Qualitative analyses

The qualitative determination of a metal is realized by comparison of the mass spectrum of the sample with those of a reference sample. Using low resolution mass spectrometry the sample must have a simple composition to prevent superposition of atomic ions and cluster ions from the components. An alternative possibility is the identification of a metal from a more complex sample using high resolution mass spectrometry. High mass resolution enables a precise mass determination in the ppm range, i.e. +0.1 m.m.u. (millimass unit) at 100 m.u. (mass units). Complex 

Qualitative analysis is, in principle, very simple with XRF and is based on the accurate measurement of the energy, or wavelength, of the fluorescent lines observed. Since many WD-XRF spectrometers operate sequentially, a 20 scan needs to be performed. The identification of trace constituents in a sample can sometimes be complicated by the presence of higher order reflections or satellite lines from major elements. With energy-dispersive XRF, the entire X-ray spectrum is acquired simultaneously. The identification of the peaks, however, is rendered difficult by the comparatively low resolution of the ED detector. In qualitative analysis programs, the process is simplified by overplotting so called KLM markers onto 

The aim of qualitative analysis is to identify the peaks on the chromatogram or a specific component in the eluate. If the chemical nature of the peak is totally unknown, the special techniques described in Section 6.10 may be used as a basis or, alternatively, enough material must be collected from preparative or semi-preparative HPLC (Chapter 21) for the peaks to be identified using various analytical methods. 

If one or several components in the sample mixture are presumed, then a comparison of k values of reference and sample under identical chromatographic conditions is the easiest means of analysis. If a reference compound has the same retention time as a peak in the chromatogram, then the two substances could be identical. However, it is necessary to make some more tests in order to obtain a higher degree of certainty  

As mentioned above, the suspect peak must be analysed before absolute certainty can be established. However, qualitative analysis can be improved without 

Practical High-Performance Liquid Chromatography, Fifth edition Veronika R. Meyer 

By far more evident but also more demanding are the special methods mentioned in 

Practical High-Performance Liquid Chromatography, Fourth edition Veronika R. Meyer 2004 John Wiley Sons, Ltd ISBN 0-470-09377-3 (Hardback) 0-470-09378-1 (Paperback) 

By far more evident but also more demanding are the special methods mentioned in Section 6.10 in particular, the diode array detector and the coupling with mass spectroscopy are instruments for qualitative analysis. 

Due to the widespread use of solvents in the environment, an initial screening of samples for VOCs, either qualitatively or semi-qualitatively using mass spectrometric detection, has become a frequently used approach for identifying the type and extent of any pollution. For qualitative screening of samples the reconstructed total ion chromatogram (TIC) is generated and the peaks of interest selected. A check should be made that the peaks selected are not present in the blank at similar intensity. 

A representative spectrum of each peak in turn is examined, after background subtraction if necessary, and submitted to a library search. An experienced GC-MS analyst must interpret the validity of the library matches. If the library match is considered to be unequivocal, the identification is reported. If isomer specificity is not certain, but elemental composition is considered unequivocal the fit is reported without specific isomer identifiers. If the compound type is unequivocal, but specific compound identification is not possible, then the compound class is reported. If no library matches are considered to be reasonable, then the component is designated as unknown. Individual laboratories should always establish their own criteria for reporting compounds as positively identified. 

Another ion profile often encountered from background ions is one in which the intensity increases or falls at a regular rate throughout the analysis. This often occurs in LC-MS during gradient elution when the ion is associated with only one component of the mobile phase. 

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If the molecular species were at m/z 195 (case (b) above) the ion of m/z 163 is generated by a loss of 32 Da. A similar loss from the adduct ion would not be unusual, in this case an ion at m/z (217 — 32), i.e. m/z 185 would be expected. No significant ion of this m/z value is observed and while this is not conclusive it would suggest that this is not the explanation. 

The third possibility is that the molecular species is m/z 163 and that m/z 195 and m/z 217 are both adducts. If this is the case, it must be possible to explain the differences of 32 Da and 54 Da easily. Can this be done Commonly occurring adducts in electrospray involve the mobile phase and either sodium (relative molecular mass (RMM) 23) or potassium (RMM 39). The simplest interpretation of this spectrum is that the molecular weight of the analyte is 162, the ion at m/z 163 is the protonated species, that at m/z 195 is (M + H + CH30H)+ and that at m/z 217 is (M + Na + CH3OH)+. Since the HPLC mobile phase contained methanol (molecular weight of 32), this is not an unreasonable conclusion. 

