Optical absorbance detection limits improving

Now, one must consider how to Improve optical absorbance detection limits, that Is - how to reduce noise. One strategy Is to Increase I through use of a fixed wavelength detector based on a discrete line lamp and an Isolation filter to select the UV line of Interest generated by the lamp (typically Zn, Cd or Hg lamps having major lines at 214 nm, 229 nm, 254 nm, respectively). 

Improving the concentration detection limit is the goal of much analytical research and development. While miniaturization leading to lower mass detection limits is by no means trivial, it is at least conceptually obvious how to proceed. On the other hand, approaches to better concentration detection limits often require considerable creativity. In some cases, better detectors offer lower detection limits. Because properties of molecules differ, it is difficult to be globally accurate in a statement of relative merits of detectors, but experience shows that the inherent detection limits for compounds that are well suited for each detector are fluorescence < electrospray ionization mass spectrometry (ESI-MS) electrochemistry < optical absorbance. It is worth noting that low detection limit is correlated with the selectivity of the detector. In fact, in real samples of sufficient complexity (are there any real samples that are not complex ), Nagels has shown that detection limits correlate... 

The range of analytes accessible to SP(M)E/CE is wide. Drugs, pollutants (and very hydrophobic ones like polyaromatic hydrocarbon, PAHs), proteins/peptides have all been determined using the methods described herein. There does not seem to be any sacrifice in separation modes, either. CE, capillary isoelectric focusing, MEKC, nonaqueous CE can all function with some form of SP(M)E. Methods of detection are similarly broad, encompassing at least the three most common optical absorbance, laser-induced fluorescence, and MS. It is perhaps foolish to attempt to generalize, but it does seem that an improvement in concentration detection limits of about 100-fold can be realized through SPME in conjunction with CE. 

With optical detection, the overall time resolution is limited by the different velocities of fast electrons and photons in condensed media this results in loss of synchronization as the two beams pass through the sample cell. This desynchronization is approximately 10 ps cm in water [145], so the optical path length has to be reduced proportionally to achieve the improved time resolution provided by subpicosecond pulses. There is thus a compromise between having short time resolution (short optical path) and high absorbance signals (long optical path). 

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