Yes the K-PANOPA kit can be used to measure free amino nitrogen (FAN).
A traditional method to measure nitrogen is the formol method and correlation exists between the two methods (formol and PANOPA) that is well documented in scientific literature. However higher values are usually expected from the formol method since it includes measurement of ammonia - this is known as yeast assimilable nitrogen (YAN). YAN is FAN plus ammonia.
The PANOPA method measures primary amino nitrogen (PAN) from free amino acids except proline however proline is not assimilated under anaerobic conditions such as occurs during alcoholic fermentation.
Recommended sample preparation method for dried fermentation samples (powders):
Add 1 g of dried sample to a 100 mL volumetric flask and make to 100 mL with distilled water. Mix thoroughly until fully hydrated or dissolved then filter through Whatman No. 1 filter paper or centrifuge at 13000 rpm in a bench top centrifuge. Use the clear filtrate / supernatant in the K-PANOPA assay. If it the primary amino value is too high repeat the assay with a dilution of the filtrate / supernatant. If it is too low repeat the extraction using a lower volume of distilled water.