Extraneous peaks

Another advantage of the Savitsky-Golay method is that derivatives of these functions can also be determined from the method of least squares. This method can be used to determine alpha-peak temperatures automatically since the first derivative changes sign at the peak temperature. The advantage of smoothing is that the number of extraneous peaks due to noise has been minimized. 

During a proton NMR examination of a CCI4 solution of MejNsBgFs, an extraneous peak was observed in the spectrum, although the borazine was known to be analytically and mass spectrometrically pure. One microliter of the solution was subjected to GC/MS analysis. Peaks identified as trimethylsilane (TMS) and CCI4 were obtained followed by the expected MesNjBsFs (m/e 177, 176, etc.). An additional component... 

The responses of these three detectors to a variety of organophosphorus molecules have often been compared the results seem to vary from compound to compound165,179,217,238,289. In many instruments the stream is split and passes through several detectors for parallel measurements184,187,298. The flame photometric detectors are the most selective for phosphorus, yield less extraneous peaks and make the identification work easier188. 

A chromatographic analysis that suffers from variation due to extraction losses, incomplete derivatization, column losses, extraneous peaks, and so on, will probably not be greatly aided by automatic integration. The precision enhancement comes largely from elimination of elements of manual methods that tend to reduce precision. 

Figure FI. 3.4 shows HPLC chromatograms for anthocyanidins generated from acid hydrolysis of concord grape and strawberry juices. Extraneous peaks may be present because of incomplete hydrolysis, and degradation and polymerization of the labile aglycons even more of a problem. For acylated anthocyanins, higher yields of anthocyanidins will be achieved if the sample is first saponified (see Basic Protocol 3) and then subjected to acid hydrolysis (see Basic Protocol 2).

When contamination collects on a column, poor peak shapes (usually tailing) and extraneous peaks will appear with an increase in backpressure. Therefore, samples should always be filtered before injection. Mobile phases should be filtered a few days after preparation to remove any particles and prevent microbial... 

The basic difference between the integrator and the computer is that the latter stores more information and can be more flexible with how it handles it. The computer, with the right software, can regenerate all or part of the run with all the stored points that make up the chromatogram, blow it up or shrink it down, leave out extraneous peaks, or do a point-by-point comparison with other curves. Flexibility adds complications setting up and using the computer is more complicated and costly than an integrator. 

Sample extracts injected into the GC can cause loss of detector sensitivity, shorten the lifetime of a column, produce extraneous peaks, and deteriorate peak resolution and column efficiency. The sample extracts may be purified by one or more of the following techniques ... 

Figure 6 shows a typical chromatogram obtained from such a procedure. In this chromatogram, the elution of the thio-tetrazole, the R and S isomers of moxalactam, and the moxa-lactam decarboxylated product are shown. In this test for other related substances, only those substances which are not dealt with by specific tests are considered. Quantitative information is obtained by summing the response for all the extraneous peaks and comparing them to the sum of the response for the R and S isomers of a diluted moxalactam reference standard. The assumption is made that all of these materials have similar spectral response characteristics at 254 nm. 

In this procedure, the HPLC analysis is carried out on a DuPont Zorbax ODS column using methanol, acetonitrile and water 10 2 1 at the mobile phase. This system resolves vitamins D3 from D2 and from degradation products and other fat soluble vitamins. Didecyl and dinonyl phthalate were used as the internal standards. The latter was included for use in the event that extraneous peaks interfered with the didecyl phthalate peak. Figure 11 shows a chromatogram of an extract of a multivitamin formulation with the two added internal standards. 

Interfacing the TEA to both a gas and a HPLC has been shown to be selective to nitro-based explosives (NG, PETN, EGDN, 2,4-DNT, TNT, RDX and HMX) determined in real world samples, such as pieces of explosives, post-blast debris, post-blast air samples, hand swabs and human blood, at picogram level sensitivity [14], The minimum detectable amount for most explosives reported was 4-5 pg injected into column. A pyrolyser temperature of 550°C for HPLC-TEA and 900°C for GC/TEA was selected. As the authors pointed out, GC uses differences in vapour pressure and solubility in the liquid phase of the column to separate compounds, whereas in HPLC polarity, physical size and shape characteristics determine the chromatographic selectivity. So, the authors reported that the use of parallel HPLC-TEA and GC-TEA techniques provides a novel self-confirmatory capability, and because of the selectivity of the technique, there was no need for sample clean-up before analysis. The detector proved to be linear over six orders of magnitude. In the determination of explosives dissolved in acetone and diluted in methanol to obtain a 10-ppm (weight/volume) solution, the authors reported that no extraneous peaks were observed even when the samples were not previously cleaned up. Neither were they observed in the analysis of post-blast debris. Controlled experiments with handswabs spiked with known amounts of explosives indicated a lower detection limit of about 10 pg injected into column. 

