The ocean is the cradle of life on Earth, playing an irreplaceable role in regulating climate and providing resources. However, with the rapid development of industry and the intensification of human activities, a large amount of mercury containing pollutants have entered the marine environment, leading to a gradual increase in mercury content in seawater.

Mercury is a highly toxic heavy metal element that can accumulate in marine organisms and be transmitted through the food chain, ultimately posing a serious threat to human health. Therefore, accurate determination of mercury content in seawater is of great significance for evaluating marine environmental quality, protecting marine ecosystems, and human health.

According to the national standard GB3097-1997 "Seawater Quality Standards", seawater can be divided into four categories based on different usage functions and protection purposes of the sea area. The limit values for mercury are 0.05 μ g/L, 0.2 μ g/L, 0.2 μ g/L, and 0.5 μ g/L, respectively. The national standard GB17378.4-2007 Marine Testing Specification Part 4: Seawater Analysis specifies the analysis method for mercury in seawater, with the first method being atomic fluorescence method.

In 2017, the National Environmental Monitoring Center issued the "Technical Regulations for Monitoring the Quality of Seawater in Coastal Areas" based on GB 17378.4-2007, which formulated the operating procedures for detecting mercury in seawater by atomic fluorescence method and supplemented relevant regulations and precautions.

The mercury content in seawater is extremely low, and the "National Technical Regulations for Monitoring the Quality of Seawater in Coastal Areas" clearly stipulate that the detection limit for mercury by atomic fluorescence method is 0.007 μ g/L. This requires instruments to have higher sensitivity and stability. Therefore, the experiment optimized and upgraded the pipeline of atomic fluorescence, increased the injection volume, improved the sensitivity and stability of the instrument, and gave the instrument an advantage in detecting mercury in seawater.

analytical method

1. Preparation of reagents

Potassium persulfate solution (50g/L): Weigh 25g of potassium persulfate, dissolve it in water, and dilute to 500mL.

Hydroxyamine hydrochloride solution (100g/L): Weigh 20g of hydroxylamine hydrochloride, dissolve it in water, and dilute to 200mL.

3% hydrochloric acid (V/V): Take 30mL of hydrochloric acid and dilute to 1000mL with deionized water.

0.035% potassium borohydride (W/V, dissolved in 0.5% potassium hydroxide solution): First, weigh 5.0g of potassium hydroxide and place it in 1000mL of deionized water. After complete dissolution, add 0.35g of pre weighed potassium borohydride and shake well.

2. Sample preparation

Processing of seawater samples: Take 100mL of seawater sample into a 250mL conical flask, add 3.0mL of concentrated hydrochloric acid and 5.0mL of potassium persulfate solution (50g/L), let it digest at room temperature for 24 hours, or heat and boil for 1 minute, then cool to room temperature, and add 2mL of hydroxylamine hydrochloride solution (100g/L) dropwise.

Simultaneously conduct two blank experiments and spiked at different concentration levels of low, medium, and high.

The treatment of adding standard to seawater samples: Accurately add 0.11mL, 0.22mL, and 0.44mL of mercury standard solution with a concentration of 0.1 μ g/mL to 100mL of seawater, and the subsequent treatment is the same as the above seawater sample.

Treatment of water quality mercury standard sample: Accurately transfer 1.0mL of water quality mercury standard sample to a 100mL volumetric flask, dilute to the mark with 3% hydrochloric acid solution, and mix well for later use.

Treatment of seawater mercury standard substance: Accurately transfer 2.0mL of seawater standard solution to a 10mL volumetric flask, add 0.3mL of concentrated hydrochloric acid, dilute to the mark with water, and mix with a spoon for later use

Inject standard series solutions in sequence: 00.00ng/mL, 0.005ng/mL, 0.01ng/mL, 0.02ng/mL, 0.04ng/mL, 0.08ng/mL, 0.16ng/mL, 0.32ng/mL, and 0.50ng/mL. Plot the standard curve with element concentration as the horizontal axis and signal value as the vertical axis. The linearity of mercury is shown in Figure 1, and the linearity and correlation coefficients are shown in Table 1. The detection limit of mercury was calculated using the method of 3.143 * SD for 7 consecutive low concentration seawater samples, and the results are shown in Table 2.

Figure 1: Standard curve of Hg

Table 1: Linear Range, Linear Regression Equation, and Correlation Coefficient

Table 2: Method Detection Limits

3. Sample measurement results and accuracy

Table 3: Sample Determination Concentration and Accuracy Results Table

4. Sample spiked recovery rate and precision

Samples of seawater 1 # and seawater 3 # were spiked at different concentration levels of low, medium, and high, respectively. The spiked samples were measured in parallel 7 times, and the spiked recovery rate and relative standard deviation were calculated.

Table 4: Sample spiked recovery rate and precision results

empirical conclusion

The experimental results show that the atomic fluorescence spectrophotometer developed by Jitian Instrument can accurately determine the content of mercury in seawater, with a detection limit of 0.0007ng/mL, good linearity in the low concentration range, good measurement repeatability, and the measurement results of quality control samples are all within the nominal range. The recovery rate of spiked samples is 101.5%~108.7%. Compared with the two methods of room temperature digestion for 24 hours and heating boiling for 1 minute, they can completely dissolve and accurately determine the mercury content in seawater, safeguarding marine ecology and health. Marine environmental monitoring is of immeasurable importance in maintaining marine ecological balance, ensuring sustainable use of marine resources, and promoting high-quality development of the marine economy.