·       Sodium And Potassium Salts Of Nitrate And Nitrite Are Added Mainly To Preserve Meat And Meat Products Such As Cured Meat And Meat Pickles.

Determination Of Nitrate And Nitrite In Foods

Principle

·       The Sample Is Clarified With Alumina Cream And The Amount Of Nitrate Present Determined By Allowing It To Diazotise Arsenilic Acid And Coupling The Diazonium Salt With N-1-Naphthylethylene Diamine. The Colour So Formed Is Extracted Into N-Butanol And The Absorbance Is Measured At 545 Nm. An Aliquot Of The Sample Is Mixed With Spongy Cadmium In Order To Reduce Any Nitrate Present And The Nitrite So Produced Is Determined In The Same Way. The Amount Of Nitrate Present Is Then Calculated By Subtracting The Nitrite From The Total.

Reagents

·       Water: This May Be Distilled Or De-Ionised But A Blank Must Be Carried Out To Check That It Is Of Satisfactory Quality For The Preparation Of The Spongy

·       Alumina Cream: Prepare A Saturated Solution Of Potassium Aluminium Sulphate And Add Ammonia Slowly With Stirring Until Ph Is 0.

·       N-Naphthylethylene Diamine: Dihydrochloride 1% In Distilled Water

·       Arsenilic Acid Monohydrate: 1% In 5M Hcl.

·       Buffer Ph, 6: Prepare 0.7M NH4Cl (37.45 Gm/L) In Distilled Water And Add 0.88 Ammonia Until The Ph Is 9.6.

·       Spongy Cadmium: Place Zinc Rods In 20 % Aqueous Cadmium Sulphate Solution And Leave For 3 Or 4 Hrs. Separate The Precipitated Cadmium, Wash Twice With Distilled Water And Then Macerate With Water For 2-3 Minutes Activate By Shaking With 2M Hcl And Then Wash At Least 5 Times With Distilled Water, Keep The Cadmium Under Distilled Water And Prepare Freshly For Each Batch Of

·       Standard Nitrite Solution: Weigh Out 0.4783 Gm Of Nano2 And Dilute To One Litre. Dilute This 10 Times To Get 10 Mgs /1 Of Nitrite Nitrogen.

·       N- Butanol

Procedure

·       Mix The Sample Thoroughly By Macerating Or Homogenizing And Weigh 5 Gm Into A 150 Ml Beaker. Add 50 Ml Water And Heat To 80ºc Stirring Gently.

·       Maintain At 80ºc For 10 Min. Add 20 Ml Alumina Cream And Transfer Gently To A 100 Ml Volumetric Flask. Cool And Dilute To Volume With Water. Mix And Filter Through Whatman No.4 Filter Paper Rejecting The First 10 Ml Of Filtrate.

·       The Filter Paper Must Be Previously Washed With At Least 100 Ml Of Hot Water To Remove The Small Amounts Of Nitrate That’ It May Have Contained

(A)Determination Of Nitrite:

·       Pipette 10 Ml Of Filtrate Into A 50 Ml Volumetric Flask, Add 2 Ml Of’ Arsenilic Acid Solution And Mix. Leave For 5 Minutes, Then Add 2 Ml Of Napthylethylenediamine Solution. Mix And Leave For 10 Minutes. If The Solution Is Clear, Dilute To 50 Ml With Water And Read The Absorbance At 538 Nm Using A 1 Cm Cell. If The Solution Is Cloudy, Transfer To A 100 Ml Separator, Saturate With Salt And Extract With N-Butanol Using 20, 15 And Then 5 Ml. Pass The Butanol Extracts Through A Small Cotton Pledget In A Funnel Into A Dry 50 Ml Calibrated Flask And Dilute To Volume With N – Butanol. Read The Absorbance At 545 Nm. In A 1 Cm Cell.

B)Determination Of Nitrate:

·       Pipette 10 Ml Of Filtrate Into A Small Stoppered Conical Flask. Add 5 Ml Of Buffer Solution And One Gram Of Wet Cadmium. Stopper The Flask And Shake For 5 Min. Filter The Solution Through A Washed Filter Paper Into A 50 Ml Volumetric Flask Rinsing The Cadmium And The Filter Paper With 5ml Water. Determine The Nitrite In The Filtrate As Given Above Starting At “Add 2 Ml Of Arsenilic Acid Solution”.

(C)Preparation Of Standard Curve:

·       Pipette Into A Series Of 50 Ml Volumetric Flasks Dilute Standard Solution Of Nano2 Containing 2-15 µg Of Nitrite Nitrogen And Develop The Colour As Given In The Procedure For Nitrite. Read The Absorbance And Plot Standard Curve. Repeat The Experiment And Extract The Colour With N-Butanol And Read The Absorbance At 545 Nm And Also Plot A Standard Curve For This Solvent. From The Graph Calculate The Nitrite Content Before And After Reduction And Calculate The Nitrate Content By Subtraction.