SPE-LC-APCI

Applications With the current use of soft ionisation techniques in LC-MS, i.e. ESI and APCI, the application of MS/MS is almost obligatory for confirmatory purposes. However, an alternative mass-spectrometric strategy may be based on the use of oaToF-MS, which enables accurate mass determination at 5 ppm. This allows calculation of the elemental composition of an unknown analyte. In combination with retention time data, UV spectra and the isotope pattern in the mass spectrum, this should permit straightforward identification of unknown analytes. Hogenboom et al. [132] used such an approach for identification and confirmation of analytes by means of on-line SPE-LC-ESI-oaToFMS. Off-line SPE-LC-APCI-MS has been used to determine fluorescence whitening agents (FWAs) in surface waters of a Catalan industrialised area [138]. Similarly, Alonso et al. [139] used off-line SPE-LC-DAD-ISP-MS for the analysis of industrial textile waters. SPE functions here mainly as a preconcentration device. 

Liquid chromatography with ISP or ACPI followed by tandem MS-MS was used to analyze a 17-pesticide mixture. Both approaches gave similar product ion spectra from protonated molecules and an MS-MS library was set up for more than 60 pesticides and their degradation products. The library was successfully used for searching product ion-ion spectra from SPE/LC-APCI-MS-MS at low levels (10 ng/L) in tap water (54). 

Online SPE-LC-UV/DAD with 40 /rm octadecyl sUica precolumns was developed for the determination of 11 organophosphorus compounds in ground- and wastewater samples with average error varying from 4 to 65%. The main problems encountered were the determination of dichlorvos, mevinphos, and malathion due to their low UV absorbance, the early breakthroughs of dichlorvos and mevinphos, and interferences in wastewater samples. SPE-LC-APCI/MS with 10 /rm... 

In a SPE-LC-APCI-MS/MS study of 37 polar herbicides in water, (mainly triazines, phenylureas, and phenoxy acids), a 5- to 50-fold improved detectability was observed for the combined acetonitrile desorption-methanol gradient procedure, compared to the traditional acetonitrile only approach. 

Figure 3 SPE-LC-APCI-MS chromatogram of 200 ml tap water spiked with 0.04 ng ml of pesticides and 0.05 ng ml IS tert-butylazine in positive-ion mode and dinoterb in negative-ion mode). Peak identification 1, bentazone 2, Vamidothion 3,4-nitrophenol 4, MCPA 5, mecoprop 6, dinoseb 7, atrazine 8, isoproturon 9, ametryn 10, malathion 11, fenotrothion 12, molinate 13, prometryn 14, terbutryn and 15, parathion-ethyl. (Reprinted with permission from Aguilar C, Ferrer I, Bormll F, Marce RM, and Barcelo D (1998) Comparison of automated on-line solid-phase extraction followed by liquid chromatography-mass spectrometry with atmospheric-pressure chemical ionization and particle-beam mass spectrometry for the determination of a priority group of pesticides in environmental waters. Journal of Chromatography A 794 147-163 Elsevier.)...

Amide herbicides - preconcentration using SPMDs then bioassay. (2) Diethanol amides by solid-phase extraction-liquid chromatography-atmospheric pressure chemical ionization/electrospray ionization mass spectrometry (SPE-LC-APCI/ESI-MS) o-Phthaldialdehyde derivatization then reversed-phase LC with fluorescence defecfion. Chiral derivafizafion permifs separation of optical isomers on standard LC columns Anion exchange LC Ion-pair liquid chromatography... 

Immunosorbents have also found applicability in on-line SPE analysis. An antibody is immobilized on to a silica support and used as an affinity ligand to retain targeted analytes. Components not recognized by the antibody are not retained and some degree of selectivity is attained. Recoveries of 87-103% were obtained for atrazine, simazine, DEA, propazine, and terbuthylazine at the 0.2 xgL concentration level when using immunosorbent SPE (80 mg silica and 2 mg anti-atrazine and anti-chlortoluron antibodies) on-line with LC/APcI-MS however, this method is not applicable to DIA (0% recovery). This compound may be better retained when using an... 

A number of reports in the literature indicate that matrix effect is dependent on ionization type, sample preparation, and bio-fluid type [104,108,114, 116-119]. In 2003, Dams et al. [119] demonstrated that the APCI was less susceptible to matrix effect, thereby allowing for simplification of sample preparation prior to LC/MS/MS analysis without jeopardizing the quality of quantitative data, as shown in Table 7-8. More recently, Souverain et al. [117] investigated the matrix effect in bio-analysis of illicit drugs with both LC/ESI-MS/MS and LC/APCI-MS/MS. Four procedures—liquid-liquid extraction (LLE), SPE, protein precipitation (PP) with acetonitrile (ACN), and protein precipitation with perchloric acid (PA)— were tested to evaluate... 

