Overview of GB/T 17140-1997 Standard

GB/T 17140-1997 is an important method standard in Chinese national standards for the determination of lead and cadmium in soil quality. This standard adopts the KI-MIBK extraction flame atomic absorption spectrophotometry method, which is suitable for the quantitative analysis of trace lead and cadmium in soil.

This method uses a potassium iodide (KI) and methyl isobutyl ketone (MIBK) extraction system to separate and enrich lead and cadmium from soil digestion solutions, and then measures them with a flame atomic absorption spectrophotometer, featuring high sensitivity and good selectivity.

Method Principle

After acid digestion of soil samples, lead and cadmium enter the solution in ionic form. In an acidic medium, potassium iodide is added, and lead and cadmium form stable complexes with iodide ions.

These complexes can be quantitatively extracted by methyl isobutyl ketone (MIBK), thereby achieving separation from matrix elements. The extracted organic phase is directly aspirated into the flame atomic absorption spectrophotometer, and the absorbance is measured at specific wavelengths. The lead and cadmium content is calculated based on the standard curve.

Reagents and Instruments

Main Reagents

  • Nitric acid (HNO₃): Guaranteed reagent grade, used for sample digestion.
  • Hydrochloric acid (HCl): Guaranteed reagent grade, used for adjusting acidity.
  • Potassium iodide (KI): Analytical reagent grade, used to prepare the extraction complexing agent.
  • Methyl isobutyl ketone (MIBK): Analytical reagent grade, extraction solvent.
  • Lead and cadmium standard solutions: Used for plotting the standard curve.

Main Instruments

  • Flame atomic absorption spectrophotometer: Equipped with lead and cadmium hollow cathode lamps.
  • Separatory funnel: 125 mL or 250 mL.
  • Electric heating plate or microwave digestion instrument: Used for soil sample digestion.
  • Analytical balance: Sensitivity 0.0001 g.

Analysis Procedure

1. Sample Digestion

  1. Weigh 0.5 g of air-dried soil sample (accurate to 0.0001 g) into a digestion tube.
  2. Add an appropriate amount of nitric acid-hydrochloric acid mixed acid, place on an electric heating plate and heat for digestion until the solution is clear.
  3. After cooling, make up to volume, filter, and take the filtrate for testing.

2. Extraction and Separation

  1. Take a certain volume of digestion solution into a separatory funnel, add potassium iodide solution, and shake well.
  2. Add MIBK and shake thoroughly for extraction for 2-3 minutes.
  3. Allow to stand for layer separation, discard the aqueous phase, and retain the organic phase.

3. Instrument Measurement

  1. Set the flame atomic absorption spectrophotometer parameters: lead wavelength 283.3 nm, cadmium wavelength 228.8 nm.
  2. Zero with MIBK, and measure the absorbance of the standard series and samples.
  3. Calculate the lead and cadmium concentrations based on the standard curve.

Key Parameters and Conditions

Item Lead (Pb) Cadmium (Cd)
Measurement wavelength 283.3 nm 228.8 nm
Extractant MIBK MIBK
Complexing agent KI KI
Flame type Air-acetylene Air-acetylene
Detection limit Approximately 0.1 mg/kg Approximately 0.01 mg/kg

Precautions

  • The digestion process should be carried out in a fume hood to avoid acid mist hazards.
  • KI and MIBK should be prepared fresh before use to prevent oxidation or volatilization.
  • The extraction shaking time should be kept consistent to ensure stable extraction efficiency.
  • Soil samples should be air-dried, ground, and sieved to ensure representativeness.
  • Blank tests and spike recovery tests should be performed for each batch of samples to control quality.

Method Advantages and Applicability

The KI-MIBK extraction flame atomic absorption spectrophotometry method has the advantages of high sensitivity and low matrix interference, and is particularly suitable for the determination of low concentrations of lead and cadmium in soil.

This method is relatively simple to operate and low in cost, and is widely used in environmental monitoring, agricultural soil surveys, and contaminated site assessments.

GB/T 17140-1997 Soil Quality Determination of Lead and Cadmium KI-MIBK Extraction Flame Atomic Absorption Spectrophotometry

Summary

Following the GB/T 17140-1997 standard and using the KI-MIBK extraction flame atomic absorption spectrophotometry method, the lead and cadmium content in soil can be accurately determined.

Experimenters need to strictly control the digestion, extraction, and measurement conditions to ensure reliable data and provide a scientific basis for soil environmental quality assessment.