Kindly refer ICMR's book "Phytochemical and reference standards of selected Indian medicinal plants' vol 1, 2010

I must tell You, that from my point of view, the main problem is that you used too small amount of raw material - the plant seeds. As I know the content of trigonelline in fenugreek seeds, for instance, is about 0,4%, which means that: in 1g of such sample you will have no more than 4mg of trigonelline. I think it is easier to lose that amount of trigonelline during the preparation process than to isolate it.

Depending on the purpose and needs of the isolation process, if you want to get 10 mg of pure compound, or 100mg or 1g  you have to use a correspondingly larger amount of seeds. In some laboratories for isolation purposes workers have used  even 1 to 2 kg of raw material. At the present time, even using modern analytical methods, descent below 100g of raw material does not give much chance to get measurable amounts of pure compound. I wasn't looking for methodology of receiving trigonelline yet , but I hope that my today advice will be useful for You. Good luck