Hydrogen-Oxygen Combustion Apparatus V 5 According to the Wickbold-Method
The Proven Wickbold Method: The Wickbold method has been a proven success for about 30 years. It was formerly developed for the disintegration or organic samples in petrochemistry, to determine halogens and sulphur. This method is very suitable for sulphur contents of 1 to 50,000 ppm and chlorine contents of 0.5 to 10 ppm. Certainly, substances with higher contents can also be disintegrated.
In the course of time, however, this method has also proved suitable for the disintegration of organic samples, whose content of mercury, arsenic and selenium is to be determined. Lately, the Wickbold method has also been used for the determination of EOX and the detection of sulphur in spruce/ and pine needles.
In comparsion with other disintegration methods, oxidizing combustion in a hydrogen-oxygen flame (above 2000°C) has the advantage that after disintegration, the elements to be determined are on hand as ions in a hydrous solution. Very often, the analytical determination can directly be performed in this solution, because it is free from excess disintegration auxiliaries.
Therefore, this method is used increasingly in the analyses of trace metallic elements in organic matrices. In the case of very low trace element concentrations, the continuous flame combustion permits consumption of a larger quantity of substance, thereby ensuring a concentration above the level of detection. Through simple concentration of the aqueous solution, it is possible to achieve the necessary concentration levels for the use of, for example, AAS. Furthermore, by the addition of complex formers the metallic trace elements can be enriched. In particular, the method is suitable for the precipitate exchange reaction on a thin sulphide layer to enrich heavy metals for the trace determination by the AAS and X-ray fluorescent methods. Using pre-enriching techniques, limits of detection in aqueous solutions in the ng/I range are achievable.
For still better operating convience and additionally higher reliability the combustion apparatus type 5 is available. It was designed according to ergonomic principles. High reliability and operational convience characterise the new development of this apparatus. All display and control elements are – easily visible – coordinated on a console.
The control of the inert and combustion gas is carried out by convenient handoperated valves on the front side of the console.
On the front panel of the console there are two valves on the left side, these are for controlling the working pressure, as well as a mixing valve which allows the convenient distribution of the gases when used with the solid burners. By using a throttle and by-pass valve, it is possible to maintain constant pressure under varying operation conditions. The manometer is easily readable on the lateral front of the console. Situated underneath it are all the switches and buttons for the electrical control of the apparatus.
The blocking of all gas flows is achieved with magnetic valves so that the handoperated needle valves are used exclusively to control the gas flow. Electronic safety circuits control the apparatus in operation. Extinguishing of the main flame or failure of the cooling water system automatically switches off the gass supplies.
Multi switches control the gas supply to the individual quartz glass burners. LED (light emitting diodes) above the appertaining control valves and flowmeters, indicate the working position of the magnetic valves. A further light-emitting-diode indicates the operation of the cooling water. A fixture for supporting the quartz glass burner during intervals between combustion processes is equipped with an electrical ignition system. Burner ignition is simply achieved by push button. Change-over to main flame takes place automatically on removal of the burner. If it is not indroduced immediately in the combustion chamber, the flame will extinguish after a short time.
The combustion apparatus type 5 contains an absorption vessel with a rising device according to Dr. Brüning and Roth, which permits the continuous operation with series analyses. The rinsing device on the top end of the absorption vessel allows the addition of absorption solutions as well as quantitative rinsing of the inner wall. The burner remains operational throughout.
The long combustion chamber of the apparatus allows a rapid combustion of large quantities of substances. After intensive cooling, the gas flow reaches the absorption vessel distributed into fine bubbles by a frit. This allows the combustion products to be washed out quanti-tatively by the absorption vessel. Due to the bubbling effect, a large gas/ liquid interface is produced in the absorption vessel, resulting in a maximum of product exchange. The geo-metrical surface of the absorption vessel is very small and the absorption of trace elements on the glass is minimal.
The outlet for the analysis solution is placed immediately above the frit plate of the absorption vessel. Draining of the liquid into a measuring flask is achieved by means of a multi-way tap. This controls, by means of mutual locking, the gas extraction, the ventilation of the measuring flask and the outflow of the liquid, thus excluding the possibility of operational faults. In order to achieve shorter flow paths for the liquids, the taps on the rinsing device and ab-sorption vessel are not built into the console as individual control elements.