Fatty acids detection limits

In situ quantitation The fluorimetric analysis was carried out in long-wavelength UV light (A c = 365 nm An > 560 nm). The detection limit for fatty acids was ca. 100 ng per chromatogram zone. 

Quinones, lipid-soluble substances involved in electron transport, can also be used as biomarkers. Lipski et al. (155) u.sed quinone analyses, physiological tests, and fatty acid profiles to differentiate Gram-negative non-fermentative bacteria isolated from biofilters. Quinone type was found to be an efficient method to group isolates prior to the analysis of results from the physiological tests. The detection of quinones appears to be restricted to the discrimination of isolated colonies and has limited potential to the analysis of mixed populations. 

Carboxylic acids present no exceptional problems in reversed phase analysis, although detectability may be a limitation in the analysis of simple fatty acids. Wine acids, including succinic, acetic, citric, lactic, malic, and tartaric,... 

To perform fed-batch experiments with P. putida a method had to be developed to prevent carbon limitation and to prevent a buildup of the concentration of the fatty acids to inhibitory levels. HPLC methods to measure the concentration of aliphatic substrates and octanoic acid have been reported, but these are not suitable for the detection of long chain fatty acids in a watery phase due to their low solubility. Instead Huijberts et al. [55, 56] developed a method in which discrete pulses of fatty acids were added to fed-batch cultures. Substrate exhaustion was detected by a sudden increase in dissolved oxygen tension and this signal was used to trigger the injection of another fatty acid pulse into the... 

This specification is for butter oil, which is butter with the water removed. The free fatty acid limit is to detect lipolytic rancidity while peroxide value specification is to limit oxidative rancidity. The copper limit arises because copper catalyses the oxidation of fats. The absence of neutralising substances is to prevent a high titration for free fatty acids being covered up by the addition of alkali. 

The irradiation of unsaturated fatty acids in foods predominantly results in the formation of a hydroperoxyl radical and then the formation of a hydroperoxide. The hydroperoxides are generally unstable in foods and break down to form mainly carbonyl compounds, many of which have low odor threshold, and contribute to the rancid notes often detected when fat-rich foods are irradiated [18]. In the absence of air, their formation is limited. 

The intra- and inter-assay variation is determined in tenfold analyses of a pool plasma sample. Table 3.4.2 shows the results of these measurements. The linearity of this method should be assessed for all analytes. Pristanic acid and the C26 0 fatty acid were linear up to 16 pmol/1, phytanic acid to 100 pmol/l and the C22 0 and C24 0 fatty acid to 200 pmol/1. The lower detection limit for all analytes was at a level of less than 0.01 pmol/l, for the lower reporting levels (LOQ), an analysis of a blank solution was taken into account. The blank levels of the analytes phytanic acid, pristanic acid, and fatty acids C22 0, C24 0 and C26 0 were 0.04, 0.01, 0.41, 0.68 and... 

Another sensitive colorimetric procedure is that of Mackenzie et al (1967), which utilizes the dye Rhodamine B to form benzene-soluble complexes with fatty acids. Nakai et al. (1970) developed a rapid, simple method for screening rancid milk based on the foregoing procedure. The test is said to detect rancid milk with an ADV above 1.2. Like the copper or cobalt soap method, the Rhodamine B reagent is also limited to the longer-chain fatty acids. Kason et al (1972) used the method employing Rhodamine 6G of Chakrabarty et al (1969) to investigate... 

AS Treatability and Environmental Concentrations. Studies of AS degradation in the environment or during actual sewage treatment have been limited because specific analytical methods to measure AS were not available until recently. We developed a method that isolated AS from water samples on a strong anion-exchange column. The AS were then hydrolyzed to a fatty acid and analyzed by gas chromatography with flame-ionization detection (GC-FID). The method has a detection limit of 5 xg/L per component (50). 

All of the described procedures use emulsified substrate. Although the p-nitrophenyl laurate assay cocktail is stable for 3 days at 4°C, the emulsified olive oil substrates (or other triacylglycerol-based substrate systems) should be made fresh daily and rehomogenized periodically and when separation is visually evident. Use of day-old emulsion substrate will yield increased blank values for titratable acidity, and this effectively compromises the limit of detection of activity. Emulsified substrates should be in liquid form at common assay conditions (20° to 50°C), and partially solidified substrates (those rich in long-chain saturated fatty acids) will cause interfacial irregularities and confound the assessment of lipases in ways that cannot be accounted for. 

Cooper and Anders (20) reported the HPLC analysis of unsaturated C l8 and C20 fatty acids. Since the methylene-interrupted polyunsaturated acids show no specific UV absorption, the 2-naphtacylesters were prepared for UV detection at 254 nm [the column was a 3-ft X 0.07-in.-lD stainless steel tube packed withCORASIL-Ci8, methanol/water(85 15) served as the eluent, and a flow rate of 12 ml/h was obtained at a pressure of 300 psig]. The lower detection limit was 4-90 ng of ester. 

Method 2 (p-nitrobenzyl ester). To the residue are added 3 ml of ethanol and a 20-fold excess of 1 -p-nitrobenzyl-3-p-tolyltriazene [43]. The contents are mixed, loosely covered and heated at a gentle reflux for 1 h. The solution is cooled and an aliquot portion is subjected to chromatography. The derivatives are non-polar compared to the reagent and the parent fatty acid, and may be separated on silica gel with non-polar solvents such as hexane-diethyl ether. HPLC should also be useful with a system similar to that used for the benzyl esters. The limits of detection of the p-nitrobenzyl derivatives should be significantly lower than those of the benzyl esters. 

The lipid organization in equimolar mixtures of cholesterol, synthetic CER, and free fatty acids closely resembles that in stratum corneum, as both LPP (12.2 nm) and SPP (5.4 nm) are present, the lateral packing of the lipids is orthorhombic, a minor fraction of cholesterol phase separates into crystalline domains, and no additional phases can be detected. Interestingly, free fatty acids are required for proper lipid organization, as only in their presence a dominant formation of the LPP could be detected. This might be related to the limited acyl chain length distribution present in these CER mixtures. 

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