Product number 1414003 is a United States Pharmacopeia (USP) reference standard used in analytical method validation, system suitability testing, assays, and quality control checks. It has not been validated for use in cell culture applications.
Product number M8407 is a methotrexate hydrate that has been tested for cell culture: https://www.sigmaaldrich.com/US/en/product/sigma/m8407
Methotrexate is insoluble in water, ethanol, chloroform, and ether. It is, however, soluble in solutions of mineral acids and in dilute solutions of alkali hydroxides and carbonates. (1) Methotrexate is unstable in basic solution. (2) For cell culture work, a stock solution of methotrexate is prepared using a minimum amount of 1 M NaOH and then diluted with saline or medium. The diluted stock remains active at 4–8 °C for about a week or at –20 °C for about a month.
References
1. Martindale: the Extra Pharmacopoeia, 29th ed., p. 636 (1989).
2. Merck Index, 12th ed., #6065 (1996).