The second series consists of only two ions, m/z 229 and m/z 251, and therefore either m/z 251 is an adduct of the molecular species oi m/z 229, or m/z 229 is a fragment arising from the dissociation of the ion at m/z 251. The mass difference is 22 Da, which is most easily explained in terms of m/z 251 arising from a sodium adduct, with the ion at m/z 229 corresponding to the (M + H)+ species. 

The major apphcation of SPR methods in studying DNA-protein binding is extracting the kinetic parameters of an interaction. However, quaUtative analysis of the sensorgram can also provide useful information. 

A significant part of defining the problem is the decision between performing a qualitative analysis and a quantitative analysis. Often the problem is first tackled with a qualitative analysis, followed by a quantitative analysis for specific analytes. The analyst needs to conununicate with the customer who is requesting the analysis. Two-way communication is important, to be certain that the problem to be solved is understood and to be sure that the customer understands the capabilities and limitations of the analysis. 

Qualitative analysis is the branch of analytical chemistry that is concerned with questions such as What makes this water smell bad Is there gold in this rock sample Is this sparkling stone a diamond or cubic zirconia Is this plastic itan made of polyvinyl chloride, polyethylene, or polycarbonate What is this white powder  

Some methods for qualitative analysis are nondestructive, that is, they provide information about what is in the sample without destroying the sample. These are often the best techniques to begin with, because the sample can be used for subsequent analyses if necessary. To identify what elements are present in a sample nondestructively, a qualitative elemental analysis method such as X-ray fluorescence (XRF) spectroscopy can be used. Modem XRF instruments, discussed in Chapter 8, can identify all elements from sodium to uranium, and some instruments can measure elements from beryllium to uranium. The sample is usually not harmed by XRF analysis. For example, XRF could easily distinguish a diamond from cubic zirconia. Diamond is, of course, a crystalline form of carbon most XRF instruments would see no elemental signal from the carbon in a diamond but would see a strong signal from the element zirconium in cubic zirconia, a crystalline compound of zirconium and oxygen. Qualitative molecular analysis will teU us what molecules are present in a material. The nondestructive identification of molecular compounds present in a sample can 

Many methods used for qualitative analysis are destructive either the sample is consumed during the analysis or must be chemically altered in order to be analyzed. The most sensitive and comprehensive elemental analysis methods for inorganic analysis are ICP atomic emission spectrometry (ICP-AES or ICP optical emission spectrometry [ICP-OES]), discussed in Chapter 7, and ICP-MS, discussed in Chapters 9 and 10. These techniques can identify almost all the elanents in the periodic table, even when only trace amounts are present, but often require that the sample be in the form of a solution. If the sample is a rock or a piece of glass or a piece of biological tissue, the sample usually must be dissolved in some way to provide a solution for analysis. We will see how this is done later in this chapter. The analyst can determine accurately what elements are present, but information about the molecules in the sample is often lost in the sample preparation process. The advantage of ICP-OES and ICP-MS is that they are very sensitive concentrations at or below 1 ppb of most elements can be detected using these methods. 

If organic compounds occur in mixtures, separation of the mixture often must be done before the individual components can be identified. Techniques such as gas chromatography (GC), liquid chromatography (LC), and capillary electrophoresis (CE) are often used to separate mixtures of organic compounds prior to identification of the components. These methods are discussed in Chapters 11 through 13. 

It is often desirable to perform a test to determine whether a surfactant is present and, if so, whether it is anionic, cationic, or nonionic. There are a number of booklength works of varying age presenting wet chemical methods for qualitative identification of surfactants and other organic compounds (1-3). However, these are not much used because the most convenient tests for qualitative analysis are those which require equipment already in daily use in the laboratory. Recently, this means sophisticated apparatus designed for quantitative analysis. Thus, most of the qualitative chemical tests have been supplanted by molecular spectroscopic analyses, esjjecially IR and MS analyses. 

