Peak analysis identification

Most EDS systems are controlled by minicomputers or microcomputers and are easy to use for the basic operations of spectrum collection and peak identification, even for the computer illiterate. However, the use of advanced analysis techniques, including deconvolution of overlapped peaks, background subtraction, and quantitative analysis will require some extra training, which usually is provided at installation or available at special schools. 

Reliable quantification is based on peak-search software that combines peak location, peak identification, and element deduction. Element deduction means that, for unambiguous detection, at least two of the principal peaks must be detected for each analyte of interest. In trace analysis, only the strongest peaks can be detected and special attention must be paid to interfering satellites and spurious peaks. 

Figure 11.12 GC analysis of (a) urine sample spiked with opiates 3 p.g/ml) and (b) blank urine sample. Peak identification is as follows 1, dihydrocodeine 2, codeine 3, ethylmor-phine 4, moipliine 5, heroin. Reprinted from Journal of Chromatography, A 771, T. Hyotylainen et al., Determination of morphine and its analogues in urine by on-line coupled reversed-phase liquied cliromatography-gas clrromatography with on-line derivatization, pp. 360-365, copyright 1997, with permission from Elsevier Science.

Figure 11.14 Analysis of amphetamines by GC-NPD following HS-SPME exti action from human hair (a) Normal hair (b) normal hair after addition of amphetamine (1.5 ng) and methamphetamine (16.1 ng) (c) hair of an amphetamine abuser. Peak identification is as follows 1, a-phenethylamine (internal standard) 2, amphetamine 3, methamphetamine 4, N-propyl-/3-phenethyamine (internal standard). Reprinted from Journal of Chronatography, B 707,1. Koide et ai, Determination of amphetamine and methamphetamine in human hair by headspace solid-phase microextraction and gas cliromatography with niti ogen-phosphoms detection, pp. 99 -104, copyright 1998, with permission from Elsevier Science.

Electropherograms of a urine sample (8 ml) spiked with non-steroidal anti-inflammatory drugs (10 p-g/ml each) after direct CE analysis (b) and at-line SPE-CE (c). Peak identification is as follows I, ibuprofen N, naproxen K, ketoprofen P, flurbiprofen. Reprinted from Journal of Chromatography, 6 719, J. R. Veraait et al., At-line solid-phase exti action for capillary electrophoresis application to negatively charged solutes, pp. 199-208, copyright 1998, with permission from Elsevier Science. 

Figure 11.19 SPME-CE analysis of urine samples (a) blank urine (a) directly injected and extracted for (b) 5 (c) 10 and (d) 30 min (b) Urine spiked with barbiturates, extracted for (e) 30 and (f, g) 5 min. Peak identification is as follows 1, pentobaitibal 2, butabarbital 3, secobarbital 4, amobarbital 5, aprobarbital 6, mephobarbital 7, butalbital 8, thiopental. Concenti ations used are 0.15-1.0 ppm (e, f) and 0.05-0.3 ppm (g). Reprinted from Analytical Chemistry, 69, S. Li and S. G. Weber, Determination of barbiturates by solid-phase microexti action and capillary electrophoresis, pp. 1217-1222, copyright 1997, with permission from the American Chemical Society.

Figure 12.10 Microcolumn SEC-LC analysis of an acrylonitrile-butadiene-styrene (ABS) teipolymer sample (a) SEC ti ace (b) EC ti ace. SEC conditions fused-silica column (30 cm X 250 mm i.d.) packed with PL-GEL (50 A pore size, 5 mm particle diameter) eluent, THE at a flow rate of 2.0 mL/min injection size, 200 nL UV detection at 254 nm x represents the polymer additive fraction (6 p-L) tr ansferred to EC system. EC conditions NovaPak CIS Column (15 cm X 4.6 mm i.d.) eluent, acetonitrile-water (60 40) to (95 5) in 15 min gradient flow rate of 1.5 mL/min detection at 214 nm. Peaks identification is follows 1, styrene-acrylonitrile 2, styrene 3, benzylbutyl phthalate 4, nonylphenol isomers 5, Vanox 2246 6, Topanol 7, unknown 8, Tinuvin 328 9, Irganox 1076 10, unknown. Reprinted with permission from Ref. (14).

