The KPA's technology is based on the measurement of a sample's phosphorescence taken at selected time intervals to determine the precise concentration of the analyte. Superb selectivity is achieved by use of three parameters:
1. Excitation Wavelength
The uranium sample and reference are excited by firing the nitrogen laser at 337 nm. This excites the dye laser to produce an excitation wavelength of 420 nm. Each analysis is a repetition of 50 second cycles. A 3 nsec. laser pulse initiates each cycle.
1. Excitation Wavelength
The uranium sample and reference are excited by firing the nitrogen laser at 337 nm. This excites the dye laser to produce an excitation wavelength of 420 nm. Each analysis is a repetition of 50 second cycles. A 3 nsec. laser pulse initiates each cycle.
2. Emission Wavelength
A 515-nm band-pass filter is used to filter the emission signal and to pass the 515-nm uranium peak. Phosphorescence is a delayed emission of 10 -4 -10 seconds. Sensitive photomultiplier tubes and photon counting circuitry count the phosphorescent decay events emitted from the sample and reference.
A 515-nm band-pass filter is used to filter the emission signal and to pass the 515-nm uranium peak. Phosphorescence is a delayed emission of 10 -4 -10 seconds. Sensitive photomultiplier tubes and photon counting circuitry count the phosphorescent decay events emitted from the sample and reference.
3. Decay Time
The measured phosphorescence is resolved over time to discriminate against other light emitting species. The counted phosphorescent events are sorted by time and accumulated in bins or time-gates. Time-gates for short times contain decay information for short-lived processes other than phosphorescence and are ignored. The time-gates selected will only contain decay information for phosphorescence.
The measured phosphorescence is resolved over time to discriminate against other light emitting species. The counted phosphorescent events are sorted by time and accumulated in bins or time-gates. Time-gates for short times contain decay information for short-lived processes other than phosphorescence and are ignored. The time-gates selected will only contain decay information for phosphorescence.
Phosphorescence is measured by KPA as a function of time and relates it to the concentration of the analyte. Phosphorescence is a first order kinetic process, thus it is a simple matter to relate the sample signal to the concentration of the analyte by selecting the appropriate time domain. Reference data are used to correct results to background conditions.
The KPA's technology is easily applied to uranium chemistry. The KPA is unique for its analysis by "Oxidation State". U (VI) complexes are soluble and phosphoresce. U(IV) exists primarily as its oxide. KPA detects the emission from U(VI) present in solution as uranyl ion UO22+. However, U(IV) is insoluble and does not phosphoresce. Therefore, U(IV) is oxidized to U(VI) in acid before the sample is analyzed by KPA. Ultimately the KPA analyzes for chemical species.
The KPA is operated with an IBM compatible personal computer. The KPA offers control and data management via Chemchek's KPAWin software
The KPA is operated with an IBM compatible personal computer. The KPA offers control and data management via Chemchek's KPAWin software
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