Visual examination of the sample may be sufficient to show the presence of a surfactant. If the sample foams on being shaken, or if an aqueous fluid wets the sides of its container without droplet formation, or if an emulsion forms upon addition of water and hydrophobic solvent, it can be presumed that a surfactant is present. More evidence is obtained by measuring the surface tension of the solution, either directly or electrochemi-cally. An often-overlooked method for detecting additives is elemental analysis. Frequently, an inexpensive determination of total sulfur or nitrogen content is sufficient to provide confirmation of the presence of an anionic or cationic surfactant. 

If formulated products are examined, it is generally necessary to perform an initial separation of the surfactant before any of the qualitative tests can be used. The exceptions are the color indicator tests, which often give useful information even in the presence of inorganic salts and other compounds. Other tests require that the surfactant, if not pure, at 

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Nowadays, the most common approach to qualitative analysis is examination of the isolated surfactant by molecular spectroscopy IR, NMR, and MS analyses. The result of this examination is normally sufficient to tell whether the surfactant fraction is pure and what classes of compounds are present. Further analytical strategy is developed based upon this information. 

Results of the 11 DNA minicircles of the series [28] are shown in Fig. 5(a) and (b) in the form of plots of the relative amounts of the two, sometimes three, adjacent topoisomers in the relaxation equilibrium distributions as functions of their ALk [29]. The pBR control nucleosome plot (Fig. 5(a)) shows shoulders or peaks centered at ALk values around —1.7, —1, and —0.5, which correspond to the closed 

These observations (confirmed by AES studies) indicate that after longer oxidation times the top surface is completely covered by lithium compounds, i.e. that the oxidation of lithium has become dominant. This implies a depletion of the element within the metal surface, i.e. the presence of a soft surface layer. 

It is usually simple to find an orientation in the mass spectra. For example, in the mass spectrum of SSMS, LIMS, GDMS or LA-ICP-MS of a graphite or graphite mixture sample, carbon cluster ions (C + with n = 1-24) occur with an exactly constant mass difference of 12u. As described in 

Inorganic Mass Spectrometry Principles and Applications J. S. Becker 2007 John Wiley Sons, Ltd 

A question frequently asked is the detection limit of this technique. First, all elements of the periodic table can be observed with approximately equal sensitivity 23,62) except hydrogen which does not possess closed electron shells. However, XPS is by no means a trace method and concentrations below 100 ppm certainly cause problems. Fig. 10 exemplifies this with a steel sample containing 250 ppm of niobium and nitrogen. The spectra were obtained in an observation time of 500 sec each and show despite the short accumulation a good signal to noise ratio. On the other hand, if the element to be investigated is enriched on the surface, much lower concentrations than in the bulk material would be sufficient. Even fractions of a monolayer can be observed in the XPS-spectrum. 

Identifying pharmaceuticals, whether APIs or excipients used to manufacture products, and the end products themselves is among the routine tests needed to control pharmaceutical manufacturing processes. Pharmacopoeias have compiled a wide range of analytical methods for the identification of pharmaceutical APIs and usually several tests for a product are recommended. The process can be labor-intensive and time-consuming with these conventional methods. This has raised the need for alternative, faster methods also ensuring reliable identification. Of the four spectroscopic techniques reviewed in this book, IR and Raman spectroscopy are suitable for the unequivocal identification of pharmaceuticals as their spectra are compound-specific no two compounds other than pairs of enantiomers or oligomers possess the same IR spectrum. However, IR spectrometry is confronted with some practical constraints such as the need to pretreat the sample. The introduction of substantial instrumental improvements and the spread of attenuated total reflectance (ATR) and IR microscopy techniques have considerably expanded the scope of IR spectroscopy in the pharmaceutical field. Raman spectroscopy, 

The assignment of nC signals in the NMR spectra of lignins (Table 5 4 4, Fig 5 4 5a and b) is based on spectral information derived from studies of 

G = guaiacyl, H = p-hydroxyphenyl, S - syringyl, e = etherified, ne = nonetherified aFor nomenclature, see Fig 5 4 6 

An empirical substituent chemical shift (SCS) additivity rule has been established by which the shift of a particular aromatic carbon in the yS-O-4, /f-5 and 5-5 substructures of lignin can be estimated by summation of the different substituent effects (Hassi et al 1987, Drumond et al 1989) This method helps to distinguish among overlapping signals and improves assignment 

