Principles and Practice of ABA Analysis - Abscisic Acid: Metabolism, Transport and Signaling - page 421

et al. 2005 ; Pacáková et al. 1997 ; Liu et al. 2002 ; Xie et al. 2011 ). However,
traditional LLE method is time- and solvent consuming because it involves too
many steps. Therefore, it has been used decreasingly in phytohormonal analysis
(Fu et al. 2011 ).
Recently, liquid-liquid microextraction (LLME) in two application modes
including hollow fiber-based liquid-liquid-liquid microextraction (HF-LLLME)
and dispersive liquid-liquid microextraction (DLLME) have been applied for the
further purification of phytohormones (Wu and Hu 2009 ; Liu et al. 2010 ; Gupta
et al. 2011 ). HF-LLLME has been used for the simultaneous extraction and
enrichment of four acidic phytohormones (IAA, ABA, SA, and JA) from natural
coconut juice samples. This method provided good enrichment factors (48- to 243-
fold) and high recoveries (88.3-119.1 %) for the target phytohormones, along with
excellent sample cleanup capability (Wu and Hu 2009 ). DLLME has been applied
for the simultaneous extraction and enrichment of major classes of phytohor-
mones and plant growth regulators (GA, ABA, SA, IAA, IBA, indole-3-propionic
acid (IPA), 1-naphthylacetic acid (NAA), and kinetin riboside (KR)) from crude
extract, and exhibited several merits including high enrichment efficiency and
reduced sample preparation time (Lu et al. 2010 ). However, both CHCl 3 (extrac-
tion solvent) and acetone (disperser solvent) are toxic, volatile, and flammable,
thus safe and environmentally friendly solvents are desired in the LLME purifi-
cation of phytohormones. Although LLME is a fast and low solvent-consuming
method, the complicated organic solvent selection criteria and experimental design
still limit its application (Fu et al. 2011 ).
21.2.2.2 Solid-Phase Extraction
Solid-phase extraction (SPE) using cartridges and disc-shaped devices is a widely
used sample preparation technique for isolation, enrichment, clean-up, and
medium exchange. The target compounds are separated from other compounds
dissolved or suspended in the same liquid mixture by SPE according to different
physicochemical properties of the compounds on the basis of diverse interactions,
including adsorption, hydrogen bonding, polar and nonpolar interactions, cation,
anion exchange or size exclusion (Poole 2003 ). Compared to the LLE method,
SPE benefits from low intrinsic cost, shorter processing time, low solvent con-
sumption, and simpler processing procedure, thus it affords the possibility of high-
throughput device for sample preparation.
Many kinds of solid particulate medium based on inorganic oxides, low-
specificity compound (chemically bonded, porous polymer, and carbon), and
group-selective (ion exchange, mixed-mode, macrocyclic, restricted access, immu-
noaffinity, and molecularly imprinted polymer) materials can be used as sorbents
of SPE (Poole 2003 ), and several commercial SPE columns, such as Sep-Pak C 18 ,
Oasis HLB, Oasis MCX, and Oasis MAX, are available for the further purifica-
tion of phytohormones including ABA from crude plant extracts by using differ-
ent separation modes (Dobrev et al. 2005 ; Liu et al. 2010 ; Fu et al. 2011 ). Among