Determination of BTEX in Solid Waste by Gas Chromatography

Solid waste pollution has become a major challenge in the field of environmental protection. BTEX (such as benzene, toluene, ethylbenzene, etc.), as typical organic pollutants, pose significant threats to the ecological environment and human health due to their high toxicity, strong mobility, and potential carcinogenic risks. These pollutants originate not only from industrial production and municipal waste, but can also enter the environment through landfill disposal, waste accumulation, or improper handling, thereby contaminating soil, groundwater, and surrounding ecosystems. Therefore, accurate detection of BTEX in solid waste is crucial.

This paper references "Solid Waste—Determination of BTEX—Headspace/Gas Chromatography Method" (HJ 975-2018) and utilizes the Wayeal’s Gas Chromatograph GC6100 equipped with an FID detector and headspace sampler for the detection of BTEX in solid waste.

Keywords: BTEX, Headspace, Gas chromatography, FID Detector, Solid Waste.

1. Experiment Method

1.1 Instrument Configuration

Table 1 Configuration List of Gas Chromatograph

1.2 Experimental Materials and Auxiliary Equipment

Reference standard solution of 8 BTEX components in methanol (1000μg/mL): Certified commercially standard solution, stored in airtight containers under dark conditions at temperatures below 4°C.

Standard working solution 1 of 8 BTEX components in methanol (10μg/mL): Accurately pipette 100μL of the reference standard solution and dilute to 10mL with water. Prepare fresh before use.

Standard working solution 2 of 8 BTEX components in methanol (100μg/mL): Accurately pipette 1000μL of the reference standard solution and dilute to 10mL with water. Prepare fresh before use.

Methanol: Chromatographic grade

Phosphoric acid: GR grade

Quartz sand: 0.30-0.85mm (50-20 mesh). Heated in a muffle furnace at 400°C for 4 hours, then transferred to a ground-glass stoppered bottle for sealed storage after cooling.

Sodium chloride: GR grade (heated in a muffle furnace at 400°C for 4 hours before use, then transferred to a ground-glass stoppered bottle and stored in a desiccator for subsequent application).

Saturated sodium chloride solution: Measure 500mL of water, add phosphoric acid dropwise to adjust pH ≤ 2, add 180g of sodium chloride, dissolve and mix thoroughly. Store at temperatures below 4°C.

Carrier gas: High-purity nitrogen

Hydrogen generator

Air generator

Fully automatic headspace sampler: Temperature control accuracy of ±1°C.

Headspace vials: Glass headspace vials (20mL).

1.3 Test Conditions

1.3.1 Reference Conditions for Headspace Sampler

Heating equilibrium temperature: 95℃

Heating equilibrium time: 50min

Injection valve temperature: 100°C;

Transfer line temperature: 110°C;

Injection volume: 1.0 mL (quantitative loop).

1.3.2 Reference Conditions for Gas Chromatograph

Chromatographic column: Wax capillary column, 30m*0.32mm*0.5μm.

Temperature programming: Initial column temperature 40°C, hold for 5 minutes; then increased to 90°C at a rate of 5°C/min and hold for 5 minutes.

Column flow rate: 2mL/min

Injection port temperature: 200℃

Detector temperature: 250℃

Air flow rate: 300mL/min

Hydrogen flow rate: 40 mL/min.

Make-up flow rate: 25 mL/min.

Split injection: Split ratio 10:1.

1.4 Solution Preparation

BTEX Linear Standard Working Solutions

Add 2g of quartz sand and 10mL of saturated sodium chloride solution sequentially into 7 headspace vials. Then add 0μL, 5μL, 10μL, 20μL of standard working solution 1 (10μg/mL) and 5μL, 10μL, 40μL of standard working solution 2 (100μg/mL) respectively into each corresponding vial. Seal immediately to prepare standard series with target compound masses of 0μg, 0.05μg, 0.10μg, 0.20μg, 0.50μg, 1.00μg, and 4.00μg respectively.

