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Analytical Method: Calcium in tomato

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. 114815  Spectroquant Calcium Test
Cat.No. 100731  Sulfuric acid 95 - 97 % for analysis
Cat.No. 107209  Hydrogen peroxide 30 % (Perhydrol®) for analysis
Cat.No. 105590  Sodium hydroxide solution 32 %
Cat.No. 116754  Water for analysis

 
Sample preparation:
Homogenize the chopped tomatoes in a blender. Mix 5 g tomatoes with 2.5 ml of sulfuric acid 95 - 97 % for analysis in a 400-ml glass beaker (The solution turns brown to black). Weakly heat the mixture on a hob in the fume cupboard until SO3 begins to develop. Let the solution cool down and carefully add about 1 ml of Perhydrol® to the mixture.
By heating up the sample again gas evolutes and the solution becomes slightly lighter. After the reaction has finished, heat until SO3 begins to develop. If the mixture turns brown or black in color again, cool, add Perhydrol® and reheat. Repeat this procedure as many times as necessary to receive a clear, colorless solution. As a rule, this requires 6 - 8 ml Perhydrol®. At the end completely boil off the superfluous Perhydrol®.
After cooling, transfer the sample into a 50-ml glass beaker by using 20 ml water for analysis and adjust the pH to 6.0 - 7.0 with sodium hydroxide solution 32 % by using a pH-meter.
Transfer the solution to a 50-ml volumetric flask and make up the mark with water for analysis.

Analysis:
Determine the Ca content with the above mentioned test kit. Use the measuring range 5.0 - 80.0 mg/l Ca.

Calculation:
Calcium content in mg/kg = analysis value in mg/l Ca   x 10

 
Notes:
The glassware and the cells must be free from surfactants!
It is thus recommended to leave these items to stand filled with alcoholic hydrochloric acid (25 ml of hydrochloric acid 25 % + 75 ml of 2-propanol) for several hours and subsequently rinse them thoroughly with water for analysis.

 

addition [mg/kg]  ß [mg/kg]  recovery percentage % 

comparison measurement [mg/kg]

 ICP-MS

ICP-OES
0 149 - 136 147
100 246 97    
200 322 87 340  
300 416 89    
400 490 85 550  

 

 

 

addition [mg/kg] ß [mg/kg] recovery percentage %
0 111 -
100 195 84
200 296 93
300 384 91
400 455 86

 

 

 

Materials

     
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