metal pollution in seawater is a crucial aspect of marine environmental protection. Inductively coupled plasma mass spectrometry (ICP-MS) has become an ideal technique for determining heavy metal elements in seawater due to its high sensitivity, wide linear dynamic range, and ability to analyze multiple elements simultaneously. However, seawater has a high salinity matrix (salinity approximately 35 g / L, mainly NaCl), and direct sample injection analysis faces several technical challenges: 1. Salt deposition clogging the cone: Major ions such as Na and Ca crystallize at the sampling cone and retrieval cone openings, and even the entire interface region, leading to signal drift and even instrument malfunction. Traditional methods require diluting seawater by more than 10 times, and the testing conditions are stringent, making it difficult to meet the requirements of ordinary laboratories; 2. Matrix inhibition effect: High total dissolved solids (TDS) reduce atomization and ionization efficiency, causing systematic errors; 3. Multi-atom ion interference: For example, Cr, Ni, Cu, Zn, As, and Cd are affected by various ions. 1 H 35 Cl 16 O⁺、 23 Na 37 Cl , 40 Ar 23 Na⁺、 32 S 18 O 16 O⁺、 40 Ca 35 Cl⁺、 95 Mo 16 O⁺ multi-atom ion mass spectrometry is affected by interference, while elements such as Pb are not affected. In order to ensure the sensitivity of elements without interference, the conventional kinetic energy discrimination (KED) mode requires multiple helium flow rates, which affects the test efficiency; 4. Poor long-term stability: When continuously injecting samples, the cone deposits accumulate, causing signal drift. Frequent cleaning and maintenance are required, making it impossible to achieve high-throughput analysis.

[0003] Existing technologies typically employ dilution methods or offline / online separation and enrichment, but these methods suffer from drawbacks such as cumbersome operation, high reagent consumption, low analytical efficiency, or high equipment costs. For example, the method described in "HY / T147.1-2013 Marine Monitoring Technical Specification" involves diluting the sample tenfold before quantification using matrix matching, which is inefficient and places extremely stringent requirements on reagents and consumables.

[0004] To address the problems of existing technologies, this invention provides a method for direct ICP-MS injection determination of trace heavy metal elements in seawater. This method is resistant to salt deposition, has minimal interference, and exhibits high long-term stability, making it suitable for efficient detection of heavy metals in seawater. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for direct injection determination of trace heavy metal elements in seawater by ICP-MS, wherein the main steps are: simple sample acidification and filtration pretreatment, online mixing of three internal standard elements in hydrochloric acid matrix, targeted parameter configuration of ICP-MS, and standard addition method for quantification.

[0006] To achieve the objectives of this invention, the technical solution adopted is as follows: A method for direct sample introduction determination of trace heavy metal elements in seawater using inductively coupled plasma mass spectrometry includes the following steps: (1) Sample pretreatment: Nitric acid was added to the seawater sample for acidification, so that the volume fraction of nitric acid relative to the seawater sample was 0.5%-2% (v / v), and the sample was filtered through a 0.45μm aqueous phase filter membrane to obtain the acidified sample solution. (2) Online internal standard mixing: The acidified sample solution was mixed with a solution containing... through a three-way mixing connector. 73 Ge 125 Te and 187 The internal standard solution of Re is mixed online, and the mixed solution is pumped into the glass concentric nebulizer of ICP-MS by a peristaltic pump; The internal standard solution matrix is ​​an aqueous solution containing 3% by volume hydrochloric acid, where the 3% by volume is expressed as 3% (v / v); the concentration of Ge is 500 μg / l, and the concentrations of Te and Re are both 50 μg / l.

