Chemistry Reference
In-Depth Information
non-quantitative recovery of cyanide preclude the use of direct injection to determine
total cyanide in samples containing copper and nickel. These samples may be analysed
after acid distillation and caustic trapping. The cyanide in the caustic solution can then be
determined by ion chromatography with electrochemical detection.
Category 3 includes those cyanides which are inert and therefore totally undissociated,
such as Au(CN)
2
−
(log B
2
=38.3), Fe(CN)
6
3−
(log B
6
= 42) and Co(CN)
6
3−
(log B
6
=64).
No free cyanide was detected for these complexes. Although these complexes do not
elute under the chromatographic conditions used, they can be eluted and determined by
using different chromatographic conditions and conductivity detection.
Samples containing both free cyanide (or weakly complexed cyanide) and strongly
complexed cyanide can be analysed for free cyanide by direct injection. The
determination of total cyanide (both free and strongly complexed) requires distillation of
the sample with caustic trapping.
The application of this technique is also discussed under multianion analysis in section
12.2.3.
2.57.2
Preconcentration
The application of preconcentration techniques is discussed in section 15.1.6.
2.58
Mixed halides
2.58.1
Ion selective electrodes
Trojanowicz and Lewardowski [192] have described a multiple potentiometric system for
the continuous determination of chloride, fluoride, nitrate and ammonia in non saline
waters. They describe a flowthrough system for the simultaneous determination of
chloride (30-150mg L
−1
), fluoride (0.08-0.4mg L
−1
), nitrate (5-20mg L
−1
) and ammonia
(0.05-0.5mg L
−1
). Solid state chloride and fluoride electrodes, a PVC membrane nitrate
electrode and a gas-sensing Orion 95-10 ammonia electrode were employed, the air-
segmented sample stream being mixed with appropriate buffering solutions before
entering the measuring cell. During continuous operation, calibration twice daily was
necessary to eliminate the effects of potential drift. Best results were obtained when the
chloride-nitrate ratio in the calibrating solution was similar to that in the non saline water
being analysed (14:1).
Apparatus
Peristaltic multichannel pump type DP2-2 VEB MLW (GDR) with tubings from Ismatec
(Switzerland). Ionalyzer Orion (USA) model 801A and digital printer model 751.
Homemade electronic electrode switch for 5 channels, controlled by digital printer.
Thermostat model U-1 from VEB MLW (GDR). The following electrodes were used as
sensors—Chloride electrode from MERA-ELWRO (Poland), home made fluoride
electrode, nitrate electrode with solid silver contact and PVC membrane containing
bathophenanthroline-nickel(II) complex and 2-nitrophenyloctyl ether, ammonia electrode
Orion (USA) model 95-10.
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