Sample hydrolysis

The use of internal standards is somewhat controversial.115 There is agreement that an internal standard may be used as a correction for injection volume or to correct for pipetting errors. If an internal standard is included before sample hydrolysis or derivatization, it must be verified that the recovery of the internal standard peak is highly predictable. Ideally, the internal standard is unaffected by sample handling. Using an internal standard to correct for adsorptive or chemical losses is not generally approved, since the concentration of the standard may be altered by the conditions of sample preparation. An example of internal vs. external standards is given in Chapter 4. 

Recent approaches to the amino acid analysis of foods require maceration of the sample, hydrolysis of the proteins with HC1, and filtration. The resulting material may still include proteins (and fragmented peptides), carbohydrates, salts, urea, and lipids. The solution is then passed through a small column of cation exchanger (with a nominal cross-linking of at least 8%) in... 

Tryptophan is commonly determined by one of two general categories of sample hydrolysis (a) chemical hydrolysis in base (NaOH, LiOH, etc.) or (b) enzymatic hydrolysis. Attempts to adapt the standard acid hydrolysis to accommodate the problematic amino acids will be addressed in later subsections of this chapter. 

Human adipose tissue (CDDs) Addition of [37CI]2,3,7,8-TCDD to sample hydrolysis with KOH, ethanol, and heat extraction with petroleum ether washing of organic layer with water and H2S04 volume reduction clean-up on silica gel elution with hexane clean-up on alumina elution with CH2CI2 volume reduction redissolution in tridecane HRGC/LRMS (EI/SIM) 10 ppt No data Schecter et al. 1985b... 

Murray [91] has described a gas chromatographic method for the determination in water of triarylphosphate esters (lmol S-140, tricresyl phosphate, cresol phosphate). These substances are used commercially as lubricant oil and plastic additives, hydraulic fluids and plasticisers. The method involves extraction from the samples, hydrolysis and measurement of the individual phenols by gas chromatography as the trimethylsilyl derivatives. The lower detection limit was about 3ppm. 

A good solvent should (i) not react with the drugs being analysed (in this case, for example, with the hydroxide groups of some opiates), (ii) be volatile, to allow rapid application of a small spot of solvent and at the same time concentrate the sample prior to analysis, (Hi) freely dissolve all of the drugs of interest, so that they are determined quantitatively and at the same time no solid material is present in the mixture immediately prior to analysis after removal of the insoluble adulterants, and (iv) be free of water, to prevent deactivation of the silica gel and to reduce the risk of sample hydrolysis during the process of sample application to the TLC plate. 

Relatively stable d/l ratios for diverse samples may also result from racemization during sample hydrolysis and processing. For example, in a comprehensive study Kaiser and Benner (2005) noted that D-amino acids in HMWDOM are overestimated following acid hydrolysis. However, based on the magnitude of the racemization blank and observed patterns within marine samples these authors concluded that the overestimation is neghgible compared to naturally occurring concentrations of some D-amino acids (Dittmar ei a/., 2001 Kaiser and Benner, 2005 McCarthy etai, 1998). However, the distinct matrix of marine samples may introduce additional crossreactions that have not been quantified. For example, one study noted a positive correlation between d/l ratios and saHnity (Dittmar et ai, 2001). 

High background counts (> twice normal background) usually indicate a problem with sample hydrolysis. Check hydrolysis incubation time and temperature, and PCA concentration. Ensure that substrate is added to the bottom of the tube... 

Measurement of total urinary metanephrines using spectrophotometric methods has also been reported." " After sample hydrolysis and isolation of metanephrines by ion-exchange chromatography, the hydroxyl- and amino-containing side-chains were oxidatively cleaved by periodate. Oxidation of both NM and MN resulted in the formation of a common end product, vanillin, which was measured spectrophotometricafly at 360 nm. This method was, however, susceptible to interferences from other compounds such as methylglucamine and the 4-hydroxylated metabolite of propranolol." Furthermore, the method did not differentiate between NM and MN, and results were only semi-quantitative for grossly increased concentrations of total metanephrines." " ... 

