UV/fluorescence detection

A second pyroreactor has been added to the system as back-up, to minimize the system down-time due to furnace heating element failure. The system has been expanded to also perform sulphur determination by oxidative combustion with UV fluorescence detection. The current sample load for the system is greater than 12 000 samples per year with a maximum capacity of the system, operating under optimum conditions, of greater than 40 000 samples per year. 

Air analysis may be performed by U.S.EPA Method TO 13 (U.S.EPA 1988), which is quite similar to the above method. PAH-bound particles and vapors (many compounds may partially volatilize after collection) may be trapped on a filter and adsorbent (XAD-2, Tenax, or polyurethane foam), and then desorbed with a solvent. The solvent extract is then concentrated and analyzed by HPLC (UV/Fluorescence detection), GC-FID, or GC/MS (preferably in SIM mode). Because of very low level of detection required for many carcinogenic PAHs, including benzo(a)pyrene, the method suggests the sampling of a very high volume of air (more than 300,000 L). 

The determination of NPEO in wastewaters is usually aeeomplished using HPLC coupled to UV-fluorescence detection 2 or by HRGC-MS. While the former allows the detection of the series up to 20... 

Polar phenols can be analysed by HPLC with UV-absorption (at about 280nm) and/or UV-fluorescence detection (excitation at 230nm emission at 590 nm) with the same type of C18-reversed phase columns that are used for the... 

EDCs in the environment are often analyzed using GC or LC based instrumental techniques. GC coupled with an electron capture detector (BCD), a nitrogen-phosphorus detector (NPD), or mass spectrometry (MS) has been the preferred method due to its excellent sensitivity and separation capability on a capillary column. High performance liquid chromatography (HPLC) with various detectors such as ultraviolet detection (UV), fluorescence detection (FLD), MS, and more recently tandem MS (MS/MS) has also been used for analysis of some EDCs, especially for the polar compounds. Analytical techniques for each class of EDCs will be discussed in the following section. 

Rapid Determination of Sulfur in Liquid Hydrocarbons for At-Line Process Applications Using Combustion/Oxidation and UV-Fluorescence Detection... 

KEYWORDS rapid sulfur analysis, gasoline analysis, diesel analysis, ultra low sulfim in diesel, combustion/oxidation UV-fluorescence detection, fast on-line/at process sulfur determination... 

In a second on-line application paper, Tarkanic and Crnko (AntekIPAC) describe an online instrument based on ASTM Test Method D 5453, UV-Fluorescence Detection. The latter is a widely used method in the oil industry for low and ultra-low levels of sulfur. The online instrument appears to be very stable and fast (< 1 min per analysis) over extensive periods of field operations. 

UV or fluorescence can also be integrated in a LC-MS setup. In such cases the UV or fluorescence detector needs to be placed before the MS detector or the flow needs to be split one line for MS detection and one line for UV/ fluorescence detection. 

Microchip electrophoresis with label-free detection using deep UV fluorescence detection with excitation at 266 nm was applied by Ohla et al. (2011) for the determination of biologically active compounds (dopamine, serotonin, tryptophan, tyrosine, and the isoquinoline alkaloid salsolinol) in bananas, in less than 1 min. For comparison purposes, microchip electrophoresis was also coupled with MS detection using microfluidic... 

Note that in liquid phase chromatography there are no detectors that are both sensitive and universal, that is, which respond linearly to solute concentration regardless of its chemical nature. In fact, the refractometer detects all solutes but it is not very sensitive its response depends evidently on the difference in refractive indices between solvent and solute whereas absorption and UV fluorescence methods respond only to aromatics, an advantage in numerous applications. Unfortunately, their coefficient of response (in ultraviolet, absorptivity is the term used) is highly variable among individual components. 

More specific methods involve chromatographic separation of the retinoids and carotenoids followed by an appropriate detection method. This subject has been reviewed (57). Typically, hplc techniques are used and are coupled with detection by uv. For the retinoids, fluorescent detection is possible and picogram quantities of retinol in plasma have been measured (58—62). These techniques are particularly powerful for the separation of isomers. Owing to the thermal lability of these compounds, gc methods have also been used but to a lesser extent. Recently, the utiUty of cool-on-column injection methods for these materials has been demonstrated (63). 

Numerous high pressure Hquid chromatographic techniques have been reported for specific sample forms vegetable oHs (55,56), animal feeds (57,58), seta (59,60), plasma (61,62), foods (63,64), and tissues (63). Some of the methods requite a saponification step to remove fats, to release tocopherols from ceHs, and/or to free tocopherols from their esters. AH requite an extraction step to remove the tocopherols from the sample matrix. The methods include both normal and reverse-phase hplc with either uv absorbance or fluorescence detection. AppHcation of supercritical fluid (qv) chromatography has been reported for analysis of tocopherols in marine oHs (65). 

After the dipped or sprayed chromatogram has been dried in a stream of cold air long-wave UV light (2 = 365 nm) reveals fluorescent yellow zones (flavonoids). Sterigmatocystine, which can be detected without derivatization on account of its red intrinsic fluorescence (detection limit 0.5 pg), also fluoresces pale yellow after being heated to 80°C [9] or 100°C [13] for 10 min on the other hand, citrinine, zearalenone and vomitoxin fluoresce blue. 

