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How to optmize the Detector 2 Signal A in the detector default method is set to sample 250,100, reference 360,100, that is, the average absorbance from 200 – 300 nm minus the average absorbance from 300 – 400 nm. As all analytes show higher absorbance at 200 – 300 nm than at 300 – 400 nm, this signal will show you virtually every compound which can be detected by UV absorbance. Many compounds show absorbance bands in the spectrum. Figure 10 shows the spectrum of anisic acid as an example. To optimize for lowest possible detectable concentrations of anisic acid, set the sample wavelength to the peak of the absorbance band (that is, 252 nm) and the sample bandwidth to the width of the absorbance band (that is, 30 nm). A reference of 360,100 is adequate. Anisic acid does not absorb in this range. If you work with high concentrations, you may get better linearity above 1.5 AU by setting the sample wavelength to a valley in the spectrum, like 225 nm for anisic acid. Anisic acid Absorbance (mAU) sample wavelength 252 nm Reference bandwidth 100 nm 30 nm bandwidth Reference wavelength 360 Wavelength (nm) Figure 10 Optimization of Wavelength Setting 1100 Series DAD and MWD Reference Manual 37
