Exchange SPE

A wide variety of SPE materials and cartridges are commercially available for example, alkyl-diol silica-based restrictive access materials (RAMs) and a variety of silica- and polymer-based SPE materials of different binding abilities and capacities. Reversed-phase, size-exclusion, ion-exchange SPE, and turbulence flow methods will be discussed in this chapter related to real-world applications. 

Both HPLC and GC-MS were employed for the separation, identification and quantitation of the decomposition products of indigo and indigo carmine. The chemical structures of the dyes are shown in Fig. 3.73. Carboxylic acids were preconcentrated before HPLC analysis either by ion-exchange SPE or by solid-phase microextraction. HPLC measurements were performed in a Sarasep column (300 X 7.8 mm i.d.) using 5 mM H2S04 at a flow rate of 0.7 ml/min. Analytes were detected at 215 nm. The main intermediates formed during the photocatalytic decomposition are compiled in Table 3.26. The results demonstrated that... 

The column-switching system was applied to the determination of STR and DIHS in pork and bovine muscle and kidney. Perchloric acid was used to precipitate proteins and extract analytes from the tissue. The clear supernatant was further cleaned up by an offline SPE on a cation-exchange SPE column. After the washing of the cartridge with water, the analytes were eluted with phosphate buffer (pH 8.0) and diluted with HSA, perchloric acid, and water. The enrichment was achieved in the online mode. After loading the sample, the enrichment precolumn was flushed with HSA at pH 3.3 for 5 min. Using the ratio of MeCN to aqueous component of 83 17... 

Varian Bond Elut—Cation Exchange SPE Columns, www.chromtech.com/ 2001catalog/separatePgS/125.pdf (August 20, 2009). 

Ionic water-soluble compounds can be retained by ion-exchange sorbents or by reversed-phase (RP) sorbents if ionization is controlled by ion suppression (i.e., by pH control that produces the nonionized form). In ion-exchange SPE, retention occurs at a sample pH at which the analyte is in its ionic form, whereas the analyte is desorbed in its neutral form if the analytes are ionic over the entire pH range, desorption occurs by using a solution of appropriate ionic strength [92],... 

Alternatively, ionic compounds can be recovered from solution on hydrophobic sorbents using ion-pair SPE (IP-SPE). Carson [121] notes that advantages of IP-SPE over ion-suppression RP-SPE or ion-exchange SPE include selectivity, compatibility with aqueous samples and rapid evaporative concentration of eluents, and potential application to multiclass multiresidue analysis. IP reagents (e.g., 1-dodecanesulfonic acid for pairing with basic analytes or tetrabutylammonium hydrogen sulfate for pairing with... 

Figure 13-13. Comparison of choice of sample preparation on MRM signal intensity of an investigation compound. The injection volume was 40pL.The count per second (CPS) signifies the detector (an electron multiplier) response. Protein precipitation (PPT), hydrophilic-lipophilic balanced co-polymer-based SPE (Oasis HLB- copolymer of styrene, divinylbenzene and -vinylpirrolidone monomers the hydrophihc refers to the NVP monomer, and the lipophilic refers to the SDVB monomers), and strong anion exchange SPE (Max) (all in 96-well plate format) were used in control rat plasma (unpublished data).

Method development for the LC-MS analysis of HAA in meat was performed by the gronp of Galceran [83-90]. Initially, complex mnlti-step extraction and sample pretreatment methods were applied, e.g, hqnid extraction from meat, clean-up by solid-supported LLE, and ion-exchange SPE. Later on, different SPE procednres for sample clean-np were evalnated [85]. A combination of solid-supported-LLE and SPE on C18 material was most efficient in selective elution of the polar and less polar HAA. LC was first performed on a lOOxl-mm-lD Cig column (5 pm) with 50% acetonitrile in 5 nunol/1 aqueous ammonium acetate (pH 6.7) at a flow-rate of 50 pEmin. ESl-MS was applied in SIM mode, enabling detection of HAA at 1-6 pg/kg in beef extracts [83]. 

Figure 2.12. Mechanism of ion-exchange SPE for 2,4-D. [Reproduced in modified form from Zief and Kiser (1987) and published with permission.]...

However, in order for the cation-exchange mechanism to work on atrazine, the pH of the sample must be lower than the pAT, of the analyte. This would require lowering the pH of the sample to 1.0, and a substantial amount of acid is required for this process. Furthermore, acidification to this low of a pH will protonate the organic acids naturally present in the water sample and increase the possibility of interferences when the sample is eluted from the SPE sorbent. Furthermore, the bonded-phase ion-exchange SPE cartridges are not capable of operating at this low of pH because of dissolution of the silica matrix, although it would be possible to use a polymeric sorbent. 

Metal cations may be isolated from water samples by ion-exchange SPE using... 

Figure 6.12. Example of a separation of anionic and nonionic surfactants using ion-exchange SPE.

Folates are generally present in low concentration in foods thus, any method of analysis requires isolation and sensitive detection (Vahteristo et. al., 1996). The method described here uses extraction of the folic acid (Fig. 9.13) with rapid microwave heating and enzymatic deconjugation with hog-kidney con-jugase and chicken pancreatic enzymes. The extracts are purified with strong anion-exchange SPE. The final analysis is with HPLC. 

The sample extracts were purified and concentrated by strong anion-exchange SPE (SAX) with 3 mL volume. 

There are numerous methods for the analysis of alkyl methylphosphonic acids in urine and blood, mostly using GC-MS and GC-MS-MS. These have been recently reviewed (Black and Muir, 2003 Black and Noort, 2005) and only a representative selection is summarized here. Isolation from urine is usually achieved by hydrophobic SPE (Cis, Cs or polymeric) at low pH, or by anion-exchange SPE. Phosphonic acids require derivatization for GC-MS analysis, and at least four different derivatives have been applied to biomedical samples. Silylation (trimethylsilyl or rm-butyldimethylsilyl) are commonly used for environmental analysis and were used in the analyses of samples from casualties of the Mat-sumoto and Tokyo terrorist attacks (e.g. Minami et al, 1997 Nakajima et al, 1998). In these cases, the first samples were collected within hours of the exposure and the detection limits... 

Sample preparation Prepare an anion-exchange SPE cartridge in a 6 mL syringe barrel with a filter paper disc in the bottom. Pack with DEAE-A-25 Sephadex in PBS to a bed volume of 3 mL, wash with PBS, place filter paper on top. Add 500 ji-L serum to SPE cartridge, add 500 pL PBS to SPE cartridge, wash with 4 mL PBS, elute with 5 mL 1 M NaCl, iiyect a 100 pL aliquot of the eluate. (PBS weis 8 g NaCl, 1.15 g Na2HP04, 0.2 g KCl, and 0.2 g KH2PO4 in 1 L water, pH 7.2.)... 

---