Volatile products are formed in the latter two reactions. The mechanism of degradation of condensation polymers is often complicated by the presence of traces of water which are difficult to eliminate from the samples. Hydrolysis then occurs at high temperature and competes with the pure thermal degradation. New chain ends are formed which may in some cases markedly affect the polymer stability. 

Sample Hydrolysis Ratio R Calcination temperature/time (K/h) Surface area (mV )... 

Several enzyme immunoassays are now commercially available, all of which include sample hydrolysis, extraction and purification steps. However, a recently developed radioimmunoassay can measure free S-iso-PGF levels reliably in most body fluids without any extraction or hydrolysis procedures (Basu, 1998a). This method can also be used to measure total levels (esterified and free) of 8-iso-PGp2 in sites of interest, such as tissues or biological fluid collected from certain key organs (Sddergren et al., 2000, 2001). 

Since complete sample hydrolysis is accomplished in the chemically active column and hydrogen chloride is retained, the only gas reaching the thermistor is pure hydrogen. A complete column calibration and detector response is thus achieved by the use of hydrogen alone. 

WE Lambert, L Vanneste, AP De Leenheer. Enzymatic sample hydrolysis and HPLC in a study of phylloquinone concentration in human milk. Clin Chem 38(9) 1743-1748, 1992. 

Hydrolysis of Potassium Ethyl Sulphate. Dissolve about i g. of the crystals in about 4 ml. of cold distilled water, and divide the solution into two portions, a) To one portion, add barium chloride solution. If pure potassium ethyl sulphate were used, no precipitate should now form, as barium ethyl sulphate is soluble in water. Actually however, almost all samples of potassium ethyl sulphate contain traces of potassium hydrogen sulphate formed by slight hydrolysis of the ethyl compound during the evaporation of its solution, and barium chloride almost invariably gives a faint precipitate of barium sulphate. b) To the second portion, add 2-3 drops of concentrated hydrochloric acid, and boil the mixture gently for about one minute. Cool, add distilled water if necessary until the solution has its former volume, and then add barium chloride as before. A markedly heavier precipitate of barium sulphate separates. The hydrolysis of the potassium ethyl sulphate is hastened considerably by the presence of the free acid Caustic alkalis have a similar, but not quite so rapid an effect. 

The crystalline sodium sulphide (NajS,9H20) used to prepare the disulphide is very deliquescent, and only a sample which has been kept in a well-stoppered bottle and therefore reasonably dry should be used. A sample from a badly-stoppered bottle may contain, in addition to the crystals, a certain amount of aqueous solution, in which hydrolysis and partial decomposition will have occurred such a sample should therefore be rejected. Add 4 2 g. of finely powdered sulphur to a solution of 16 g. of the crystalline sodium sulphide in 60 ml. of water, and boil the mixture gently for a few minutes until a clear solution of the disulphide is obtained. 

Does not reduce ammoniacal silver nitrate or Fehling s solution. If, however, the sucrose solution is warmed for some time with the reagent in question, slight hydrolysis to glucose and fructose does take place and reduction then occurs occasionally samples of sucrose will rapidly give a silver mirror, presumably owing to impurities. 

The same method can clearly be applied to the quantitative saponifica- tion or hydrolysis of most esters. Hence it may equally well be used for the quantitative estimation of a known ester in a crude sample. 

The hydrolysis of sulfonate esters of 2 octanol is stereospecific and proceeds with complete inversion of configuration Write a structural formula that shows the stereochemistry of the 2 octanol formed by hydrolysis of an opti cally pure sample of (S) (+) 1 methylheptyl p toluenesulfonate identify the prod uct as / or S and deduce its specific rotation... 

In an extension of the work described m the preceding section Bender showed that basic ester hydrolysis was not concerted and like acid hydrolysis took place by way of a tetrahedral intermediate The nature of the experiment was the same and the results were similar to those observed m the acid catalyzed reaction Ethyl benzoate enriched m 0 at the carbonyl oxygen was subjected to hydrolysis m base and samples were isolated before saponification was complete The recovered ethyl benzoate was found to have lost a por tion of Its isotopic label consistent with the formation of a tetrahedral intermediate... 