Figure 12.14 Chromatographic analysis of aniline (a) Precolumn chromatogram (the compound represented by the shaded peak is solvent flushed) (b) main column chromatogram without cryotrapping (c) main column chromatogram with ciyottapping. Conditions DCS, two columns and two ovens, with and without ciyottapping facilities columns OV-17 (25 m X 0.32 mm i.d., 1.0 p.m d.f.) and HP-1 (50 m X 0.32 mm, 1.05 p.m df). Peak identification is as follows 1, benzene 2, cyclohexane 3, cyclohexylamine 4, cyclohexanol 5, phenol 6, aniline 7, toluidine 8, nittobenzene 9, dicyclohexylamine. Reprinted with permission from Ref. (20).

Figure 12.23 SFC-SFC analysis, involving a rotaiy valve interface, of a standard coal tar sample (SRM 1597). Two fractions were collected from the first SFC separation (a) and then analyzed simultaneously in the second SFC system (h) cuts a and h are taken between 20.2 and 21.2 min, and 38.7 and 40.2 min, respectively. Peak identification is as follows 1, tii-phenylene 2, chrysene 3, henzo[g/ i]perylene 4, antliracene. Reprinted from Analytical Chemistry, 62, Z. Juvancz et al, Multidimensional packed capillary coupled to open tubular column supercritical fluid chromatography using a valve-switcliing interface , pp. 1384-1388, copyright 1990, with permission from the American Chemical Society.

Figure 14.16 Typical cliromatograms of LC (a) and SFC (b) analysis of aromatics in diesel fuel. Peak identification is as follows 1, total saturates 2, total aromatics 3, mono-aromatics 4, higher-ring aromatics.

Figure 15.1 Separation of pesticides from butter by using LC-GC-ECD. Peak identification is as follows 1, HCB 2, lindane 5, aldrin 7, o,p -DDE 10, endrin 11, o,p -DDT 13, p,p -DDT peaks 3, 4, 6, 8, 9, 12, 14, 15 and 16 were not identified. Adapted from Journal of High Resolution Chromatography, 13, R. Barcarolo, Coupled EC-GC a new method for the on-line analysis of organchlorine pesticide residues in fat , pp. 465-469, 1990, with permission from Wiley-VCH.

Figure 15.7 Cliromatographic separation of cliiral hydroxy acids from Pseudomonas aeruginosa without (a) and with (h) co-injection of racemic standards. Peak identification is as follows 1, 3-hydroxy decanoic acid, methyl ester 2, 3-hydroxy dodecanoic acid, methyl ester 3, 2-hydroxy dodecanoic acid, methyl ester. Adapted from Journal of High Resolution Chromatography, 18, A. Kaunzinger et al., Stereo differentiation and simultaneous analysis of 2- and 3-hydroxyalkanoic acids from hiomemhranes hy multidimensional gas cliromatog-raphy , pp. 191 -193, 1995, with permission from Wiley-VCH. (continuedp. 419)...

Figure 15.11 (a) Total ion clnomatogram of a Grob test mixture obtained on an Rtx-1701 column, and (b) re-injection of the entire clnomatogram on to an Rtx-5 column. Peak identification is as follows a, 2,3-butanediol b, decane c, undecane d, 1-octanol e, nonanal f, 2,6-dimethylphenol g, 2-ethylhexanoic acid h, 2,6-dimethylaniline i, decanoic acid methyl ester ], dicyclohexylamine k, undecanoic acid, methyl ester 1, dodecanoic acid, methyl ester. Adapted from Journal of High Resolution Chromatography, 21, M. J. Tomlinson and C. L. Wilkins, Evaluation of a semi-automated multidimensional gas chromatography-infrared-mass specti ometry system for initant analysis , pp. 347-354, 1998, with permission from Wiley-VCH. 

HPLC-NMR analysis in a closed-circuit reveals the stereochemical information for elucidating the structures of unknown compounds (Albert 2002). In contrast to the technique of off-line separation, sample collection, and peak identification closed-circuit analysis guarantees the absence of isomerization and degradation. Very often only small amounts of sample are available after extraction. 

Modem pulse height analysers essentially contain dedicated digital computers which store and process data, as well as control the display and operation of the instrument. The computer will usually provide spectrum smoothing, peak search, peak identification, and peak integration routines. Peak identification may be made by reference to a spectrum library and radionuclide listing. Figure 10.15 summarizes such a pulse height analysis system. 

