Method and apparatus for measuring cyanide

A system for measuring cyanides in a sample employs a photoillumination component for producing ultraviolet radiation to dissociate cyanides contained in an alkaline sample. The system includes filtering components interposed between the photoillumination components and an alkaline sample to be tested for passing lower frequency ultraviolet radiation to produce an irradiated sample in which cyanides have been dissociated, while blocking high frequency ultraviolet radiation to inhibit thiocyanate dissociation. Thin-film distillation components are included for separating cyanide from the irradiated sample to produce recovered cyanide for measurement purposes, and measuring components are provide for receiving the recovered cyanide generating a recordable signal indicative of recovered cyanide quantity.

TECHNICAL FIELD 
This invention relates generally to a method and apparatus for measuring 
the amount of cyanide in a sample, and it more particularly relates to 
such a method and apparatus having improved cyanide separation 
capabilities. 
BACKGROUND ART 
The toxic compounds called cyanides threaten our health and environment. 
Harmful to man, and even more so to aquatic life, these compounds are 
produced and introduced into our environment in many damaging ways, so 
that it is important to understand and restrict this form of environmental 
pollution. Measuring the cyanides in a selected sample is one important 
step in the process of improving the environment. 
Of the various existing types and kinds of analytical methology and related 
apparatus employed to measure cyanides, automated systems have achieved 
notable results. For example, refer to U.S. Pat. No. 4,265,857, and to a 
publication entitled "Chemistry of Wastewater Technology" published by Ann 
Arbor Science Publishers, Inc. of Ann Arbor Michigan, Library of Congress 
Catalog Card No. 76-50991, ISBN 0 250 40185-1, which are incorporated 
herein by reference. 
As described in Chapter 20 of "Chemistry of Wastewater Technology," such an 
automated system involves the steps of separation, absorption, and 
measurement, with ultraviolet irradiation being employed to dissociate 
cyanides in the process of separation, along with thin-film distillation 
and chemical absorption techniques. 
A typical ultraviolet radiation unit includes an ultraviolet lamp, 
surrounded by a quartz coil, through which is passed an acidic sample to 
be tested. The quartz coil passes all of the several energy levels, or 
spectral lines, of ultraviolet radiation produced by the ultraviolet lamp, 
of wave lengths between approximately 150 millimicrons and 400 
millimicrons. This spectrum of ultraviolet radiation causes the break down 
of all cyanide complexes, including the strong iron and cobalt cyanide 
complexes. The cobalt complex is dissociated by the ultraviolet radiation 
both of approximately 255 millimicrons, and of approximately 310 
millimicrons. In this manner, the cyanides are dissociated for subsequent 
measurement. 
The thin-film distillation separates the resulting hydrogen cyanide gas, 
and the HCN gas is then absorbed in a sodium hydroxide solution for 
subsequent colorimetric measuring. Thus, all of the cyanides can be 
detected and measured in a large number of different samples in a 
continuous, automated manner. 
The quartz coil in the conventional irradiation unit of the system is 
permeable to all, or at least substantially all, of the ultraviolet 
spectrum, thereby enabling the ultraviolet radiation to break down all of 
the cyanide complexes in the acidic sample. However, thiocyanate (SCN) is 
also dissociated, and therefore, is detected along with the cyanides, 
thereby causing somewhat inaccurate higher cyanide measurements. Thus, 
dissociation of the thiocyanate is unwanted and undesirable for most 
applications. Consequently, while the present cyanide detection 
measurement system is satisfactory for most applications, it would be 
highly desirable to have a cyanide measurement system, which would 
dissociate all the cyanide complexes, including the strong cobalt complex, 
without dissociating thiocyanate. 
DISCLOSURE OF INVENTION 
Therefore, the principal object of the present invention is to provide a 
new and improved measurement method and apparatus for indicating the 
amount of cyanide in a sample, without detecting or indicating the 
presence of thiocyanate, in a convenient and precise manner. 
It is a further object of the present invention to provide such a new and 
improved method and apparatus, which enables dissociation of strong 
cyanide complexes, including cobalt and iron complexes, without the 
dissociation of thiocyanate. 
Yet another object of the present invention is to provide such an improved 
method and apparatus, which requires only simple modifications of 
exisiting systems. 
Briefly, the above and further objects of the present invention are 
realized by providing a new and improved system for measuring cyanides in 
liquid samples. 
The system includes a filtering component interposed between an ultraviolet 
photoillumination device and a sample to be tested, for passing only lower 
frequency ultraviolet radiation to irradiate the sample for breaking up 
cyanide complexes contained therein, while blocking high frequency 
ultraviolet radiation to inhibit the dissociation of the thiocyanate. 
