CN110702774A - Method for measuring total arsenic in sediment - Google Patents

Abstract

The invention discloses a method for measuring total arsenic in sediments. The present invention firstly prepares a standard solution, an internal standard solution and a solution to be tested, wherein the solution to be tested has undergone pretreatment. Then, the standard solution was diluted with 1% nitric acid by volume to various gradient concentrations, and the absorbance values of the standard solutions with different concentrations were measured by ICP-MS to prepare a standard curve of arsenic. Finally, the arsenic element in the solution to be tested is measured by ICP-MS to obtain the absorbance value of arsenic in the solution to be tested, and the detected absorbance value of arsenic is compared with the standard curve of arsenic to obtain the The arsenic element content in the solution to be tested is obtained, and then the arsenic element content in the marine sediment is obtained. The present invention omits part of the pre-processing steps, directly on the machine, and the steps are simpler. At the same time, ICP-MS is used, the instrument precision is higher, and the determination is more accurate.

Description

A kind of determination method of total arsenic in sediment

technical field

The invention belongs to the technical field of analysis and detection, and relates to a method for measuring total arsenic in sediments.

Background technique

The total arsenic in sediments is currently determined by atomic fluorescence method. Specifically, after microwave digestion with 6 ml of nitric acid, 5 ml of thiourea ascorbic acid and 5 ml of hydrochloric acid are added to make the volume to 50 ml, and left for at least 30 minutes, and then measured by atomic fluorescence spectrometer.

The disadvantages of this method are: 1. The process is cumbersome and needs to be digested with aqua regia water bath or nitric acid, and then add acid and thiourea-ascorbic acid to the volume. 2. The sediment is not completely digested, and occasionally there are still solid particles remaining after the digestion. 3. The measured quality control samples often appear low, and the data are inaccurate. 4. The atomic fluorescence instrument will start to increase the absorbance value after half an hour of measurement. When the number of samples is large, for example, after measuring 50 samples, and then entering the first sample, the absorbance value will increase; If the level is above 15%, sometimes the instrument state is not good or the preheating time is not enough, and the measured concentration may even be more than 2 times worse.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the prior art, the present invention provides a method for measuring total arsenic in sediments.

The technical scheme adopted by the present invention to solve the technical problem is:

The present invention includes the following steps:

Step 1. Prepare standard solution: prepare arsenic standard solution with a concentration of 1.0ug/ml.

Step 2. Prepare the internal standard solution: prepare the internal standard solution with a concentration of 1.0ug/mL.

Step 3. Prepare the solution to be tested: take 2.0ml of the pre-digested supernatant, and make up to 50ml with pure water.

The pretreatment is as follows: Weigh 0.1-0.5 g of a dry sample of sediment, add 5 ml of nitric acid, 4 ml of hydrofluoric acid, carry out microwave digestion, then add 2 ml of perchloric acid, drive off the acid, and then use ultrapure water to dilute to a volume of 50ml.

Step 4. Select the standard solution in step 1, dilute it into a plurality of gradient concentrations with nitric acid with a volume concentration of 1%, and measure the absorbance values of the standard solutions of different concentrations by inductively coupled plasma mass spectrometry ICP-MS respectively, and prepare. into a standard curve for arsenic.

Step 5. Measure the arsenic element in the solution to be tested described in step 3 by inductively coupled plasma mass spectrometry ICP-MS to obtain the absorbance value of arsenic in the solution to be tested, and compare the detected absorbance value of arsenic with arsenic. The standard curve is compared to obtain the arsenic content in the solution to be tested, and then the arsenic content in the marine sediments is obtained.

Further, the arsenic standard solution described in step 1 is prepared by diluting the arsenic standard solution with a concentration of 1000ug/ml using a nitric acid solution with a volume concentration ratio of 1%.

Further, the diluted concentrations of the standard solution described in step 4 are 0ug/L, 5g/L, 10ug/L, 30ug/L, 50ug/L and 100ug/L, respectively.