Many pharmaceutical compounds contain chromophores that make them suitable for analysis by UV/Vis absorption. Products that have been analyzed in this fashion include antibiotics, hormones, vitamins, and analgesics. One example of the use of UV absorption is in determining the purity of aspirin tablets, for which the active ingredient is acetylsalicylic acid. Salicylic acid, which is produced by the hydrolysis of acetylsalicylic acid, is an undesirable impurity in aspirin tablets, and should not be present at more than 0.01% w/w. Samples can be screened for unacceptable levels of salicylic acid by monitoring the absorbance at a wavelength of... 

Cobalt difluoride [10026-17-2] C0F2, is a pink solid having a magnetic moment of 4, 266 x 10 J/T (4.6 Bohr magneton) (1) and closely resembling the ferrous (Fep2) compounds. Physical properties are Hsted in Table 1. Cobalt(II) fluoride is highly stable. No decomposition or hydrolysis has been observed in samples stored in plastic containers for over three years. 

Bromine ttifluoride is commercially available at a minimum purity of 98% (108). Free Br2 is maintained at less than 2%. Other minor impurities are HF and BrF. Free Br2 content estimates are based on color, with material containing less than 0.5% Br2 having a straw color, and ca 2% Br2 an amber-red color. Fluoride content can be obtained by controlled hydrolysis of a sample and standard analysis for fluorine content. Bromine ttifluoride is too high boiling and reactive for gas chromatographic analysis. It is shipped as a Hquid in steel cylinders in quantities of 91 kg or less. The cylinders are fitted with either a valve or plug to faciUtate insertion of a dip tube. Bromine ttifluoride is classified as an oxidizer and poison by DOT. 

The methacrylates ate slightly to essentially nontoxic to fish and other aquatic species. Hydrolysis data suggest rapid breakdown at alkaline conditions, and studies show that MMA is ultimately biodegradable ia sewage sludge samples. Based on this information, the methacrylates ate not considered to be a significant environmental hazard. 

The freezing point of trimellitic anhydride, the maximum temperature reached during crystallization of a molten sample, is a measure of the product purity. Impurities and trimellitic acid formed by hydrolysis depress the freezing point. 

At strains over 300% the stress occurs mostiy in the amorphous regions up to the point where the sample breaks. AH of the grades exhibit permanent set, and the curves of grades with a Shore Hardness of 55 and higher exhibit a yield point. This means that parts have to be designed for low strains to stay within the area of elastic recovery. Special grades of elastomer are available to provide hydrolysis resistance (194), improved heat aging (195), and improved uv-stabihty (196). 

The ease of hydrolysis of metal alkoxides makes metal analysis a comparatively simple task. In many cases, the metal may be estimated by hydrolysis of a sample in a cmcible, and ignition to the metal oxide. Alternatively, the metal ion may be brought into solution by hydrolysis of a sample with dilute acid, followed by a standard analytical procedure for a solution of that particular metal. If the alcohol Hberated during the hydrolysis is likely to cause interference, it may be distilled from the solution by boiling. 

For the higher alkoxy groups, standard carbon and hydrogen analysis may be used, although careful sample preparation is required because of the ease of hydrolysis. Quantitative vapor-phase chromatography of alcohol Hberated during hydrolysis may also be used, but care must be taken in this case to ensure that hydrolysis is complete before the estimation is carried out. 

For deterrnination of tryptophan, 4 M methanesulfonic acid hydrolysis is employed (18). For cystine, the protein is reduced with 2-mercaptoethanol, the resultant cysteine residue is carboxymethylated with iodoacetic acid, and then the protein sample is hydroly2ed. Also, a one-pot method with mercaptoethanesulfonic acid has been developed for tryptophan and cystine (19). 

From the solubiUty product data the thermodynamic tendency of a metal hydroxide to precipitate as a function of pH can be deterrnined. The actual solubihties on complex samples must be deterrnined empirically however, general predictions can be made regarding metal—metal separations by hydrolysis. 

---