Dissolved sampling

One of the well known advantages of resonance Raman spectroscopy is that samples dissolved in water can be studied since water is transparent in the visible region. Furthennore, many molecules of biophysical interest assume their native state in water. For this reason, resonance Raman spectroscopy has been particularly strongly embraced in the biophysical connnunity. 

Weigh out accurately about 1 25 g. of the sample, dissolve it in water and make the solution up to 250 ml. Titrate this solution against 25 ml. of the standard Fehling s solution, precisely as before. 

The choice of solvent cannot usually be made on the basis of theoretical considerations alone (see below), but must be experimentally determined, if no information is already available. About 0 -1 g. of the powdered substance is placed in a small test-tube (75 X 11 or 110 X 12 mm.) and the solvent is added a drop at a time (best with a calibrated dropper. Fig. 11, 27, 1) with continuous shaking of the test-tube. After about 1 ml. of the solvent has been added, the mixture is heated to boiling, due precautions being taken if the solvent is inflammable. If the sample dissolves easily in 1 ml. of cold solvent or upon gentle warming, the solvent is unsuitable. If aU the solid does not dissolve, more 11,27,1. solvent is added in 0-5 ml. portions, and again heated to boiling after each addition. If 3 ml. of solvent is added and the substance... 

In many applications of mass spectrometry, it is necessary to obtain a mass spectrum from a sample dissolved in a solvent. The solution cannot be passed directly into the mass spectrometer because, in the high vacuum, the rapidly vaporizing solvent would entail a large pressure increase, causing the instrument to shut down. 

Analytical and Test Methods. The acid number of terephthahc acid discussed above is a titration of a sample dissolved in pyridine, using a sodium or potassium hydroxide titrant. However, specifications on certain impurities are so strict that this test caimot, as a practical matter, be failed. Its use has been discontinued by some manufacturers. 

The aniline and sulphuric acid are cautiously mixed in a round flask (250 c.c.) and heated to 180—190° in an oil or metal bath for four to five hours until a sample dissolved in water remains clear on the addition of caustic soda in excess and no aniline separates. The product is poured into cold water, which precipitates the sulphanilic acid as a grey ciystalline mass.It is filtered, washed with a little cold water, recrystallised from hot water with the addition of a little animal charcoal, and dried in the air. Yield, 25 — 30 grams. 

Procedure. Weigh out accurately about 5 g of the oil sample, dissolve in a small volume of white spirit and transfer to a 50 mL graduated flask use the same solvent to wash out the weighing bottle and finally to make up the solution to the mark. 

The simplicity mentioned above exists for various kinds of samples that meet the fundamental requirements laid down in Chapters 6 and 7. Examples are a thin film on a suitable substrate, a sample dissolved at low concentration in a solvent transparent to x-rays, or a sample uniformly dispersed in a similarly transparent medium. In all cases, scattered x-rays should be at a minimum to keep the background low. From the point of view taken here, a trace is thus regarded as a major constituent in a sample if sensible absorption and enhancement effects are absent—if, that is, Equation 7-3 is valid. 

Ion HPLC Sample dissolved in water, separation on Dionex 480 nm Drinks, instant 0 ... 

Samples dissolved in methanol, diluted in water and injected in Spherisorb ODS-2 colunm, elution with water/acetonitrile (7 3) containing 5 mM octylamineZ-phosphoric acid at pH 6.4 Separation on STR ODS-II colunms and gradient elution with 20 mM anunonium phosphate buffer (pH 6.8)/isopropanol (25 1 v v) and acetonitrile) at 40°C... 

The sample dissolved in a weak (nonpolar for siliea gel), volatile solvent is applied as a narrow band across the plate. Manual applieation can be aehieved with a pipet or syringe gnided by a ruler, or roimd spots ean be placed close together, side by side, in a line. Sample applieation instruments are available commercially, e.g., a meehan-ical streaker from Analtech and an antomated spray-on apparatus from CAMAG. 

For soil samples, dissolve the residue in an appropriate volume of acetonitrile prior to HPLC analysis. 

Teeth Sample dissolved in HN03, purified by TRU-spec column and electrodeposition a -Spectrometry 2.7 fCi/sample 98% Culot et al. 1997... 

LD), in which flash vaporisation of the sample is induced, may be applied. Other techniques which permit detection of less-volatile chemical species are FD (with simultaneous desorption/ionisation of molecules), FAB (with the sample dissolved (dispersed) in a suitable liquid) and SIMS (based on bombardment of a solid surface with high-energy ions). LD-FUCR-MS is superior to FAB-MS for polymer/additive identification because it gives molecular ion fragmentation [83],... 

Proton nmr spectra of fractions A, B and C and all bottoms products were recorded on a Varian HA lOOnmr spectrometer using a solution of the sample dissolved in pyridine-d5. Spectra were run at room temperature with tetra methyl silane (TMS) as an internal standard, with a sweep width of 0 to 1000 cps from TMS. Fraction D and the whole coal were only partly soluble in pyridine and it was therefore not possible to get representative spectra from them. 

Figure 25 H NMR spectrum of the film sample dissolved in 1 part trichlorobenzene and 2 parts ortho-dichlorobenzene. 

Table 9-1 Results from 20 repeat readings of 5 g of sample dissolved in 100 ml water...

Fig. 3 Prepared ZnO QDs embedded in Si02 matrix under (a) ordinary and (b) UV (365 nm excitation) lamps. (A) Solid samples, (B) samples dissolved in ethanol, and (C) samples dissolved in water. Photographs were taken with a digital camera just after completion of synthesis, (c) TEM Image of symmetrically dispersed ZnO QDs embedded in Si02 matrix. (Figure adapted from [40])...

Prepare the samples dissolved in water or non-amine-containing buffer at an expected concentration level that falls within the standard curve range. The assay can tolerate the presence of most buffer salts, denaturants, and detergents. However, the standard curve should be run in the same buffer environment as the samples to obtain consistent response. 

Germanium in samples dissolved in water or dioxane or dispersed into borax disks can be determined by XRF (X-ray fluorescence), using Ka radiation and arsenic as internal standard24. 

Two steel samples, dissolved in 50 cm3, each 1.000 g, gave the following absorbances ... 

The NMR spectrum of calcitriol, recorded on a Varian XL-100/Nicolet TT-100 pulsed Fourier Transform NMR spectrometer, with internal deuterium lock, is shown in Figure 2 (2). The spectrum was recorded using a solution of 0.84 mg of sample dissolved in 50 microliters of CD OD (100%D) containing 1% v/v tetramethylsilane in a 1.7 mm capillary tube. The spectral assignments are given in Table I. 

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