APCI herbicides

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. 

Electrospray ionization (ESI) and APCI are the two popular API techniques that will be discussed here. The applications to the analysis of pesticides that will be discussed include imidazolinone herbicides, phenoxy acid herbicides, and A-methyl carbamate insecticides. Matrix effects with respect to quantitation also will be discussed. Eor the... 

Liquid chromatography -APCI-MS is applicable to many different types of pesticide structures, such as triazines, phenylurea herbicides, acetanilides, and OPPs. A study of 12 pesticides and pesticide degradation products demonstrated the sensitivity of the technique for OPP determination, with detection limits for water samples of about 0.001-0.005 /zg/L (32). 

Diphenyl-ether herbicides such as aclonifen, bifenox and lactofen are relatively new herbicides, used for weed control in the growth of seeded legumes, such as soybeans. MS and MS-MS of five neutral diphenyl-ethers herbicides and three acid metabolites was reported [64]. Negative-ion ESI is preferred for the acidic compounds [47, 64] and either negative-ion APCI [64] or positive-ion ESI [47] is used for the neutral ones. Stmcture informative fragmentation was observed in negative-ion MS-MS [64]. 

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. 

In order to determine ureas and metabolites of triazines and ureas in agricultural soils, reverse-phase liquid chromatography was used with atmospheric pressure chemical ionization/mass spectrometry (APCI/MS), in positive mode. Gas chromatography/ion trap mass spectrometry was used in MS/MS mode to analyze the parent compounds of the triazines and chloroacetanilides. Method performance was much better in GC-MS/MS than in LC-MS, and acetochlor LOQ was dramatically improved by using GC-MS/MS, this herbicide being very poorly ionized into the APCI interface. 

A comparison between APCI-LC/MS and PB-LC/MS was conducted for the determination of a priority group of herbicides in water, including phenylureas, triazines, and chlorophenoxy acids. The potential of both ionization techniques for the monitoring of environmental matrixes was demonstrated. However, APCI was approximately ten-fold more sensitive than PB, both in negative and positive ionization mode. ... 

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. 

As regards identification purposes, the use of exhaustive libraries in GC/MS became a routine operation in most laboratories. In contrast, these libraries are still scarce in LC-MS applications, mainly because ESI-MS and APCI-MS spectra are strongly influenced by the instrument settings, the EC conditions, and the sample type. Therefore, much more effort should be paid to define identification and confirmation criteria for herbicide analysis by these ionization techniques. In this way, a confirmation criterion was successfully evaluated on triazines by Flow Injection Analysis... 

APCI- and ESI-LC-MS in the ion-pair LC-mode was used to characterised the quaternary ammonium herbicides diquat, paraquat, difenzoquat, mepiquat and chlor-mequat in spiked tap water samples after SPE (Sep-Pak silica). Detection limits down to 0.1-4 pg L were obtained and reproducibility results were reported [347]. 

The organophosphorus herbicide butamifos and its 4-nitrophenyl derivative were submitted to photodegradation. Products were analysed by APCI-LC-MS. 

Phenoxy carboxylic acids. The application of APCI in the determination of the polar acidic phenoxycarboxyHc acids led to unsatisfactory results. Nevertheless this method was apphed by Santos et al. [348] for the determination of the 2,4-D, MCPA and MCPP herbicides and their degradation products in trace quantities in estuarine waters of drainage of the Ebro delta. Response for the very polar acidic compounds preferentially ionised by ESI in the negative mode with excellent sensitivity [176, 325] in the APCI mode, however, was reduced (cf. 15.3.3.2 ESI, orga-nophosphones compounds) [348]. Results obtained by APCI or PBl, however, proved an increased sensitivity of APCI compared to PBl [320]. 

APCI-LC-MS [325] was applied to determine phenylurea herbicides in water samples with detection limits all in the low pg range, whereas ESI-LC-MS was used to analyse the acidic polar pesticides. Under APCI conditions the specific fragment ion of phenylureas mjz 72 corresponding to [0=C=N (CH3)2] could be observed [325]. Fragmentation pathways were presented. In a TSP-LC-MS study covering 15 phenylurea and thiourea pesticides APCI-LC-MS/MS was used to elucidate fragmentation behavior observed under TSP conditions [175]. 

ESI-LC-MS was used to characterise and differentiate the triazine herbicides atrazine, terbuthylazine, propazine and prometryn. In source CID spectra were reported. Low-energy CID of [M-tH] ions confirmed the characteristic fragmentation patterns and permitted distinction of isomeric triazines [555]. Results obtained from ESI-LC-MS and APCI-LC-MS and MS/MS for the analysis of polar triazine pesticides in water confirmed a better performance of APCI compared to ESI (cf. 15.3.3.2 APCI, triazines) [325]. 

Triazines, amides, phenylureas, triazoles, triazinones, benzimidazoles, phenoxyalkanoic herbicides LC/MS and LC/MS/MS ESI (-) for acidic compounds APCI ( + ) 20-100 pgmr 2-6pgmr Environmental water... 

Mass spectrometry Some herbicides can be determined directly in unextracted solid samples by thermolysis-APCI-MS/MS (a single MS process is strongly affected by matrix interferences). The condition for satisfactory results is the thermal stability of the analytes under the analytical conditions, yielding mass spectra with intense molecular ions at higher mie values. Determination of atrazine, ame-tryn, and propazine fall in the 10-100 pg ml range... 

Most of the modern pesticides and their degradation products are characterized by medium to high polarity and thermal lability. Neutral and basic compounds (phenylureas, triazines) are more sensitive using APCI (especially in positive ion mode), while cationic and anionic herbicides (e.g., bipyridylium ions, sulfonic acids) are more sensitive using ESI (especially in negative ion mode). Based on comparative analysis of 75 pesticides, the so-called ionization-continuum diagram illustrates the relationship between compound acidity and appropriate ionization modes (Figure 2). 

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... 

LC-MS tandem apparatus equipped with ESI and APCI in both PI and NI modes was evaluated [133]. This study investigated the effects of matrix interferences on the analytical performance of a triple-quadrupole detector coupled to various reversed-phase liquid chromatographic. In Table 19.8, selected LC and GC methods for assaying herbicides and fungicides in water are listed. 

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