Polychlorinated biphenyls evaporation

The sample is extracted with a mixture of hexane, acetone and water. After separation, the hexane phase is reduced in volume and divided into two aliquots, one of which is first shaken with 7% fuming sulphuric acid to remove lipids, and then with cyanide to eliminate interference by elemental sulphur. The other aliquot is evaporated to dryness and heated with ethanolic potassium hydroxide. The two aliquots are injected into a gas chromatograph fitted with a glass capillary column and an electron capture detector. Hexabromobenzene is used as an internal standard. Polychlorinated biphenyls are determined quantitatively by comparing the peaks of the sample with those of Clophen A... 

Such analytical measurements are necessary to establish concentrations for most agents in the environment. How much benzene is present in the air at gasoline stations as a result of its evaporation from gasoline What is the concentration of arsenic in water running off the surface of a hazardous waste site where unknown amounts of arsenic were buried over many years What is the polychlorinated biphenyl (PCB) concentration in fish swimming in waters next to a hazardous waste site known to contain this substance How much aflatoxin is in a batch of peanut butter The most reliable answers to these questions are those resulting from chemical analysis. 

GC-MS can be used to analyze organochlorine pesticides, for example, a-, [3-, y-HCH, HCB, and polychlorinated biphenyls (PCB). The components are quantified by using an internal standard. Furthermore, a calibration is performed with a standard mixture containing known concentrations of the components to be measured and one or more components not contained in the sample (internal standards). The calibration is followed by injection of the sample containing known amounts of internal standards. Quantification is relative to the internal standard. In this way, the sample extract volume will not be included in the calculations, and it is not necessary to accurately determine the final sample volume after evaporation of the injection volume. The GC-MS instrument should be calibrated every day. The sensitivity of the mass spectrometer can, for instance, be controlled daily by determining the signal-to-noise ratio for a given amount of a chosen component (PCB-101 could be one such component). For further details of the method, the reader is referred to different manuals and papers on the subject.417... 

Concentrate the extract in a rotary evaporator or in a Kuderna-Danish evaporator to approx. 1 ml (without an air flow). Inject the extract into a chromatographic column of 12 mm diameter and 15 cm height, which has previously been packed to half height with n-hexane, then to a height of 7 cm with florisil and above that 1 cm of hexane-toluene mixture 1 1, maintaining a drop rate of 1 to 2 drops/second (3 to 5 ml/min). For the separation of non-polar interfering substances (in particular polychlorinated biphenyls... 

Fill., filtration Evap., evaporation FI. det., fluorimetric detection SLE, solid-liquid extraction SEC, size-exclusion chromatography MD, microwave digestion LLE, liquid-liquid extraction Imm., immunoassay Phot, det., photometric detection FI. det., fluorimetric detection BOD, biological oxygen demand DOM, dissolved oxygen measurement SPE, solid-phase extraction Centr., centrifugation Mix., vortex mixing PCBs, polychlorinated biphenyls Pot. det., potentiometric detection TCP, 3,5,6-trichloro-2-pyridinol. 

Volatility is a function of the vapor pressure of a compound. Vapor pressures at a particular temperature can vary over many orders of magnitude. Of common organic liquids, diethyl ether has one of the highest vapor pressures, whereas those of polychlorinated biphenyls (PCBs) are very low. When a volatile liquid is present in soil or in water, its water solubihty also determines how well it evaporates. For... 

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