Direct aqueous injection method

The limit of detection for the direct aqueous injection method is comparable to that of the membrane inlet-PTR-MS but, unlike the latter, the former is not restricted to those compounds that show good permeability through the membrane. Furthermore the response time is as short as 20 s, making it possible to monitor relatively rapid changes in VOC sample concentration. An excellent illustration of the potential for direct aqueous injection is the detection of a variety of polychlorinated biphenyls and organic isocyanates in water using PTR-MS [11],... 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

The direct aqueous injection and LC/MS/MS muiti-residue method determines aiachior, acetochior, metoiachior and their soii metaboiites in water sampies. The accuracy of the anaiyticai method is estimated based on the recovery of known concentrations of each metaboiite fortified into controi water sampies that are then carried through the anaiyticai procedure. The method was vaiidated over the range 0.25-20 qg kg for aii components and is presented in Section 7. 

This analytical method determines levels of major oxanilate and sulfonate soil metabolites of acetochlor, alachlor, and metolachlor in groundwater and surface water. The method consists of analysis of environmental samples by direct aqueous injection reversed-phase LC/MS/MS. 

Hcxanc can be determined in biological fluids and tissues and breath using a variety of analytical methods. Representative methods are summarized in Table 6-1. Most methods utilize gas chromatographic (GC) techniques for determination of -hexane. The three methods used for preparation of biological fluids and tissues for analysis are solvent extraction, direct aqueous injection, and headspace extraction. Breath samples are usually collected on adsorbent traps or in sampling bags or canisters prior to analysis by GC. 

Munch, J.W. 1995. EPA, Method 531.1—Measurement of V-methylcarbamoyloximes and /V-mclhyl-carbamates in water by direct aqueous injection HPLC with post column derivatization, Revision 3.1. Washington, DC. 

Calibration is carried out using standard calibration curves. The simplicity, repeatability, and low cost of the method have allowed its use for routine determination of trihalomethanes in tap water. SOME has also been compared with solid phase microextraction (SPME), purge and trap (P T), and direct aqueous injection (DAI) [10]. This technique offers accuracy comparable with that obtained using P T and DAI. With respect to conventional LEE, the SDME method is more accurate. In contrast to DAI and P T, it requires no special equipment. SDME has been used for extraction of chlorophenols [II], pesticides [12, 13], warfare agents [14], and butanone derivatives [15], and for control of food products [16]. The low costs of the SDME method (typical GC syringe and 2-3 pL of solvent), simplicity, and short extraction time (approximately 15 min) make it particularly suitable for preliminary analyses of organic pollutants in water samples. It can also be an effective alternative to SPME, as it does not require the use of expensive instrumentation. 

Despite the potential for direct aqueous injection of water samples into reverse phase systems, there are very few cases where this is possible due to the low detection levels normally required for environmental analysis. Using direct aqueous injection and coulometric electrochemical detection, the analysis of phenol and chlorophenols and 2-mercaptobenzothiazole have been achieved at trace levels (methods with limits of detection for phenol 0.034 ngp and 0.8 pgl for mercaptobenzothiazole have been achieved). There is a potential for the use of direct aqueous injection for the analysis of phenol in effluents using fluorescence detection which would be expected to detect down to low mg T. Direct aqueous injection has been used in an automated system similar to that shown in Figure 11.1. The trace enrichment cartridge was replaced by a large sample loop (50 pi) and a coulometric electrochemical detector used instead of the UV detector. 

In direct aqueous injection (DAI-GC/MS) aqueous samples are injected into the GC system without any pre-treatment except filtration or centrifugation (if necessary) as well as addition of an internal standard. The lack of pre-treatment steps makes the method attractive because such steps are both time consuming and artefact-prone. Furthermore, it is the method with the least demands on sample volume, with 50 xL or even less being sufficient. A special advan-... 

VFA analysis with headspace introduction has been explored as an alternative to direct aqueous injections. The method was developed for routine analysis of wastewater. Carry-over effects were minimized by using three aquatic wash cycles in between sample injections and headspace matrix effects are accounted for by employing 2-ethylbutyric acid as internal standard. However, the authors advise that standard addition should be employed if severe sample matrix effects are observed. ... 

Method 5031 describes an azeotropic distillation technique for the determination of nonpurgeable, water-soluble VOCs that are present in aqueous environmental samples. The sample is distilled in an azeotropic distillation apparatus, followed by direct aqueous injection of the distillate into a GC or GC MS system. The method is not amenable to automation. The distillation is time-consuming and is limited to a small number of samples. 

