Glyoxal analysis

Preparation of calibration curve for methyl glyoxal analysis. The calibration curve for methyl glyoxas was prepared using N-methylacetamide as an internal standard. N-Methylacetamide was added to each standard reaction mixture of methyl glyoxal (1.0-7.5 mg) and 0.75 g of cysteamine in 70 ml of dichloromethane at pH 6. 

All dichloromethane examined showed 2-14 ppm of formaldehyde contamination. Several clean up methods were applied to remove formaldehyde such as washing with sodium bisulfite, treatment with active charcoal of Porapak Q porous polymer without success. Trace levels of formaldehyde in solvents may be impossible to remove. Therefore, chloroform was used as the solvent for formaldehyde analysis in further experiments. The amount of contaminant obtained from a blank solvent was always subtracted from the values of actual results. Dichloromethane was, however, used for methyl glyoxal analysis. The extraction efficiency of chloroform and dichloromethane was almost identical. Dichloromethane was easier to use for a liquid-liquid continuous extraction than chloroform because of its lower boiling point. 

The results of formaldehyde and methyl glyoxal analysis in commercial foods are shown in Table VIII. Formaldehyde was identified in the levels of 3.7-17 ppm in coffee obtained from various commercial sources. It was found at higher levels in instant coffees than in brewed coffee. This suggests that formaldehyde may escape from coffee during brewing. Formaldehyde has been reported in coffee volatiles by several researchers (31). There are however, no reports on quantitative analysis of formaldehyde in coffee prior to the present study. 

Dinitrophenyl-hydrazine has been successfully employed in the analysis of simple aldehydes, substituted aldehydes, glyoxal and gluteraldehyde (43-45), all the isomers of the C3 to C7 aliphatic ketones (44,45) and in the determination of formaldehyde in tobacco smoke (46). 

Cotham WE, Metz TO, Ferguson PL, et al. Proteomic analysis of arginine adducts on glyoxal-modified ribonuclease. Mol. Cell. Proteomics 2004 3 1145-1153. 

Reactions of carbonyl compounds such as pyridine 2-carboxaldehyde, glyoxal, biacetyl, or benzil with 2-aminothiophenol on an Fe + template give benzothiazolinate (198) complexes. The complex from pyridine 2-carboxaldehyde, for example, was formulated, on the basis of NMR and Mossbauer spectroscopy and of analysis (C, H, N, and Fe) as the bis-(A,iS)-ligand-bis-aqua complexes of (199), an isomeric form in equilibrium with (198). However as they are diamagnetic it seems more likely that they are [Fe(199)2] 2H20, containing terdentate (N,N,S) (199), than the proposed [Fe(199)2(H20)2]. 

Analysis. Ca gives a brick-red flame coloration, indicating that various optical spectroscopies will be effective in its determination. Ca is quantitatively determined by colorimetry down to 100 ppb using murexide or o-cresolphthalein, by atomic absorption spectroscopy (AAS) to 20 ppb, to 1 ppb by electrothermal absorption spectroscopy (ETAS), to 0.01 ppb by inductively-coupled plasma emission spectroscopy (ICPES), and to 10 ppb by inductively-coupled plasma mass spectroscopy (ICPMS). A spot test for Ca which extends to 3 ppm is provided by glyoxal bis(2-hydroxyanil). 

Recently (55) it has been shown that the S- state of glyoxal photodissociates in the absence of collisions. It was only natural that a study on the photodissociation dynamics should quickly follow, since many interesting questions were raised in the original study. Through product analysis they could identify two primary processes, namely,... 

In 1962 Paldus was awarded a National Research Council of Canada Postdoctoral Fellowship and joined the Division of Pure Physics at NRC to work in the Larger Molecules Section (LMS) under the supervision of Dr. D. A. Ramsay. This was just at the time when new, high resolution spectrographs were being obtained at LMS and computers were beginning to help with the analysis of complex molecular spectra. Aided by these new tools, Paldus embarked on an analysis of the vibrational and rotational fine structure of glyoxal electronic spectra. 

T. Hayashi and T. Shibamoto, Analysis of methyl glyoxal in foods and beverages, J. Agric. Food Chem., 1985, 33, 1090-1093. 