2. Result and Experiment

2.1 Qualitative Analysis of Standard Samples

Fig 1 Chromatogram of BTEX Standard Solution (1.00μg)

Table 2 Chromatographic Parameters of BTEX Standard Solution (1.00μg)

Note: As the chromatograms shows above, the resolution between all BTEX component peaks exceeds 1.5, meeting the requirements for analytical applications.

2.2 Linear

Fig 2 BTEX Standard Curve and Correlation Coefficient

Note: The concentration levels for the BTEX standard working curve in this test were 0μg, 0.05 μg, 0.10μg, 0.20μg, 0.50μg, 1.00μg, and 4.00μg. All BTEX components demonstrated excellent linearity with correlation coefficients >0.999, meeting the requirements for analytical applications.

2.3 Precision

Fig 3 Reproducibility Chromatograms of BTEX in Solid Waste Sample (0.025mg/kg)

Fig 4 Reproducibility Chromatograms of BTEX in Solid Waste Sample (0.100mg/kg)

Fig 5 Reproducibility Chromatograms of BTEX in Solid Waste Sample (0.500mg/kg)

Table 3 Chromatographic Parameters of BTEX in Solid Waste Samples

Note: Six replicate determinations were performed on BTEX mixed standard samples at concentration levels of 0.025mg/kg, 0.100mg/kg, and 0.500mg/kg. The relative standard deviations (RSD) were 1.1-2.4%, 1.2-2.4%, and 0.8-1.6%, respectively. All chromatographic peaks demonstrated relative deviations complying with standard requirements.

2.4 LOD

Fig 6 Chromatograms for Detection Limit of BTEX in Solid Waste Sample (0.025mg/kg)

Table 4 Method Detection Limits and Lower Limits of Quantification for BTEX Components

Eight replicate injections of a benzene compound solution (0.025 mg/kg) in solid waste samples were performed. Calculations indicate that when the solid waste sample size is 2 g, the detection limit of this method ranges from 0.001 to 0.004 mg/kg, and the lower limit of quantification ranges from 0.004 to 0.016 mg/kg, meeting the standard requirements.

2.5 Sample Test

Sample pretreatment: Add 2g of solid waste sample and 10mL of saturated sodium chloride solution into a headspace vial. Seal the vial immediately and oscillate at 150 cycles/min for 10 minutes using a reciprocating shaker. Subsequently, perform analysis using the headspace sampler.

Fig 7 Chromatogram of Solid Waste Sample Analysis

Note: Following standard pretreatment procedures, the solid waste sample was analyzed after sampling. No BTEX compounds were detected in the solid waste sample.

2.6 Recovery Test

Table 5 Chromatography Parameters of BTEX in the Solid Waste

Note: Eight replicate tests were conducted on solid waste samples spiked with low, medium, and high concentrations of BTEX. The recovery rates for all BTEX components met standard requirements.

3. Conclusion

This method employed the Wayeal Gas Chromatograph GC6100 equipped with an FID detector and headspace sampler for the determination of BTEX in solid waste. Experimental results showed that the resolution between all BTEX component peaks exceeded 1.5, meeting analytical requirements. When the standard working curve concentrations ranged from 0.05 to 4.0μg, all BTEX components sshowed excellent linearity with correlation coefficients >0.999, fulfilling analytical demands. The method's precision, detection limits, and recovery rates all complied with standard specifications. After pretreatment, no BTEX compounds were detected in the test samples, indicating normal results. This demonstrates that the method utilizing the Wayeal GC6100 instrument satisfies the requirements for BTEX determination in solid waste.

4. Attention

The solvents and reference standards used in the experiment are classified as hazardous chemicals. All solution preparation and sample pretreatment procedures must be conducted inside a fume hood. Operators shall wear appropriate laboratory personal protective equipment as required, avoiding any contact with skin and clothing.