Filtering techniques, phase interference

An on-line concentration, isolation, and Hquid chromatographic separation method for the analysis of trace organics in natural waters has been described (63). Concentration and isolation are accompHshed with two precolumns connected in series the first acts as a filter for removal of interferences the second actually concentrates target solutes. The technique is appHcable even if no selective sorbent is available for the specific analyte of interest. Detection limits of less than 0.1 ppb were achieved for polar herbicides (qv) in the chlorotriazine and phenylurea classes. A novel method for deterrnination of tetracyclines in animal tissues and fluids was developed with sample extraction and cleanup based on tendency of tetracyclines to chelate with divalent metal ions (64). The metal chelate affinity precolumn was connected on-line to reversed-phase hplc column, and detection limits for several different tetracyclines in a variety of matrices were in the 10—50 ppb range. 

We have employed this phase-sensitive pump-probe technique to further investigate the multiphoton ionization of Na2 with 618-nm femtosecond pulses as discussed in the previous paragraph and have observed the interference of the A E and 2 Tlg wavepackets created by the first pulse and those created by the second pulse in the Na2+ signal. The amplitude of the high-frequency oscillations in the Na2+ signal was obtained as a function of pump-probe delay by filtering the transient with the laser frequency. It is shown in Fig. 8 (top). Below the averaged Na2+ transient of Fig. 4 is... 

The use of computer control allows sequential filter cycle data to be acquired in a repeatable and reliable manner with a minimum of operator interference. By defining the desired cycle phases through a software algorithm, a cake formation phase can be directly followed by the chosen combination of washing and deliquoring. The real time measurement of experimental parameters also allows continuous display of results and the use of on-line analysis techniques as an experiment proceeds. 

Classical extraction techniques, such as liquid liquid extraction were used by Pietta et al (1995) to avoid matrix interferences, and Gagliardis research group (1987, 1989) proposed liquid liquid extraction to separate the target UV filters into two groups, avoiding the interferences that some UV filters caused on the others. Moreover, Wang (1999) employed MeOH as a liquid liquid extraction solvent to extract the target UV filters from chloroform, which was used to dissolve lipstick samples, to be injected into a reverse-phase LC system. 

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