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1. Method Overview

After digestion, the sample is atomized in a graphite furnace, and the absorbance is measured at 357.9 nm. Within a certain concentration range, the absorbance value of chromium is proportional to its content, and quantitative analysis is performed by comparison with the standard series.

2. 2. Instruments and Reagents

2.1 Instruments and Equipment

2.1.1 Testing Instruments

Graphite Furnace Atomic Absorption Spectrophotometer (Chromium hollow cathode lamp)

Circulating Water System

Argon Gas (Purity≥99.99%)

2.1.2 Pretreatment Equipment

Porcelain Crucible

Electric Furnace

Micropipette

Testing tube

2.2 Reagents

2.2.1 Reagents

Nitric Acid (MOS grade)

Nitric Acid Solution (1+99) (Measure 1 mL of nitric acid, add to 99 mL of water, and mix well)

2.3 Standards

2.3.1 Stock Solution

GSB 04-1740-2004 (National Liquid Standard Sample – Chromium)

3. 3. Operation Procedure

3.1 Sample Preparation

3.1.1 Preparation of Test Solution

Weigh 5 g of the sample accurately to 0.1 g, place it in a 100 mL porcelain crucible, heat it on an electric furnace until it burns. Remove it and place it in a fume hood. After the sulfur burns out completely, heat it on the electric furnace for about 5 minutes. Remove and cool it. Add 5 mL of nitric acid and 15 mL of water, heat until the residue is completely dissolved. After cooling, transfer it to a 25 mL colorimetric tube, dilute to the mark with water, and shake well.

3.1.2 Preparation of Standard Solutions

Preparation of Chromium Standard Intermediate Solution (1000 μg/mL):

Accurately pipette 100 μL of the chromium national standard solution into a 100 mL volumetric flask, and dilute to the mark with (1+99) nitric acid to obtain a chromium standard intermediate solution of 1 μg/mL.

Preparation of Chromium Standard Series:

Pipette 0.0, 0.25, 0.5, 1.0, 2.0 mL of the chromium standard intermediate solution (1000 μg/mL) into 100 mL volumetric flasks, and add (1+99) nitric acid to the mark to obtain chromium standard series of 0.0, 2.5, 5.0, 10.0, 20.0 ng/mL.

3.2 Sample Testing

(1) Testing Conditions

Reference conditions for graphite furnace atomic absorption spectrophotometer:

Wavelength (nm)    357.9

Spectral Bandwidth (nm)   0.4

Element Lamp Current (mA)   2.0

Filter Coefficient   0.1

Integration Time (s)   2

(2) Sample Testing Procedure

Open the argon gas cylinder and adjust the argon pressure gauge to 0.5 MPa. Adjust the instrument to its optimal working state, and measure the absorbance of the reagent blank, standard series, and sample solution at 357.9 nm.

Subtract the absorbance of the zero standard solution from the absorbance of each standard solution. Take the mass concentration of chromium (μg/L) as the abscissa and the corresponding absorbance as the ordinate to plot the working curve. According to the measured absorbance of the test solution and the blank test solution, find the mass of chromium from the working curve.

3.3 Result Calculation

어디:

X = Chromium content in the sample, in milligrams per kilogram (mg/kg);

ρ= Mass concentration of chromium in the sample solution, in micrograms per liter (μg/L);

Ρ0 = Mass concentration of chromium in the blank solution, in micrograms per liter (μg/L);

V = Constant volume of the sample digestion solution, in milliliters (mL);

m = Sample weight, in grams (g);

1000 = Conversion coefficient.