Fig.4 SPE-LC-DAD analysis of a wastewater sample. Peak identification number and peak retention times (min) (I) azinphosmethy, (11) parathion-methyl, (4) malathion, (3) feni-trothion, (8) azinphos-ethyl, (6) chlorphenvinphos, (10) parathion-ethyl, (7) diazinon [from ref. 21]...

As a consequence of the development of extraction methods for STA based on mixed-mode SPE columns, as well as of the recent introduction of instruments for the automated sample preparation allowing efficient evaporation and derivatization of the extracts, full automation of STA methods based on GC-MS analysis is also available. It needs GC-MS instalments equipped with an HP PrepStation System. The samples directly injected by the PrepStation are analyzed by full scan GC-MS. Using macrocommands, peak identification and reporting of the results are also automated. Each ion of interest is automatically selected, retention time is calculated, and the peak area is determined. All data are checked for interference, peak selection, and baseline determination. 

Another parameter often measured is the adjusted retention time, Ur. This is the difference between the retention time of a given component and the retention time of an unretained substance, tM, which is often air for GC and the sample solvent for HPLC. Thus, the adjusted retention time is a measure of the exact time a mixture component spends in the stationary phase. Figure 11.17 shows how this measurement is made. The most important use of this retention time information is in peak identification, or qualitative analysis. This subject will be discussed in more detail in Chapter 12. 

Fig. 2.132. Chromatogram of spinach, stored frozen until analysis by HPLC (A) and after acidifying the same pigment extract with 0.2ml M HC1 per 10 ml extract and exposure to air and light for 15 h at 20°C (B). Zinc-phtalocyanine was used as an internal standard (IS). Peak identification 1 = chlorophyll-b 2 = chlorophyll-a x = unknown degradation product 3 = IS 4 = pheophytin-b 5 = pheophytin-a 6 = chlorophyll-b 7 = chlorophyll-a 8 = pheophytin-b 9 = pheophytin-a. Reprinted with permission from T. Bohn et al. [303].

With the introduction of diode-array technology in the 1980s, a further dimension is now possible because coupled LC-UV with diode array detection (DAD) allows the chromatographic eluent to be scanned for UV-visible spectral data, which are stored and can later be compared with a library for peak identification. This increases the power of HPLC analysis... 

The main benefits of the mass chromatographic system can be summarized as follows. (1) Precise quantitative analysis can be performed without individual peak calibration. (2) Molecular weights are readily determined for compounds that can be gas chromatographed. (3) Peak identification is usually possible by the combined use of molecular weight and retention data (when such data are available). (4) The unique trap design and dual aspects of the instrument are ideally suited for evolved gas analysis from thermal analyzers, catalyst studies, etc. These benefits will be discussed throughout the paper with emphasis oriented to the polymer field. 

Photodiode array detection has three major advantages for HPLC analysis (26) (a) multiple-wavelength detection, (b) peak identification, and (c) peak-purity determination. Since PDA can record the characteristic UV spectra of the different phenolics as they elute from the column, characterization and peak-purity information can be facilitated through comparison of the spectra at the front, the apex, and the tail of each peak. Furthermore, the rapid calculation of absorbance ratios between different wavelengths is possible, which can be used to classify the spectra by functional groups or by other criteria (Table 1). 

Since the work of Manley and Shubiak (182), who were the first to apply HPLC to anthocyanin analysis, numerous HPLC techniques have been developed for the separation and quantification of anthocyanins and anthocyanidins. Nowadays HPLC has become the method of choice, because it offers the advantage that it is a rapid, sensitive, and quantitative method. For the peak identification and quantitative evaluation of chromatograms, the use of pure anthocyanin standards is recommended however, only a limited, but constantly increasing, number of substances is avail-... 

TOFSIMS analysis. The positive and negative TOFSEMS spectra of the same films are shown in Fig. 2. It should be noted that these were acquired in the low mass resolution mode, hence the peak identification is not completely unequivocal in some cases. 

GC unit. Peak identification is as follows 1, benzylalcohol 2, testosterone propionate 3, testosterone isocaproate 4, testosterone phenylpropionate 5, testosterone decanoate 6, oil matrix (b) GC analysis of the transfer (4 pd) from the micro SEC system (c) Direct GC analysis of a standard solution of the steroid esters. Reprinted from Proceedings of the 10th Symposium on Capillary Chromatography, M. Ghys et al, On-line micro size-exclusion chromatography-capillary gas chromatography, 1989, with permission from Wiley-VCH. 

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