Peak capacity large losses

A large number of overlapping peaks Is visually discernible In these simulations, and yet the component number Is considerably less than the peak capacity. Only 105 maxima are observed In the first and 99 maxima In the second simulation. Respective losses of 55 and 61 components result If each maximum Is associated with a single component. These losses justify our earlier assertion that the total component number may be easily underestimated even from a high resolution chromatogram. 

For samples that meet the solubility requirements of the SEC approach, analyses were also reported for additives in polymers such as PVC and PS [28,29]. Direct SEC analysis of PVC additives such as plasticisers and thermal stabilisers in dissolution mode has been described [28,30,31 ]. In the analysis of a dissolved PS sample using a SEC column of narrow pore size, the group of additives was separated on a normal-phase column after elution of the polymer peak [21]. Column-loading capacity of HPSEC for the analysis of additives, their degradation products and any other low-MW compounds present in plastics has been evaluated for PS/HMBT, PVC/TNPP and PVC/TETO (glyceryl tri[l-14C] epoxyoleate) [31]. It was shown that HPSEC can be used to separate low-MW compounds from relatively large amounts of polymers without serious loss of resolution of the additives the technique has also been used for the group analysis of chlorohydrin transformation products of the TETO model compound [32]. 

The low flow rate in the microbore column ensures sample volumes compatible with the secondary conventional column and permits the injection of a small volume onto the secondary column, making the transfer of incompatible solvents possible without peak shape deterioration or resolution losses [63], The possible disadvantage could be the lower sample capacity of microbore LC columns. However, in LCxLC, a sensitivity enhancement can be obtained if the formation of compressed solute bands at the head of the secondary column is achieved during the transfer from the first to the second dimension. Moreover, a larger volume can be injected into the first-dimension microcolumn, used as a highly efficient pre-separation step, and a limited decrease in efficiency due to a large injection volume can be tolerated. 

Pyridine or another solvent with a large solvation capacity (acetonitrile, dimethyl-formamide) are mostly used as solvents in the silylation reactions. Pyridine provides on some phases a broad tailing peak and can overlap lower components. Lehrfeld [85] therefore developed a procedure for the removal of pyridine from the sample before the analysis. During the derivatization anhydrous conditions are essential because the derivatives are decomposed by traces of water. However, a method has been described for the preparation of silyl derivatives even in the presence of water its principle consists in the addition of such a large excess of the silylating agent that all of the water present is removed [86]. This can be of importance in the treatment of samples that cannot be previously dried as losses of more volatile components could occur. The extent to which the presence of water affects the reaction yield and whether or not a large excess of by-products has an adverse effect must be tested, however. 

Each transformer must have enough capacity to handle the peak load of its specific load area. Combined transformer capacity requirements, therefore, may exceed those of a conventional simple radial system. This approach resnlts in rednced losses, improved voltage regulation, rednced cost of feeder circuits, and no need for large low-voltage feeder circuit breakers. 

The large irreversible capacity observed on the initial cycle may be attributed to a partial reduction of the native surface oxide and the formation of an SEI layer, as previously discussed for the silicon system. The peaks in the differential capacity [350 mV (insertion) and 500 mV (extraction)] in the first cycle disappear after the first few cycles and are indicative of the solid-electrol5de reaction to form the SEI layer. The first cycle capacity loss is approximately 70% of what was observed in the Li-Si system. The lower irreversible capacity on the first cycle is attributed to a reduced native oxide layer, which is only a few monolayers thick. 

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