Multiclass Screening Research Articles

Development and validation of a rapid and wide-scope qualitative screening method for detection and identification of organic pollutants in natural water and wastewater by gas chromatography time-of-flight mass spectrometry

In this work, a multiclass screening method for organic contaminants in natural and wastewater has been developed and validated for qualitative purposes, i.e. to ensure the reliable and sensitive identification of compounds detected in samples at a certain level of concentration. The screening is based on the use of GC-TOF MS, and the sample procedure involves solid phase extraction with C 18 cartridges. Around 150 organic contaminants from different chemical families were investigated, including PAHs, octyl/nonyl phenols, PCBs, PBDEs and a notable number of pesticides, such as insecticides (organochlorines, organophosphorus, carbamates and pyrethroids), herbicides (triazines and chloroacetanilides), fungicides and several relevant metabolites. Surface water, ground water and effluent wastewater were spiked with all target analytes at three concentration levels (0.02, 0.1 and 1 μg/L). Influent wastewater and raw leachate from a municipal solid waste treatment plant were spiked at two levels (0.1 and 1 μg/L). Up to five m/ z ions were evaluated for every compound. The identification criterion was the presence of, at least, two m/ z ions at the expected retention time, measured at their accurate mass, and the accomplishment of the Q/ q i intensity ratio within specified tolerances. The vast majority of compounds investigated were correctly identified in the samples spiked at 1 μg/L. When analyte concentration was lowered down to 0.1 μg/L the identification was more problematic, especially in complex-matrix samples like influent wastewater. On the contrary, many contaminants could be properly identified at the lowest level 0.02 μg/L in cleaner matrices. The procedure was applied to the screening of water samples of different origin and matrix composition and allowed the detection of several target contaminants. A highly reliable identification could be carried out thanks to the sensitive full-spectrum acquisition at accurate mass, the high selectivity reached with the use of narrow-mass window extracted ion chromatograms, the low mass errors observed in the positive detections and the Q/ q ratio accomplishment.

Process targeting with multi-class screening and measurement error

In this paper, a Process Targeting model for a three-class screening problem is developed. The model extends the work in the literature by incorporating a measurement error present in inspection systems. The strategy adopted, to nullify the effect of measurement error, is to introduce the concept of 'cut-off points', i.e. the decision during inspection is based on these cut-off points rather than specification limits of the various product grades. This model considers cut-off points as decision variables. In addition, an illustrative example is presented that compares model performance with the model presented in Min and Jang (1997). Sensitivity analysis is also conducted to study the effect of various model parameters, particularly measurement error on expected profit, optimal process mean and cut-off points.

Optimum mean value and screening limits for production processes with multi-class screening

This paper presents the problem of jointly determining the optimum process mean and screening limits for each market in situations where there are several markets with different price/cost structures. All items are inspected prior to shipment, and the inspection is performed on a variable which is highly correlated with the quality characteristic of interest. It is assumed that that quality characteristic is normally distributed with an unknown mean and a known variance. A profit model is constructed which involves selling price, production cost, penalty cost and inspection cost. Methods for finding the optimum process mean and screening limits for each market are presented.