Further, the measurement conditions of inductively coupled plasma mass spectrometry ICP-MS are as follows: room temperature: 20°C to 28°C; humidity: ≤80%. Argon gas: 650～750KPa, Helium gas: 60～100KPa. Circulating water: distilled water 230～400KPa. Exhaust air volume: 10 to 15 m/s.

The beneficial effects of the present invention are as follows: a. Compared with the atomic fluorescence spectrometer, the method saves part of the pretreatment steps (steps such as adding thiourea ascorbic acid), directly on the machine, and the steps are simpler. b. Using ICP-MS, the precision of the instrument is higher and the determination is more accurate (generally there is no low quality control sample) c. The stability is stronger, the curve R is basically easy to achieve above 0.9995, and the RSD of the sample is mostly in the 5% or less.

Detailed ways

The present invention will be further described below in conjunction with the examples.

The steps of this embodiment include:

Step 1. Preparation of standard solution: prepare arsenic standard solution with a concentration of 1.0ug/ml (dilute the arsenic standard solution with a concentration of 1000ug/ml with 1% nitric acid solution).

Step 2. Preparation of internal standard solution: prepare an internal standard solution with a concentration of 1.0ug/mL.

Step 3. Preparation of the solution to be tested: take 2.0 ml of the supernatant that has been digested by pretreatment, and dilute to 50 ml with pure water. The pretreatment is as follows: Weigh 0.1000-0.5000 grams of dry sediment samples (wet samples need to calculate moisture content), add 5ml nitric acid, 4ml hydrofluoric acid, carry out microwave digestion in the high temperature and high pressure environment of the digestion tank, and then add 2ml high temperature Chloric acid, remove the acid, and make up to 50ml with ultrapure water.

The sediment solution digested by ordinary atomic fluorescence method cannot be used for ICP-MS measurement, and it is easy to cause 1. Incomplete digestion will affect the results 2. Incomplete digestion will block and destroy the instrument. The pretreatment method in this example is in the digestion tank. Under the premise of high temperature and high pressure digestion, 2 times of enhanced acid digestion was carried out, and the supernatant was taken for 2 times after constant volume to ensure that arsenic in sediments could be determined normally by ICP-MS. )

Step 4. Select the standard solution in step 1, dilute it with 1% nitric acid to several gradient concentrations (the highest concentration is 100ug/L, such as 0, 5, 10, 30, 50, 100ug/L), pass ICP-MS The absorbance values of the standard solutions with different concentrations were measured respectively, and the standard curve of arsenic was made. In the standard HJ 680-2013, the highest point concentration is generally 10ug/L, but in the actual experiment, it is found that the concentration in the sediment is generally a few, and occasionally there are concentrations of 10 or more ug/L, or even 30 or more ug/L. In order to reflect the rationality of the curve, the concentration at the highest point of the curve was increased to 100ug/L.

Step 5. Measure the arsenic element in the solution to be tested described in step 3 by ICP-MS, obtain the absorbance value of arsenic in the solution to be tested, and compare the detected absorbance value of arsenic with the standard curve of arsenic. Yes, the content of arsenic in the solution to be tested is obtained, and then the content of arsenic in the marine sediment is obtained.

Among them, the use conditions of ICP-MS in the determination process: room temperature: 20 ℃ ~ 28 ℃; humidity: ≤ 80%. Argon gas: 650～750KPa, Helium gas: 60～100KPa. Circulating water: distilled water 230～400KPa. Exhaust air volume: 10 to 15 m/s.

