Sample oxidation

In electrochemical cells sample oxidation produces an electric current proportional to the concentration of test substance. Sometimes interferences by other contaminants can be problematic and in general the method is poorer than IR. Portable and static instruments based on this method are available for specific chemicals, e.g. carbon monoxide, chlorine, hydrogen sulphide. 

Ahmad studied specimens of an Al-Li-Cu-Mg-Zr alloy designated 8090 in the form of specimens between 1 mm and 3 mm in thickness cut from an extruded bar of cross-sectional dimensions 51 mm x 25 mm. An XPS spectrum of the surface of a sample oxidized for 5 min at 530°C in air is shown in Figure 2.6. In addition to the peaks of carbon, oxygen and magnesium, there is a lithium (Li Is) peak at 56eV binding energy. 

Analytical Methods. Liquid scintillation counting (LSC) was done using Packard Models 3375 and 3380 Liquid Scintillation Spectrometers equipped with automatic external standards. Solid samples were combusted in a Packard model 306 Sample Oxidizer prior to LSC analysis. 

The results of ashing ejqperiments on the samples from wet oxidation experiments conducted at 285°C are contained in Table X. The loading factors of the oxidized oil samples are dramatically reduced compared to those for samples oxidized at 225°C (see Table VI). The amount of residual coke per gram of bitumen available in each sample can also be seen to have undergone a dramatic reduction as have the estimates of cox(s)> the amount of available carbon converted to coke, compared to the lower temperature wet oxidation s tudy. 

The quality of the polymer, its photo-oxidation and thermo-oxidation history expressed in concentration of hydroperoxides, carbonyl groups or of other oxidized structures and terminal groups. The rate of an oxidative attack may then be related to the average molar mass and to its distribution, and to the ratio of amorphous/crystalline structures. Polymers cannot be simply ordered according to the intensity of light emission at a given temperature. The chemiluminescence-time patterns are related with the rate of sample oxidation, but they may differ from one to the next polymer. 

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. 

The determination of dissolved organic carbon by oxidation methods in water comprises three analytical steps the removal of inorganic carbon from the sample, oxidation of the organic compounds to carbon dioxide, and the quantitative determination of the resulting carbon dioxide. The methods of oxidation can be classified into three major groups ... 

Similar results were obtained when carbon was oxidized in liquid medium. Carbon in aqueous suspension is attacked by many oxidizing agents, e.g., permanganate (49-32), chromate (52-54), hypochlorite (52, 55), persulfate (52, 56, 57), and bromate ions (52, 56, 57) chlorine (49), dilute nitric acid (52,58), and concentrated nitric acid (28). The neutralization behavior against the four bases used in Table I was studied with a few samples oxidized in liquid medium (45, 46). The same ratio was observed as with the oxygen-treated carbons, except that twice the amount of groups reacting with sodium bicarbonate was found (Table III). 

Puri and collaborators (3d, 59) found that the amount of CO2 given off on heating to 1200° was always equivalent to the Ba(OH)2 or NaOH neutralization. Evolution of COj was complete between 750 and 900°. Samples oxidized in liquid medium evolved more COg in relation to CO on heating than did samples treated with oxygen (3d, 55). Puri and Bansal (59) suggested that the neutralization of alkali was caused by carbon dioxide chemisorbed on the carbon surface ( COg complex ). If carboxyl groups were responsible, 1 mole of COg should be formed for each equivalent of alkali consumed. The author of this article thinks, as will be shown below, that very likely carboxyl groups of different environment are responsible for bicarbonate and carbonate neutralization as well as COg evolution. 

IN THE TIP OF THE FLAME, THE STRONG HEAT OXIDIZES METAL IN THE TEST SAMPLE. OXIDE COLORS BEAD. 

Kupranycz et al. (60) reported the presence of dimeric triglycerides in various butterfat samples oxidized at 185°C in the presence of air for 8 and 16 h. Nonpolar and polar dimeric TGs were found in lard samples used in deep fat frying (61). 

In a further method, sample digests are prepared according to method 1(c) of the Analytical Methods Committee [ 100] using precautions described subsequently [101]. The resulting 100 ml of digest, which is in normally 5% v/v sulfuric acid, should not be colourless and should contain any suspended solids. At the same time, prepare two reagent blanks from the volume of acid used in sample oxidation. 

Blood and plasma samples are taken on Combusto Cones (e.g. PerkinElmer Life Sciences), weighed, dried at room temperature, combusted in a sample Oxidizer (e.g. PerkinElmer Life Sciences, Model Oximate 80/307, Frankfurt am Main, Germany) and the 14 CO2 formed is absorbed with Carbo-Sorb (e.g. PerkinElmer Life Sciences), The subsequent radioactivity measurements are carried out after addition of scintillator to the samples. 

Is a simple contact mixture of a sample oxidizer and red phosphorus more or less sensitive than mixtures of potassium nitrate and red phosphorus or of potassium chlorate and red phosphorus. 

Sample Oxidizer-combustible mixtures, lg or 5g Ignitor Pb 3 0 4 (70wt%)-Si(30wt.%), lg or 2g Igniting method Nichrome wire heater, ignition from below. 

Third, difficult samples of materials containing 3H or 14C (e.g., tissue slices, etc.) can be converted to 3H20 or 14C02 in commercially available sample oxidizers. These units burn samples under controlled conditions and then separate the 3H20 and the 14C02 for counting in an acceptable scintillation cocktail. Sample oxidation also eliminates color-quenching problems. 

The disadvantages of both wet and dry ashing which have only been outlined here, have led to the development of alternative methods for sample oxidation based on these two techniques. These are wet ashing using vapour phase attack or at elevated pressures, and dry ashing at low temperatures and pressures with reactive 02. 

Fig. 21. Time-resolved FTIR spectra of the ethene polymerization reaction on a l.Owt.% Cr/silica sample oxidized at 923 K and CO-reduced at 623 K (ethene pressure = 1010 Pa). The CH2 stretching region is reported. (Unpublished spectra obtained by reproducing the experimental procedure described in Reference (20S).)...

Reaction of NPA. Chymotrypsin samples oxidized with NBS to different degrees of inactivation were treated with NPA or C -labeled NPA at pH 5.0 or at pH 6.0. The acetylation of the enzyme by NPA is retarded by the NBS oxidation of the protein. The rates of acetylation of various oxidized chymotrypsin samples at pH 5.0 paralleled their relative activities toward V-acetyl-L-tyrosine-Ethyl ester (ATE). However, the net release of p-nitrophenol, measured after the rate of its liberation had approached that of spontaneous hydrolysis, corresponded to a considerable acetylation... 

Raman chemical imaging can be employed to access the homogeneity and the structural stability in terms of oxidation rates, onset of hematite, and organic contamination of as-precipitate and oxidized iron oxide samples. Oxidation-related Raman features have been established by comparative study of bulk oxides and nanoparticles attained in two different oxidation states, suggesting that the solid nanophase synthesized had a mixed magnetite-maghemite composition [52]. 

Useful for the digestion of metals, alloys and biological samples. Oxidizing attack on many samples not dissolved by HCI liberates trace metals as the soluble nitrate salt... 

Figure 1 shows RP-HPLC chromatograms of KGF samples oxidized by hydrogen peroxide under various conditions. KGF eluted as peak A in panel 1. Oxidized KGF eluted at earlier retention times (panels 2-5). As the temperature, the duration of incubation, or the... 

---