[0007] (3) ICP-MS parameter configuration: The measurements were performed using an ICP-MS system equipped with a multipole collision cell, with the operating parameters set as follows: RF power 1500-1600W, sampling depth (i.e., the distance between the sample cone opening and the coil) 10-12mm, helium gas is introduced into the multipole collision reaction cell at a flow rate of 4-6mL / min, dilution gas flow rate of 0.2-0.3L / min, nebulizing gas flow rate of 0.7-0.8L / min, nebulization chamber cooling temperature of 2-6℃, plasma gas flow rate of 16-18L / min, no cleaning time is required between adjacent samples; ΔH is set to -0.4 to -0.55. The extraction lens voltage of the ICP-MS is 140-160V.

[0008] The settings for the atomizing gas and diluting gas flow rates, along with the cooling temperature of the atomizing chamber, optimize the aerosol particle size distribution and effectively control the total amount of salt entering the plasma.

[0009] The multipole collision cell is set to a single helium flow rate to avoid switching between multiple helium flow rates, as multiple flow rates require more stabilization time and affect testing efficiency. ΔH is an important method parameter for ICP-MS. By setting the energy barrier for ions with different mass numbers using the ΔH parameter, differentiated elimination of interference from polyatomic ions can be achieved efficiently. Different values ​​are set for multi-element testing; the more negative the value, the stronger the ability to eliminate mass spectrometry interference. Differential interference elimination capabilities can be achieved based on the strength of the interference without affecting testing time. Specific settings are as follows: ΔH for Cd is set to -0.55; ΔH for Pb, Te, and Rh is set to -0.5; ΔH for Zn, As, Cr, Cu, and Ge is set to -0.45; and ΔH for Cu and Ni is set to -0.4.

[0010] (4) Standard addition method for quantification: A standard addition method was used to prepare a spiking series. In the same analytical sequence, a 1% (v / v) nitric acid blank solution, the sample solution, and the spiking solution were measured sequentially. The net signal intensity of each element, corrected for internal standard, was linearly fitted to the spiking concentration, and extrapolated to zero to obtain the concentration of various trace heavy metal elements in the sample solution. These trace heavy metal elements included Cr, Ni, Cu, Zn, As, Cd, and Pb. The five spiking concentration levels of the standard addition method are set as follows: 1, 2.5, 5, 7.5, and 20 μg / l. The internal standard is added online through a three-way mixing connector. The three internal standards are used as follows: internal standard Ge is used to correct Cr, Ni, Cu, Zn, and As; internal standard Te is used to correct Cd; and internal standard Re is used to correct Pb.

[0011] The long-term stability of the method of the present invention was verified as follows: After 101 consecutive injections of seawater sample solution without sample cleaning, the experimental results showed that the internal standard recovery rate remained at 87%-105%, and the standard material certificate value was within the allowable error range. After the sequence was completed, a spike recovery experiment was performed, which still ensured that each element was within the range of 92%-103%.

[0012] The method of the present invention has the following beneficial effects: 1. Parameter-Coordinated Salt Deposition Resistance: By rationally setting the atomization chamber temperature and dilution gas flow rate, the coordinated operation of various parameters optimizes the aerosol particle size distribution, reduces the total amount of salt entering the plasma, and overcomes the problems of mass spectrometry interference, matrix effects, and signal drift in the direct injection determination of trace element impurities in high-salt seawater matrices. More importantly, no cleaning time is required between adjacent samples (cleaning time is 0 seconds), and cone deposition does not cause signal attenuation; instead, the transport efficiency of low-mass-number ions is slowly improved. This is because the deposition layer alters the ion transport path, forming an adaptive signal compensation mechanism.

[0013] 2. Differential Interference Elimination: By using a multipole collision cell with different energy barriers set by the ΔH parameter at a single helium flow rate (4-6 mL / min), differential interference is eliminated. 40 Ca 35 Cl、 40 Ar 35 Cl、 40 Ar 23 Interference from polyatomic ions such as Na⁺ is eliminated, eliminating the need for repeated switching of collision or reaction gases and ensuring analysis speed.

[0014] 3. Ultra-long-term stability: Under conditions of 101 consecutive actual seawater injections without rinsing, the internal standard... 73 Ge 125 Te、 187 The Re recovery rate remained stable at 87%-105%, and the average value of the target element was consistent with the value certified by the standard material, thus fully achieving the target.