Thin-film distillation components are included for separating cyanide from 
the irradiated sample to produce recovered cyanide for measurement 
purposes, and measuring components are provide for receiving the recovered 
cyanide and for generating a recordable signal indicative of the amount of 
recovered cyanide without any indication of thiocyanate. 
Thus, the method and apparatus of this invention alleviates the 
above-mentioned drawbacks of existing techniques. The filter blocks 
ultraviolet radiation in the range of approximately 150 millimicrons and 
approximately 290 millimicrons, to inhibit thiocyanate dissociation, while 
passing the remaining longer ultraviolet wavelengths. 
The pH of the sample is raised to enable the strong cobalt cyanide 
complexes to be completely broken up as well. In this regard, in prior 
known systems, the samples are acidic, and are irradiated with 
non-filtered quartz irradiation units to provide a complete dissociation 
of the cyanide complexes, as well as the release of the unwanted 
thiocyanate. However, it has been discovered that an alkaline sample 
combined with the filtered irradiation, achieves total break down of 
cyanide complexes, without dissociating thiocynate. In this manner, more 
convenient cyanide measurements are provided, with only a simple 
modification of existing systems.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings, and more particularly to FIG. 1, there is 
shown a cyanide measuring system 10, which is constructed according to the 
present invention, and which is used to measure the different amounts of 
different cyanides, contained in a series of different water samples 
admitted seriatim to the system 10 at an inlet 12B. The system 10 
generally comprises a separation section including a photoillumination 
irradiation unit 11A for causing the break down of cyanide complexes in 
the water samples being pumped through it. A 11A thin-film distillation 
unit 11B separates cyanide from the irradiated samples to produce 
recovered cyanide for measuring purposes. An absorption section 11C 
provides for the sodium hydroxide absorption of the hydrogen cyanide gas 
evolved from the samples. A measurement section 11D automatically measures 
the cyanide in the samples from the section 11C. 
A segmented flow pump 12 transfers the samples and reagents to the system 
10 at inputs 12A-12N and 12P to outputs, 13, 15-21. The samples (usually 
made alkaline for preservation) are mixed with a suitable quantity of 
nitrogen by admitting them to an inlet 13 to a sample mixing coil 25, to 
provide the vehicle for the segmented flow of the series of water samples 
to be tested. In the system 10, air can be used in place of nitrogen. 
The photoillumination unit 11A is in the form of a filtered ultraviolet 
irradiation unit 30, which irradiates the series of segmented samples 
flowing through it from the coil 25, to dissociate the cyanide complexes 
contained in the samples. The unit 30 emits light in only a limited porton 
of the ultraviolet spectrum, namely, between approximately 290 
millimicrons and approximately 400 millimicrons wavelengths of ultraviolet 
radiation, for dissociating the cyanides from their cyanide complexes, 
without dissociating thiocyanate. 
The irradiated samples flowing continuously from the outlet of the 
irradiation unit 30 are mixed with a suitable acid mixture via a line 15, 
as well as air under pressure received via a line 16. The continuous 
thin-film evaporation unit 11B receives the aerated acidified samples for 
separating the cyanides from the samples. The evaporation unit 11B is 
disclosed more fully in the foregoing mentioned U.S. patent. The thin-film 
evaporation unit 11B causes hydrogen cyanide gas to be released, together 
with some water, from the acidified samples in a continuous segmented flow 
basis. The water is condensed back, and the hydrogen cyanide gas is 
absorbed via the absorption section 11C. 
The segmented samples flowing from the outlet of the thin-film evaporation 
unit are mixed with sodium hydroxide from a line 17 in the section 11C, 
which is an absorption coil 50. In this regard, the hydrogen cyanide gas 
is forced with air through the coil, simultaneously with sodium hydroxide, 
as more fully described in the foregoing mentioned publication, to recover 
the hydrogen cyanides in each sample. 
The outlet of the absorption coil 50 is pumped back through the pump 12 via 
a return line 18, to be mixed with a suitable buffer and segmented by air, 
to a sample mixing coil 55. 
The outlet of the sample mixing coil 55 is mixed with chloramine-T from a 
line 19, in a mixing coil 57, where it is mixed with a color reagent from 
a line 20 from the pump 12. 
The outlet of the mixing coil 57 is connected through a mixing coil 60 to a 
colorimeter 65 and discharged through a line 66, with the pump 12 driving 
the system and exhausting it from the line 21. 
The colorimeter provides a recordable signal indicative of the recovered 
cyanide quantities to an input of a recorder 70, connected to a printer 
75. 
