Biological Fiber Extraction Methods

As an alternative to conventional methods of dew and water retting, Murdy [8] investigated the feasibility of silage retting. By applying solid state retting in an enclosed facility, she aimed to recover fermented polysaccharides. 

Retting time depends on the plant species. While okra bast fibers can be obtained after a duration of 15 - 30 days [14,22] it takes several months to extract fibers from corn husk by water retting [13]. The author has not been able to extract fibers from reed leaves and stalks even after two years of immersion in water tanks. 

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Bacci et al. [39] treated nettle stalks with boiling soda solution xmtil the bark, the source of fiber, was easily removed from the core of the stalk than performed alkalization treatment on the bark. Enzymatical fiber retting maybe faster and more reproducible than the traditional biological fiber retting methods and is extensively studied for flax and hemp extraction enhancement [39]. 

Solid phase microextraction (SPME) was introduced by Arthur and Pawliszyn over 20 years ago [44]. It is a straightforward, solvent-free, and fast sample extraction method. SPME has become a widely used technique in many areas of analytical chemistry, such as food analysis, environmental sampling, forensics/toxicology, and biological analysis. Recent reviews have been published showing the latest development of this versatile extraction method [45 8]. SPME is based on the partition of the analyte between the extraction phase and the matrix. The technique can be used to monitor analytes in liquid samples or in the headspace and is basically compatible with HPLC and CE, but most applications are made by GC. As indicated by its name, it is not an exhaustive extraction technique and only a fraction of the target analyte is actually extracted. The quantity of analyte extracted is proportional to its concentration, as long as the equilibrium between the analyte in the fiber and the sample is reached. It provides linear results for wide concentrations of analytes (typically from levels of parts per million to parts per billion). 

Solid-phase microextraction (SPME) [63] is normally used for sample collection, pre-concentration and desalting before analysis. It is usually used off-line. However, SPME can be implemented in temporal monitoring of biomolecules with low to medium temporal resolution (minutes, hours) [64]. In one method, SPME fibers were used to sample metabolites from live animals followed by analysis using LC-MS [65]. The method enabled extraction of metabolites directly in the tissue of moving animals. It was not necessary to withdraw a representative biological sample for analysis. In this case, the amount of analyte extracted into the SPME fiber was independent of the sample volume [65]. Recently, SPME was also coupled on-line with a MS ion source operated at atmospheric pressure [66]. 

Detection limits reach ca 1 nM when background or capacitive currents are filtered or compensated, in transient methods such as differential pulse polarography (DPP) or voltammetry. Numerous redox molecules, either metabolites or drugs, may be determined in biological samples either directly or after an extraction procedure[3,4]. Particularly miniaturized electrodes using carbon fibers or paste may be implanted and allow the continuous monitoring of some metabolites and drugs in neuronal tissues or arteries[5-8]. 

Solid-phase microextraction (SPME) is a recent sample preparation technique for trace analysis by GC (12). It is a simple, solvent-free method that uses a polar or nonpolar coated fused-silica fiber to directly extract analytes from various matrices (usually aqueous). It can be used in a headspace mode as well. After the fiber is removed from the sample, it is transferred to the heated inlet of a chromatographic system and the analytes are thermally desorbed for analysis. The technique works well for the analysis of trace analytes in water or urine. It has been applied in the field of forensic science in the analysis of fire debris, explosives, and drugs in biological fluids (13-15). 

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