Analytical Method: Sulfite in Shrimps
Instruments and Reagents
Product No. 173016 Spectroquant® VIS Spectrophotometer Prove 100 or
Product No. 173017 Spectroquant® UV/VIS Spectrophotometer Prove 300 or
Product No. 173018 Spectroquant® UV/VIS Spectrophotometer Prove 600 or
Product No. 109748 Spectroquant® Photometer NOVA 30 or
Product No. 109751 Spectroquant® Photometer NOVA 60 or
Product No. 173632 Spectroquant® Colorimeter Move 100
Product No. 114946 Rectangular cells 10 mm and/or
Product No. 114947 Rectangular cells 20 mm and/or
Product No. 114944 Rectangular cells 50 mm
Product No. 101746 Spectroquant® Sulfite Test
Product No. 109535 MColorpHast™ Universal indicator strips pH 0 - 14
Product No. 137085 Sodium hydroxide solution 0.05 mol/l
Product No. 108418 Titriplex® III
Product 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® Product No. 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 |
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