1. Problem Phenomenon:

Methanol content in raw olive leaf material and ethanol solvent is both within standard limits. However, methanol test result of final olive leaf extract exceeds the standard by GC detection. The excessive value is not caused by residual methanol introduced in production, but methanol is secondarily generated by thermal
decomposition of the sample under high temperature of GC detection, leading to false positive over-standard result.

2. Root Cause:

Olive leaf naturally contains endogenous substances such as pectin, methoxylated polysaccharides, oleuropein, phenolic acid methyl esters and terpenoid methyl esters.

The temperature of GC/GC-MS injection port is usually 200～280℃. When the sample is heated instantly at high temperature:

1. The methoxy groups (-COOCH₃) on the structure of pectin and methoxylated polysaccharides in cell walls undergo thermal cleavage and demethylation, hydrolyzing to produce methanol;

2. Characteristic active ingredients in olive leaves (oleuropein, hydroxytyrosol methyl ester, rosmarinic acid methyl ester and other phenolic & terpenoid methyl esters) undergo decarboxylation and demethylation at high temperature, releasing methanol;

3. Older raw leaves, excessive drying temperature, ultra-fine crushing and higher extract concentration will increase methanol generated by thermal decomposition, directly causing over-standard detection value.

3. Identification of True Over-standard vs False Positive:

1. Low Temperature Verification: 

Adopt cold headspace ≤80℃ or normal-temperature direct liquid extraction without high-temperature heating, only test original free methanol in the sample. If qualified at low temperature but over-limit by high-temperature GC, it is confirmed as false positive caused by high temperature thermal decomposition.

2. GC-MS Characteristic Ion Judgment: 

Characteristic ions of methanol: m/z 31, 32. Impure chromatographic peak accompanied by ester and phenolic fragment ions indicates thermal decomposition by-products, not real residual methanol.

3. Injection Port Residence Time Comparison:

The longer the sample stays at high temperature in the injection port, the higher the methanol peak, which is typical thermally induced generation.

4. Solutions:

4.1 Production Control:

4.1.1 Prioritize fresh young olive leaves and reduce old leaves feeding to lower content of pectin and methyl ester precursors;

4.1.2 Dry raw materials at low temperature ＜60℃ to avoid high-temperature coking and modification;

4.1.3 Control extraction temperature at 40～60℃, keep the system neutral or weakly acidic to prevent premature hydrolysis of methyl ester;

4.1.4 Apply membrane separation and low-temperature short-path molecular distillation to remove thermolabile macromolecular pectin and esters.

4.2 Detection Optimization:

4.2.1 Use cold headspace 60～80℃ equilibrium method to detect free methanol;

4.2.2 Reduce GC injection port temperature to 150～180℃ and adopt inert liner;

Confirm results by GC-MS to eliminate false positive interference from thermal decomposition.

5. Summary:

The core reason for excessive methanol detection in olive leaf extract is not methanol residue introduced during production, but methanol generated by thermal decomposition of pectin and methyl ester substances in olive leaves under high temperature of GC detection, which is a false positive. This problem can be effectively solved by controlling thermal decomposition precursors in production and optimizing low-temperature conditions in detection.