Determination of BTEX in Water by Wayeal GC6100 Gas Chromatograph

The determination of BTEX in water was performed using an Anhui Instrument GC6100 gas chromatograph configured with a flame ionization detector (FID) and a headspace sampler, in accordance with the standard method "Water Quality—Determination of Benzene Homologues—Headspace/Gas Chromatography" (HJ 1067-2019).

Keywords: BTEX, headspace, gas chromatograph, FID detector, water.

1. Experiment Method

1.1 Instrument Configuration

Table 1 Configuration List of Gas Chromatograph System

1.2 Experiment Material and Equipment

Standard stock solution of 8 BTEX in methanol (1000μg/mL): Prepared from a commercially obtained certified reference material. Stored sealed and protected from light at temperatures below 4°C.

Working standard solution of 8 BTEX in methanol (50μg/mL): Pipette 500μL of the standard stock solution was diluted to 10mL with water. This solution was prepared fresh prior to use.

Methanol: Chromatographic Grade

Sodium chloride: GR (Heat at 500°C - 550°C for 2 hours before use. Cool to room temperature and store in a desiccator).

Carrier gas: High-purity nitrogen

Hydrogen generator

Air generator

Fully Automated Headspace Sampler with a temperature control accuracy of ±1°C.

Headspace vials: Glass headspace vials (20mL).

1.3 Test Conditions

1.3.1 Headspace Sampler Reference Conditions

Heating temperature: 80°C

Heating time: 30min

Injection valve temperature: 100°C

Transfer line temperature: 100°C

Injection volume: 1.0mL (sample loop)

1.3.2 Gas Chromatography Reference Conditions

Column: Wax capillary column, 30m×0.32 mm×0.5μm

Temperature programming: 40°C (5 min hold) → 5°C/min → 90°C (5 min hold)

Column flow rate: 2mL/min

Injection port temperature: 200℃

Detector temperature: 250°C

Air flow rate: 300mL/min

Hydrogen flow rate: 40mL/min

Make-up Flow Rate: 25 mL/min

Split injection: split ratio 10:1

1.4 Solution preparation

1.4.1 Linear Calibration Standards of BTEX

Preparation of calibration standards: Add 3g of sodium chloride to each of the seven headspace vials in advance. Then, sequentially add 10.0mL, 10.0mL, 10.0mL, 9.8mL, 9.6mL, 9.2mL, and 7.6mL of water, followed by the sequential addition of 5.00μL, 20.0μL, 50.0μL, 0.20mL, 0.40mL, 0.80mL, and 2.40mL of the standard working solution using pipette. This prepares a standard series with target compound concentrations of 0.025mg/L, 0.100mg/L, 0.250mg/L, 1.00mg/L, 2mg/L, 4mg/L, and 12mg/.

1.4.2 BTEX LOD Standard (0.025μg/mL)

Pipette an appropriate volume of the BTEX standard working solution (50μg/mL) and dilute it with water to prepare an LOD standard at a concentration of 0.025μg/mL.

2. Result and Discussion

2.1 Qualitative Analysis by Standard Comparison

Fig 1 Blank Chromatogram

Fig 2 Chromatogram of BTEX Standard Solution (1μg/mL)

Table 2 Chromatography Parameters of BTEX Standard Solution (1μg/mL)

Note: As shown in the chromatogram above, the resolution between all BTEX components was greater than 1.5, which meets the requirements for analytical purposes.

2.2 Linearity

Fig 3 BTEX Standard Curve and Correlation Coefficient

Note: The concentration of standard working curves for BTEX analysis in this test are 0.025μg/mL、0.100μg/mL、0.250μg/mL、1.00μg/mL、2μg/mL、4μg/mL、12μg/mL. All components in the BTEX standard solution demonstrated excellent linearity, with correlation coefficients (R) greater than 0.999, meeting the requirements for analytical applications.

2.3 Precision

Fig 4 Chromatogram of BTEX Standard Solution (0.025μg/mL)

Fig 5 Chromatogram of BTEX Standard Solution (2μg/mL)

Fig 6 Chromatogram of BTEX Standard Solution (10μg/mL)

Table 3 Precision Results for BTEX in Water

Note: Six replicate determinations were performed on BTEX mixed standard samples at concentration levels of 0.025μg/mL, 2μg/mL, and 10μg/mL. The relative standard deviations (RSDs) obtained were 0–3.9%, 1.1–2.5%, and 1.4–2.2%, respectively. The relative deviations of the chromatographic peaks for all compounds complied with standard requirements.

2.4 Limit of Detection

Fig 7 Chromatogram of BTEX LOD Standard (0.025μg/mL)

Table 4 LOD and LOQ for Each BTEX Compound

The BTEX standard solution (0.025 μg/mL) was injected repeatedly for 8 times. Based on the calculation, when the sample volume is 10.0 mL, the LOD of this method ranges from 1μg/L to 2μg/L, and the LOQ ranges from 4μg/L to 8μg/L, which complies with standard requirements.

2.5 Sample Testing

Fig 8 Chromatogram of Surface Water Sample

A 3g of sodium chloride was pre-added to a headspace vial. Then pipette 10mL of the surface water sample into the vial, which was immediately sealed and shaken gently to mix. Upon analysis, BTEX were not detected in the surface water sample.

2.6 Spike Recovery Test

Fig 9 Chromatogram of Spiked Surface Water Sample

Table 5 Spike Recovery of Surface Water

A 0.5μg/mL spiked surface water sample was analyzed in six replicates, yielding a spike recovery range of 99.0% to 107.4%.

3. Conclusion

The analysis was performed by using Wayeal GC6100 gas chromatograph equipped with a flame ionization detector (FID) and a headspace autosampler for the determination of BTEX in water. The experimental results demonstrated that the resolution between all BTEX component peaks exceeded 1.5, meeting the requirements for analytical applications. The standard working curve for BTEX, covering a concentration range of 0.025-12μg/mL, showed excellent linearity with correlation coefficients (R) greater than 0.999, meeting the requirements for analytical applications. All validation parameters—including precision, LOD, LOQ, and spike recovery results—conformed to standard specifications, confirming the method's suitability for reliable determination of BTEX in water samples.