Environmental Engineering Reference
In-Depth Information
cessary. In addition, the sample preparation steps have to be harmonized
with the instrumental set-up chosen for determination. It is not surprising
therefore, that the experts of the field have recently made the overall conclu-
sion that sample treatment is one of the most challenging steps in speciation
analyses [3].
2
Sample Preparation Methods for Organotin Analysis
Sample preparation techniques for speciation analyses generally consist of
several steps [11]. The necessary steps depend on the physico-chemical char-
acteristics of the analytes to be determined and of the matrix to be analyzed.
Furthermore, the suitability of the sample preparation steps with the chosen
determination technique must also be assured.
Generally, the instrument combinations applied for speciation analysis are
composed of a selective and sensitive detector coupled with some chromato-
graphic separation step [high performance liquid chromatography (HPLC),
gas chromatography (GC), gel electrophoresis (GE)] to provide time-resolved
introduction of the analytes into the detector [5]. These separation tech-
niques, especially GC, establish certain physico-chemical requirements for
the analytes. This usually demands that the applied sample preparation pro-
cedure isolates the target species—by extraction—from the matrix and then
converts them into suitable forms for separation. Derivatization is the most
frequent approach to fulfil this task in the case where GC is chosen to carry
out the separation. Besides producing volatile and thermally stable species,
it reduces the occurrence of possible interferences during the subsequent an-
alytical steps, particularly at the detection stage. These two steps must be
considered crucial as low extraction efficiencies and
/
or low derivatization
yields may lead to the underestimation of the actual analyte concentration
in the investigated sample [8, 9]. Before the chromatographic separation, the
phase containing the derivatized target analytes is often submitted to purifi-
cation, by a so-called clean-up step. Furthermore, a preconcentration step
is often included in order to improve the limit of detection of the overall
method, mostly combined either with extraction or derivatization. These ma-
jor steps are often further composed of a series of minor operations such as
pH adjustment, agitation, change of solvent, phase separation, transfer from
one vessel to another, dilution, evaporation of organic phase etc. [6].
Each single one of these sample preparation steps (both minor and major)
is associated with possible sources of error. In general, all considerations that
apply to trace organic analysis, also apply to speciation analysis, but in add-
ition, due to the properties of the main target analytes of speciation analysis,
the organometallic compounds, particular precautions have to be taken [7],
specially for preserving the original form of the considered analytes.
