manual of methods for determining micronutrients in fortified foods
manual of methods for determining micronutrients in fortified foods
manual of methods for determining micronutrients in fortified foods
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IX. Calculations<br />
1. Calculate the average <strong>of</strong> the %T <strong>for</strong> each standard concentration.<br />
2. Plot “y” (the average %T)vrs. “x” (volume <strong>of</strong> standard solution-1 ng/mL <strong>in</strong> each tube (mL)). A<br />
curve similar to the one below will be obta<strong>in</strong>ed, which is practically a parabolic curve. Calculate the<br />
second-degree equation <strong>for</strong> the curve which will be:<br />
y = ax 2 + bx + c<br />
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The response curves from different assays will not be necessarily co<strong>in</strong>cident.<br />
3. Determ<strong>in</strong>e the “equivalent volume <strong>of</strong> folic acid standard <strong>in</strong> each tube” <strong>of</strong> sample assay solution by<br />
<strong>in</strong>terpolat<strong>in</strong>g from standard curve or solve the second degree equation <strong>for</strong> x, us<strong>in</strong>g the follow<strong>in</strong>g <strong>for</strong>mula:<br />
x = −b ± b2 − 4a(c −%T)<br />
2a<br />
Do not use the values <strong>for</strong> 0.5 mL and 5 mL.<br />
4. Divide each value obta<strong>in</strong>ed by the quantity <strong>in</strong> mL sample extract added to each tube. That is 1, 2, 3<br />
€<br />
or 4 mL. The value obta<strong>in</strong>ed will be “the equivalent mL standard/mL”.<br />
5. Sum all the values obta<strong>in</strong>ed <strong>for</strong> one sample and then divide by the total number <strong>of</strong> tubes used (8).<br />
This will be the first average.<br />
6. Calculate the range: average (obta<strong>in</strong>ed <strong>in</strong> the previous step) ± 10 %.<br />
7. Calculate a new average after discard<strong>in</strong>g the %T values that are not with<strong>in</strong> the calculated range. Do<br />
not discard more than 2/3 values, that is more than 3 values. If more than 3 values are discarded,<br />
then the assay is <strong>in</strong>valid and it must be repeated.<br />
8. Calculate the concentration <strong>of</strong> folic acid with the follow<strong>in</strong>g equation:<br />
Folic acid(mg/kg) =<br />
X<br />
1000 x V 3<br />
x V 1<br />
V 2<br />
w s<br />
x C std<br />
€<br />
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