35 0
C. Sarzanini
graphic separation (75 mM H 2 SO - 100 mM HCI- 100 mM KCI) and a cation exchange
column with higher capacity. In this way detection limits of 10 and 30 ng rl are achieved
for Cd and Pb respectively for seawater samples (200 ml) (Cardellicchio et al. 1993).
18.S
Detection and Hyphenated Techniques
Refractive index and spectrophotometric and electrochemical detectors were traditionally used in liquid chromatography, while IC introduced the use of suppressed eluent conductivity detection. Analysis of complex matrices (e.g. foods, new materials, pharmaceutical and environmental samples) and speciation studies, in the field of metal analysis,
are fundamental topics and have stimulated studies for the improvement of detection
sensitivity and selectivity. For instance, spectrophotometric or electrochemical detection were coupled with post-column reactions, but a new approach, hyphenation, has
become the emerging field of research. Hyphenation concerns the coupling of unconventional detectors with LC. This means that atomic spectroscopies (absorption and emission: flame, graphite furnace, hydride generation, cold vapour, plasma) were applied to LC.
In the field of atomic emission techniques, the majority of applications have been
based on inductively-coupled plasma (ICP). This source is more suitable for LC since
the chromatographic flow rate is compatible with conventional, i.e. pneumatic chamber, ICP interfaces. The use of an ultrasonic nebulizer or direct injection nebulization
(DIN), with microbore columns, increased transport efficiency to the ICP interface. Finally, ICP has been used as a source for mass spectrometry (MS) and ICP-MS has become one of the most powerful techniques for speciation analysis when coupled with
separation procedures.
For more details both the advances in detection techniques for IC (Buchberger and
Haddad 1997), and the ICP-MS detection modes for chromatography and capillary electrophoresis (Sutton et al.1997), have recently been reviewed. Some examples, concerning difficult sample analysis (e.g. rare earth) or metal speciation (As, Se, Hg and Cr),
will be given hereafter.
The determination of rare earth elements is critical due to the nature of the samples,
e.g. nuclear-power waste, rock samples. An ion-exchange chromatographic separation
of rare earth elements in seven geological reference materials to remove matrix interferences in ICP-AES determination (Farinas et al. 1995) as well as a review of their
determination (Kumar 1994) could summarize the classic approaches to rare earth
element separation and determination. Reversed phase columns with both isocratic
and gradient separation were coupled with ICP-MS detection. Isocratic conditions
allowed rare earth separation into groups but was preferred for the powerful selectivity of ICP-MS, enabling 0.4-5.0 flg rl detection limits, and for providing reduced time
for analysis (Braverman 1992). Another example is the ICP-MS determination of fission product isotopes. U or U + Pu are preeluted with 1 M HCI or 0.4 M HN03, and
isobaric overlaps, present in direct mass spectrometric determinations, are removed
as shown by measurements of isotopic composition of Nd in a high U and Pu matrix
(Rollin et al. 1996). Finally the separation of some lanthanides with chelating chromatography must be mentioned (Kobayashi et al. 1992), where an HCI solution, instead
of a ligand, was used as a mobile phase coupled with a selective chelating resin, namely
a porous polymer impregnated with 2-ethylhexyl hydrogen 2-ethylhexyl phospho nate
C. Sarzanini
graphic separation (75 mM H 2 SO - 100 mM HCI- 100 mM KCI) and a cation exchange
column with higher capacity. In this way detection limits of 10 and 30 ng rl are achieved
for Cd and Pb respectively for seawater samples (200 ml) (Cardellicchio et al. 1993).
18.S
Detection and Hyphenated Techniques
Refractive index and spectrophotometric and electrochemical detectors were traditionally used in liquid chromatography, while IC introduced the use of suppressed eluent conductivity detection. Analysis of complex matrices (e.g. foods, new materials, pharmaceutical and environmental samples) and speciation studies, in the field of metal analysis,
are fundamental topics and have stimulated studies for the improvement of detection
sensitivity and selectivity. For instance, spectrophotometric or electrochemical detection were coupled with post-column reactions, but a new approach, hyphenation, has
become the emerging field of research. Hyphenation concerns the coupling of unconventional detectors with LC. This means that atomic spectroscopies (absorption and emission: flame, graphite furnace, hydride generation, cold vapour, plasma) were applied to LC.
In the field of atomic emission techniques, the majority of applications have been
based on inductively-coupled plasma (ICP). This source is more suitable for LC since
the chromatographic flow rate is compatible with conventional, i.e. pneumatic chamber, ICP interfaces. The use of an ultrasonic nebulizer or direct injection nebulization
(DIN), with microbore columns, increased transport efficiency to the ICP interface. Finally, ICP has been used as a source for mass spectrometry (MS) and ICP-MS has become one of the most powerful techniques for speciation analysis when coupled with
separation procedures.
For more details both the advances in detection techniques for IC (Buchberger and
Haddad 1997), and the ICP-MS detection modes for chromatography and capillary electrophoresis (Sutton et al.1997), have recently been reviewed. Some examples, concerning difficult sample analysis (e.g. rare earth) or metal speciation (As, Se, Hg and Cr),
will be given hereafter.
The determination of rare earth elements is critical due to the nature of the samples,
e.g. nuclear-power waste, rock samples. An ion-exchange chromatographic separation
of rare earth elements in seven geological reference materials to remove matrix interferences in ICP-AES determination (Farinas et al. 1995) as well as a review of their
determination (Kumar 1994) could summarize the classic approaches to rare earth
element separation and determination. Reversed phase columns with both isocratic
and gradient separation were coupled with ICP-MS detection. Isocratic conditions
allowed rare earth separation into groups but was preferred for the powerful selectivity of ICP-MS, enabling 0.4-5.0 flg rl detection limits, and for providing reduced time
for analysis (Braverman 1992). Another example is the ICP-MS determination of fission product isotopes. U or U + Pu are preeluted with 1 M HCI or 0.4 M HN03, and
isobaric overlaps, present in direct mass spectrometric determinations, are removed
as shown by measurements of isotopic composition of Nd in a high U and Pu matrix
(Rollin et al. 1996). Finally the separation of some lanthanides with chelating chromatography must be mentioned (Kobayashi et al. 1992), where an HCI solution, instead
of a ligand, was used as a mobile phase coupled with a selective chelating resin, namely
a porous polymer impregnated with 2-ethylhexyl hydrogen 2-ethylhexyl phospho nate