CHAPTER 18 • Metals Analysis by High Performance Liquid Chromatography
347
performance chelation ion chromatography (HPCrC) the order of retention of metal
ions, including earth metals, is reversed with respect to lIC and so barium is eluted
first as a sharp peak followed by Sr, Mg and Ca. The barium separation and determination at mg rl concentration in 1600 mg rl Ca samples with neutral hydrophobic
resin (PS-DVB), precedingly impregnated with methylthymol blue (3,3'-bis[N,Ndi(carboxymethyl)aminomethyllthymol-sulfonephthalein) coupled with an acid elution (0.5 M KN03 + 0.5 M lactic acid) and UV detection by post-column reaction (4(2-pyridylazo)-resorcinol + ZnEDTA) (Paull et al. 1994a) was successfully achieved
showing a detection limit of 3 flg rl for Ba and Sr, as well as Sr and Ca separation was
optimized in milk powder analysis with a phthalein purple (0-cresolphthalein-3',3"bis-methyleneiminodiacetic acid) impregnated column (Jones et al.1994). Similar studies devoted to transition metal determination (Jones et al. 1992; Challenger et al.
1992,1993) resulted in an interesting procedure using a 10 flm particle size, 100 A pore
size PS-DVB resin impregnated with Xylenol Orange, stable from pH 0.5 to 11.5 (Paull
et al. 1994b). The stationary phase enables Ca and Mg removal during the sample oncolumn pre concentration at pH 6 and the separation and determination of Zn, Pb, Ni
and Cu with a step-gradient pH elution. The only drawback of the method is Cd-Mn
co elution, but satisfactory results are obtained for seawater samples (CASS-2 certified
sample). This is a good example showing how small variations in chelating ability
between dyes can be very useful in allowing specific separations. A recent paper provides ample details on an investigation into the parameters involved in the production of a range of dye impregnated chelating columns (10 chelating dyes, mainly based
on triphenylmethane or azo based dyes); for preconcentration and separation of alkaline earth, transition and heavy metals at trace levels within an application devoted
to Ai determination in sea water (Paull and Jones 1996). Finally Haddad et al. developed the dynamic chelating chromatography (Paull et al. 1998) by studying a procedure where a polymeric reversed-phase was dynamically coated with the methylthymol
blue (MTB) ligand. The new system, compared to MTB precoated chelating columns
enabling only the separation of alkaline earth metals, allows the separation of transition and heavy metals. pH and MTB concentration are the key parameters for the retention, and the method is suitable for samples at high ionic strength values (1.0 M NaCI).
18.3.6
Multimode and Multidimensional Liquid Chromatography
Multimode and multidimensional chromatographic techniques respectively involve:
a. the use of two different mechanisms, e.g. ion exchange coupled with ion exclusion
chromatography
b. the use of two or more columns "switching" the total flux or a portion of eluate to
each other
The multimode technique is not usually employed for liquid chromatography of
metal ions but, in this field, there are some applications of liquid-gas chromatography.
The multidimensional technique is also known as "heart cut" column switching. The
term "column switching" includes all techniques by which the direction of the flow of
the mobile phase is changed by valves so that the effluent (or a portion of it) from the
347
performance chelation ion chromatography (HPCrC) the order of retention of metal
ions, including earth metals, is reversed with respect to lIC and so barium is eluted
first as a sharp peak followed by Sr, Mg and Ca. The barium separation and determination at mg rl concentration in 1600 mg rl Ca samples with neutral hydrophobic
resin (PS-DVB), precedingly impregnated with methylthymol blue (3,3'-bis[N,Ndi(carboxymethyl)aminomethyllthymol-sulfonephthalein) coupled with an acid elution (0.5 M KN03 + 0.5 M lactic acid) and UV detection by post-column reaction (4(2-pyridylazo)-resorcinol + ZnEDTA) (Paull et al. 1994a) was successfully achieved
showing a detection limit of 3 flg rl for Ba and Sr, as well as Sr and Ca separation was
optimized in milk powder analysis with a phthalein purple (0-cresolphthalein-3',3"bis-methyleneiminodiacetic acid) impregnated column (Jones et al.1994). Similar studies devoted to transition metal determination (Jones et al. 1992; Challenger et al.
1992,1993) resulted in an interesting procedure using a 10 flm particle size, 100 A pore
size PS-DVB resin impregnated with Xylenol Orange, stable from pH 0.5 to 11.5 (Paull
et al. 1994b). The stationary phase enables Ca and Mg removal during the sample oncolumn pre concentration at pH 6 and the separation and determination of Zn, Pb, Ni
and Cu with a step-gradient pH elution. The only drawback of the method is Cd-Mn
co elution, but satisfactory results are obtained for seawater samples (CASS-2 certified
sample). This is a good example showing how small variations in chelating ability
between dyes can be very useful in allowing specific separations. A recent paper provides ample details on an investigation into the parameters involved in the production of a range of dye impregnated chelating columns (10 chelating dyes, mainly based
on triphenylmethane or azo based dyes); for preconcentration and separation of alkaline earth, transition and heavy metals at trace levels within an application devoted
to Ai determination in sea water (Paull and Jones 1996). Finally Haddad et al. developed the dynamic chelating chromatography (Paull et al. 1998) by studying a procedure where a polymeric reversed-phase was dynamically coated with the methylthymol
blue (MTB) ligand. The new system, compared to MTB precoated chelating columns
enabling only the separation of alkaline earth metals, allows the separation of transition and heavy metals. pH and MTB concentration are the key parameters for the retention, and the method is suitable for samples at high ionic strength values (1.0 M NaCI).
18.3.6
Multimode and Multidimensional Liquid Chromatography
Multimode and multidimensional chromatographic techniques respectively involve:
a. the use of two different mechanisms, e.g. ion exchange coupled with ion exclusion
chromatography
b. the use of two or more columns "switching" the total flux or a portion of eluate to
each other
The multimode technique is not usually employed for liquid chromatography of
metal ions but, in this field, there are some applications of liquid-gas chromatography.
The multidimensional technique is also known as "heart cut" column switching. The
term "column switching" includes all techniques by which the direction of the flow of
the mobile phase is changed by valves so that the effluent (or a portion of it) from the