Anions in seawater - Determination of Anions in Natural and Treated Waters - page 409

Table 3.15 Plasma system components, and operating conditions

Spectrometer ARL 3400 C Quantovac; 1 m Paschen-Range mounting; grating ruled 1080 lines

mm −1 , 0.309nm mm −1 reciprocal linear dispersion (3rd order). Primary slit width
20µm, secondary slit 50µm, Hamamatsu R-306 photomultiplier tube

Wavelength 180.73nm. 3rd order

Readout Digital readout of mean signal from three 1 0s integrations

Frequency 27.12MHz

Forward
power

1080W

Reflected
power

5W

Observation
height

17mm above load coil

Coolant 11 L min −1 , plasma 1.2L min −1 , carrier 1L min -1 , light path purge 1.5L
min −1

Argon flow
rates

Nebuliser Concentric glass, J.E.Meinhard model TR-30-A3

Source: Reproduced with permission from Elsevier Science [218]

Lebel [215] has described an automated chelometric method for the determination of
sulphate in seawater. This method utilises the potentiometric end-point method for back-
titration of excess barium against EDTA following precipitation of sulphate as barium
sulphate. An amalgamated silver electrode was used in conjunction with a calomel
reference electrode in an automatic titration assembly consisting of a 2.5ml electrical
autoburette and a pH meter coupled to a recorder. Recovery of added sulphate was
between 99 and 101% standard deviations of successive analyses less than 0.5% of the
mean.

3.29.2 Spectrophotometric method
Sulphate has been determined spectrophotometrically by means of the methylthymolblue
method [216,217]. In this method the seawater is passed through a cation exchange
column to exchange metal ions for the hydrogen form sulphate ion then reacts with
barium methylthymol blue complex to form barium sulphate. The released grey coloured
methylthymol blue in alkaline medium is evaluated spectrophotometrically at 460nm.

3.29.3 Inductively coupled plasma atomic emission spectrometry
Inductively coupled plasma emission spectrometry has also been used to determine
sulphate directly in non saline waters [218].
By monitoring the 180.73nm sulphur line, it was possible to detect 0.08mg L −1