Chemical analyses and physical property measurements made on the starting materials and the products of the ammonium fluotitanate reactions are shown in Table 2. The analytical data for the products of the iron ammonium fluoride reaction are shown in Table 3. Following treatment, the various zeolite products contained up to 16.1 wt.% Ti02 in the zeolites treated with ammonium fluotitanate, and up to 16.9 wt.% Fe203 in the zeolites treated with ammonium Iron fluoride. X-ray powder diffraction intensity is decreased in the substituted products, but retention of oxygen and water adsorption capacity indicates that pore volume has been retained. No extraneous peaks due to other crystalline phases were observed in the X-ray powder diffraction patterns of well washed products. 

The use of detectors such as the electron capture deteetor (ECD) for the identification of amenable compounds and the alkali flame ionisation detector (AFID) for the detection of compounds containing phosphorus and nitrogen, removes many of the extraneous peaks frequently observed when non-seleetive deteetors such as the flame ionisation... 

Impurity enhancement techniques such as fraction collection and phase equilibrium purification can be used to provide enriched samples for use in the method development process.23 When using the fraction collection approach, one or more cuts (fractions) of the chromatographic separation of a bulk lot or mother liquor are isolated. The excess solvent in these fractions is then evaporated to achieve the desired concentration enhancement. These fractions typically contain extraneous peaks because of the presence of salts in the mobile phase or sample degradation during the concentration step. The salts can be removed by extraction and/or a LC cleanup step. To insure that these extraneous peaks/artifacts are not identified as key peaks for separation, the original bulk lot or mother liquor should be included in the method development sample set. The same holds true for phase-equilibrium-purification supernatants. 

As indicated, all EI mass peaks are found in LAMMA, along with many extraneous peaks that might confuse a novice mass spectroscoplst, but experienced organic mass spectroscoplsts can "see" the pertinent peaks. This points out the high level background required in the early ( ) stages of any... 

While It Is evident that the spectra of these unknown organic materials contain recognizable fragments, there are many extraneous peaks beyond EI that add a great deal of uncertainty In analyzing unknown organic materials. Considerable and rather basic studies of the fragmentation paths of this new and different means of Ionization must be done to sort out... 

Sevenich and Fritz found an eluent containing 2.0 x 10 - M ethylenediammonium tartrate to be effective for separating several divalent metal cations [13]. Calculations from ionization constants showed ethylenediamine to be fully protonated (EnH2 ) at pH 5.0 or below. The adjusted retention times for several metal ions were obtained as a function of eluent pH (Table 7.6). The retention times increased in almost every case between pH 5 and 6. Furthermore, some minor extraneous peaks appeared in this pH region. A buffer pH of 4.5 was selected as giving generally the best results. 

Automation has truly revolutionized analysis, but the contribution of the skilled analyst has increased rather than diminished. The occurrence of extraneous peaks in chromatograms due to unexpected compounds should not be merely accepted blindly but their structures should be verified. A good example is the occurrence in sediment samples of a compound which had the same GC retention time as PCB 77 (3,3, 4,4 -tetrachlorobiphenyl) but which on... 

Nitryl hexafluoroarsenate is a white crystalline solid that is stable at room temperature and sensitive to moisture. The product is identified and its purity established (extraneous peaks are not observed) by infrared spectra (Nujol and... 

Evenson, Jones, and Darcey (33) extracted acidified serum with chloroform, evaporated the extract, took up the residue in a chloroform solution of dehydroisoandrosterone acetate internal standard, and analyzed the solution for both primidone and dipiienyl-hydantoin by gas chromatography. The average recovery of primidone from serum was 98 percent. High grade chloroform was used to avoid extraneous peaks ... 

Regardless of which procedure is followed the sample chromatograms from the receiving lab should be compared to the chromatograms from the originating lab to assure there are no unexplained or extraneous peaks. In addition the limit of quantitation should be determined by the receiving lab to assure the sensitivity of the method with their equipment. If the method uses response factors for calculation these should also be checked in the new lab to assure there are no significant differences. 

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