Thus, the method and system of this invention provides dissociation of all 
cyanide complexes, including cobalt complexes, without thiocyanate 
interference. It achieves this by employing an alkaline sample with a new 
and improved ultraviolet irradiation unit, which filters selected 
ultraviolet energy levels to inhibit the thiocyanate break down. 
It is a feature of the present invention to acidify the samples with the 
acid mixture via line 15, after the irradiation, rather than prior to it, 
for the purpose of causing the stronger cyanide complexes, such as the 
cobalt complexes, to break down, without the break down of thiocyanate. 
Considering now the filtered ultraviolet irradiation unit 30 with reference 
to FIG. 2 unit 30. An opague metal housing 31 confines therein a 
vertically disposed ultraviolet lamp 32 for emitting a full spectrum of 
ultraviolet radiation. A clear glass tube 33 surrounds the lamp 32 and is 
supported vertically by first and second rings 34 and 35. The rings 34 and 
35 are supported respectively, in turn, by a plurality of support rods 36 
and a support screen 37. 
A clear glass coil 38 is supported by a plurality of upright support rods 
39 and surrounds the ultraviolet lamp 32. In this position, the segmented 
samples flowing through the glass coil 38 are irradiated by ultraviolet 
radiation, a fan 40 cools the unit 30. 
The glass tube 33 is clear glass and serves as a filter to pass ultraviolet 
wavelengths of between about 290 millimicrons and about 400 millimicrons, 
and to block the shorter ultraviolet wavelength. The result is that all of 
the cyanide complexes including iron complexes are dissociated, except the 
strong cobalt complex is only partially dissociated. By using the alkaline 
samples, instead of acidified ones, for irradiation, even the cobalt 
complex breaks down. 
In operation, samples are passed through the glass coil 38 to produce the 
irradiated samples in which cyanides have been dissociated, without 
dissociating thiocyanate. 
FIG. 3 is a block diagram of a two-channel system 100 for detecting 
thiocyanate in the samples. In one channel, the glass system 10 is 
employed to provide output signals indicative of the complete cyanides. 
The second channel includes a conventional quartz system 110, as disclosed 
in the foregoing mentioned publication, to provide an indication of the 
complete cyanides as well as thiocyanates from the same samples. 
Samples are communicated through line 101, and reagents are communicated 
through line 102, and are coupled to inputs 111 and 112 of quartz UV 
cyanide system 110 and glass UV cyanide system 10. System 110 is similar 
to system 10, and employs a conventional quartz ultraviolet irradiation 
unit (not shown), in place of the filtered ultraviolet irradiation unit 
30, to provide a full spectrum of ultraviolet radiation, thereby 
dissociating all of the cyanides and thiocyanates in each sample. 
The output of system 110 is an electrical signal 113 indicative of all of 
the dissociated cyanide and thiocyanate for each sample. The output of 
system 10 is an electrical signal 114 indicative of the dissociated 
cyanides without any thiocyanate (SCN). These two output signals may be 
produced by the output of a colorimeter, such as a colorimeter 65 in FIG. 
1. Other conventional techniques may also be employed for generating the 
signals. The signals are coupled to a suitable conventional subtraction 
circuit 130, which produces an electrical output signal 131 indicative of 
the difference between the input signals 113 and 114. Thus, the output 
signal 131 indicates the amount of thiocyanate (SCN), in the samples under 
test. 
Thus, the method and apparatus of this invention provides convenient 
measurements of complete cyanides and also of thiocyanate contained in the 
samples, if desired. 
The quartz system 110 differs from the system 10, only by the fact that the 
glass tube 33 is replaced with a quartz tube (not shown), and that the 
acid mixture is added with the nitrogen to the samples prior to 
irradiation. Thus, only minor differences exist between the two systems. 
Therefore, the signal 131 is the difference between the two measurements 
made by the two channels, and provides an indication of the thiocyanate 
contained in each sample under test. 
An advantage of the two-channel technique for measuring thiocyanate, is 
that color and turbidity of the samples, does not interfere with the 
measurements. Conventional direct colormetric measurements of thiocyanate 
are subjected to interferences from color and turbidity, when present in 
the samples. With the automated system of this invention, total cyanide, 
which completely includes all the strong cyanide complexes (even the 
strong cobalt complex), is conveniently measured without the presence of 
thiocyanate. 
While a particular embodiment of the present invention has been disclosed, 
it is to be understood that various different modifications are possible 
and are contemplated within the true spirit and scope of the appended 
claims. For example, there are other techniques for filtering the 
ultraviolet irradiation, such as by eliminating the tube 33, and using 
only the glass coil 38 to serve as the filter. There is no intention, 
therefore, of limitations to the exact abstract or disclosure herein 
presented.