Milliabsorbance units

A second source of error may be in the detector. Detector linearity is an idealization useful over a certain concentration range. While UV detectors are usually linear from a few milliabsorbance units (MAU) to 1 or 2 absorbance units (AU), permitting quantitation in the parts per thousand level, many detectors are linear over only one or two decades of operation. One approach in extending the effective linear range of a detector is high-low injection.58 In this approach, an accurate dilution of a stock sample solution is prepared. The area of the major peak is estimated with the dilution, and the area of the minor peak is estimated with the concentrated stock. This method, of course, relies on linear recovery from the column. Another detector-related source of error that is a particular source of frustration in communicating... 

I (1) Magnetic spin of a nucleus, angular MAU Weight average molecular weight Milliabsorbance unit... 

FIGURE 1.43 Representative HPLC chromatograms of vitamin D metabolites.162 (A) late-eluting peaks (B) calibrator in extracted serum (C) sample from patient with low 25(OH)D3 treated with vitamin D2 (D) sample from patient with high concentrations of 25(OH)D3. Int. Std. = internal standard mAU = milliabsorbance units. (Reproduced with permission from the American Association for Clinical Chemistry.)... 

If the peak has a Gaussian shape, the maximum absorption for the peak would be co 1.5 times the mean absorption, i.e. in this case 0.05 or 50 milliabsorbance units (mAU). 

Finally, however, it is the advantages (3) and (4) which really have a marked effect on NIR applications. The wavelength precision and reproducibility achievable with a good FTIR analyser design translates into long-term spectroscopic stability both within one analyser and across multiple analysers, so that measurement errors between analysers are in the region of a single milliabsorbance unit. For the untroubled development of NIR calibration models, and their maintainability over time, this of itself is critically important. 

Fig. 1.16. Scparaiion of theobromine (/). theophylline (2) and caffeine (.t) in aquet>us-organic ((A) methanol-water. % 70) and micellar ((B) 0.02 mol/l CTAB in wa(er) mobile pha.ses. Column Sila,sorb SPH Cs. 7.5 im (300 x 3.6 mm i d.) (low rale I ml/min. detection UV, 254 nm. temperature 25 C. Deteelor response in milliabsorbance units.

Copper and Lead. Using the conditions described above, copper and lead determinations were made on 1-1. distilled water solutions spiked with a known quantity of copper and lead. The results of these analyses are shown in Figure 2. Both copper and lead give linear standard curves. For copper the recovery is 97%, and the standard error is 0.5 milli-absorbance units. For lead the recovery is 95%, and the standard error is 0.4 milliabsorbance units. Both copper and lead are recovered reproducibly with high yields. 

Fig. 15.12. I. Representative curve for theophylline using graph paper and A = 216 milliabsorbance units provided by Syva Co.. With the ABA-100 analyzer some of the calibrator points are above the projected straight line. II. A saturation curve for theophylline with the EMIT assay, using the ABA-100 in the normal kinetic mode, showed that the A is significantly higher. III. The data shown in II can be fitted to a Hill equation, using the computer program of Atkins (1973), giving A = 514, //i, = 300 /ig/ml, and n = 0.56. The various instrumental adaptations will result in different values of A, Hn2, and . From Dietzler et al., 1980 courtesy Dr. D. N. Dietzler and Clinica Chimica Acta.

Figure 5.8 Simplified spectrochromatogram for an incompletely resolved peak in HPLC with diode array detection. Absorbance is given in milliabsorbance units.

Table 5.3 Absorbances in milliabsorbance units for the spectrochro-matogram in Figure 5S.

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