Castro et al. [57] studied the influence of various ion-pair agents on the response of diquat and paraquat. The ion-pair LC separation is based on a 0.5-40% acetonitrile gradient in 15 mmol/1 aqueous HFBA. The compounds were analysed in tap water after a Sep-Pak sample pretreatment. The detection limits were 0.9 and 4.7 pg/1 in ESI and 0.1 and 1.8 pg/1 in APCI for diquat and paraquat, respectively. In a subsequent study [58], on-line SPE is performed on EN h-8 disks, after addition of 15 mmol/1 HFBA to the filtered drinking water sample. Detection limits were 50 and 60 ng/1 for diquat and paraquat, respectively. Further improvement of the detection limits to 30 ng/1 for both compounds was achieved by the use of on-line SPE-LC-MS-MS. The intra-day and inter-day precision for diquat were 9.4% and 12.8%, respectively [60]. In another study from the same group [95], an oa-TOF-MS, operated in full-spectram acquisition mode, and a triple-quadrapole instrament, operated in SRM mode, were compared. The detection limits with the triple-quadmpole instmment were at least tenfold better than those obtained with the oa-TOF instmment, i.e., 60 and 3 ng/1 in tap water for paraquat and diquat, respectively. 

T.C.R. Santos, J.C. Rocha, D. Barcelo, Determination of rice herbicides, their transformation products and clofibric acid using on-line SPE-LC with DAD and APCI-MS detection, J. Chromatogr. A, 879 (2000) 3. 

C. Aguilar, 1. Ferrer, F. Borrull, R. M. Marce, D. Barcelo, Monitoring of pesticides in river water based on samples previously stored in polymeric cartridges followed by on-line SPE-LC-DAD and confirmation by APCI-MS, Anal. Chim Acta, 386 (1999) 237. 

D. Puig, I. Solgoner, M. Grasserbauer, D. Barcelb, Ppt level determination of priority methyl-, nitro- and chlorophenols in river water samples by automated on-line SPE-LC-MS using APCI and ESI interfaces. Anal. Chem., 69 (1997) 2756. 

D.A. McLoughlin, T.V. Olah, J.D. Gilbert, A direct technique for the simultaneous determination of 10 drug candidates in plasma by LC-APCI-MS interfaced to a Prospekt SPE system, J. Pharm. Biomed. Anal., 15 (1997) 1893. 

Bogusz et al. [68] reported the LC-APCI-MS analysis of sixteen phenethylamines after SPE. Subsequently, optimization of the mobile-phase composition for the LC-ESI-MS analysis of methylamphetamine and related compounds was described [69]. Methanol in the mobile phase resulted in a slightly higher abundance of the [M+H]. Formic acid was preferred over other additives. Microporous ultrafiltration was used in the sample pretreatment of urine samples. The intra-assay and inter-assay precision and accuracy in the 100-1000 ng/ml range were 2.3-6.3%, 0.8-5.9%, and 1.6-6%, respectively, for amphetamine in urine. 

Blanchflower et al. [43] reported the analysis of TC, oxy-TC, and chlor-TC in pig mnscle and kidney tissne by after extraction in a glycine-HCl buffer and solid-phase extraction (SPE) clean np of the extracts. Gradient LC-APCI-MS was performed with 10-90% acetonitrile in water with 0.04% heptafluorobutyric acid, 10 mmol/1 oxalic acid, and 10 gmol/1 EDTA. Detection limits were 10 gg/kg in muscle and 20 gg/kg in kidney. Ion ratio measurements, e.g., on m/z 410, 426, and 445 for tetracycline, were performed for confirmation. 

Organonitrogen pesticides SPE with graphitixed carbon black or LLE GC-NPD, LC-APCI-MS... 

A number of LC—MS/MS based methods have been developed for their trace analysis in environmental samples. For water analysis, LC—ESI—MS/MS is the technique of choice however, in recent studies, UHPLC separation and APCI ionization has become increasingly popular. Pedrouzo et al. [78] developed a new UHPLC—MS/MS method using solventless stir-bar sorptive extraction to investigate four UV filters, dihydroxy methoxybenzophenone (DHMB), benzophenone-3 (BP-3), octocrylene (OC), and ethylhexyl dimethyl-aminobenzoate (OD-PABA) in surface water and wastewater. Detection limits of 2.5 ng/1 and 10 ng/1, respectively, were achieved. Recently, Wick, Fink, and Temes combined LC—ESI—MS/MS and LC—APCI—MS/MS after SPE extraction for the determination of five UV filters in wastewater and surface water [79]. Quantification limits achieved ranged from 0.5 to 5 ng/I and 2.5 to 50 ng/I in surface water and wastewater, respectively. An innovative method, more simple and rapid, based on the direct analysis of the surface of a polydimethylsiloxane-coated stir bar previously used to extract the UV filters from water was developed by Flaunschmidt et al. [80]. With this direct analysis in real time (DART) —MS method, seven UV filters were... 

