Sample preliminary treatment

Fluoride ion, and weak acids and bases do not interfere, but nitrate, nitrite, perchlorate, thiocyanate, chromate, chlorate, iodide, and bromide do. Since analysis of almost all boron-containing compounds requires a preliminary treatment which ultimately results in an aqueous boric acid sample, this procedure may be regarded as a gravimetric determination of boron. 

In view of the foregoing remarks, it is clear that all glassware used in the preliminary treatment of samples to be subjected to stripping voltammetry, as well as the apparatus to be used in the actual determination, must be scrupulously cleaned. It is usually recommended that glassware be soaked for some hours in pure nitric acid (6 M), or in a 10 per cent solution of pure 70 per cent perchloric acid, followed by washing with de-ionised water. 

Dissolution procedures are described for gram samples of graphite or pyrolytic carbon, milligram samples of irradiated fuel particles, and for more readily oxidised forms of carbon, such as charcoal. The first two methods involve heating the samples with mixtures of 70% perchloric and 90% nitric acids (10 1), and must only be used for graphite or pyrolytic carbon. Other forms of carbon must not be oxidised in this way (to avoid explosions), but by a preliminary treatment with nitric acid alone and in portions. 

These data are consistent with the results obtained by Barry (16) who investigated the influence of the preliminary treatment of a specimen of ZnO on the sign of the photoadsorption effect with respect to oxygen. The specimen was first calcined at a high temperature in oxygen and then cooled to room temperature, at which adsorption was subsequently carried out. The untreated specimens showed photodesorption, while on the samples treated by the procedure indicated (saturation with oxygen) there was observed photoadsorption. 

Let us now turn to a comparison of theory with experiment. Comparing (95), (84), and (68), we find that the dependence of the photocatalytic effect K on the position of the Fermi level at the surface s and in the bulk cv of an unexcited sample for the oxidation of water is the same as for the oxidation of CO or for the hydrogen-deuterium exchange reaction. For this reason, such factors as the introduction of impurities into a specimen, the adsorption of gases on the surface of the specimen, and the preliminary treatment of the specimen will exert the same influence on the photocatalytic effect in all the three reactions indicated above. The dependence of K on the intensity I of the exciting light must also be the same in all the three cases. 

Procedure Cholinesterase activity in analyzed tissue or the matrix (biotest with immobilized AChE) is determined in the incubation media [consisting of substrate ATCh - 34 mmol maleate buffer 0.1 M, pH = 6.0- 6.5 ml sodium citrate 0.1 M - 0.5 ml CuS045H20 0.03M -1.0 ml distilled H20 (or inhibitor in variant with toxin analyzed) -1.0 ml potassium ferricyanide 0.005 M -1 ml.] Volume of incubation media in one test - 400 mcl. As a blank (control sample), a treatment of the exposure without the substrate is used. If inhibitory effects of allelochemical (or any toxin) are analyzed, before the substrate addition the sample was preliminary exposed to allelochemical inhibitor. Two methods for the AChE-biotests may be recommended (i) in microcells ( stationary conditions ) and (ii) in flowing columns-reactors ( dynamic conditions ). 

Samples of rutile Ti02 were outgassed at elevated temperatures in some instances this was followed by subsequent exposure to 02 at 150°C. The following results were obtained by the BET analysis of N2 adsorption after various preliminary treatments ... 

The intensities of the bands of irreversibly chemisorbed CO change according to the preliminary treatment of the sample. This suggests that other adsorbates, e.g. water, can inhibit the CO chemisorption on the Pd(II) ions. We observe that ... 

Prior to the chromatographic separation of amino acids on Dowex 50 columns, Carsten (C5) first desalts the urine sample on Amberlite IR 100 or Duolite C 3 and removes most of the nitrogenous bases on Amberlite IRA 400. This preliminary treatment allows for amino acid separations at ordinary temperatures using 2M and 4M HC1 on H+ columns for elution, instead of buffer mixtures a single column of 25 g of Dowex 50 is sufficient for all amino acids and 350-375 one-milliliter fractions are collected. The resolving power of this method does not seem to be as satisfactory as Moore and Stein s procedures, and it is not less time nor labor consuming. 

