Determination of polycyclic aromatic hydrocarbons in marine sediments by high-performance liquid chromatography after microwave-assisted extraction with micellar media.
A simple and rapid method is developed for extraction and determination of polycyclic aromatic hydrocarbons (PAHs) in marine sediments. The procedure was based on the microwave-assisted extraction of PAHs in marine sediment samples using a micellar medium of Polyoxyethylene 10 lauryl ether as extractant. Two-level factorial designs have been used to optimize the microwave extraction process. The analysis of extracts has been carried out by HPLC with UV detection. Fortified sediments gave an average recovery between 85.70 and 100.73%, with a relative standard deviation of 1.77-7.0% for PAHs with a ring number higher than three.
Microwave-assisted micellar extraction coupled with solid-phase extraction for preconcentration of pharmaceuticals in molluscs prior to determination by HPLC.
A simple and specific analytical method was developed and tested for the determination of pharmaceuticals in mollusc samples. A combination of microwave-assisted micellar extraction (MAME) and solid-phase extraction (SPE) using a non-ionic surfactant, polyoxyethylene 10 lauryl ether, was examined to extract and determine simultaneously a group of pharmaceuticals such as carbamazepine, clorfibric acid, ketoprofen, naproxen, bezafibrate and ibuprofen by liquid chromatography using UV-diode array detector. The MAME extraction performance was evaluated by studying various parameters such as the volume and concentration of surfactant and microwave conditions. Finally, an OASIS HLB cartridge was used as an optimum SPE sorbent to clean up the extracts and preconcentrate the selected analytes. The proposed method showed satisfactory linearity and reproducibility (between 3 and 15%), as well as detection limits ranging from 30 to 220 ng/g. Finally, the method was successfully applied to the determination of the target pharmaceuticals in various kinds of mollusc samples. This study has demonstrated that microwave-assisted micellar extraction with solid-phase extraction may be used as a viable alternative to conventional methods for the extraction of pharmaceuticals in this type of matrices.
CALIBRATION IN QUANTITATIVE-ANALYSIS .2. CONFIDENCE-REGIONS FOR THE SAMPLE CONTENT IN THE CASE OF LINEAR CALIBRATION RELATIONS
The precision of analytical results determined from linear calibration graphs is discussed. It is assumed that the standard deviation of the analytical procedure has the same value sx for all calibration levels and for the sample measurements. The collective and individual influence exerted by the number of both calibration and sample measurements (N and n, respectively) on the precision of the results is calculated on the basis of widths of confidence intervals. In addition, the effects on precision caused by the distribution of the calibration measurements over the calibration range and by the location of the sample in the analytical range are calculated. A quantity, comprising an “eccentricity term”, is developed, which contributes to better insight into the problems considered. For the special case that the k calibration levels are equidistant and the same number of replicate measurements m is made at each of these levels (km = N), the length of the confidence region is given by δx = 4sx (n-1 + z/N)12 for α = 0.05. The value of z depends on the “eccentricity” of the sample value compared to the centre of gravity of the calibration values, and on the value of k. If the sample value coincides with the centre of gravity of the calibration values, z = 1. If the sample value coincides with one of the extreme values of the calibration experiments, the value of z increases to z = 2.00 for k = 2 and to z = 3.81 for k = 32.