Another successful adaptation of the fully extended DFG S19 approach is the determination of, e.g., fenpyroximate in all type of berries by LC/MS/MS with APCI monitoring of positive ions directly in the S19 raw extract, and further the determination of trifluralin by LC/MS/MS with APCI monitoring of negative ions after performing a short SPE cleanup on an ion-exchange material. Similar approaches have used CC/MS/MS for, e.g., fenpropimorph and kresoxim methyl in St. John s Wort and peppermint. 

Crescenzi et al. developed a multi-residue method for pesticides including propanil in drinking water, river water and groundwater based on SPE and LC/MS detection. The recoveries of the pesticides by this method were >80%. Santos etal. developed an on-line SPE method followed by LC/PAD and LC/MS detection in a simultaneous method for anilides and two degradation products (4-chloro-2-methylphenol and 2,4-dichlorophenol) of acidic herbicides in estuarine water samples. To determine the major degradation product of propanil, 3,4-dichloroaniline, the positive ion mode is needed for atmospheric pressure chemical ionization mass spectrometry (APCI/MS) detection. The LOD of 3,4-dichloroaniline by APCI/MS was 0.1-0.02 ng mL for 50-mL water samples. 

Reversed-phase Cig chromatography column. Keystone Scientific Betasil, 100 x 2.0-mm i.d., 5-pm particle size, 100 A, Part No. 105-701-2-CPF TSQ 7000 LC/MS/MS system with electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) interface and gradient high-performance liquid chromatography (HPLC) unit, or equivalent Vacuum manifold for use with SPE cartridges (Varian Vac Elut 10 or equivalent)... 

Polymeric precolumns of styrene-divinylbenzene were used by Aguilar et al. to monitor pesticides in river water. Water samples (50 mL) were trace enriched on-line followed by analysis using LC combined with diode-array detection. LC atmospheric pressure chemical ionization (APCI) MS was used for confirmatory purposes. It was found that after the pesticides had been extracted from the water sample, they could be stored on the precartridges for up to 3 months without any detectable degradation. This work illustrates an advantage of SPE for water samples. Many pesticides which may not be stable when stored in water, even at low temperature, may be extracted and/or enriched on SPE media and stored under freezer conditions with no detectable degradation. This provides an excellent way to store samples for later analysis. 

For confirmation of low concentrations of NPEO homologues in complex samples from the Elbe river, APCI—LC—MS—MS(+) was applied to record the substance-characteristic ion mass trace of m/z 291. The SPE isolates contained complex mixtures of different surfactants. The presence of NPEOs in these complex samples was confirmed by generating the precursor ion mass spectrum of m/z 291 applying MS— MS in the FIA-APCI(+) mode. This spectrum, showed in Fig. 2.6.5, presents the characteristic series of ions of NPEOs at m/z 458, 502,...,678, all equally spaced with A m/z 44 u. Besides the NPEOs, small amounts of impurities could be observed because of the very low concentrations of NPEOs in the water sample [25]. In the foam sample, the identity of NPEOs could be easily confirmed by APCI-FIA-MS-MS(+) because of their high concentrations in this matrix. The LC-... 

Fig. 2.6.6. APCI-LC-MS-MS(+) (CID) daughter ion mass spectrum of [M + NH4]+ ion at m/z 678 generated from Cig-SPE of foam sample. Compound could be identified as non-ionic surfactant NPEO (CgHi9-C6H4-0-(CH2-CH2-0)m-H) (inset)... 

As expected, LC separation of the dichloromethane/acetone SPE eluate in the RP-mode, presented as FIA-APCI-MS(+) in Fig. 2.12.13, was impossible because the alkyl ethoxy amines as cationic surfactants could not be eluted under conventional RP-separation conditions [37, 53]. The use of methane sulfonic acid for ion-pairing resulted in the separation of the compounds in the methanol eluate as shown as TIC (d) and selected ion trace masses (m/z 504 (a), 670 (b), and 802 (c)) in Fig. 2.12.14. Here, the short-chain ethoxy amines were eluted later than the more polar long-chain homologues [39]. 

Puig et al. [450] determined ng/1 levels of priority methyl-, nitro-, and chloro-phenols in river water samples by an automated on-line SPE technique, followed by liquid chromatography-mass spectrometry (LC-MS) using atmospheric pressure chemical ionization (APCI) and ion spray interfaces. 

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