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Sample Preparation - Poor tin (Sn) recoveries for food analyses

 
I am doing dissolved tin analysis on different kinds of pineapple fruit products ( e.g. solid packs and juice) and I have encountered some errors to my results, specifically to my recoveries. May I ask for any suggestions (as to what you've mentioned in your site) regarding this type of sample? Thank you!
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Poor recoveries for Sn can generally be attributed to either an incomplete sample digestion, or instability of Sn in the digested sample. Could you please provide details as to exactly how the samples are prepared, including any digestion procedures, acids, or reagents used?

 

Thank you for the quick response. 
The sample is ready for analysis as we receive it. Solid packs are well-blended and placed in a closed plastic container while juices are placed either in a can or in a plastic container. As for the procedure of the analysis, it is done through the following steps:

  1. Weighing 10 grams of sample in a porcelain dish
  2. Charring of samples in a hot plate
  3. Ashing charred samples in a muffle furnace set at 500-550 degrees Celsius until completely ashed
  4. Adding 5ml of 6N HCl to ashed sample. (Acidified sample in a porcelain dish is covered with watch glass and allowed to digest for 2 hours)
  5. Transferring digested sample into 50mL Volumetric flask and diluting it to volume with deionized water
  6. Filtering diluted sample through #42 Whatman filter paper
  7. Instrument measurement
 

Thank you for the additional information. It is possible that the poor Sn recoveries are due to the formation of unstable Sn(II) compounds during the digestion (e.g., stannous chloride). We would recommend a sulfated ashing technique where mL quantities of H2SO4 are added after charring and before ashing. If that does not help with Sn recoveries, then H2SO4 can be added before charring (a ‘wet’ ashing technique) with the dropwise addition of H2O2 to promote oxidation to Sn(IV). Be aware that liquid samples will tend to foam during charring so constant attention is advised.

Posted: 09/06/18 03:43:18

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