What we need to understand is how the insulating defects within a conductor can modify the current of failure If. For that, we shall consider the two limits which can be easily analysed. The first is the dilute limit when the defects are in small quantity, i.e. p is near 1. In such a case, the defects can be seen as isolated units without interaction. The second limit is when 

We begin with the system in which there is one defect, with a size equal to the length scale of this particular sample. In a perfect sample, the current lines are all parallel to one another and perpendicular to the electrode surfaces (Fig. 2.3a). In Fig. 2.3(b) we show a sample with one defect which is chosen spherical in three dimensions (3D) or circular in two dimensions (2D). In an intuitive way, one can draw the current lines around the defects when it is supposed that far from the defect the current lines are not perturbed (Fig. 2.3b). The modification of the lines gives an enhancement of the current density immediately to the right and the left of the defect. 

The enhancement factor for the current density gives a decrease of the failure current If. In accordance with what we said in the introduction, the current of the entire first failure here is also the failure current for the sample. Once the regions immediately adjacent to the defect fail, the current density will increase on the sides of this new defect and by propagation the whole sample fails. The sample will be divided into two pieces after the failure. 

We thus expect a rapid decrease of the quantity If p) in the vicinity of p = 1. We can either have a true discontinuity of the failure current or maybe only an infinite derivative dif/dp at p = 1. Only an exact calculation can give the answer. 

We now consider larger defects but in a small quantity, i.e. we are still in the vicinity of p = 1. In this dilute limit there is no interaction between the defects. The important question is what is the most dangerous defect or, in other words, what is the defect which will introduce the largest enhancement of the current density  

We should note that the primary X-ray source of XRF includes both continuous and characteristic radiation. The continuous X-rays generate the background of the spectrum. The primary 

Modern X-ray spectrometers are equipped with computer software that is fully capable of identifying the possible elements from a spectrum. We can input the elements that possibly exist in the specimen into the software for qualitative analysis. The computer software will mark peak positions of the input elements in the spectrum. Also, the software will generate such peak lines with correct relative intensities in a spectrum, for example, a correct intensity ratio of Ka to Kfi. With computer assistance, the errors in element identification can be reduced to minimum. 

Since it is important to know whether an observed line is due to an element in the sample or to an element in the x-ray tube target, a preliminary investigation should be made of the spectrum emitted by the target alone. For this purpose a substance like carbon or a plastic is placed in the sample holder and irradiated in the usual way such a substance merely scatters part of the primary radiation into the spectrometer, and does not contribute any observable fluorescent radiation of its own. The spectrum so obtained will disclose the characteristic lines of the target and of any impurities it may contain. 

The most efficient identification procedure involves the determination in rapid succession of retention data (retention volumes, or preferably retention factors) for the components of a mixture and a series of authentic compounds. This method permits straightforward identification of components known to be present in the mixture, and it can also rule out the presence of other possible components. However, it cannot positively identify the presence of a given, isolated component. It is recommended that such determinations be carried out using similar amounts of compounds, and that a number of spike analyses be performed, where small amounts of authentic compounds are added to the mixture in order to approximately double the sizes of unknown peaks. Comparison of 

Giddings and Davis [55] have shown that, for complex mixtures, analyte retention data tend to reflect a Poisson distribution. This result permits a simple calculation of the probability of finding a certain number of singlets, doublets, and higher-order multiplets in the course of analyzing a mixture of m components on a column with a peak capacity n. If the ratio mhi is not small, the probability is low. This confirms that there is little chance of separating a complex mixture on the first phase selected [56]. Method development is a long and onerous process because the probability of random success is low. 

In practice, qualitative analysis is made easier by the use of retention indices I [39]  

The precision of retention data can be quite high [38], [58]. This is related to the precision with which the peak maximum can be located i.e.. it depends on column efficiency and on the signal-to-noise ratio. Reproducibility depends on the stability of the experimental parameters (i.e., the mobile-phase flow rate and the temperature). Reproducibility also depends on the stability of the. stationary phase, which is. unfortunately, much less satisfactory than often assumed. In gas-liquid 

The accuracy of retention data is still more questionable than their reproducibility. Poor batch-to-batch reproducibility for silica-based phases has plagued LC for a generation. For this reason, retention data cannot be compiled in the same way as spectra. Such data collections have limited usefulness, providing orders of magnitude for relative retention rather than accurate information on which an analyst can rely for the identification of unknowns. Precision and accuracy with respect to absolute and relative retention data have been discussed in great detail [58]. 

