Filters absorption procedure

Olafsson [427] has described a semiautomated determination of manganese in seawater using leucomalachite green. The autoanalyser had a 620 nm interference filter and 50 minute flow cells. Findings indicated initial poor precision was related to pFl, temperature, and time variations. With strict controls on sample acidity and reaction conditions, the semiautomated method had high precision, at least as good as that achieved by preconcentration and atomic absorption procedures, and provided precise, rapid, shipboard information... 

Absorption methods are analogous to optical absorption procedures in which the attenuation of a band or line of X-radialion is the analytical variable. Wavelength selection is accomplished with a monochromator such as that shown in Figure 12-9 or by a filter technique similar to that illustrated in Figure 12-8. Alternatively, the monochromatic radiation front a radioactive source may be used. 

Ultrafiltration utilizes membrane filters with small pore sizes ranging from O.OlS t to in order to collect small particles, to separate small particle sizes, or to obtain particle-free solutions for a variety of applications. Membrane filters are characterized by a smallness and uniformity of pore size difficult to achieve with cellulosic filters. They are further characterized by thinness, strength, flexibility, low absorption and adsorption, and a flat surface texture. These properties are useful for a variety of analytical procedures. In the analytical laboratory, ultrafiltration is especially useful for gravimetric analysis, optical microscopy, and X-ray fluorescence studies. 

Calf thymus (CT) DNA was first fragmented by sonication, then purified by a standard procedure. Agarose gel electrophoresis for the sonicated CT DNA revealed a distribution in molecular weight ranging from 30 kDa to 260 kDa which is equivalent in base pairs (bp) from 40 to 400 (1 bp = 660 Da). The DNA fragments were reacted with HEDS in the presence of l-cyclohexyl-3-(2-morpholinoethyl) carbodi-imide metho-p-toluenesulfonate (CMC/jTs). Finally, the reaction mixture was gel-filtered and the macro-molecular fractions, when displayed the characteristic absorption of 260 nm of the nucleic bases, were collected. 

The collection behaviour of chromium species was examined as follows. Seawater (400 ml) spiked with 10-8 M Crm, CrVI, and Crm organic complexes labelled with 51Cr was adjusted to the desired pH by hydrochloric acid or sodium hydroxide. An appropriate amount of hydrated iron (III) or bismuth oxide was added the oxide precipitates were prepared separately and washed thoroughly with distilled water before use [200]. After about 24 h, the samples were filtered on 0.4 pm nucleopore filters. The separated precipitates were dissolved with hydrochloric acid, and the solutions thus obtained were used for /-activity measurements. In the examination of solvent extraction, chromium was measured by using 51Cr, while iron and bismuth were measured by electrothermal atomic absorption spectrometry. The decomposition of organic complexes and other procedures were also examined by electrothermal atomic absorption spectrometry. 

The precision of absorption measurements depends upon the degree of sophistication of the instrumentation and on the chemical species involved, both of which can affect the apparent validity of the Beer-Lambert law. Where a single absorbing species exhibiting a broad flat maximum is to be determined, adequate results can often be achieved with a simple filter-photometer. In the visible region, this technique is known as colorimetry. The inherent disadvantage of colorimetric procedures using simple filter instruments with a broad bandpass lies in the invalidation of the Beer-Lambert law and the lack of compatibility between results from different... 

Procedure Dissolve accurately 22.5 mg of /ram-clomiphene citrate and 52.5 mg of cis-clomiphene citrate (approx. 1 2.3) into 10 ml of DW in a clean 50 ml separating funnel. Add to it 1 ml solution of sodium hydroxide (5% w/v in DW). In the alkaline medium the base is liberated which is extracted successively with 3 portions of solvent ether (10 ml each). The combined ethereal layer is washed with two portions of DW (10 ml each). The resulting ethereal fraction is dried over anhydrous sodium sulphate, filter, evaporate to diyness carefully over an electric water-bath and dissolve the residue in 1 ml of CS2. Now, record the absorption curve in a 0.2 mm cell over the range 12.50 to 14.00 pm. Calculate the absorbance for the peaks at 13.16 and 13.51 pm respectively by employing the base-line method (see section 3. l. B in this chapter) between the minima at 12.66 and 13.89 pm. 

Procedure To the sample which contains 20-300 /xg of pertechnetate in 5-20 ml of solution, are added potassium perchlorate solution (2 ml, 1 mg KCIO per ml) and enough NaCl to make the solution approximately 1 M. The solution is heated and neutralized with ammonia. Pertechnetate is precipitated with aqueous 5 % tetraphenylarsonium chloride reagent. The precipitate is filtered, washed and dried, and a 2-mg portion is mixed with potassium bromide (300 mg). The mixture is pressed to form a clear disc by the usual technique. The infrared spectrum is recorded between 10 and 12 /x. The peak absorption is measured at 11.09 /X by the base-line technique. 

Results(79) from a Round Robin analyses for the lead content of air particulate filters were given along with the average values obtained from 65 laboratories participating in the study. The procedures used by the other laboratories included x-ray, FAA, flameless atomic absorption, emission spectrometric, and dithizone-spectropho-tometric. The overall analytical agreement was very good. 

The correction for the pyrolytic production of elemental carbon is accomplished by measuring the amount of elemental carbon oxidation necessary to return the filter reflectance to its initial value. This is facilitated by the three-step elemental carbon oxidation which produces a relatively slow initial rise in the reflectance. A typical output is shown in Figure 3. The pyrolysis correction corresponds to the shaded area which is added to peaks 1 and 2 to give the corrected value for organic carbon. This procedure assumes that the mass absorption coefficient of the pyrolytically produced elemental carbon is the same as that of the original elemental carbon. Research to test this assumption is continuing. 

Alternatively, the bomb combustion dissolution procedure can be combined with the hydride evolution method previously described for arsenic, tin, and bismuth. After completion of the bomb combustion and absorption of gases into the 10 ml of water, the solids are filtered out and the filtrate collected into a 50 ml volumetric flask containg 20 ml of hydrochloric acid. This is a suitable stock solution for the hydride evolution method. 

Simplified analytical procedures for determination of gas-phase organic acids would be very beneficial. Currently, the acids are collected by using impregnated filters, denuder tubes, or water absorption techniques and then an ion chromatographic analysis. Normally, the collection and analysis steps are decoupled in time (i.e, samples collected at a field site are returned to a home laboratory for IC analysis). Once again, blank samples must be utilized to compensate for contamination during transport and storage prior to analysis. 

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