DIFFERENT FIELDS OF APPLICATIONS - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 295

A complexation of the traces with a NaDBDTC solution (sodium dibutyldi-
thiocarbamate) leads to a coprecipitation. Subsequent adsorption of the
carbamate traces by a reverse-phase column (e.g., Chromosorb, E. Merck,
Darmstadt, Germany) and a final elution of the adsorbed complexes by 2 ml of
subboiled chloroform gives an enriched eluate (by a factor of about 50). After
the final solution is spiked with an internal standard, an aliquot of 10-100 μ lis
analyzed as already described. The detection limits for the aqueous solutions
including the filtrate are about 0.1 ng/ml.
The suspended matter separated from the filtrate can be collected on
Nuclepore filters (Nuclepore Corp., Pleasanton, California), weighed, and
digested by concentrated nitric acid or a mixture of nitric and hydrofluoric
acid (2 : 1). The determination by TXRF can be carried out as usual. Detection
limits go down to 5 μ g/g; precision and accuracy are characterized by a relative
standard deviation of about 10% [6].
The determination of mercury in wastewater is difficult because of its high
vapor pressure at room temperature, which leads to the evaporation and loss of
this element. Vázquez and colleagues used APDC (ammonium pyrrolidine
dithiocarbamate) or EDTA (ethylenediaminetetraacetic acid) and oxalic acid
(HOOC-COOH, dicarboxylic acid) for trapping traces of mercury in industrial
wastewaters [9]. The method was applied to control a cleaning process of
effluents. Kregsamer and coworkers recommend a complexation of mercury
with thiourea CS(NH 2 ) 2 at pH = 10. After deposition of 10 μ l droplets on a
quartz reflector, mercury could be determined in wastewater samples, such as
industrial and municipal effluents [10].
Some national and international programs have been carried out for pollu-
tion control of rain water, river water, and seawater in the 1980s and 1990s. The
river Elbe [6,11,12] was tested systematically for contaminants, and appropriate
actions were taken for regeneration. Trace contaminants in the open Atlantic
Ocean were studied at several deep-water stations [13], and heavy-metal traces
and pollutant transfer were investigated in the North Sea [14,15]. These field
experiments demonstrated the ability of TXRF to automatically handle scores
of water samples with a high degree of reliability.
An impressive example stems from Prange etal . [11,12] who investigated the
water quality of the river Elbe in an extensive international environmental
research project. A specific task was the determination of arsenic in the filtrate,
in suspended matter, and sediment of the river. Figure 5.2 shows the profile of
arsenic in suspended matter along the river from its source to the mouth. The
water samples were taken with the help of a helicopter and analyzed by TXRF
after pressure filtration. Scandium was used as internal standard. Related to the
dry mass of the suspended matter, the average content was found to be about
45 μ g/g. In the years from 1993 to 1998, pollution from industrial districts has
been reduced significantly.
Some recent examples for analyses of drinking water [16], rain water [17],
river water [18], freshwater [19], and seawater [20] prove the efficiency of
TXRF. Drinking water could be analyzed directly without preconcentration.