How to synthesize and preparation of dinitrosalicylic acid (DNSA)
1. Synthesis
DNSA is a chemical reagent used for quantitative analysis of reducing sugar. It can be used to accurately estimate the amount of sugar present in a sample. DNSA is expensive to purchase, but the precursor, salicylic acid is cheap. Here’s how we can prepare dinitrosalicylic acid (DNSA) from salicylic acid.
Nitrating acid preparation.
The first step is mix concentrated nitric acid with concentrated sulphuric acid in the ratio 1:5, up to 100g. The result is a hot solution called nitrating acid, which must be cooled before use. This mixtures is cooled in an ice bath to 0 degrees Celsius, while being stirred by a magnetic stirrer.
Salicylic acid preparation
After cooling, 15 grams of salicylic acid is added to the solution while still stirring. This is added slowly while stirring and cooling is going on, until the solution becomes viscous.
Solidification
The resulting thick product is poured into a beaker with iced distilled water where it is allowed to solidify. 440
The resulting precipitate contains the required products and other by products as impurities. The solidified product is filtered to remove filtrate containing the desired products, washing frequently with distilled water.
Crystallization
The next step is crystallization. After crystallization, unwanted products separated from the wanted products, and can easily be removed. The crystals are then dried. Re dissolution and recrystallization is advised to ensure higher purity of synthesized dinitrosalicylic acid.
Test of purity
Carry out test or melting point (m.p) analysis to determine purity. M.p of dinitrosalicylic acid, 173oC.
1. Preparation of Dinitrosalicylic acid (DNSA) reagent
Step 1: to a beaker of about 100ml, add 80mL of 0.5M sodium hydroxide (NaOH) solution
Step 2: To said beaker, slowly ad 2.18g of DNSA crystal prepared in previous step to the NaOH solution. Heat at 70oC and stir slowly to dissolve the DNSA.
Step 3: Finally, add 30g of pure Rochelle’s salt (sodium potassium tartrate) to the beaker containing the solution, and stir until dissolve.
Step 4: cool down (ice bath can be used) to room temperature, transfer whole content to a volumetric flask of about 100mL. And finally make up to 100mL mark with distilled water.
Step 5: Transfer to a reagent bottle and store in a dark, dry place until required for use for 3-4 weeks. 440