GB/T 17137-1997 Determination of Total Chromium in Soil by Flame Atomic Absorption Spectrometry

This article provides a detailed interpretation of GB/T 17137-1997, the flame atomic absorption spectrophotometric method for the determination of total chromium in soil quality. It covers the method principle, reagents and instruments, operating procedures, result calculation, and precautions, offering a standard operating guide for environmental monitoring and soil testing personnel.

2022-02-23 admin Views 495

Standard Overview

GB/T 17137-1997 is the authoritative method in Chinese national standards for the determination of total chromium in soil quality, employing flame atomic absorption spectrophotometry. This standard is applicable to the determination of total chromium content in soil and provides a reliable basis for environmental monitoring, agricultural soil surveys, and pollution assessment.

Method Principle

After acid digestion of soil samples, chromium enters the solution in ionic form. In a flame atomic absorption spectrophotometer, chromium atoms are atomized in an air-acetylene flame and absorb light at a specific wavelength. The absorbance is proportional to the chromium concentration, and quantification is performed via a standard curve.

Key Reactions

Digestion: Chromium in soil is converted to a soluble state by mixed acids such as hydrofluoric acid, nitric acid, and perchloric acid.
Atomization: Chromium ions are reduced to ground-state atoms in the flame.
Absorption: Ground-state chromium atoms absorb the characteristic spectral line at 357.9 nm.

Reagents and Instruments

Main Reagents

Guaranteed reagent grade nitric acid, hydrofluoric acid, perchloric acid.
Chromium standard stock solution (1 mg/mL).
Deionized water (resistivity ≥18 MΩ·cm).

Main Instruments

Flame atomic absorption spectrophotometer equipped with a chromium hollow cathode lamp.
Air-acetylene flame system.
PTFE crucibles, electric hot plate, analytical balance.

Operating Procedures

Sample Preparation: Air-dry, grind, and sieve soil through a 100-mesh sieve.
Digestion: Weigh 0.2–0.5 g of sample, add mixed acid, heat and digest until white fumes are exhausted, and dissolve the residue with dilute nitric acid.
Volume Adjustment: Filter and dilute to 50 mL.
Standard Curve: Prepare a chromium standard series of 0–2.0 μg/mL and measure absorbance.
Sample Measurement: Measure the sample solution under the same conditions and record the absorbance.

Result Calculation

Total chromium content (mg/kg) = (C × V × f) / m, where C is the concentration obtained from the standard curve (μg/mL), V is the final volume (mL), f is the dilution factor, and m is the sample mass (g).

Precautions

Digestion must be performed in a fume hood to avoid acid mist hazards.
Use perchloric acid with caution to prevent explosions.
Optimize flame conditions to ensure chromium atomization efficiency.
Perform blank tests and spike recovery for each batch of samples.

Parameter	Specification
Detection Limit	0.5 mg/kg
Measurement Range	1–50 mg/kg
Recovery	90%–105%
Relative Standard Deviation	≤5%