In another simple method of direct aqueous injection GC, water is selectively removed by diffusion across a permselective membrane prior to the sample entering the GC column. Injection volumes are 1-20 pi. 

It is almost always important to avoid direct contact of the water with the GC column. The direct aqueous injection technique is a simple and useful method for determination at relatively high concentrations. 

The in-tube SPME method is suitable for the extraction of less volatile or thermally labile HCAs compounds [89]. The food sample is treated with HCl followed by centrifugation, the sample supernatant is neutralized with NaOH, and the HCAs are extracted by the Blue Rayon adsorption method. This method can selectively adsorb compounds having polycyclic planar molecular structures, such as HCAs, in order to concentrate them from the aqueous solution. The extract is passed through a syringe micro filter, and a capillary colunm is used as a SPME device. This column is placed between the injection loop and the injection needle of the auto sampler. The method is simple, rapid, automatic, and gives 3-20 times higher sensitivity in comparison with the direct liquid injection method [89]. 

D3695 Standard Test Method for Volatile Alcohols in Water by Direct Aqueous-Injection GC D3710 Boiling Range Distribution of... 

For the red wines (82-84), which were injected directly into the HPLC without sample preparation, a ternary-gradient system using aqueous acetic acid (1% and 5% or 6%), and acidified acetonitrile (acetonitrile-acetic acid-water, 30 5 6) was used for cinnamic acid derivatives, catechins, flavonols, flavonol glycosides, and proanthocyanidins. Due to the large number of peaks, the gradient was extended to 150 min for the resolution of many peaks of important phenolics. This direct injection method was able to separate phenolic acids and esters, catechins, proanthocyanidins, flavonols, flavonol glycosides, and other compounds (such as tyrosol, and rrans-resveratrol) in wine in a single analysis. However, use of acetic acid did not permit the detector (PDA) to be used to record the UV spectra of phenolics below 240 nm (84). 

Most AEC methods use direct sample injections vial a sample loop, thus achieving adequate detection limits." " Aqueous sample matrices usually do not require any sample pretreatment other than possibly filtration prior to injection. For matrices such as airborne particles, soil, or filters from air collection devices, organic acids are commonly transferred into an aqueous solution which can then be injected directly into the ion chromatograph. ° ° ... 

Because of the complex matrix, most of the methods involve a sample preparation step using either distillation" or extraction," which is then followed by either GC/FID or HPLC measurement of mostly VFAs. GC methods employed for VFA measurement in wastewater should also be apphcable to landfill leachates. " Most of these wastewater methods do not require an extensive sample preparation step other than filtration, acidification, and perhaps dilution. In fact, one method for landfill leachates took this approach using direct aqueous GC injections after dilution in conjunction with deuterated internal standards. ... 

Eichler and Wahl have attempted an isotopic study ( Os and Os) of the exchange reaction between Os(dipy)3 and Os(dipy)3 using a direct injection technique so that reaction times 7 x 10 sec were possible. With total osmium 10" M in aqueous sulphate media at 0 °C complete exchange was observed. The separation methods used were, (a) perchlorate precipitation (in presence of iron(II) carrier) and (6) extraction with p-toluenesulphonic acid in nitromethane, of the osmium(II) complex. A lower limit of 1 x 10 l.mole. sec was placed on the rate coefficient (0 °C, 3.0 M H2SO4). Dietrich and Wahl using the line broadening effect produced by Os(dipy)3 on the nmr spectrum of Os(dipy)3 have been able to propose a value of > 5x 10" l.mole . sec at 6 °C in D2O (0.14 M [Cr] and 5x10 M [D- ]). 

Specifically for triazines in water, multi-residue methods incorporating SPE and LC/MS/MS will soon be available that are capable of measuring numerous parent compounds and all their relevant degradates (including the hydroxytriazines) in one analysis. Continued increases in liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) sensitivity will lead to methods requiring no aqueous sample preparation at all, and portions of water samples will be injected directly into the LC column. The use of SPE and GC or LC coupled with MS and MS/MS systems will also be applied routinely to the analysis of more complex sample matrices such as soil and crop and animal tissues. However, the analyte(s) must first be removed from the sample matrix, and additional research is needed to develop more efficient extraction procedures. Increased selectivity during extraction also simplifies the sample purification requirements prior to injection. Certainly, miniaturization of all aspects of the analysis (sample extraction, purification, and instrumentation) will continue, and some of this may involve SEE, subcritical and microwave extraction, sonication, others or even combinations of these techniques for the initial isolation of the analyte(s) from the bulk of the sample matrix. 

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