Analytical Method: Sulfite in shrimps

Instruments and Reagents:

Cat.No. 173016  Spectroquant® VIS Spectrophotometer Prove 100 or

Cat.No. 173017  Spectroquant® UV/VIS Spectrophotometer Prove 300 or

Cat.No. 173018  Spectroquant® UV/VIS Spectrophotometer Prove 600 or

Cat.No. 109748  Spectroquant® Photometer NOVA 30 or

Cat.No. 109751  Spectroquant® Photometer NOVA 60 or

Cat.No. 173632  Spectroquant® Colorimeter Move 100

Cat.No. 114946  Rectangular cells 10 mm and/or

Cat.No. 114947  Rectangular cells 20 mm and/or

Cat.No. 114944  Rectangular cells 50 mm
Cat.No. 101746  Spectroquant® Sulfite Test
Cat.No. 109535  MColorpHastTM Universal indicator strips pH 0 - 14
Cat.No. 137085  Sodium hydroxide solution 0.05 mol/l 
Cat.No. 108418  Titriplex® III
Cat.No. 116754  Water for analysis
 
Reagent 1:

Place about 50 ml 0.05 molar sodium hydroxide solution into a 100-ml Erlenmeyer flask. Subsequently dissolve 0.005 g Titriplex® III in it and make up to the mark with sodium hydroxide solution. Cool this solution with an EDTA concentration of 50 mg/l in the refrigerator or on ice to about 0 - 4°C.

 
Reaction:
In neutral solution, sulfite ions react with 2.2'-dinitro-5.5'-dithiodibenzoic acid (Ellman's reagent) to form an organic thiosulfate. This reaction results in the release of a thiol that is determined photometrically.
 
Measurement range:
1.0 - 60.0 mg/l SO32-
 
Sample preparation:

Homogenize 10 g of ready-to-cook shrimps and 50 ml of cooled sodium hydroxide/EDTA solution in a mixer for about 1 minute. Subsequently transfer the entire sample, with the aid of another 50 ml of sodium hydroxide/EDTA solution and 100 ml of ice-cooled water for analysis, to a 250-ml volumetric flask and stir on a magnetic stirrer for about 20 min. Any foam present should disappear. Subsequently make up to the mark with water for analysis and swirl the flask to homogenize. Then filter through a fluted filter, discarding the first few milliliters.
 
Note: The shrimps must be processed rapidly, as sulfite is quickly oxidized in air. Opened packages have only about ¼ of the original content after 24 hours.
 
Analysis:
The measurement is carried out with the above mentioned test set.
 

 

Calculation:
Measured value [mg/l] x 25 = sulfite content [mg/kg]       (kg and l equalized)
 
Results: Different shrimp samples were tested.

Sample Measured value
[mg/l] 
Spectroquant®
Recovery rate [%]

Shrimp 1 

40.2  -

Shrimp 1 spiked with 2 mg/l sulfite 

42.7 101.2

Shrimp 1 spiked with 4 mg/l sulfite 

44.3 100.2

Shrimp 1 spiked with 6 mg/l sulfite 

46.1 99.8

Shrimp 1 spiked with 8 mg/l sulfite 

48.0 99.6

Shrimp 1 spiked with 10 mg/l sulfite 

49.6 98.8


 

Sample Measured value
[mg/l] 
Spectroquant®
Recovery rate [%]

Shrimp 2 

37.8  -

Shrimp 2 spiked with 2 mg/l sulfite 

39.6 99.5

Shrimp 2 spiked with 4 mg/l sulfite 

40.3 96.4

Shrimp 2 spiked with 6 mg/l sulfite 

41.2 94.1

Shrimp 2 spiked with 8 mg/l sulfite 

45.2 98.7

Shrimp 2 spiked with 10 mg/l sulfite 

48.6 101.7


 

Sample Measured value
[mg/l] 
Spectroquant®
Comparative measurement
value [mg/l]
MColortest® Cat. 111148

Shrimp 3 measurement 1 

41.8 41.3

Shrimp 3 measurement 2 

42.6 40.6

Shrimp 3 measurement 3 

41.7 41.3


 

 

 

Materials

     
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