Chloride, automatic determination

The use of a pair of identical metallic electrodes to establish the equivalence point in amperometric titrations offers the advantages of simplicity of equipment and elimination of the need to prepare and maintain a reference electrode. This type of system has been incorporated into equipment designed for the routine automatic determination of a single species, usually with a coulometric generated reagent. An example of this type of system is an instrument for the automatic determination of chloride in samples of serum, sweat, tissue extracts, pesticides, and food products. Here, the reagent is silver ion coulometrically generated from a silver anode. The indicator system consists of a pair of twin silver electrodes that are maintained at a potential of perhaps 0.1 V. Before the equivalence point in the titration of chloride ion, there is essentially no current because no easily reduced species is present in the solution. Consequently, electron transfer at the cathode is precluded and that... 

Skjemstad, J.O. and Reeve, R., The automatic determination of ppb levels ammonia, nitrate plus nitrite and phosphate in water in the presence of added mercury 11 chloride. Journal of Environmental Quality 7,137,1978. 

The combined acetone extracts were extracted six times with one-fourth volume of ethylene dichloride and the ethylene dichloride extract was evaporated under vacuum to leave the steroid residue. This steroid residue was taken up in a minimum of methylene chloride and applied to the top of a column packed with 30 grams of silica which had been previously triturated with 21 ml of ethylene glycol. Then various developing mixtures, saturated with ethylene glycol, were passed over the column. Cuts were made as each steroid was eluted as determined by the lowering of the absorption of light at 240 mp on the automatic chromatographic fraction cutter. 

Suitable PLOT columns for the determination of vinyl chloride monomer in PVC include 15.00 m, 0.53 mm bonded polystyrene-divinyl benzene and 30 m, 0.53 mm porous divinyl benzene homopolymer types. Typical responses for vinyl chloride monomer standards (0.06, 0.19 and 0.31 mg/1) in N,N-d imethylaceta-mide expressed as mg/kg vinyl chloride (PVC sample) using the 30 m homopolymer column and flame ionisation detection are shown in Figure 38. An automatic static headspace sampler was employed. 

Note Current (circa 1981) computer search lists the CA Registry No of VCM as [75-01-4] Analysis E. Sistig, Recent Methods and Trends of Automatic Analyzers in the Chemical Industry. .. Vinyl Chloride. .. ppm Range , Proc 5 th IntCongrChemEngrgChemEquipDes-Autom, Prague (1975) CA 36, 8217 (1977) [The instruments with the ability to determine 0 to 20 ppm of VCM with an accuracy > 2 ppm include flame ionization detectors (FID), gas chromatographs using FID, dispersive IR analyzers with spectrometer cells, analyzers based on electrical conduction with upstream combstn chambers, and analyzers with Cl sensitive test paper]... 

In addition to the analysis of the thermal stability of the perchloric acid organic reaction media mixtures, a procedure was worked out to determine the fate of the perchloric acid by chlorine analysis of the batch, effluent streams, etc. Preliminary analyses on selected process samples showed no tendency for perchloric acid to concentrate in recycle material and therefore build up in the reactor. A total of less than 1% of the initial charge of perchloric acid (total chlorides calculated as perchloric acid) was found in the combined recovered acid-ester and olefin fractions. Less than 1 % of the initial charge of perchloric acid was found in the finished ester. The analytical method used was an oxygen bomb decomposition, followed by titration of chlorides with 0.0liV silver nitrate, using a recording automatic titrator. The eventual fate of the perchloric acid catalyst was... 

The types of automatic titrator which have just been described are not usually found in a clinical laboratory. There have, however, been some recent reports on the use of such devices for the determination of chloride in body fluids. For comparative purposes, the following discussion will deal with some of the newer modifications in the determination of chloride by electroanalysis. 

The stated variability is certainly within acceptable limits, as are the recovery values reported. It would seem likely that there is room for this rapid, accurate automatic device for chloride determination in many laboratories. The cost of the silver wire reagent is low. There is some need for cleanliness and proper care of both the generator and indicator electrodes. 

Another method for determination of chloride by automatic means is discussed in the section on the Autoanalyzer. 

Fu and Mak [238,239] dealt with acyl alkyl esters of amino acids with various combinations of acyl and alkyl moieties in comprehensive studies. They evaluated and determined optimal conditions for their preparation they selected acylation with the aid of the anhydride or chloride of the appropriate acid as the first step. They performed the reaction at 20-30°C with vigorous stirring for 10 min, with subsequent esterification with the appropriate alcohol in dry benzene in the presence of Amberlite IR-120 (H+). They further evaluated their retention properties on both Carbowax 20M and GE-XE-60, and the relationships between these properties and their structure. Kolb and Hoser [240] described a microdevice in which the derivatives were prepared with the aid of opened aluminium or gold capsules (20-/J volume) which acted as a microreactor in an automatic capsule—dosage system (MS 41). As an example they demonstrated the application of their device to the preparation of HFB-methyl esters. 

A number of instrument manufacturers offer automatic coulometric titrators, most of which employ a potentiometric end point. Some of these instruments are multipurpose and can be used for the determination of a variety of species. Others are designed for a single type of analysis. Examples of the latter are chloride titrators, in which silver ion is generated coulometrically sulfur dioxide monitors, where anodically generated bromine oxidizes the analyte to sulfate ions carbon dioxide monitors, in which the gas, absorbed in monoethanolamine, is titrated with coulometrically generated base and water titrators, in which Karl Fischer reagent (see Section 20C-5) is generated electrolytically. 

Material Balance. The next step is the material balance. Here it is necessary to specify the end use of the product. If it is to be electrical, that automatically fixes the catalyst which can be used. The Sales Department s prognostication as to the demand for the product will fix the over-all production. (It is wise for the engineer to get this in writing.) At this point, some laboratory work should be done in order to determine a satisfactory formulation. In this particular case, suspension polymerization of vinyl chloride is rather simple, if the correct formulation is used, so the time consumed need not be great. It will now be possible to settle on a material balance. 

The major serum electrolytes—sodium, potassium, calcium, magnesium, chloride, and bicarbonate (CO2)—are fairly easy to determine. The metals are most readily determined by the use of fiame-spectrophotometiic or atomic absorption methods, although colorimetric methods exist for calcium and magnesium. Calcium and, less frequently, magnesium are also titrated with EDTA. Ion-selective electrodes are used for the routine analysis of sodium, potassium, and calcium. Bicarbonate is analyzed also by titration against standard acid (see Experiment 8) in addition to a manometric method. Chloride is widely determined by automatic coulometric titration with electrogenerated silver ion. 

Since the early days of analytical applications of ion-selective electrodes they have been used in clinical analysis. The progress in construction and miniaturisation of electrodes as well as contemporary development of computerised potentiometric apparatus have led to the production of automatic analyzers designed especially for clinical applications/ The high degree of response selectivity of the membrane sensors used today eliminates practically the mutual interaction of various blood, serum, plasma or urine components. Nevertheless when drugs or their metabolites are introduced into the body they in some cases may influence the electrode response and cause errors in estimation of the content of the ions present naturally, i.e., potassium, sodium, calcium and chloride. Such parasitic effects may be caused by the interaction of drugs with the electrode membrane. The aim of this study was to check whether some selected drugs can influence the determination of the above mentioned electrolyte ions in the serum. 

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