Impurities retention time

Although a TLC test (silica gel Merck 60 F254, ethyl acetate/hexane 20 80 elution, UV and chromic-sulfuric acid visualization) of this oil reveals only one spot (Rf 0.6), capillary GLC (Hewlett-Packard HP-5, 25 m x 0.2 mm x 0.5 pm, 200°C) shows in addition to methyloctalone 3 (retention time, 10.9 min), an 8% impurity (retention time, 11.7 min) which is probably the regioisomer 4. 

Relatively high (typically 980—1200°C) temperatures are required to decompose spent acids at reasonable burner retention times. Temperatures depend on the type of spent acid. A wide variety of spent acids can be processed in this way, but costs escalate rapidly when the sulfuric acid concentration in spent acid (impurity-free basis) falls below about 75%. A few relatively uncontaminated spent acids can be reused without decomposition by evaporating the excess water in concentrators, or by mixing in fresh sulfuric acid of high concentration. Weak spent acids are frequently concentrated by evaporation prior to decomposition. 

The purity of the product is greater than 99% as determined by gas chromatographic analysis using a 6-m. column of 30% Carbowax 20M on 60-80 Chromosorb W. The major impurity (<1%) was shown to be 3-heptanol by comparison of gas chromatographic retention times and mass spectral fragmentation patterns with those of an authentic sample. 

The contents of the receiver and trap are combined with the aid of a few drops of dichloromethane and distilled through a 15-cm. Vigreux column under reduced pressure. After only a few drops of forerun, the main fraction is 2.87-3.17 g. (60-66%) of 5-hexynal, b.p. 61-62° (30 mm.), w20d 1.4447, df 0.875 (Notes 11-13). Cas chromatographic analysis (Note 14) shows this material to contain 3-5% of unidentified impurities with longer retention times (Note 15). 

The checkers found that gas chromatographic analysis of one sample using a 305 cm. by 0.3 cm. column packed with 10% SF-96 on Chromosorb P operated at 70° with a 60 ml./minute helium carrier gas flow rate gave five minor impurity peaks, two at shorter retention times, and three at longer retention times. None of these impurities was present in greater than 1.1% total impurities wrere 3%. 

In a continuous process, ground PET bottles (830 parts) in an aqueous slurry were pumped into an autoclave equipped with a stirrer and maintained at 450-550 psig pressure and 191-232°C. Ammonium hydroxide (300 parts) solution consisting of water (7857 parts), ethylene glycol (493 parts), and ammonium sulfate (918 parts) was introduced into the reactor. The retention time in the reactor varied from 5 to 45 min. The aqueous diammonium terephthalate and edtylene glycol solution was withdrawn from the reactor and filtered while hot to remove solid impurities such as pigments, pieces of metal caps, labels, and cap liners. Hie filtrate was acidified widi sulfuric acid solution to liberate the TPA product. Hie recovered TPA usually had a purity of 99% or higher. 

It follows that measurements must be made with a precision of about 0.2 second if quantitative results are to be of any value. It is seen from figure 4 that the experimental points lie very close to the line and a fairly accurate measurement of the distribution of the two isotopes can be obtained from retention time measurements. This method has very limited areas of application and is given here, more to demonstrate the effect of unresolved impurities on retention time, than to suggest it as an alternative to adequate chromatographic resolution. In some cases, however, particularly in the analysis of isotopes, it may be the only practical way to obtain a quantitative evaluation of the mixture by a liquid chromatographic method. 

Figure 9. HPLC analysis of a monomer, fraction showing retention times and identification (1,2, and 3) represent MM A, styrene, and n-BMA at 200 nm (4 and 5) represent MM A and styrene at 254 nm (6) are THF impurity peaks...

Sedimentation and dissolved air flotation are the most common clarification processes for removal of precipitates. Either sedimentation or flotation is often preceded by chemical coagulation or precipitation, which converts dissolved pollutants to a suspended form, and by flocculation, which enhances clarification by flocculating suspended solids into larger, more easily separating particles. Simple sedimentation normally requires a long retention time to adequately reduce the solids content. The detention time of dissolved air flotation, however, is much shorter. When chemicals are used, retention times are reduced and clarification removal efficiency of either sedimentation or flotation is increased. A properly operated clarification system is capable of efficient removal of suspended solids, metal hydroxides, and other wastewater impurities.10-12... 

No impurity peak that has a retention time greater than Lindane will have a peak height greater than that produced by 10 pg/mL Heptachlorepoxide (ECD) and 5 pg/mL Parathion (NPD). Hydrocarbon analysis... 

Compound impurities can lead to biased results when plate readers are used for detection since the total absorbance at a particular wavelength is employed for the determinations. The yt/PLC system employed in these determinations can easily compensate for this problem since only the value for the peak area due to the compound (at the corresponding retention time) is considered for the calculations. For example, in the case of a nifedipine sample, purity was determined to be... 

FIGURE 14.11 Comparison of chromatography performance obtained from gradient nano LC at 1.25 iL/min (900 psi) and 10 /tL/min (7200 psi) flow rates. Column was 3 cm x 150 /rm, packed with 1.8 fim C18 particles. Reproducible retention time and peak areas for two antidepressant drugs and their impurities are shown. 

The produced fluids and gases are typically directed into separation vessels. Under the influence of gravity, pressure, heat, retention times, and sometimes electrical fields, separation of the various phases of gas, oil, and water occurs so that they can be drawn off in separate streams. Suspended solids such as sediment and salt will also be removed. Deadly hydrogen sulfide (H2S), is sometimes also encountered, which is extracted simultaneously with the petroleum production. Crude oil containing H2S can be shipped by pipeline and used as a refinery feed but it is undesirable for tanker or long pipeline transport. The normal commercial concentration of impurities in crude oil sales is usually less than 0.5% BS W (Basic Sediment and Water) and 10 Ptb (Pounds of salt per 1,000 barrels of oil). The produced liquids and gases are then transported to a gas plant or refinery by truck, railroad tank car, ship, or pipeline. Large oil field areas normally have direct outlets to major, common-carrier pipelines. 

This product exhibits one major gas chromatographic peak (retention time 2.3 minutes, silicone fluid QF4 on Chromosorb P) as well as one minor, unidentified, more rapidly eluted impurity. The product has strong infrared absorption (CC14 solution) at 1470, 1240, and 1130 cm.-1. 

RP-HPLC determination of trace impurities of the toxic 4-aminopyridine in the central system-stimulating drug 3,4-diaminopyridine can be performed on condition that the impurity has a lower retention time. This was accomplished on applying ion pairing with dodecanesulfonate to maximize selectivity LOD 50 ppm of the impurity in the drug154. 

FIGURE 7 (a) Impurity profile of Intermediate produced by the new process. Peaks after 8 min were impurities that were not previously observed when the Intermediate was produced via the old process, (b) Chromatogram of the drug substance made from intermediate of poor quality. Peak at 22 min retention time is the drug substance Impurity at 36 min retention time was a new impurity and failed specifications. 

As mentioned previously, process related impurities are typically starting materials, by-products of side reactions, intermediates, or reagents. Starting materials are easy to identify as their structure is known, and their retention times can be quickly compared to known standards during method development. Reagents that are organic in nature could fall into... 

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