Nota and Improta [813] determined cyanide in coke oven waste water by gas chromatography. The method is based on treatment of the sample with bromine and direct selective determination of the cyanogen bromide by gas solid chromatography using a BrCN selective electron capture detector. No preliminary treatment of the sample to remove interferences is necessary in this method, and in this sense it has distinct advantages over many of the earlier procedures. Bromine also oxidises thiocyanate to cyanogen bromide. Previous treatment of the sample with aqueous formaldehyde destroys thiocyanate and prevents its interference. 

It is noteworthy that in practice even the reverse of the above may occur. Often it is necessary to analyse compounds that are too volatile. Significant losses during the preliminary treatment of the sample (e.g., extraction, removal of the solvent), due to this volatility, may introduce errors into the quantitative evaluation. Analysis of volatile carboxylic acids in biological samples is an example. Conversion of these compounds into less volatile derivatives is therefore advantageous from the viewpoint of both GC proper and preliminary isolation of the compounds and sample treatment. 

The sample to be analysed does not require any particular sample pre-treatment. However, in the case of musts or cloudy wines, a preliminary clarification by centrifugation or filtration is recommended in order to prevent system blockage. Carbon dioxide levels exceeding 750mg/L should be reduced or eliminated before analysis to avoid degassing of the sample in the analytical circuit. 

Laser-excited atomic fluorescence spectrometry allowed for the determination of Pb in Vostok deep ice cores with a precision of 20% (63, 64). Values of 2-40 pg g were measured for ages spanning the 155,000-26,000 years BP. The technique permitted sample volumes as low as 20 pi to be dealt with without any preliminary treatment, thus greatly facilitating contamination control. 

An alternative to drying samples before beginning an analysis is to determine the water content when the samples are weighed for analysis so that the results can be corrected to a dry basis. In any event, many analyses are preceded by some sort of preliminary treatment designed to take into account the presence of water. 

In the present work an attempt has been made to optimize the parameters related to the extraction of antioxidants (with ASE) from Spirulina platensis using only environmentally clean solvents such as water, ethanol and mixtures. Thus, as a first approach, a study about different sample pre-treatments and how these affect both, the extraction yield and the final antioxidant activity has been performed. Moreover, a relationship between the efficient concentration (ECso) and the final composition of the solvent (as a function of the dielectric constant) has been studied and a preliminary characterization of the chemical composition of one of the best antioxidant extract has been done using an optimised CE-DAD method. 

The extent of hydration and hydroxylation of silica surface, and also the adsorption properties (per unit of silica surface), are different for samples having different specific surface area under the same conditions of preliminary treatment. The extent decreases with an increase in the specific surface area. 

Ooh = 1) is obtained after preliminary treatment of the samples in vacuo at 180-200 °C, when for each Si atom there is approximately one OH group. The average value of the silanol number for such a state, aon = 4.6 OH groups per square nanometer, is a physicochemical constant (it is independent of the type of the amorphous silica used, the method of preparing it, and the structural characteristics, that is, the specific surface area, the type of pores, the distribution of the pores according to their diameter, the packing density of the particles, and the skeleton structure of Si02). 

The preliminary treatment of the sample for ion microscopy is precisely that customary in work with the electron emission microscope (69), With tungsten, for example, three mil 218 wire is spot welded onto ten mil tungsten supports and briefly heated to 2500°K in a hydrogen atmosphere. The sample is then pointed by electrolytic etching in 3,5N KOH, at 2 volts ac. 

The temperatures of the preliminary treatment and exchange experiments were sufficiently high that one might suggest that the structure of the samples under study should change. However, the data on nitrogen adsorption provided evidence in favor of retaining the structure. 

Another strategy for locating hydroxyl groups in steroids involves a sandwich technique [196] injection of the product of preliminary treatment of the sample with TSIM or BSTFA along with ethyl- or propyldimethylsilylimidazole results in the displacement of trimethylsilyl groups by the larger alkylsilyl groups only from... 

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