Comparison and evaluation of the specificity and binding capacity of commercial and in house affinity columns used in sample preparation for analysis of growth-promoting drugs

Immunoaffinity chromatography (IAC) and affinity chromatography (AC:) are widely used for extraction of drugs from biological samples. Fifteen column types were purchased from five different manufacturers and;their ability to bind specific drugs including beta-agonists and anabolic steroids over a range of analyte concentrations in fortified bovine urine samples was assessed. The performance data obtained from these columns were compared with columns produced in this laboratory (in house columns). The in house columns gave the highest recoveries, ranging from 92 to 100% at the 1 ng spiking concentration, for five of the seven analytes assessed. Forty percent (11 of 27) of all the commercial column assessments recorded recoveries of less than 50% even when the lowest spiking concentration was applied (1 ng). For one manufacturer, only one of seven different columns purchased delivered extraction efficiencies greater than 50%. The extraction efficiencies of the clenbuterol columns were the highest with all commercially prepared columns showing at least 50% binding of radiolabelled tracer. Recoveries of alpha-nortestosterone were the lowest. The variability of these products with respect to quality control requires constant monitoring.

Effectiveness of granular columns in containing settlement

Laboratory-based research studies and full-scale evaluations of the behaviour of ground improved with granular columns are ample regarding bearing capacity, but limited in respect to the settlement response. This paper presents a laboratory model study that considers the settlement performance of isolated pad footings bearing on reinforced sand deposits under the influence of a fluctuating groundwater table. This is a particularly onerous condition for loose sand deposits in coastal areas which may undergo significant collapse settlement over time. Loose and dense experimental sand beds were constructed and the performance of rigid footings under a maintained load and bearing on sand incorporating different column configurations were monitored under cycling of the water table over a period of 28 days, with one filling/empting cycle every 18 h. It was found that settlement, while greatly reduced compared with unreinforced footings, was ongoing and typically occurred at a much greater rate for loose sand than dense sand. Also, settlement rates were slightly higher for fully penetrating than partially penetrating columns and also for footings reinforced by a column group rather than a single column. This was attributed to the migration of sand grains into the larger column voids.

A laboratory based model study. Experimental observations of footings supported on soft clay reinforced with granular columns.

The inclusion of granular columns in soft clay deposits leads to improvements in bearing capacity and overall stiffness along with a reduction in consolidation settlement. Many laboratory investigations have focused on aspects of bearing capacity, but published data on settlement performance is limited. This paper reports on some interesting findings obtained from a laboratory model study in respect of these issues. In this investigation, 300 mm diameter by 400 mm long samples of soft kaolin clay were reinforced with single or multiple granular columns of various lengths using the displacement and replacement installation methods. The experimental findings revealed that, for the same area replacement ratio, limited settlement reduction was achieved for single long floating columns and end-bearing column groups. Marginal improvements in settlement performance were also achieved for columns installed by the displacement method. No settlement reduction was achieved for short single floating columns while short floating granular column groups produced increased settlements. These observations were verified using contact pressure measurements between the footing and column/surrounding clay.

Granular columns for stabilizing slopes

A series of small-scale tests was undertaken to verify if granular anchors could be used as a slope stabilisation technique. The nature of the material used and the resulting loading configuration are described here. The work confirms that the inclusion of anchors within a slope mass, irrespective of their number or orientation, significantly enhances the capacity and ductility of the failure mode. The small-scale nature of this research did influence the observed capacities, but the overarching hypothesis was confirmed. A simple analysis method is proposed that allows designers to accurately remediate natural or man-made slopes using existing analytical methods for slope stability.

A technique for reducing strain concentrations in FRP wrapped concrete columns

Existing studies have shown conclusively that the measured fibre reinforced polymer (FRP) rupture strain in FRP wrapped concrete columns is usually significantly smaller than the rupture strain obtained from flat coupon tests. One of the main causes for this phenomenon is the existence of geometrical discontinuities at both ends of the FRP sheets. This study proposes a new strengthening method in which continuous FRP spiral wrapping is used to eliminate strain concentrations due to the geometrical discontinuities and thus increase the FRP rupture strain at column failure. The effect of the spiral angle of FRP on the FRP rupture strain in FRP wrapped specimens was experimentally investigated. The test results indicate that the spiral wrapping with a small angle with respect to the column circumference can significantly increase the strain efficiency of FRP and thus enhance the axial compression capacity of the strengthened cylinders.