Tandem with a host of myriad of environmental matrices to affect the matrix effect, quantification of CECs is challenging both with GC-MS and LC-MS. Matrix effect exists due to the co-eluted, interfering compounds in the sample extract that have similar ions in the Mass Spectrometry or MS-MS segment. It may also arise from the interaction between the target analytes and those co-extracted matrix components during sample preparation and in the ionization chamber. The former is more common in GC-MS and GC-MS-MS analysis, and might be encountered in LC-MS and LC-MS-MS analysis. GC-MS and GC-MS-MS are still the commonly used techniques because of their wide availability in environmental laboratories. GC-MS or GC-MS-MS also suffers less from matrix effect that is more commonly observed in electrospray ionization -based LC-MS or LC-MS-MS. Environmental concentrations of CECs exist in the ng L -1 or µg L-1 ranges. Extraction is a necessary step to concentrate the analytes prior to instrumental analysis. Solid Phase Extraction is the most common technique applied sample preparation and purification in the analysis of CECs. SPE separation depends on the kind of solid stationary phase through which the sample is passed, and on the types of target compound. The target compounds adhere to the stationary phase,frambuesa o mora while impurities in the sample are washed away, obtaining a clear extract. This procedure uses a vacuum manifold and has the advantage that 12 or 24 solid phase extraction cartridges can be prepared simultaneously, thus minimizing time and effort for sample preparation.
The target compounds are finally eluted from the stationary phase using an appropriate solvent. The effectiveness of solid phase extraction cartridges have been widely researched; the best being ENV+, Oasis HLB, Oasis MAXSPE, Oasis MCX, Strata-X, Lichrolut C18 and LiChrolut EN for pre-concentration in aqueous samples. Since most pharmaceuticals and personal care products are polar, non-volatile, and thermally labile compounds unsuitable for GC separation, derivatization is necessary after extraction and elution from the aqueous sample and prior to GC-MS analysis of polar compounds. Various derivatization agents have been applied to various CECs. However, this comes with inaccuracy of the method and it can affect the losses of analytes that cannot be fully derivatized. Also, derivatization uses highly toxic and carcinogenic diazomethane, or less frequently, acid anhydrides, benzyl halides, and aklylchloroformates. Derivatization can be incomplete, inhibiting completely the analysis of some compounds. Some compounds are also thermolabile and decompose during GC analysis. However, after derivatization, compounds improve in both volatility and thermal stability. The final step of sample preparation before elution is the clean up of the extract. This step is usually added to enhance the accuracy and reproducibility of the results by eliminating matrix effects and generally any impurities occurring in the final extract that can interfere with the analysis. The clean up step is usually performed with SPE cartridges, as described in. SPE is a step with a double goal: sample concentration and cleanup, and takes place before the derivatization. However, while sample clean up may help remove those interfering compounds, it is time consuming and runs the risk of losing analytes of interest, especially those that were polar to begin with.
Allowing better chromatographic separation allows the analytes to be eluted in an appropriate time interval, avoiding coeluting with matrix components. Nevertheless, matrix effect can hardly ever be eliminated. Initial method validation can help document and qualify the performance of the GC-MS to analyze the test compounds, as well as the pretreatment steps to concentrate and provide for injection into GCMS. Initial method validation provides method performance parameters such as method recoveries, precision, and matrix effect to deliver consistent estimation of the analyte concentrations. It is becoming crucial to properly assess the risk posed by the presence of CECs in the environment. This research has aimed to develop a multi-residue analytical method for GC-MS that has allowed for simultaneous monitoring of CECs. This provides the ease of evaluating different physical-chemical varieties of CECs simultaneously without having to undergo different processes for certain types of trace organic compounds. Since GC-MS has wide availability around the world, the multi-residue analytical method allows many researchers to gain a larger understanding of the derivatization and extraction processes possible for a multitude of contaminants. Thus, the occurrence, distribution, and fate of CECs will be better monitored and more efficiently regulated. In this study, we used N–Nmethyltriflouroacetamide to initially derivatize 50 compounds in GC-MS. This analytical method was developed using the approach by Yu and Wu such that 14 compounds in his study were derivatized and analyzed in GC-MS. In addition to his 14 compounds, this study has successfully included 1 additional anti-inflammatory drug, 2 cardiovascular drugs/beta blockers, 1 estrogen, 1 personal care product, 7 pesticides, and 4 plasticizers using MTBSTFA and GC-MS.