From the theory of chromatography, the retention volume Vr for a liquid solid system is given by  

It should be noted that Ka is the characteristic that will permit the identification of the solute. Now both Vq and Ag will vary from column to column, depending on its packing density and, thus, the variability of Vq is eliminated by chromatographing a completely non-adsorbed solute N, which will have a a retention volume equivalent to V. Thus, the corrected retention volume V r is given by 

The only variable left to eliminate is Ag, and this can be eliminated by chromatographing another standard solute S added to the original mixture containing solute A, 

The function V r(a)/V r(s) is called the retention ratio of solute A to the standard solute S and is the value that permits the identification of solute A to be confirmed as its value depends only on Ka and Kg both of which are solely characteristic of the solute and phase system and not dependent on the packing characteristics of the column. 

At a constant flow rate, all retention volume measurements can be replaced by retention times. 

The simplest and most-studied example of series reactions is 

The behavior of Cr can be understood in terms of the rate equation for R. The narrate of formation of R is the difference between the rate at which R is formed from A and the rate at which R is converted to S, i.e., 

IfR is the desired product, as is often the case, the exact location of the maximum in the Cr/Cao curve is critical. This point corresponds to the highest possible value of the yield, F(R/A), since F(R/A) = Cr/Cao when there is no R in the feed. If the reactor is operated at a time that is less than topt. the final concentration of R is lower than it could be because not enough A has been converted to R. The yield F(R/A) also is less than its maximum possible value. On the other hand, if the reactor is operated for a time that is longer than topt then the final concentration of R again is less than it could be, this time because too much R has been converted to S. The yield 7(R/A) again is less than its value at the optimum time. 

Show that the value of the optunum time fopt is given by 

show that the maximum yield of R, i.e., the value of r/Cao at topt is given by 

Molecules, in general, do not possess enough energy at room temperature to reach electronically excited states since the energy difference between the ground state and the first electronically excited state is relatively high. As a consequence almost all molecules at around 298 K are in their ground state. 

The discussion reported in Sect. 3.3 about the general absorption characteristics of different families of molecules makes clear how it can be realistic that the spectra of two different substances present in the same sample show very similar profiles. In such cases, in order to distinguish between two different substances. 

The second derivative is generally more functional to clearly localize the absorption maximum than the first one, since it presents its characteristic minimum at the same wavelength of the maximum of the absorption band (Fig. 3.3, line (—)). 

Moreover, in this case, the noise is generally lower than for the first derivative function. 

In conclusion transforming the absorbance spectrum into its derivative (bofli of the first or second order) can be very useful in order to evidence differences between spectra, to solve superimposed bands in qualitative analysis and, in quantitative analysis, to decrease the effects of the interferences generated by diffusion, by the matrix or by other species that absorb in the same areas. 

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When subjected to an electron bombardment whose energy level is much higher than that of hydrocarbon covalent bonds (about 10 eV), a molecule of mass A/loses an electron and forms the molecular ion, the bonds break and produce an entirely new series of ions or fragments . Taken together, the fragments relative intensities constitute a constant for the molecule and can serve to identify it this is the basis of qualitative analysis. 

This is used extensively for qualitative analysis, for it is a rapid process and requires simple apparatus. The adsorbent is usually a layer, about 0 23 mni. thick, of silica gel or alumina, with an inactive binder, e.g. calcium sulphate, to increase the strength of the layer.. A. i i slurry of the absorbent and methanol is commonly coated on glass plates (5 20 cm. or 20 x 20 cm.), but microscope... 

In similar circumstances, silver salts leave a residue of metallic silver lead and copper salts usually leave a residue of the corresponding oxide calcium and barium salts leave a resirlne of the carbonate or oxide. Identify the metal in all such cases by the usual tests of qualitative inorganic analysis. Metals other than the above are seldom encountered in elementan qualitative analysis. 

