Automated SPE

The SPE process can be performed either on-line or offline. The procedure using SPE cartridges with a vacum manifold is known as off-line SPE, and the eluate from the cartridge is introduced into the chromatographic instrument after concentration and reconstitution of sample extracts. In 

A high-throughput method that combines on-line extraction and determination by LC-MS/MS has been developed for the screening of 13 multi-class antibacterials (macrolides, fluoroquinolones, lincosamides, and trimethoprim) in different animal muscle tissues. After sample deproteinization with acetontirile, the extracts were directly loaded onto the SPE cartridge, packed with an Oasis HLB 

---

Advances in autosampler technology have encouraged the development of fully automated SPE procedures that require minimal manual intervention. Automated... 

Several sample preparation techniques are performed inside the inlet system. Large-volume injection can be carried out by a number of methods including programmed temperature vaporisation (PTV). Automated SPE may be interfaced to GC using a PTV injector for large volume injection. SPE-PTV-GC with on-column injection is suited to analysis of thermola-bile compounds. 

Principles and Characteristics Although early published methods using SPE for sample preparation avoided use of GC because of the reported lack of cleanliness of the extraction device, SPE-GC is now a mature technique. Off-line SPE-GC is well documented [62,63] but less attractive, mainly in terms of analyte detectability (only an aliquot of the extract is injected into the chromatograph), precision, miniaturisation and automation, and solvent consumption. The interface of SPE with GC consists of a transfer capillary introduced into a retention gap via an on-column injector. Automated SPE may be interfaced to GC-MS using a PTV injector for large-volume injection [64]. LVI actually is the basic and critical step in any SPE-to-GC transfer of analytes. Suitable solvents for LVI-GC include pentane, hexane, methyl- and ethylacetate, and diethyl or methyl-f-butyl ether. Large-volume PTV permits injection of some 100 iL of sample extract, a 100-fold increase compared to conventional GC injection. Consequently, detection limits can be improved by a factor of 100, without... 

Planas C, Palacios O, Ventura F, Rivera J, Caixach J (2008) Analysis of nitrosamines in water by automated SPE and isotope dilution GC/HRMS - Occurrence in the different steps of a drinking water treatment plant, and in chlorinated samples from a reservoir and a sewage treatment plant effluent. Talanta 76 906-913... 

Ivermectin (IVER) is a drug with a broad spectrum of activity against gastrointestinal nematodes and lung parasites in food-producing animals. In the EU, the maximum residue levels set for IVER in the liver of sheep, pigs, and cattle are 15,15, and 100 tg/kg, respectively (217). The use of automated SPE equipment was described for IVER HPLC analysis in animal liver samples. This automated system, ASPEC, was used for the SPE purification step in order to provide more efficient and faster sample preparation. Some tests were performed to obtain recovery and repeatability data. The mean recovery for spiked samples was more than 90% in the concentration range of 7.5-30 tg/kg. 

LOD was defined as the lowest concentration for which the two monitored transitions could be detected, and the peak area of the quantifier transition was, at least, three times the background noise. LOD was 0.5 ng/mL for all analytes. LLOQ was defined as the lowest concentration that could be quantified with appropriate imprecision (coefficient of variation (%CV) <20%) and inaccuracy (mean relative error (MRE) 20%). LLOQ was 2 ng/mL in oral fluid, and 2-4 ng/mL in plasma for most of the analytes. Carryover after automated SPE of clomipramine at 1,000 ng/ mL was half of the signal obtained at 2 ng/mL therefore, LLOQ in plasma was increased to 10 ng/mL for this analyte. 

A rapid, automated procedure for single-step and simultaneous extraction of cocaine and 11 related compounds was developed by Lewis et al. [95]. Fluid and tissue specimens were extracted using an automated SPE system (Zymark Rapid-Trace) with a Bond Elute-Certify I cartridge. Samples were derivatized with pentafluoro-propionic anhydride/2,2,3,3,3-pentafluoro-l-propanol prior to GC-MS analysis. The method allowed differentiation between smoking crack and intranasal/intravenous cocaine use and was able to elucidate whether ethanol and cocaine were used simultaneously. Another way to determine cocaine in biological matrices is to measure its metabolites and/or degradation products. MEG is produced when... 