The work presented here consists of a meticulous and successful development of a method for 29 emerging compounds in tertiary treated greenhouse runoff water. High purity solvents such as Optima-LC/MS-grade MeOH, Optima-grade ethyl acetate , HPLC grade acetone and 37% hydrochloric acid were supplied by Fisher Scientific. Ethylenediaminetetraacetic acid disodium salt dehydrate was 99.7% from J.T. Baker Chemical Co.. N-tert-Butyldimethylsilyl-Nmethyltrifluoroacetamide, purity >97%, , was obtained from Sigma Aldrich. Pesticide grade glass wool was purchased from Supelco. Deionized water was in-house produced. Nitrogen 99.97% and helium 99.999% gases were purchased from Airgas. Both individual stock standard and isotopically labeled internal standard solutions were prepared on a weight basis in methanol. After preparation,producción macetas de 11 litros standards were stored at -20 °C in darkness. A mixture of all contaminants was then prepared by appropriate dilution of individual stock solutions in MeOH in volumetric flasks. For calculations of labeled diluted standards and internal standards see Supplementary Data. A 2-L aqueous solution at 400 µg L-1 , named as “spiking solution”, was freshly prepared in a volumetric flask every week during the project performance. A separate mixture of isotopically labeled internal standards and further dilutions, used for internal standard calibration, was similarly prepared in MeOH.After reviewing the scientific literature available and considering the analytes’ physical-chemical features and the type of target samples, the following extraction method protocol was used as a starting point. 1) Onehundred mL of deionized water was fortified at 200 ng L-1 of the target CECs in a volumetric flask. 2) In this study, we have chosen Waters Oasis HLB cartridge to pretreat polar and nonpolar compounds using the same extraction conditions. The resulting solution was then concentrated by SPE in a Waters Oasis HLB 60 mg, 3 mL cartridge , which was previously activated with 4 mL of methanol and then conditioned with 4 mL of deionized water. 3) Once the extraction was finished, the cartridge was dried under vacuum for 30 min to remove excess of water, and unless eluted immediately, samples were stored at -20 °C wrapped in aluminum foil. 4) The cartridge elution was carried out in 2×2 mL of MeOH. 5) Extract was then evaporated to dryness under a gentle nitrogen stream at room temperature and reconstituted in a 2 mL GC glass vial in a mixture of 900 μL of ethyl acetate and 100 μL of the derivatization agent MTBSTFA; and finally, 6) The resulting solution underwent 60 min at 70 °C to foster the derivatization reaction, and after, the extract was vortexed, cooled off, and then analyzed by GCMS.
Several parameters, such as concentration rate, sample size, and type of SPE cartridge were optimized. Sample pH adjustment and addition of chelating agents were also assessed for optimization. Each feature was tested in triplicate in the order described below. Once a parameter was optimized, it was incorporated in the method protocol for the optimization of the subsequent parameters. Sensitivity and accuracy were the criteria followed to select each parameter. In order to increase the method sensitivity, acquisition windows were established using the following criteria: 1) No more than 15 ions were monitored in each one; 2) The isotopically labeled internal standards were included in the same window as their corresponding analytes; and 3) The window had to be long enough to be trustworthy in case a change in the retention time took place. Having all this into consideration, two separate instrumental methods, Method 1 and Method 2, had to be created, both of them sharing the same chromatographic conditions. However, Method 1 and Method 2 differed in the acquisition windows as well as in the SIM ions monitored in each of them. Appendix A shows the target compounds and their SIM ions monitored for each of them recorded by Method 1 and Method 2 distributed in acquisition windows. One primary and two secondary ions, used for quantification and confirmation, respectively, were monitored in all cases except for 17β- estradiol, which presented a poor fragmentation, so only one secondary ion was registered. Acquisition stopped at min 29 and 25 for Method 1 and Method 2, respectively, to prevent damage and pollution of the MS detector. Eleven minutes of solvent delay were set in both methods to prevent damage in the filament. Therefore, each sample extract was intended to undergo two consecutive injections, one for Method 1 and then Method 2. Phytophthora species are Oomycete organisms within the Kingdom Stramenopila that can cause diseases on a wide variety of agricultural crops and non-cultivated plants. Worldwide, several species, including P. citrophthora, P. syringae, P. nicotianae, P. citricola, P. palmivora, and P. hibernalis, are pathogens of citrus. Within California, many of these including P. citrophthora, P. syringae, P. parasitica, and P. hibernalis have been recovered from citrus. These species are active at different times of the year with P. syringae and P. hibernalis present in the cooler seasons, P. parasitica during the summer, and P. citrophthora mostly causing disease during spring, fall, and winter. They are all capable of causing brown rot of citrus fruit in the orchard and after harvest in storage or during transit. P. citrophthora and P. parasitica will also cause root rot and gummosis in the orchard which can make the establishment of new plantings difficult, leading to slow tree decline and reductions in productivity once introduced.Epidemics have occurred as far back as 1863-1870 in Italy in which large numbers of lemon trees were destroyed due to gummosis caused by Phytophthora citrophthora and P. parasitica, along with additional outbreaks in nearby Greece where most of the lemon trees on the island of Paros were destroyed between 1869 to 1880. More recently, it was estimated that within California, Phytophthora root rot outbreaks can continue to lead to yield losses of up to 46% if left unmanaged. The California citrus industry is economically important for both the state and country. Fruit produced in California is primarily earmarked for fresh consumption, with the state producing roughly 59% of the total citrus grown within the United States, valued at around 2.4 billion dollars. Recently, P. syringae and P. hibernalis were designated quarantine pathogens in China, an important export country for the California citrus industry, following the detection of brown rot infected fruit shipped from California to Chinese ports. Both species were previously considered of minor importance, but in recent years, P. syringae has been commonly found causing brown rot of fruit during the winter harvest season in the major citrus production areas in the Central Valley of California. This subsequently led to the restriction of the California citrus trade and extensive monetary losses. As of 2016, California citrus exports to China, which is one of the top 15 export countries for California citrus, were valued at $133 million dollars , underlining the importance of preventing future trade restrictions to this important market due to phytosanitary issues caused by Phytophthora spp. The root and soil phases in the disease cycle of Phytophthora spp. are directly connected with the brown rot phase. Under favorable conditions, mainly wetness, high inoculum levels in the soil will cause root rot which can be especially detrimental in nurseries and in the establishment of new orchards. This is when disease management is most critical. It has been shown that trees grown in soil infested with P. parasitica or P. citrophthora prior to repotting to larger containers were later less afflicted with dieback or stunted growth when treated with soil applications of mefenoxam and fosetyl-Al than trees that were not treated.