I am using flame atomic absorption spectroscopy (F-AAS) to determine metals in alcoholic beverages. The samples are processed with the mixture of HNO3 65% and H2O2 30% after being dealcoholized. While the other metals' results are acceptable, calcium show a worse result. The recovery of the spiked sample is bad, only 20% (sometimes it is unsignificant). Please give me some reasons to explain this phenomenon.
Thank you for all the responses.
Hi!
How much alcohol can be in the samples? What is the method used to remove alcohol from the sample? Is only nitric acid present in the measured solutions, i.e. calibration solutions and sample solutions, and in the same concentration, and what is this concentration? What calcium concentrations are measured in solutions? When preparing measured solutions and samples with control addition, do you use the same calcium solution as the starting solution? What concentrations of sulfates may be present in sample solutions? Can phosphates and silicates also be present in sample solutions, at concentrations of many mg/L? Do you use any additional substances, e.g. lanthanum, when measuring calcium using the FAAS technique? Can you use a C2H2+N2O flame instead of C2H2+air to measure calcium? Is the control addition of calcium to the sample or to the sample solution not less than the initial amount of calcium in the sample (in the test volume) or in the sample solution?
ZJ
The poor recovery of calcium in your flame atomic absorption spectroscopy (F-AAS) analysis of alcoholic beverages after processing with a mixture of HNO3 65% and H2O2 30% could be attributed to several factors:
1-Interference from Matrix Effects: These matrix effects can lead to reduced recovery rates for calcium.
2-Chemical Reactions: Calcium can form complexes with other components present in the sample or react with the acids used during sample preparation, leading to incomplete recovery during the analysis process
3-Incomplete Sample Preparation
4-Instrumental Factors
To improve the recovery of calcium in your F-AAS analysis of alcoholic beverages, it is recommended to:
-Optimize the sample preparation method to ensure complete digestion and extraction of calcium.
-Consider using different acid mixtures or adjusting the concentrations to minimize interference and enhance calcium recovery.
-Verify the calibration and performance of the F-AAS instrument specifically for calcium analysis to ensure accurate results
What sort of calcium concentrations are you trying to measure? What sort of beverages? Fruit based (wines/ciders), grains (beers), or distilled (spirits)? These all have widely differing typical Ca concentrations, as well as widely differing alcohol concentrations, which will affect the required sensitivity for calcium detection.
According to Uždavinienė and Tautkus 2007:Article Determination of calcium in mineral waters by flame atomic a...
, their linear range was 0.2-8ug/ml or 0.2 to 8ppm which is not a particularly wide range for beverages. Their lower limit of detection was 0.05ppm.If you are spiking extremely low concentrations perhaps you are unable to recover the full amount because you are in the non-linear range.
Is it possible you are losing the Ca during the dealcoholisation step? How exactly are you performing this?
*Did you mean "unsignificant" or "not measurable"?
You say "The samples are processed with the mixture of HNO3 65% and H2O2 30% after being dealcoholized." How was the sample dealcoholized, since you are evidently not using the HNO3/H2O2 oxidation step to get rid of the alcohol? What do you expect to get rid of in this oxidation step?
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