If the metabolite is freely soluble, it should be stored in a dry condition in the dark at a low temperature. There is much less chance of chemical change if the compound is not in solution. Take care not to open the container before it has reached room temperature otherwise water will condense inside the cold container and may affect the stability. If the specific activity of the compound is very high (not likely with metabolites) other forces come into play and decomosition can take place.

It is better to you evaporate all of solvent and storage it at -20 or -080 oC. If you purge Argon or nitrogen gases to the vial, the duration of metabolite will be longer.

If you have to store your samples in solvent, it is better to use solvent like DMSO than using methanol.

I think for storing the samples, especially extracts and isolated compounds, use of solvents is not a good option for long time storage. Solvent (DMSO, alcohols etc.) are good for small time storage.

So, If u want to store them for long time then remove solent by evaporation if possible. But for sensitive samples like biologicals go directly for lyophilization. Lyophilization is the best way to store samples (biologicals, secondary metabolites) for long time.

Lyophilization is the best way to store samples (biologicals, secondary metabolites) for long time.

Is there any reasons to evaporate all solvents? And also, it is evident that the metabolites in DMSO is not easy to evaporate. Even methanol taking more time to evaporate it using Vacuum concentrator.

If the metabolite is freely soluble, it should be stored in a dry condition in the dark at a low temperature. There is much less chance of chemical change if the compound is not in solution. Take care not to open the container before it has reached room temperature otherwise water will condense inside the cold container and may affect the stability. If the specific activity of the compound is very high (not likely with metabolites) other forces come into play and decomosition can take place.

Dry storage is best for natural products, either by lyophilization (water soluble compounds, t-Butanol soluble compounds) or by evaporation.

Dry storage is the best way for longer periods. You can extract the metabolite when you are ready to analyse. Another way is to lyophilize the tissue samples and store in a refrigerator but it may not be highly suitable for long term storage

Long time storage esp. methanolic extracts lead to reduced antioxidant activity, compound degradation. If phenolics are there ,then warming up and light/air exposure even during prolonged column fractionations can lead to artifacts esp. simple phenolics polymerise and become non-moving in a tlc plate.

Firstly you should evaporate the solvents from samples via rotary evaporator. Then you will use freeze dryer to completely dried your samples. After freeze drying, you will choose a glass vial (of course standard grade--normal glass vial will be broken when you will keep it -20 deg C temp) to store your samples for long term at -20 deg C tem.

I think it is better to store your samples as dry at cool temperatures. -20 or -80 are good

Mostly the plant extracts is stored as dry powder by evaporating the sample but you may also store liquid extract at -20 degree celcius that comprises extract preparation through the ultrasonicator. You have to first dissolve the powder with solvent (1:3 w/v) and incubate for 1hr in shaking incubator and then sonicate for 10 mins. followed by centrifugation at 8000rpm for 10mins. The supernatent should be collected and can be stored at -20 degree celcius.

Better is to store a dry sample either by lyophilisation or a simple solvent remove, this in case the extraction was done by a light solvent (methanol, ethanol, ether, etc.). Of cause, sample like essential oils will be stored in their natural state after been dried on sodium sulphate. Also samples are kept in dark container

Of course, a methanol extract will prevent any bacterial growth, so the only degradation worry would be oxidations, free radicals, etc. Cold slows but does not eliminate those reactions. lyophilization does not guarantee protection from oxidative damage. One precaution could be to bubble dry nitrogen or argon through your methanol extract, saturating it while removing oxygen, then sealing. there are additives to prevent peroxides, where you would need to search the literature.

I have stored my crude organic extracts after evaporation all solvent at > -20 or at -80oC . in dark vials

Its better to dry the metabolite sample and store in a dark condition at moderate temperature rather then going for other mode of storage, as Ananthasankaran Jayalekshmy said the antioxidant capacity of the compound also diminishes.

maintain dark condition and constant temperature.

Store them in dry form. If you need some samples for later use but not disturb the whole, you can make some aliquots after you evaporate the maximum bulk solvent. First, transfer the concentrated extract solution into several pre-weighted glass vials, and then free dry them or blow dry by nitrogen gas. Alternatively, you can put all vials (not too full, ~1/3) into desiccator and apply with vacuum until dry. Weigh them and get dry weight of extract aliquots. Finally, store them at -20 or -80 °C with labels.

Evaporating the solvent ensure less possibility of chemical reaction in long storing period especial if left out of -20 degree, otherwise I left ethno-ectract at room temperature for more than a year and they still in good condition.

Methanol extract as such or dried powder and lyophilized samples appear to be the best way for preserving samples for secondary metabolite anlaysis as suggested by many.

Dry powder or lyophilized sample its best methods to storage secondary metabolie and storage at -20C.