Instrumental Analysis. A Hewlett-packard Model 5880 A GC, equipped with thermionic specific detector and a 50 m x 0.23 mm i.d. fused silica capillary column coated with Carbowax 20m, was used for quantitative analysis of thiazolidine and 2-acetylthiazolidine derived from formaldehyde and methyl glyoxal, respectively. GC peak areas were calculated with a HP 5880 A series GC integrator. The oven temperature was programmed from 70 to 180°C at 2 C/min. A Finnigan Model 3200 combination GC/MS equipped with an INCOS MS data system was used for mass spectral identification of thiazolidine derivatives. 

GC analysis of volatile aldehyde standards. A mixture of formaldehyde, acetaldehyde, propionaldehyde, isobutyl aldehyde, isovaleraldehyde, methyl glyoxal, and furfural (0.1 mg each) were added to 20 ml of cysteamine solution (6g/1 liter of deionized water). The pH of the solution was adjusted to 8 with 6 N NaOH solution. The reaction proceeded promptly to formm thiazolidine derivatives. The reaction mixture was then extracted with 2 ml of dichloromethane, and an aliquot of the extract was injected in the GC. A gas chromatoram of the extract is shown in Figure 2. 

Analysis of formaldehyde and methyl glyoxal in food samples. The... 

After a careful theoretical analysis by ab initio MO methods, Schleyer and coworkers concluded that 1,2-dioxetenes and 1,2-diazetines are non-aromatic 67t-systems with completely localized C = C double bonds and normal C-X and X-X single bonds (X = O or NH). The unsubstituted 1,2-dioxetene and 1,2-diazetine undergo conrotatory ring opening to glyoxal and a-diimine. 

Several attempts of FruA-catalyzed DHAP additions to simple aliphatic dialdehydes like glyoxal or glutaric dialdehyde have been reported in the literature, but in no case had a product been isolated and characterized [72,85]. Malonic dialdehyde cannot be used because it tends to enolize under protic conditions and engages in polycondensations. Our own extensive studies corroborate that enzymatic assays indicate a consumption of DHAP, but no defined products result according to t.Lc. or NMR analysis. Problematic also is the fact that aliphatic dialdehydes irreversibly destroy enzymatic activity by protein cross-linking [86,87]. 

Chemical methods involving derivative formation have now been largely superseded by physical methods of analysis, particularly gas chromatography. However, under some circumstances it may be impossible to use the latter techniques. Alternative chemical methods of product analysis are described by Melville and Gowenlock ", and are particularly necessary in the field of combustion . For instance, formaldehyde may be estimated by the chromotropic acid method , and glyoxalic acid and glyoxal by colorimetric methods . ... 

In the ozonolysis of 2,5-dimethylpyrrole (IV), methylglyoxal and glyoxal are formed in addition to ammonia (83%), formic acid, and acetic acid. The yield of the dioximes is about 24% and of p-nitrophenylosazones, 29 to 33%. For the molecular ratio, methylglyoxal to glyoxal, values of about 5 to 7 are found by analysis of the mixture of oximes a value of 7 has been found by analysis of the mixture of p-nitrophenylosazones. The dioximes and the p-nitrophenylosazones of both dicarbonyl compounds have been isolated in a pure form and were identified by mixed melting points with authentic samples. 

One estimate for the accuracies of the molecular constants can be obtained from the statistical standard deviations. However, experience shows that these estimates are invariably too low, owing to the neglect of systematic errors. More reliable estimates can be found by two methods. In the first, several different bands with one state in common are analyzed independently and the results compared. Thus values for the ground-state rotational constants of glyoxal-d2 obtained from the independent analyses of five bands are reproduced in Table 3. It is seen that the values forA", B , and C are consistent to 0.00025, 0.00004, and 0.00004 cm"1, respectively, whereas the standard deviations of these constants obtained from the analysis of the 0-0 band are 0.00004, 0.000008, and 0.000009 cm"1, respectively. In this example a realistic estimate for the accuracy is roughly five times the standard deviation. 

In the second method, the ground-state rotational constants obtained from the analysis of an optical spectrum are compared with the constants obtained from a microwave investigation. Some values for cw-glyoxal are given in Table 4. Again it is found that it is necessary to multiply the statistical standard deviations of the constants by factors from 3 to 6 to obtain realistic estimates of the accuracy. The correlation matrix obtained from the analysis of the optical spectrum is given in Table 5. 

TABLE 5 Correlation Matrix Obtained from the Analysis of the 0-0 Band of cfc-Glyoxal ... 

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