13
(8)
The %Mass uncertainty term is set in Setup> Meta Settings> Uncert. in Mass
% and the default value is ±0.5%. This would correspond to ±5g for a 1kg
injection, for example. For injections less than 100g, the gram scale with an
uncertainty of 0.01g should be used.
The %time uncertainty term is essentially zero and can be ignored since the
QQ calculates the delta time per sample.
The %CFT uncertainty term is set in Setup>Meta Settings> Uncert. in CF.T %
and the default value is 2.0% corresponding to plasticware calibration using
the 1000μl pipettor and the QuickFlask with a scale to within 5ml (±5g). The
uncertainty using the QuickFlask alone is ±1%. The NaCl standard should be
within 0.5%when made. If the user can attain an uncertainty of less than 2.0%
(glassware could achieve 1.5%) then the user is free to change this setting.
The Area Uncertainty term is more complicated. The Area under the curve is in
mg/l converted using CF.T and the uncertainty in the area is also in mg/l using
CF.T so those terms are on the top and bottom and cancel out. The CF.T un-
certainty term is already included in the equation. The Numerator of the Area
Uncertainty term is:
(9)
Where SE
BGEC.T
is the standard error in the BG EC.T and R is the instrument res-
olution (or the minimum EC.T step in the record, calculated during a measure-
ment). DT is the elapsed time over which the Area has been calculated
3
.
When Meta Settings>Use Regression Line is set to 0, the uncertainty in the
BGECT is calculated from the standard deviation of all BG ECT points, divided by
the square root of the number of points. This applies the central limit theorem:
(10)
Where
s
BGEC.T
is the standard deviation of the Pre- and Post- BG EC.T values. In
the QQ, this is set to 10 for each period by default, so n = 20 total.
When Meta Settings>Use Regresion is set to 1, the SE
BGEC.T
is the standard error
about the regression line. This is the same in the Salt Portal and Field Portal
when the option named “Assume Sloping BG ECT” is checked.”
3
Because of the DT term, the longer a pulse takes to come down the larger the Area Uncertainty term. Therefore there is a “Sweet Spot” of
complete mixing and shorter duration pulse that the SD practitioner is aiming for. When watching the QUncertainty on the QQ during a measurement,
the user may often see the QUn reach a minimum and then begin to increase again because of this increasing DT term.
C H A P T E R 2 : T H E ORY