[0015] 4. High analytical efficiency: Direct sample injection eliminates the need for sample dilution and inter-sample cleaning steps. Combined with online internal standard mixing and standard addition methods, it significantly shortens the analysis cycle for a single sample and is suitable for rapid screening of large batches of seawater samples. Attached Figure Description

[0016] Figure 1 Example 1 shows the trend of changes in the internal standards Ge, Te, and Re after 101 consecutive injections according to the method of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments. These embodiments are merely illustrative and do not constitute any limitation on the present invention. Based on the guidance of the present invention, all other modifications made by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0018] Instruments and reagents: An iQuad 2300 ICP-MS instrument was used, equipped with a glass concentric nebulizer and a multipole collision reaction cell. Reagents included: G3 nitric acid, hydrochloric acid, ultrapure water (resistivity ≥18.2 MΩ·cm), 1000 mg / L Ge, Te, and Re single-element standard solutions, 100 mg / L 26-element mixed standard, and certified reference material GBW(E)080040; the seawater sample used was collected from a location in Guangdong. Example 1

[0019] 1. Sample pretreatment Measure 9.9 mL of pure water with a pipette, add 0.1 mL of 65% commercially available concentrated nitric acid, filter using a 0.45 μm filter head to obtain a blank solution, denoted as BK; Measure 9.9 mL of seawater sample using a pipette, add 0.1 mL of commercially available concentrated nitric acid with a concentration of 65% to make the final nitric acid concentration 1% (v / v), and obtain a blank seawater sample solution, which is recorded as SPL; Take 9.9 mL of seawater sample with a pipette, add 0.1 mL of commercially available concentrated nitric acid with a concentration of 65% to make the final nitric acid concentration 1% (v / v), add a certain volume of 1 μg / mL mixed standard containing the element to be tested, filter with a 0.45 μm filter head to obtain the spiked seawater sample solution, which is denoted as STD1~STD5.

[0020] The typical concentrations and mixed standard addition volumes for the standard addition method are shown in Table 1 below: Table 1: Typical concentrations and mixed standard addition volumes using the standard addition method

[0021] A typical injection sequence is: three injections of BK, one injection of SPL, and one injection of STD1 to STD5 in sequence. After completion, further injection sequences are performed according to the testing requirements, and the software automatically outputs the elemental concentrations of the seawater sample.

[0022] 2. The ICP-MS operating parameters are set as follows: - RF power: 1500W - Sampling depth: 11mm - Lens extraction voltage: -140V - Plasma gas flow rate: 15 L / min - Helium flow rate (collision cell): 5 mL / min - Atomizer flow rate: 0.75L / min - Dilution gas flow rate: 0.25 L / min - Atomization chamber cooling temperature: 4℃ - Sample room cleaning time: 0 seconds 3. Selection and mixing of internal standards The internal standard solution contained Ge (500 μg / L), Te (50 μg / L), and Re (50 μg / L), with a hydrochloric acid concentration of 3% (v / v). Online mixing of the seawater sample and the internal standard solution was achieved via a three-way mixing connector; the sample tube for the seawater sample was 0.19 cm long, and the internal standard tube for the internal standard solution was 0.51 cm long.

[0023] 4. Standard addition method for quantification Five spiking series at five concentration levels were prepared using the standard addition method: 1, 2.5, 5, 7.5, and 20 μg / L. These were then injected sequentially within the same analytical sequence: blank, blank sample, and spiked sample (STD1 to STD5). The spiked concentrations were linearly fitted to the signal intensity of each element after internal standard correction, and extrapolated to the point where the signal was zero to obtain the concentration of each element in the sample solution. The concentrations of subsequent samples in the sequence were directly derived using this equation.

[0024] 5. Verification of method correctness The accuracy of the method was verified using the GBW(E)080040 standard material. A total of 11 needles were tested, and the results are shown in Tables 2 and 3 below. All measured values ​​were within the allowable error range of the certificate, proving that the method of the present invention is accurate and reliable.

