HPLC for Food Analysis phần 8 ppt

87

Analytical

parameters

Limit of detection and limit

of quantification

Selectivity

The most important parameters for food analysis are:

• limit of detection (LOD) and limit of quantification

(LOQ)

• linearity

• selectivity

• qualitative information

The LOD and LOQ of an analytical system depend on the

noise and drift of the detection equipment. Absolute detec￾tor LOD can be determined by injecting a sample directly

into the detector. It is often expressed as minimum detect￾able level, which is sometimes defined as equal to the noise

level. However, the LOD depends not only on the detector

but may also depend on the oxygen content of the mobile

phase, the injection system, peak broadening on the col￾umn, and temperature differences among system compo￾nents. Taking these factors into account, the LOD is defined

as 2 to 3 times the noise level. The LOQ is defined as 10 to

20 times the noise level. A UV detection system can be used

to measure quantitative amounts down to 500 pg per injec￾tion. The LOD can be as low as 100 pg for food compounds

such as antioxidants if detection wavelengths have been

optimized to match the extinction coefficients of as many

compounds as possible. Fluorescence and electrochemical

detectors operate in the very low picogram range. The LOD

of a mass spectrometer connected to HPLC equipment

depends on the type of interface used. Instruments with

electrospray interfaces can detect down to the picogram

range. Refractive index detectors normally are appropriate

above 500 ng.

We define the selectivity of a detection system as the ability

to select only those compounds of interest in a complex

matrix using specific compound properties. A detector is

selective if it does not respond to coeluting compounds that