This lesson explores the role of chlorine in pigments identification, focusing particularly on modern chemistry pigments such as phthalocyanine pigments. Although chlorine is not a key element in pigment identification overall, it plays an essential role in specific pigments, including phthalo green. Chlorine’s detection through XRF spectroscopy is examined, with a focus on the use of different X-ray tube filter setups to optimize its identification.
Objectives
- Understand the significance of chlorine in pigment analysis, particularly in modern chemistry pigments.
- Learn how chlorine is detected using XRF spectroscopy and its X-ray energy characteristics.
- Compare the effectiveness of different X-ray tube filter setups for identifying chlorine.
- Analyze real-life examples of chlorine detection in sodium chloride and phthalo green pigments.
Materials
- Sodium chloride (table salt)
- Phthalo green pigment (Pigments Checker).
Lesson Plan
1. Introduction to Chlorine in Pigments
- Discuss the role of chlorine in modern pigments, particularly phthalocyanine pigments.
- Demonstrate the use of an attenuation calculator to determine chlorine x-ray transmission through 10 mm of air.
3. X-ray Tube Filter Setups
- Review the three X-ray tube filter setups:
- No filter: Optimal for energies below 2.5 keV.
- Low-keV filter: For 2.5–10 keV.
- Routine filter: Suitable for higher energy ranges but less effective for chlorine.
- Discuss the borderline nature of chlorine’s energy (2.6 keV) and the choice of filter depending on the situation.
4. Lab Activity 1: Sodium Chloride Spectrum Analysis
- Introduce sodium chloride as the simplest material to detect chlorine.
- Acquire spectra using the three filter setups:
- No filter: High peak (~100,000 counts).
- Low-keV filter: Detectable peak (~5,000 counts).
- Routine filter: No detectable chlorine peak.
5. Lab Activity 2: Phthalo Green Spectrum Analysis
- Analyze phthalo green as a real-world pigment sample containing chlorine.
- Compare spectra obtained with different filter setups:
- No filter: Strong chlorine peak (~80,000 counts).
- Low-keV filter: Adequate chlorine peak (~2,000 counts).
- Routine filter: Reduced or almost undetectable chlorine peak.
- Conclude that the no-filter or low-keV setup is optimal for detecting chlorine in phthalo green.
