Detection of drugs in hair has become popular in recent years. The significantly long drug detection window (months) in hair has allowed the retrospective investigation and measurement of past consumption of drug. As the majority of drugs are basic, an extraction method was developed based on a methanolic solution for detection of basic/weak basic drugs in hair. It was compared with alkaline digestion (NaOH) followed by LLE. A filtration step with filtration vials was added and their materials were compared. After filtration, extracts were injected directly onto a C18 column coupled to Sciex ABI 2000 MSMS. The mobile phase was 50% methanol, 0.1% formic acid and 2 mM ammonium acetate (isocratic). Both methods were compared by applying them to real samples. Results showed that calibration was linear with r<sup>2</sup> of 0.991-0.999 for 20 tested analytes. The matrix effect was assessed to be between 91.4%- 110.2% for 18 analytes. PTFE filter material showed better recoveries over the GMF and PVDF based filters. Stability of analytes during extraction in general was better with methanolic incubation rather than alkaline digestion. With regard to real sample recovery, 6 out of 10 analytes recovered better with alkaline digestion. In conclusion, the methanolic method is capable of extracting most basic drugs in hair samples but only part of the total incorporated drug. Therefore, these results suggest that a combination of both methods (methanolic and alkaline extractions) in hair sample processing for general detection of basic and weak basic drugs may produce better results. However, not all basic drugs are stable under alkaline digestion
The filter cake formed
during a filtration process plays a vital
role in the success of a drilling operation. There are several factors
affecting the filter cake build-up such as drilled formation, drilling
fluid properties, and well pressure and temperature. The collective
impact of these two factors (i.e., formation and the drilling fluid)
on the filter cake build-up needs to be fully investigated. In this
study, two types of formations represented as limestone and sandstone
were used with different weighting materials to assess and compare
their impact on the filter cake properties, filtration behavior, and
solid invasion. The used weighting materials are manganese tetroxide,
ilmenite, barite, and hematite. The filter cake was formed under a
temperature of 200 °F and differential pressure of 300 psi. Nuclear
magnetic resonance spectroscopy was employed to explore the pore structure
of the used core samples. The results showed that the properties (i.e.,
shape and dimensions) of the different weighting materials are the
dominant factors compared to the formation characteristics in most
of the investigated filter cake properties. Nevertheless, the formation
properties, namely, the permeability and pore structure, have a somehow
higher contribution when it comes to the filter cake porosity and
thickness. For solid invasion, there were no clear results about the
main factor contributing to this issue.
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