linearity problem

[tinsang]

Hello guys,
I need a help regarding validation-linearity. I have to validate the assay of alpha tocopherol and phytosterol. Y intercept of Tocopherol is very bad: >6%, but the result of phytosterol is good (2,4%).
Do you have any idea?
Here is the method details below:
oven:300°c, He - Injector:320°c - detector (FID): 320°c- Splitflow: 52ml/min.
sampling parameters:
FillStrokes = 3
AirVolume = 2.0 [µl]
FillVolume = 1.0 [µl]
DownSpeed = 20 [mm/s]
SampleDepth = Bottom
DrawSpeed = NotViscousDefault
PullupDelay = 3.0 [s]
DelayAfterBubbleElimination = 2.0 [s]
BubbleEliminationSpeed = 80.0 [µl/s]
DelayBetweenStrokes = 3.0 [s]
Linearity Tocopherol:
Conc.(mg/ml) % Average area RF
1,6556 68,98 0,251924 0,152165
1,9009 79,2 0,295744 0,155581
2,1372 89,05 0,332373 0,155518
2,3743 98,93 0,367273 0,154687
2,5806 107,53 0,406002 0,157329
2,8384 118,27 0,450041 0,158554
3,0794 128,31 0,489726 0,159033
corr. coefficient: 1,53 %
corr. coefficient: 0,99965794; intercept: -0,02297248; x variable: 0,00398958 and the y intercept of 100%: -6,2%(Spez: <+-3%).
Thanks.

[Cariochemist]

Hi tinsang.

I´ve plotted your curve and saw the results you´d obtained.
Why don´t you try injecting a lower point (more diluted) ?
Are you running in isothermal mode (300ºC)? What is the column you´re using?
You may have problems with sensitivity too, or leaks. Try cleaning your FID, give a look at the H2 / Air ratio and look for leaks from injector to FID.
Give more details about it.

Best rgd;