Qualitative analysis for the elements. This includes an examination of the effect of heat upon the substance—a test which inter alia will indicate the presence of inorganic elements—and quahtative analysis for nitrogen, halogens and sulphur and, if necessary, other inorganic elements. It is clear that the presence or absence of any or all of these elements would immediately exclude from consideration certain classes of organic compounds. 

In order to detect these elements in organic compounds, it is necessary to convert them into ionlsable inorganie substanees so that the ionic tests of inoiganio qualitative analysis may be applied. This conversion may be accomplished by several methods, but the best procedure is to fuse the organic compound with metallio sodium (Lassalgne s test). In this way sodium cyanide, sodium sulphide and sodium halides are formed, which are readily identified. Thus ... 

Current research in the areas of quantitative analysis, qualitative analysis, and characterization analysis are reviewed biannually (odd-numbered years) in Analytical Chemistry s Application Reviews. ... 

See, for example, the following laboratory texts (a) Sorum, C. H. Lagowski, J. J. Introduction to Semimicro Qualitative Analysis, 5th ed. Prentice-Hall Englewood Cliffs, NJ, 1977. (b) Shriner, R. L. Fuson, R. C. Curtin, D. Y. The Systematic Identification of Organic Compounds, 5th ed. John Wiley and Sons New York, 1964. 

Adapted from Sorum, C. H. Lagowski, J. J. Introduction to Semimicro Qualitative Analysis, 5th ed. Prentice-Hall Englewood Cliffs, N. J., 1977, p. 285. 

Samples of analyte are dissolved in a suitable solvent and placed on the IR card. After the solvent evaporates, the sample s spectrum is obtained. Because the thickness of the PE or PTEE film is not uniform, the primary use for IR cards has been for qualitative analysis. Zhao and Malinowski showed how a quantitative analysis for polystyrene could be performed by adding an internal standard of KSCN to the sample. Polystyrene was monitored at 1494 cm- and KSCN at 2064 cm-. Standard solutions were prepared by placing weighed portions of polystyrene in a 10-mL volumetric flask and diluting to volume with a solution of 10 g/L KSCN in... 

There are several forms of electrophoresis. In slab gel electrophoresis the conducting buffer is retained within a porous gel of agarose or polyacrylamide. Slabs are formed by pouring the gel between two glass plates separated by spacers. Typical thicknesses are 0.25-1 mm. Gel electrophoresis is an important technique in biochemistry, in which it is frequently used for DNA sequencing. Although it is a powerful tool for the qualitative analysis of complex mixtures, it is less useful for quantitative work. 

Although aimed at the introductory class, this simple experiment provides a nice demonstration of the use of GG for a qualitative analysis. Students obtain chromatograms for several possible accelerants using headspace sampling and then analyze the headspace over a sealed sample of charred wood to determine the accelerant used in burning the wood. Separations are carried out using a wide-bore capillary column with a stationary phase of methyl 50% phenyl silicone and a flame ionization detector. 

Different light-absorbing groups, called chromophores, absorb characteristic wavelengths, opening the possibility of qualitative analysis based on the location of an absorption peak. 

The use of vibrational Raman spectroscopy in qualitative analysis has increased greatly since the introduction of lasers, which have replaced mercury arcs as monochromatic sources. Although a laser Raman spectrometer is more expensive than a typical infrared spectrometer used for qualitative analysis, it does have the advantage that low- and high-wavenumber vibrations can be observed with equal ease whereas in the infrared a different, far-infrared, spectrometer may be required for observations below about 400 cm. ... 

Qualitative Analysis. Nitric acid may be detected by the classical brown-ring test, the copper-turnings test, the reduction of nitrate to ammonia by active metal or alloy, or the nitrogen precipitation test. Nitrous acid or nitrites interfere with most of these tests, but such interference may be eliminated by acidifying with sulfuric acid, adding ammonium sulfate crystals, and evaporating to alow volume. 

Qualitative Analysis. Several quaUtative analyses can be employed. For example, in the oxamide method (59), oxaUc acid is first heated at approximately 200°C with concentrated aqueous ammonia in a sealed tube. When thiobarbituric acid is added and heated to 140°C, a condensed compound of red color forms. The analysis limit is 1.6 pg. In the diphenylamine blue method (59,60), oxaUc acid is heated with diphenylamine to form a blue color, aniline blue. The analysis limit is 5 pg. 

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