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Table 2 Rapid qualitative detection of different hazardous chemicals in milk

From: Common milk adulteration and their detection techniques

Adulterant Procedure Observation Limit of detection (v/v) (Sharma et al. 2012) References
Hydrogen peroxide A. Add to 5 mL of suspected milk sample in attest tube, an equal volume of raw milk and 5 drops of 2% solution of paraphenylenediamine. Appearance of blue color indicates the presence of hydrogen peroxide as adulterant. 0.025% (Arvind Singh et al. 2012); (Kamthania et al. 2014); (Sharma et al. 2012)
B. Take 1 mL milk sample in a test tube and add 1 mL of potassium iodide-starch reagent solution and mix well. Appearance of blue color indicates the presence of hydrogen peroxide as adulterant. 0.004% (Sharma et al. 2012)
Formalin A. Take 10 mL milk sample in attest tube. Add 5 mL conc. sulfuric acid with a little amount of ferric chloride without shaking. Appearance of violet or blue color at the junction of two liquid layers indicates the presence of formalin.   (Arvind Singh et al. 2012); (Kamthania et al. 2014)
B. Take about 5 ml of milk in a test tube. Take 1 ml of 10% ferric chloride solution in a 500 ml volumetric flask and make up the volume using concentrated hydrochloric acid. Add 5 mL from this solution to the sample in test tube. Keep the tube in boiling water bath for about 3-4 min. Appearance of brownish pink color indicates the presence of formalin. 0.1% (Sharma et al. 2012)
C. Take 1 mL of sample milk in a test tube. Take saturated solution of 1, 8- dihydroxynaphthalene-3, 6- disulphonic acid in about 72% sulfuric acid to make chromotropic acid solution. Add 1 mL of chromotropic acid solution to the sample in test tube. Appearance of brownish pink color indicates the presence of formalin. 0.05% (Sharma et al. 2012)
Ammonium sulfate A. Take 2 ml. milk in a test tube and add 0.5 ml NaOH (2%) 0.5 ml sodium hypochlorite (2%) and 0.5 ml phenol (5%) Heat in boiling water bath for 20 sec A bluish colour forms immediately, which turns deep blue afterward. Pure milk shows salmon pink colour which gradually changes to bluish after 2 hours.   (Kumar et al. 2002)
B. Take 10 ml of milk in a 50 ml stoppered test tube. Add 10 ml of TCA solution. Filter the coagulated milk through Whatman filter paper Grade 42. Take 5 ml of clear filtrate. Add few drops of barium chloride solution. Formation of milky-white precipitates indicates the presence of added sulfates like ammonium sulfate, sodium sulfate, zinc sulfate and magnesium sulfate etc. to milk 0.05% (w/v) (Sharma et al. 2012)
Urea A. Take 5 mL milk sample in a test tube. Add equal volume of 24% TCA to precipitate fat and proteins of milk. Take 1 mL filtrate and add 0.5 mL 2% sodium hypochlorite, 0.5 mL 2% sodium hydroxide and add 0.5 mL 5% phenol solution, then mix. A characteristic blue or bluish green colour develops in presence of added urea whereas pure milk remains colourless.   (Meisel 1995)
B. Take 5 ml milk in a test tube, add 0.2 ml urease (20 mg/ml) Shake well at room temperature and then add 0.1 ml Bromothymol Blue (BTB) solution (0.5%) Appearance of blue colour after 10-15 min. indicates the presence of urea in milk. Normal milk shows faint blue colour due to natural urea present in milk.   (Sharma et al. 1993); (Arvind Singh et al. 2012),
C. Take 5 mL milk sample in a test tube. Add 5 mL p-Dimethyl Amino Benzaldehyde reagent. Appearance of distinct yellow color indicates presence of added urea whereas formation of slight yellow color indicates natural urea in milk. 0.2% (w/v) (Sharma et al. 1993); (Arvind Singh et al. 2012); (Bector et al. 1998); (Kavita, 2000)
Nitrate Take 10 ml sample milk in a beaker. Add 10 ml mercuric chloride solution to it. After mixing, filter through what man No 42 filter paper. Take 1 ml filtrate in a test tube and add 4 ml of diphenyl amine sulphate or diphenylbenzidine reagent. Appearance of blue colour indicates the presence of nitrates. Pure milk sample will not develop any color. 0.2% (Sharma et al. 2011)
Benzoic and salicylic acid Take 5 mL milk sample in a test tube. Upon acidification with sulfuric acid, 0.5% ferric chloride solution is added to it drop by drop. Mix it. Five ml of milk is taken in a test tube and acidified with concentrated sulphuric acid. 0.5% ferric chloride solution is added drop by drop and mixed well. Development of buff colour indicates presence of benzoic acid and violet colour indicates salicylic acid. Appearance of buff color indicates the presence of benzoic acid whereas that of violet color indicates salicylic acid.   (Arvind Singh et al. 2012)
Borax and boric acid Take 5 mL milk sample in a test tube. Add 1 mL conc. HCl to it. A turmeric paper is dipped and it is dried in a watch glass at 100 °C. If the turmeric paper turns red, it indicates the presence of borax or boric acid.   (Arvind Singh et al. 2012)