Estimation Of Yeast Assimilable Nitrogen Using The Formol Titration Technique (Page 2 of 3) in pdf

Long version of YAN (mg/L) computational formula:

Reagents

0.05 N NaOH [sodium hydroxide] solution (Prepared from a 2:1 dilution of stock 0.1 N NaOH solution)

37% formaldehyde solution

10% NaOH solution (for normalizing formaldehyde)

pH buffers for calibration of pH meter

Equipment

(and purpose)

burette and lab stand (titration)

10 ml volumetric pipette (measuring sample)

pH meter and probe (titration end point)

25 ml volumetric flask (diluting sample with water)

magnetic stirrer and small stir bar

eye dropper (neutralize formaldehyde)

30 ml beaker (for sample)

10 ml graduated cylinder (measure formaldehyde)

50 ml beaker (normalize formaldehyde)

5-μm syringe filter (or filter paper)

Neutralizing the 37% formaldehyde solution

During storage, the pH level of formaldehyde solution tends to rapidly drop and can reach a level as low

as 3.5 or so. In order to maintain the validity of the formol titration technique, the formaldehyde must

be neutralized to a pH level of 8.0 sometime shortly before the procedure is performed. This can be

accomplished by pouring a small (e.g., 40 ml) sample of formaldehyde into a beaker, inserting a pH

probe and then adding 10% NaOH using an eye dropper until the pH reaches (and holds) a level of 8.0.

This neutralized formaldehyde should then be transferred to a sealed storage jar and used within 24

hours for optimal results. NOTE: Formaldehyde is nasty stuff. You need to make sure that you avoid any

skin contact and also must avoid breathing its fumes. Needless to say, good ventilation is a must.

Formol Titration Practice Run

When learning a new analytical technique it’s always helpful to have a “known” sample with which to

experiment. In the case of practicing the formol procedure, you probably already have a quantifiable

source of yeast assimilable nitrogen that you can use for such purposes. Almost all home wine makers

keep a supply of diammonium phosphate (aka DAP) on hand as a source of yeast food for their juices

and musts. Since DAP is 21.2% nitrogen by weight, it follows that an aqueous solution of 1 g/L of DAP

contains a nitrogen concentration of 212 mg/L. Hence, DAP and distilled water can be used to create

(unbuffered) solutions with known nitrogen concentrations that can be used to test the accuracy of your

formol titration technique.

Case Study:

Create an aqueous test solution with a 212 mg/L nitrogen concentration by adding 1g of DAP to 1 liter of

distilled water. Use this sample to run a test of the formol titration procedure.

Version 1.2 – December 7, 2012

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