Automated difficult matrix introduction (DMI) for identification of residues of washing powder on clothing with GC-MS and a LINer EXchanger (LINEX)

Importance of the Topic

Effective sample preparation is a critical step in analytical chemistry, as it directly impacts data validity and reliability. Traditional techniques often require extensive manual handling, increasing the potential for analyte loss and operational costs. Automated Difficult Matrix Introduction (DMI) addresses these challenges by minimizing human intervention and focusing on selective transfer of volatile analytes.

Objectives and Study Overview

This application note demonstrates the use of DMI coupled with gas chromatography–mass spectrometry (GC–MS) to detect trace residues of washing powder ingredients on cotton fabrics. The study compares chromatographic profiles from pure detergent samples to those obtained from washed and dried cotton pieces to evaluate the method's sensitivity and selectivity.

Methodology and Instrumentation

• Sample Preparation: Cotton pieces (3 × 1 cm) were washed in an aqueous detergent solution for 1 hour, rinsed three times with tap water, and air-dried. A small fragment (5–10 mg) was placed into a DMI micro-vial fitted with a cleaned DMI liner.
• Instrumentation: PTV injector (OPTIC 3), Shimadzu GC–MS QP2010, FOCUS and LINEX autosamplers.
• GC–MS Conditions: Inertcap wax column (0.32 mm × 60 m, 0.5 µm); temperature program 40 °C (6.3 min), then 15 °C/min to 130 °C, 3 °C/min to 250 °C (25 min hold); helium carrier gas; PTV injector ramp 35 °C to 250 °C at 5 °C/s; split 1:40 after 1.5 min.

Main Results and Discussion

Chromatograms of pure detergent and washed cotton revealed common peaks corresponding to benzyl alcohol, tetrahydrolinalool, hexadecanol, citronellol, butyl glycol, and α-isomethyl ionone. Although residue levels on cotton were substantially lower, each target compound remained detectable. Method repeatability in detergent samples yielded 4 % RSD for retention times and 13 % RSD for peak areas. The DMI approach effectively isolates volatile analytes while retaining the nonvolatile matrix in the vial.

Benefits and Practical Applications

• Reduced labor and operational costs due to minimal manual handling.
• Preservation of volatile analytes, lowering risk of sample loss.
• High sensitivity for trace-level screening in quality control and forensic investigations.

Future Trends and Applications

Potential developments include integration of DMI with high-resolution MS and tandem MS for enhanced specificity, adaptation to a broader range of complex matrices, and full automation for high-throughput screening in industrial and environmental monitoring.

Conclusion

Automated DMI-GC–MS offers a robust alternative to conventional sample preparation, enabling reliable detection of low-level wash powder residues on textiles with minimal manual intervention.

Reference

H. Jing, A. Amirav, Anal. Chem. 1997, 69, 1426–1434.