The specific measurement process is as follows:

a. Turn on the argon gas, the pressure is stable at 700kpa, turn on the circulating water and exhaust air, and clamp the peristaltic pump tube. Confirm that the vacuum degree of the fourth stage is less than 5×10-4. The sample tube and internal standard tube should be placed in deionized water at this point. The peristaltic pump is selected as the sample introduction item in the hardware conditions.

b. Carry out plasma ignition, enter the tuning mode after ignition, and confirm that the instrument state meets the testing requirements shown in Table 1

c. Establish a batch process: Arsenic and corresponding internal standard elements are selected for the acquisition elements and elements to be measured in the acquisition method, and the acquisition mode adopts the TRA mode. The acquisition mode is selected as mass spectrum, the peak type is selected as 3 points, the repetition times are 3 times, and the integration time is set as 0.3S. The data analysis method selects full quantification, and selects the internal standard; input curve concentration gradient. Click the sample list, add a sample blank, enter the sample number, and confirm the sample order.

d. Insert the sample tube into 1% nitric acid, then insert the internal standard tube into the internal standard solution in step 2 in turn, add the set batch to the queue, preheat for 15 minutes, and then start the process Determination of the sample: insert the sample tube into the standard solution of each concentration gradient in step 4 in turn to make a standard curve, then insert the solution to be tested in step 3, measure the arsenic content of the solution to be tested, and complete the determination of step 5 . In the above detection process, the internal standard tube is inserted into the internal standard solution in step 2 throughout the whole process. The function of the internal standard solution is to eliminate the matrix effect, reduce interference, and ensure the accuracy of arsenic content detection. (The time for each sample is about 45 seconds, within 10% of RSD)

e. After sample collection, rinse with 5% nitric acid solution for 5 minutes.

The specific embodiments of the technical invention have been described above in conjunction with the examples, but these descriptions should not be construed as limiting the scope of the technical invention. The protection scope of the present invention is defined by the appended claims. Any rights in the technical invention Modifications based on the requirements are all within the protection scope of the technical invention.

Claims (4)

1. A method for determining total arsenic in a deposit, comprising the steps of:

step 1, preparing a standard solution: preparing arsenic standard solution with the concentration of 1.0 ug/ml;

step 2, preparing an internal standard solution: preparing an internal standard solution with the concentration of 1.0 ug/mL;

step 3, preparing a solution to be detected: taking 2.0ml of supernatant fluid subjected to pretreatment digestion, and fixing the volume to 50ml by using pure water;

the pretreatment specifically comprises the following steps: weighing 0.1-0.5 g of dried sediment sample, adding 5ml of nitric acid and 4ml of hydrofluoric acid, performing microwave digestion, adding 2ml of perchloric acid, dispelling acid, and then using ultrapure water to fix the volume to 50 ml;

step 4, selecting the standard solution in the step 1, diluting the standard solution into a plurality of gradient concentrations by using nitric acid with the volume concentration of 1%, and respectively measuring light absorption values of the standard solution with different concentrations through inductively coupled plasma mass spectrometry (ICP-MS) to prepare an arsenic standard curve;

and 5, measuring the arsenic element in the solution to be detected in the step 3 by using inductively coupled plasma mass spectrometry (ICP-MS) to obtain a light absorption value of the arsenic in the solution to be detected, comparing the detected light absorption value of the arsenic with a standard curve of the arsenic to obtain the content of the arsenic element in the solution to be detected, and further obtaining the content of the arsenic element in the marine sediments.

2. The method for measuring according to claim 1, wherein: the arsenic standard solution in the step 1 is prepared by diluting an arsenic standard solution with the concentration of 1000ug/ml by using a nitric acid solution with the volume concentration ratio of 1%.

3. The method for measuring according to claim 1, wherein: the concentrations of the standard solution diluted in the step 4 are 0ug/L, 5 g/L, 10ug/L, 30ug/L, 50ug/L and 100ug/L respectively.

4. The method for measuring according to claim 1, wherein: the measurement conditions of inductively coupled plasma mass spectrometry ICP-MS are as follows: room temperature: 20-28 ℃; humidity: less than or equal to 80 percent; argon gas: 650-750 KPa, helium: 60 to 100 KPa; circulating water: 230-400 KPa of distilled water; air exhaust amount: 10 to 15 m/s.