Introduction - Determination of Anions in Natural and Treated Waters - page 55

Perkin-Elmer supply a range of accessories for these instruments including an
autosampler (AS-8300), an infrared spectrometer interface, an automatic headspace
accessory (HS101 and H5-6), an autoinjector device (AI-I), also a catalytic reactor and a
pyroprobe (CDS 190) and automatic thermal desorption system (ATD-50) (both useful
for examination of sediments).
The Perkin-Elmer 8700, in addition to the features of the models 8400 and 8500, has
the ability to perform multi-dimensional gas chromatography.
The optimum conditions for capillary chromatography of material heart-cut from a
packed column demand a highly sophisticated programming system. The software
provided with the model 8700 provides this, allowing methods to be linked so that pre-
column and analytical column separations are performed under optimum conditions.
Following the first run, in which components are transferred from the pre-column to the
on-line cold trap, the system will reset to a second method and, on becoming ready, the
cold trap is desorbed and the analytical run automatically started.
Other applications of the model 8700 system include fore-flushing and back-flushing
of the pre-column, either separately or in combination with heart cutting, all carried out
with complete automation by the standard instrument software.
There are many other suppliers of gas chromatography equipment, some of which are
discussed further in Table 1.9.

1.1.14 Column coupling capillary isotachoelectrophoresis
This technique has found limited applications to the determination of anions in water.
The technique offers many similar advantages to ion chromatography, namely multiple-
ion analysis, little or no sample pretreatment, speed, sensitivity and automation.

Non saline waters: chloride, fluoride, nitrate, nitrite and aminoacetate.

Sea water: bromide and sulphide.

Aqueous precipitation: chloride, fluoride and nitrate.

Waste water: chlorite, free cyanide, nitrate and nitrite.

Separation capillary columns are made in fluorinated ethylene-propylene copolymer.
Detection is achieved by conductivity cells and an a.c. conductivity mode of detection is
used for making the separations visible. The driving current is supplied by a unit enabling
independent currents to be preselected for the preseparation and final analytical stages.
The run of the analyser is controlled by a programmable timing and control unit. The
zone lengths from the conductivity detector, evaluated electronically, can be printed on a
line printer.
To satisfy the requirements for the properties of the leading electrolyte applied in the
first stage and, consequently, to decide its composition, two facts had to be taken into
account: the pH value of the leading electrolyte needs to be around 4 or less and at the
same time the separations of the macroconstituents need to be optimised by means other
than adjusting the pH of the leading electrolyte (anions of strong acids).
The choice of the leading electrolyte for the second stage, in which the