Multi-sensor systems

Details Multi-sensor systems Multi-sensor systems

1996-04-23

1998-01-20

Le, Long V.

Chemical apparatus and process disinfecting, deodorizing, preser

Analyzer, structured indicator, or manipulative laboratory...

Means for analyzing liquid or solid sample

422 681, 436 43, 436 52, 436174, 436179, 436180, G01N 27416, G01N 3508

Patent

active

057098395

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a flow through multi-sensor system including a plurality of sensing cells whereby a number of readings can be taken particularly, but not exclusively, simultaneously.
2. Discussion of the Prior Art
When monitoring solutions for the presence of additives or contaminants it is preferable to use a flow-through sample system and further, to use a sample system which is adapted to take a number of readings so as to identify the presence of a plurality of contaminants. Ideally, the sample system is adapted to take a number of readings simultaneously.
One method for sampling a solution involves the electrochemical accumulation of ionic species from an aqueous solution at a conducting substrate, followed by removal of that species from the substrate by the application or reversal of current. This technique is called Anodic Stripping Voltammetry (ASV).
In ASV, almost universally, a discrete sample is employed. However, some anodic stripping devices that have been patented allow for a flowing sample, although the overall process, whilst being periodic in its operation, is not continuous. That is to say a single sample is taken and a complicated program then ensues. Meanwhile the flow is stopped in the sample gathering part of the apparatus. As a consequence of the protracted nature of the process, periods of an hour for it's duration are not uncommon. Thus, the analytical result is of value only to very slowly changing conditions, or where the speed of update is unimportant.
Whilst anodic stripping is mainly carried out on solid substrates, improvement with mercury drop polarographic equipment in recent years, in the form of the hanging (HMD)/static mercury drop technique has allowed the use of this technique in ASV.
Unprecedented sensitivities are now commonplace with this type of polarographic equipment when applied to ASV. Although somewhat limited to a laboratory bench environment because of it's fragile nature, and whilst still mainly restricted to discrete samples, the application of electronic/electrochemical pulsing techniques, prior to and during the stripping cycle, allows sensitivities to reach at least 10.sup.-1 parts per billion for a wide range of inorganic ion and organic species. One such technique is Differential Pulse Anodic Stripping Voltammetry (DPASV).
DPASV has become a competitor for Atomic Absorption Spectroscopy (AAS) in terms of its comparable sensitivity and more importantly, no sample pre-treatment is usually necessary. In addition, when an adsorptive mode is applied, sensitivity may be increased to 10.sup.-2 parts per billion.
It will be apparent from the above that, before a chemical species can be identified using ASV, it is necessary to determine the key markers for each particular species to be determined. For example, the deposition, accumulation, reduction and oxidation potentials for each species; the flow rate of the sample, the sweep rate, the pulse rate and its magnitude; the nature of the signal response, whether it is curved or linear relative to the concentration range, the temperature effects or cross sensitivities.
The above characteristics must be identified for all those metals to be identified, and also for all of the organic species to be identified which are electrochemically detectable such as, NO.sub.2, --NO, --CO, --N.dbd.N--, --C.dbd.C-- etc, and therefore molecules such as, for example, nitro phenyls, azo and diazo compounds, quinones, aldehydes, ketones, and unsaturated compounds with double bonds such as styrene etc.
Thus, to quote some specific examples. For Lindane, DDT and BHC and Dieldrin the analysis relies upon the reduction of carbon-halogen bond. PCNB,2,4,dinitro-6-cyclohexylphenol, methyl parathion, all contain reducible nitro groups. Compounds such as sodium diethyl dithiocarbamate and methylenebisthiocynanate are detectable due to the presence of the sulphur-hydrogen and thiocyanide groups, etc.
Moreover, each of these certain groupings make their own particular contribut

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