Determination of Geosmin and 2-MIB in Water by Headspace Solid-Phase Microextraction Coupled with Gas Chromatography-Mass Spectrometry

1. Standard Solution and Sample Preparation

1.1 Remove the standard solution from the refrigerator and allow it to reach room temperature. Then, separately take GSM standard solution with concentration 100ug/mL and 2-MIB standard solution.

Add 10 µL of each liquid to 9.8 mL of methanol to obtain the standard intermediate solution with concentration 1ug/mL; take 100 µL of the standard intermediate solution and add

Transfer to 9.9 mL with methanol and dilute to volume to obtain a standard working solution with concentration 10ng/mL. If an internal standard solution is required, dilute it simultaneously. Pipette 20 mL.

Add 5 headspace vials, each containing 3.0g of NaCl (Guaranteed Reagent grade), 1 magnetic stir bars, and 10.00mL of pure water. Then add the standard solution to each.

Add 5.00, 10.00, 20.00, 50.00, and 100.00 μL of liquid. If an internal standard solution is required, add an equal volume (20 μL) immediately, cap the container, and

Vortex until NaCl is completely dissolved. Set aside.

Take 1.2 sample into a 20 mL headspace vial containing 3.0gNaCL and 1 magnetic stir bars. If an internal standard solution is available, add it.

Add 20 μL of equal volume, immediately cap, and vortex until NaCl is completely dissolved. Keep aside for later use.

2. Instrument Conditions

2.1 Column: DB-5MS (30m × 0.25mm × 0.25μm);

2.2 SPME liner (78.5mm × 6.45mm × 0.75mm);

2.3 Solid-Phase Microextraction Fiber: DVB/CAR/PDMS (50/30 μm, 1 cm fiber length)

2.4 Mass Spectrometer Conditions: Inlet Temperature 250°C; Injection Mode: Splitless; Carrier Gas: Helium, Flow Rate 1.00mL/min;

Temperature program: Hold at 60°C for 2.5min, then ramp at 8°C/min to 250°C and hold for 5 min. Ion source temperature: 250°C; Transfer

Wire temperature: 280℃; Scan mode: Selected Ion Monitoring (SIM); 2-Methylisocamphene characteristic ion: 95 (quant

quantity); 107 (qualitative 1); 135 (qualitative 2); geosmin characteristic ions: 112 (quantitative), 125 (qualitative).

2.5 Microextraction Instrument Conditions: Aging Temperature 270°C, Extraction Temperature 60°C, Equilibrium Time 10 min, Extraction Time 20 min.

Stirring speed: 600RPM; Stirring mode: Oscillate for 10s, pause for 10s; Extraction time: 3 min.

3. Results

3.1 Standard Curve

Perform mass spectrometry analysis on the prepared standard curve (Anypu 7700) to obtain the TIC plot. The elution time for 2-MIB is:

11.60min, GSM: 15.61min.

2-MIB and GSM curve correlation r2 Values are 0.9993 and 0.9998; method detection limits are 0.73ng/L and 0.52ng/L; relative standard deviations (RSD, n=6) for sample replicates are 4.06% and 4.70%; spike recovery rates in pure water are: 2-MIB 5 ng/L 80.2%~92.4%, 50ng/L 94.9%~106.3%; GSM 5 ng/L 89.8%~101.8%, 50ng/L 94.9%~105.5%. Experimental results for geosmin and 2-methylisoborneol in water demonstrate that linearity, sensitivity, precision, and accuracy meet or exceed the technical specifications defined in 2 national standard methods. This approach is widely used in solid-phase microextraction protocols for water quality testing.