Acidification analytical techniques

Reference materials with certified At and Ct values are now available from Scripps Institution of Oceanography. These materials are prepared from sterilized natural seawater, and are certified by titration against coulometrically standardized acid (At) and by manometric measurement of the CO2 released on acidification (Ct)- Regular analysis of these certified reference materials allows the analyst to check for bias and drift in the analytical technique. The use of certified reference materials in At and Ct analysis is discussed in detail in DOE (1994). 

A stabilization step is necessary in the analysis of trace elements. Usually an acidification down to pH l prevents the precipitation of dissolved components as well as sorption processes. Different concentrations of acid are used according to both, the element to be determined and the analytical technique to be used. The addition of 1% HNO3 is usually used within the determination of most trace elements. 

Yamamoto et al. [33] applied this technique to the determination of arsenic (III), arsenic (V), antimony (III), and antimony (V) in Hiroshima Bay Water. These workers used a HGA-A spectrometric method with hydrogen-nitrogen flame using sodium borohydride solution as a reductant. For the determination of arsenic (III) and antimony (III) most of the elements, other than silver (I), copper (II), tin (II), selenium (IV), and tellurium (IV), do not interfere in at least 30 000-fold excess with respect to arsenic (III) or antimony (III). This method was applied to the determination of these species in sea water and it was found that a sample size of only 100 ml is enough to determine them with a precision of 1.5-2.5%. Analytical results for surface sea water of Hiroshima Bay were 0.72 xg/l, 0.27 xg/l, and 0.22 xg/l, for arsenic (total), arsenic (III), and antimony (total), respectively, but antimony (III) was not detected. The effect of acidification on storage was also examined. 

Phenolic degradation products of lignin in Kraft black liquors were extracted with chloroform after acidification and separated by CE with UVD at 214 nm. Simple CZE was insufficient for the separation of low molecular mass phenolic and neutral degradation products of lignin. Enhanced separation was attained on turning to the MEC technique, where the analytes interact with micelles present in the carrier buffer solution . 

An automated standard addition technique is part of the analytical protocol. An aliquot of a "Tc standard solution is added to a duplicate of the sample during acidification. The "Tc standard is in a nitric acid solution of the same concentration used for sample acidification. To perform the standard addition measurement, the sample acidification monitor instrument automatically substitutes a given volume of the "Tc standard solution for an equal volume of the nitric acid. The volume of the standard solution is selected by the software to yield an estimated threefold higher signal relative to the analysis of an unspiked sample. 

By trapping a volatile analyte as a nonvolatile form these substances can strongly be enriched. Gas dialysis is used in FIA procedures and other flow-analytical methods to enhance their selectivity for volatile substances or substances, which can be converted into volatiles. The configurations shown in Figures 5A-5D are used and adapted. Table 4 summarizes the applications of the gas dialysis technique. Several nonvolatile species, e.g., acetates can be separated after acidification. Gas dialysis membranes can... 

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