Electrodriven separation techniques are destined to be included in many future multidimensional systems, as CE is increasingly accepted in the analytical laboratory. The combination of LC and CE should become easier as vendors work towards providing enhanced microscale pumps, injectors, and detectors (18). Detection is often a problem in capillary techniques due to the short path length that is inherent in the capillary. The work by Jorgenson s group mainly involved fluorescence detection to overcome this limit in the sensitivity of detection, although UV-VIS would be less restrictive in the types of analytes detected. Increasingly sensitive detectors of many types will make the use of all kinds of capillary electrophoretic techniques more popular. 

EC, electrochemical detection Flu, fluorescence detection MS, mass specu-omeu-ic detection pre-Flu, fluorescence detection after pre-column derivatization post-Flu, fluorescence detection after post-column derivatization UV, UV absorbance detection. 

The PSP toxins represent a real challenge to the analytical chemist interested in developing a method for their detection. There are a great variety of closely related toxin structures (Figure 1) and the need exists to determine the level of each individually. They are totally non-volatile and lack any useful UV absorption. These characteristics coupled with the very low levels found in most samples (sub-ppm) eliminates most traditional chromatographic techniques such as GC and HPLC with UVA S detection. However, by the conversion of the toxins to fluorescent derivatives (J), the problem of detection of the toxins is solved. It has been found that the fluorescent technique is highly sensitive and specific for PSP toxins and many of the current analytical methods for the toxins utilize fluorescent detection. With the toxin detection problem solved, the development of a useful HPLC method was possible and somewhat straightforward. 

HPLC with various detection methods (UV, fluorescence)... 

Alternatively, LC is used for the separation and quantification of PAHs using both UV and fluorescence detection. The analytes are identified based on their relative retention times and UV and/or fluorescence emission spectra. For UV detection an efficient cleanup is a prerequisite since this detection method is not very selective (almost universal for PAHs), and hence it also responds to many coeluting compounds. Due to the high specificity of fluorescence detection for most PAHs, this LC detection method is less susceptible to potential interferences. As in the case of GC the apphcation of internal standard(s) is mandatory since solvents have to be evaporated during the cleanup, which may result in partial losses of some of the more volatile analytes. 

A survey of the literature with a key phrase tissue residue analysis yielded a distribution of separation and detection techniques as outlined in Table 2. LC with either UV or fluorescence detection was the most common separation and detection technique, representing 61% of the citations. The results are an indication of the maturity of LC as a common, well-understood technique. The second most commonly used technique cited in the literature (13%) was GC with either a mass-selective or electron capture detector. GC is also a mature technology and a good choice owing to the... 

At this point, the anaiyte may not be amenabie to UV, FL, or EC detection. In this case, the best course of action may be to choose LC/MS (see Section 4.2). However, one other option is to use a pre- " or post-coiumn derivatization step to increase the detectabiiity of the anaiyte with respect to FL or UV. Fluorescent or UV labels are available for carboxylic acids," amines, phenols, and thiols. The decision to use pre- or post-column derivatization is predicated upon the functionality of the analyte available for derivatization and the rate and extent of the reaction between each derivatizing agent and the analyte. 

The increased use of IV-methyl carbamate insecticides in agriculture demands the development of selective and sensitive analytical procedures to determine trace level residues of these compounds in crops and other food products. HPLC is the technique most widely used to circumvent heat sensitivity of these pesticides. However, HPLC with UV detection lacks the selectivity and sensitivity needed for their analysis. In the late 1970s and early 1980s, HPLC using post-column hydrolysis and derivatization was developed and refined with fluorescence detection to overcome these problems. The technique relies on the post-column hydrolysis of the carbamate moiety to methylamine with subsequent derivatization to a fluorescent isoindole product. This technique is currently the most widely used HPLC method for the determination of carbamates in water" and in fruits and vegetables." " ... 

A variety of formats and options for different types of applications are possible in CE, such as micellar electrokinetic chromatography (MEKC), isotachophoresis (ITP), and capillary gel electrophoresis (CGE). The main applications for CE concern biochemical applications, but CE can also be useful in pesticide methods. The main problem with CE for residue analysis of small molecules has been the low sensitivity of detection in the narrow capillary used in the separation. With the development of extended detection pathlengths and special optics, absorbance detection can give reasonably low detection limits in clean samples. However, complex samples can be very difficult to analyze using capillary electrophoresis/ultraviolet detection (CE/UV). CE with laser-induced fluorescence detection can provide an extraordinarily low LOQ, but the analytes must be fluorescent with excitation peaks at common laser wavelengths for this approach to work. Derivatization of the analytes with appropriate fluorescent labels may be possible, as is done in biochemical applications, but pesticide analysis has not been such an important application to utilize such an approach. 

The most common final separation techniques used for agrochemicals are GC and LC. A variety of detection methods are used for GC such as electron capture detection (BCD), nitrogen-phosphorus detection (NPD), flame photometric detection (FPD) and mass spectrometry (MS). For LC, typical detection methods are ultraviolet (UV) detection, fluorescence detection or, increasingly, different types of MS. The excellent selectivity and sensitivity of LC/MS/MS instruments results in simplified analytical methodology (e.g., less cleanup, smaller sample weight and smaller aliquots of the extract). As a result, this state-of-the-art technique is becoming the detection method of choice in many residue analytical laboratories. 

HPLC and LC/MS. HPLC methodology coupled with ultraviolet (UV), fluorescence (FL), photodiode-array (PDA) and/or a mass spectrometry (MS) detection has been developed. In general, neonicotinoids can be determined by HPLC/UV. Typical HPLC operating conditions are given in Table 2. 

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