Non methane total hydrocarbon gas chromatography may encounter various problems during use. The following are common solutions and systematic treatment processes:

1、 Non methane total hydrocarbon gas chromatograph baseline drift or fluctuation is too large

1. Possible reasons

Insufficient purity of carrier gas/unstable flow rate

Check if the residual pressure of the steel cylinder is too low, causing impurities to mix in; Replace the aging molecular sieve purifier.

Confirm that the set value of the steady flow valve matches the current column front pressure demand, and use an electronic flow meter to monitor the real-time changes in the carrier gas flow rate.

Injection port contamination or gasket leakage

Clean or replace the injection gasket (it is recommended to replace it synchronously during each maintenance); Wipe the diversion plate to avoid the accumulation of sample residue.

The high-temperature baking injection system removes interference from high boiling point substances.

Abnormal sensitivity of detector

The FID detector needs to check the ratio of hydrogen to air, and the flame color should be blue and steadily burning.

Calibrate the gain of the signal amplifier to ensure that the output signal is not saturated.

2. Solution steps

① Check the carrier gas pathway in sequence → ② Perform injection port maintenance → ③ Optimize detector parameters → ④ Run blank solvent to verify baseline stability.

2、 Inaccurate quantification of non methane total hydrocarbons by gas chromatography

1. Error tracing and correction methods

-Nonlinear calibration curve

Ensure that the standard gas gradient covers the actual sample concentration range

Using multi-point forced fitting instead of single point correction, the correlation coefficient R2 needs to be greater than 0.995.

-Poor repeatability of injection

Maintain the sealing of the quantitative ring of the automatic sampler and check for blockages in the sampling needle.

Using headspace bottle pressure equilibrium method to improve the volatilization efficiency of liquid samples.

-Low desorption efficiency

The thermal desorption device needs to regularly replace the trap packing and verify the effectiveness of the analytical temperature curve.

Compare the difference in capture efficiency between packed columns and capillary columns, and install a secondary enrichment device if necessary.

2. Application of data diagnostic tools

Generate a sequence analysis report using the instrument's built-in diagnostic software, with a focus on observing:

-When the RSD value of continuous injection is greater than 3%, it indicates a system stability defect;

-The deviation of the spiked recovery rate from the range of 85% to 115% indicates the presence of matrix effect interference.