The term solid-phase extraction was introduced by personnel of the J. T. Baker Company in 1982. The method consists of retention of the analytes from a liquid or gaseous sample to a solid stationary phase and subsequent removal of analytes using an appropriate eluent. The main purpose of SPE is isolation and preconcentration of compounds of interest or sample clean-up and simplification of the matrix. Application of this sample preparation technique also allows extract fractionation. As a result of significant reduction in the volume of organic solvents used, high recovery, and the possibility of process automation, SPE is a good alternative for conventional liquid-liquid extraction. According to their affinity for the compound of interest, stationary phases are classified as follows ... 

J.P. Allanson, R.A. Biddlecombe, A.E. Jones, S. Pleasance, The use of automated SPE in the 96 well format for high throughput bioanalysis using LC coupled to MS-MS, Rapid Conunun. Mass Spectrom., 10 (1996) 811. 

The validated bioanalysis of rosuvastatin in human plasma by automated SPE in 96-well format with Oasis HLB material and positive-ion LC-ESI-MS-MS was reported using a [DJ-ILIS [54]. The stability of rosuvastatin and its potential conversion into the lactone due to sample pretreatment was thoroughly investigated. The method was applied in pharmacokinetic studies during clinical trials. A similar method was applied by the same group in the bioanalysis of the /V-desmethyl metabolite of rosuvastatin [55]. 

C.K. HuU, P.D. Martin, M.J. Warwick, E. Thomas, Quantification of the N-desmethyl metabolite of rosuvastatin in human plasma by automated SPE followed by LC-MS-MS detection, J. Pharm. Biomed. Anal., 35 (2004) 609. 

D. Zimmer, V. Pickard, W. Czembor, C. Muller, Comparison ofTFC with automated SPE in 96-well plates and LEE used as plasma sample preparation techniques for LC-MS-MS, J. Chromatogr. A, 854 (1999) 23. 

De Kanel et al. [93] described a quantitative confirmation procedure for LSD and A -desmethyl-LSD in blood, serum, plasma, and urine. Fully automated SPE pretreatment and extract evaporation were performed using a Zymark RapidTrace. LC-ESI-MS-MS was performed, using [ //jj-LSD as IS. The intra-assay and interassay precision were 2.2 and 4.4%, respectively. The detection limit was 0.025 ng/ml. Similar results in terms of figures-of-merit were reported by others. 

An excellent review of hardware for automated solid-phase extraction has been recently published by Smith and Lloyd [36]. In this review, Smith and Lloyd present an overview of at least 18 different commercially available systems for automated SPE and discuss 13 important attributes, such as the degree of automation, type and quantity of work, cost, functionality, and so on. Their discussion is intended as a guide for selecting a suitable system and it is highly recommended for this purpose. We do not attempt to redo this excellent review. Instead, we have classified the available systems into three categories (1) on-line SPE techniques, (2) discrete column workstations, and (3) 96-well workstations. Their descriptions, advantages, and limitations follow. 

As mentioned earlier, carryover is a problem for automated SPE workstations and carryover performance should always be investigated. This set of... 

GD Bowers, CP Clegg, SC Hughes, AJ Harker, S Lambert. Automated SPE and tandem MS without HPLC columns for quantifying drugs at the picogram level. LC-GC 15 48-53, 1997. 

Profile The company is a maker of HPLC equipment and specializes in selling autosamplers and automated SPE instruments. 

The combination of MUX with monolithic LC has also been investigated as a means to increase bioanalytical throughput. Deng and co-workers used four monolithic C-18 columns (4.6 x 100 mm) with a four-sprayer MUX interface to analyze twelve 96-well plates in 10 hours [105]. In this example, the analyte, oxazepam, was chromatographically separated with a run time of 2 minutes to yield an overall throughput of 30 s/sample. Note that this rate did not include sample preparation, which was performed with automated SPE with human plasma as the matrix. 

---