Distillation tearing method

A correlation may be established between the concentration of oxidized lipids and the TEARS value, expressed as MDA equivalents, in uM units. Correction is due in some cases for the interference by dyes or other factors. For example, the presence of anthocyanins in red cabbage leaves or turbiditjf causes overestimation of lipid hydroperoxides in plant tissue by the TEARS method. TEARS was used to assert the level of endogenous peroxides in hypo- and hyperthyroidism, both conditions being characterized by low lipid and lipoprotein plasma levels and enhanced oxidative metabolism . In a procedure for determination of TEARS in edible oils, the sample is placed in a centrifuge at 12000 g before measuring at 532 nm (e = 1.56 x 10 M cm ) . A usual procedure for determination of TEARS in certain complex matrices involves steam distillation of the aldehydes responsible for the value, instead of extraction. In nitrite-cured meats, excess nitrite may cause nitrosation of MDA, thus interfering with distillation. To avoid this interference sulfanilamide is added, which is converted to a diazonium salt and... 

Simultaneous Convergence Methods One drawback of some tearing methods is their relatively limited range of application. For example, the BP methods are more successful for distillation, and the SR-type methods are considered better for mixtures that exhibit a wide range of (pure-component) boiling points (see, however, our remarks above on modified BP and SR methods). Other possible drawbacks (at least in some cases) include the number of times physical properties must be evaluated (several times per outer loop iteration) if temperature- and composition-dependent physical properties are used. It is the physical properties calculations that generally dominate the computational cost of chemical process simulation problems. Other problems can arise if any of the iteration loops are hard to converge. 

The TBA test can be performed by various procedures, among which four major types have frequently been employed. These include test on the whole sample, test on an aqueous or acid extract of sample, test on a steam distillate, and test on extracted lipid from a sample (45). The test on a steam distillate (distillation method) is the most commonly used method for determining TBA value. Tarladgis et al. (46) found that the distillation of an acidihed sample was essential to liberate MA from precursor or bound forms, to produce maximal color development and, especially, to separate TEARS from the food matrix (44). Although the distillation method is the most popular TBA method, it is generally considered less accurate and reproducible than the method using food extracts (15). However, trends obtained in comparative studies always provide useful information that correspond with other measurements. Comparison of different TBA test procedures has been made by Hoyland et al. (46), Shahidi et al. (47), Pikul et al. (48), and Wang et al. (49). 

This appendix follows the instructions in the appendices to Chapters 2 and 6. Although the Aspen Plus simulator is referred to, other process simulators can be used. The three problems in this appendix all employ recycle streams in distillation columns. The procedures shown here to obtain convergence are all forms of stream tearing. Since these are not the only methods that will work, you are encouraged to experiment with other approaches. If problems persist while running the simulator, see Appendix A Aspen Plus Separations Troubleshooting Guide, at the end of the book. 

The temperature during the distillation may be monitored either with a thermometer or a stainless steel temperature probe. If a stainless steel probe is used, it must be used in conjunction with either a digital thermometer or one of the Vernier devices (see Technique 13, Section 13.4 and Technique 14, Figure 14.12). Your instructor will provide instructions about the method that you will use. Insert the thermometer (or probe) so that the bulb is level with or slightly below the cap connecting the Hickman head to the air condenser. Also use a thermometer to monitor the temperature of the heat source. Cover the top of the sand bath (if used) with a square of aluminum foil with a tear from the center of one edge to the middle. 

The theory of trajectory tear-off was extended to the section located between the cross-section of entrainer input and that of the main-feeding input in columns of sharp extractive distillation (Petlyuk Danilov, 1999), which included it into the general method of presynthesis. 

---