[0025] Table 2: Results of 11 seawater sample standard material tests

[0026] Table 3: Summary of 11 tests of national standard reference materials for seawater.

[0027]

[0028] 6. Long-term stability test The prepared seawater samples were injected 101 times consecutively without inter-sample washing. The trend of internal standard recovery rate over time is as follows: 73 Ge recovery rate: slowly increased from an initial 92% to 101%. 125 Te recovery rate: slowly increased from an initial 90% to 98%. 187 Re recovery rate: slowly increased from an initial 89% to 97%.

[0029] The trend of Ge, Te, and Re internal standard recoveries in the 101 consecutive injection tests is shown in... Figure 1The results show that the method of this invention maintains good accuracy and stability under long-term continuous injection conditions. The internal standard recovery rate increases slowly with the number of tests, and the increase is negatively correlated with the mass number (Ge>Te>Re), indicating that the cone deposition has a more significant enhancement effect on the transport of low mass number ions. By selecting multiple internal standards with different mass numbers for correction, this effect is effectively offset, ensuring long-term stability.

[0030] After testing 101 seawater samples, the recovery rates of solutions spiked with 10 μg / L were 93%-103%, further demonstrating the stability of the system.

[0031] 7. Typical method detection limit of this method The linearity was obtained by standard addition method under the seawater sample matrix, and the method detection limit was calculated by measuring ten injections of 1% HNO3 solution with three times the standard deviation. In the range of 0.0040-0.14 μg / l, the method detection limits of Cr, Ni, Cu, Zn, As, Cd and Pb were 0.064, 0.048, 0.013, 0.08, 0.014, 0.0040 and 0.0060 μg / l, respectively.

Claims

1. A method for direct injection determination of trace heavy metal elements in seawater using inductively coupled plasma mass spectrometry, comprising the following steps: (1) Sample pretreatment: Add nitric acid to the seawater sample for acidification, and filter it through an aqueous phase filter membrane to obtain the acidified sample solution; (2) Online internal standard mixing: The acidified sample solution is mixed with the solution containing... 73 Ge 125 Te and 187 The internal standard solution of Re is mixed online, and the mixed solution is pumped into the glass concentric nebulizer of ICP-MS by a peristaltic pump; (3) ICP-MS parameter configuration: An ICP-MS with a multipole collision cell was used, and the operating parameters were set as follows: The RF power is 1500-1600W, the sampling depth is 10-12mm, helium gas is introduced into the multipole collision reaction cell at a flow rate of 4-6mL / min, the dilution gas flow rate is 0.2-0.3L / min, the nebulizing gas flow rate is 0.7-0.8L / min, the nebulization chamber cooling temperature is 2-6℃, and the plasma gas flow rate is 16-18L / min; ΔH is set to -0.4 to -0.

55. (4) Standard addition method for quantification: The standard addition method is used to prepare the spiking series. In the same analytical sequence, the volume fraction of 1% nitric acid blank solution, sample solution and spiking solution are measured sequentially. The net signal intensity of each element after internal standard correction is linearly fitted to the spiking concentration and extrapolated to the point where the signal is zero to obtain the concentration of each element in the sample solution.

2. The method according to claim 1, wherein in step (1), the volume fraction of the nitric acid relative to the seawater sample is 0.5%-2%.

3. The method according to claim 1, wherein in step (2), the internal standard solution contains... 73 Ge 125 Te and 187 The Re is a 3% (v / v) dilute hydrochloric acid matrix internal standard solution, and the Ge concentration is 500 μg / l; the concentrations of Te and Re are both 50 μg / l.

4. The method according to claim 1, wherein in step (3), the extraction lens voltage of the ICP-MS is -140 to -160V.

5. The method according to claim 1, wherein in step (3), the cleaning time between adjacent samples is set to 0.

6. The method according to claim 1, wherein in step (4), the spiking concentration levels of the standard addition method are set to 3-5 gradients.

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