UV detection cell

Automatic detection of separated metal ions began at least as early as 1971 when iron (III) was eluted by hydrochloric acid from a column and detected by a UV detection cell [1]. Seymour and Fritz described a Z-type flow-through cell for UV detection at 270 nm in 1973 [2]. 

Depending on the sample and/or the matrix, dirt can cover the surface of a UV detection cell. Consequences are ... 

The dirt layer increases the formerly smooth surface area. The UV detection cell becomes an air collector and small air bubbles, possibly present in the mobile phase, are restrained and grow to a larger air bubble, resulting in spikes, noise and baseline drift and jumps. 

In summary, dirt in the UV detection cell causes inferior peak-to-noise ratio, spikes and baseline problems. 

A dirty UV detection cell can be cleaned by direct injection of... 

Avoiding mistakes is certainly easier on your nerves than fixing them. If the above-described problems are persistent, you should take a look at your sample preparation and the mobile phase components and solvents used. Unnecessary down time can also be avoided if the UV detection cell is cleaned on a regular basis, which does not take much time. 

S/N for a flow cell of only 50 nL volume. The main drawback was rather wide NMR linewidths. Behnke etal. demonstrated capillary LC/NMR in 1996 [138], using flow cells of 50 nL and 900nL and a standard saddle coil, and achieved sensitivities approximately 10 times greater than conventional LC/NMR. The approach, however, did not incorporate a UV detection cell so that stopped-flow NMR measurements had to be nuule by reference to on-flow NMR measurements. 

Foret, R, Demi, M., Kahle, V., and Bocek, R, Onhne fiber optic UV detection cell and conductivity cell for capillary zone electrophoresis. Electrophoresis, 1, 430,1986. 

NMR flow cells have so far had much larger volumes than, for example, UV detection cells because of the lower sensitivity of NMR. The effects that large-volume NMR cells have on chromatographic peak dispersion have been investigated using a modified fluorescence detector. The selection of the detection volume of an NMR flow cell is a compromise... 

Figure 6.13 Flow restrictors of different design A, linear B, tapered C, integral and D, frit. On the right side is shown a modified high pressure cell for UV detection using open tubular columns.

The detection of the migrating sample boundary in CE can be accomplished by UV, fluorescent, electrochemical, radiochemical, conductivity, and mass spectrometry (MS) means. The use of high-sensitivity detection systems is always a key issue in CE applications. The sensitivity of HPCE detectors may be at least 2 to 3 orders of magnitude better than that of HPLC detectors. Since the detection cell volume is very small, the concentration sensitivity... 

FTIR in multiply hyphenated systems may be either off-line (with on-line collection of peaks) [666,667] or directly on-line [668,669]. Off-line techniques may be essential for minor components in a mixture, where long analysis times are required for FT-based techniques (NMR, IR), or where careful optimisation of the response is needed. In an early study a prototype configuration comprised SEC, a triple quadrupole mass spectrometer, off-line evaporative FTIR with splitting after UV detection see Scheme 7.12c [667]. Off-line IR spectroscopy (LC Transform ) provides good-quality spectra with no interferences from the mobile phase and the potential for very high sensitivity. Advanced approaches consist of an HPLC system incorporating a UV diode array, FTIR (using an ATR flow-cell to obtain on-flow IR spectra), NMR and ToF-MS. 

The same considerations will apply to other nonspecific methods of detection, such as fluorescence or UV absorbance determinations. Particularly with these methods, it must be appreciated that many of the cells used to form mono-layers secrete a variety of products such as lipids and proteins into both the donor and receiver compartments. These substances can result in a variable background in solutions and may interfere with solute quantitation. Even if a chromatographic method is used with fluorescence or UV detection, these products can still interfere with the separation unless specifically accounted for. 

Polycrystalline GaN UV detectors have been realized with 15% quantum efficiency [4], This is about 1 /4 of the quantum efficiency obtained by crystalline devices. Available at a fixed price, however, their increased detection range may well compensate their lack in sensitivity. Furthermore, new semiconductor materials with a matching band gap appear as promising candidates for UV detection if the presumption of the crystallinity is given up. Titanium dioxide, zinc sulfide and zinc oxide have to be mentioned. The opto-electronic properties and also low-cost production processes for these compound semiconductors have already been investigated to some extent for solar cell applications [5]. 

Some, uPLC systems are equipped with UV absorbance detection, and other systems allow for both UV absorbance and fluorescence detection. Fluorescence detection increases the sensitivity and selectivity of certain applications and is the method of choice in many separation-based assays. The liquid (mobile phase + sample) leaving the individual flow cells designated for UV detection is transferred through capillaries to a bank of 24 flow cells designated for fluorescence detection. 

CE is based on the use of narrow-bore capillaries with internal diameters typically betwen 20 and 150 pm. Because most commercial instruments equipped with ultraviolet/visible (UV-Vis) absorption detectors use a segment of the same capillary as the detection cell, the path length in CE is much less compared to those in HPLC or spectrometry. Therefore, the most commonly used CE detectors... 

Infrared detectors are similar in construction to those used in UV detection. The main difference is that the sample cell windows are constructed of sodium chloride, potassium bromide, or calcium fluoride. A limitation of this type of detector is caused by the low transparency of many useful solvents (Skoog et al., 1998). Recent changes to interface systems that use spraying to induce rapid evaporation of the solvent provide good sensitivity and enhanced spectral quality (LaCourse, 2000). 

In contrast with UV methods where the linear range is approximately 1-2 orders of magnitude at best, the HPLC method with UV detection typically has a linear range of 3-4 orders of magnitude due to the narrow path length of the detector flow cell. For example, a simple... 

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