Ammonium acetate extraction selection

Figure 3. Anion exchange chromatogram with Particle Beam MS detection eluting with ammonium acetate buffer (selected ion monitoring, isobutane PCI) of daminozide (125 rjg) (top trace), compared to a sample of commercial apple juice extracted with a SAX SPE cartridge equivalent to 100 ppb daminozide contamination (bottom trace).

The quaternary ammonium compounds paraquat and diquat are widely used non-selective contact herbicides, which are extremely toxic to humans. Fee et al. [112] established an HPLC-MS-MS procedure for the determination of these herbicides in whole blood and urine using ethyl paraquat as internal standard. After extraction with Sep-Pak C18 cartridges, analytes were separated using ion pair chromatography with heptafluorobutyric acid in 20 mM ammonium acetate and acetonitrile gradient elution. Detection was carried out in ESI MS-MS SRM mode. Using similar separation and detection conditions, paraquat, diquat, difenzoquat, and a number of structurally related quaternary nitrogen muscle relaxants (see Section 20.2.1.3) were determined in whole blood by Ariffin and Anderson [113]. 

There are two aspects to the use of single extractants. Firstly they are used for the prediction of plant availability, plant uptake or plant growth in an agricultural context. Selective single extractants for most essential nutrient trace elements have been identified and validated for these purposes for different crops and soil types by field experiments relating plant, uptake, growth or health over several years. Of these, the most successful and widely used are EDTA, acetic acid and ammonium acetate. Similar validated extractants are also available for a few toxic elements such as molybdenum (to animals) or nickel at excess soil contents that can occur as a result of natural, geological, soil parent material contents. 

Choline and acetylcholine were extracted from mouse brain homogenates, in the presence of 2H9-choline and 2H4-acetylcholine, and the extract was analyzed directly by HPLC-MS on a column (15 cm x 4.6 mm) of Ultrasphere-I.P. ODS. The mobile phase was 0.1 M ammonium acetate-2 mM pyridine containing octanesulfonic acid (50mg/L, pH 5), and was eluted at a flow rate of 1.25mL/min. The column was coupled to a quadrupole mass spectrometer by the thermospray interface, and selected ions were monitored at mjz 104, 113, 146 and 150 for choline, [2H9] choline, acetylcholine and [2H4] acetylcholine, respectively. 

Extraction exploits the ability of cuprous ammonium acetate to form a complex selectively with butadiene, which is retained preferentially in the cuprous salt solution. The absorption of butenes is 10 to 50 times less. On the other hand, acetylenic compounds are complexed first and the process is not easily reversible. The effectiveness of the method thus depends heavily on their concentration in the feedstock, which must not exceed 5(X) ppm in practice. However, steam-cracked C4. cuts do not directly meet this specification, and prior selective hydrogenation is therefore indispensable. This require-... 

Figures 1 and 2 show relationships among concentrations of U and selected major and trace elements in spinach leaves and petioles, respectively. It is noteworthy that concentrations of U in spinach were significantly positively correlated (p<0.01) with concentrations of Fe and A1 in both leaves and petioles. These relationships suggested that the absorption and transport processes of U in spinach could be related to those of Fe and Al, as was also suggested by Kametani et al. who showed that plants with higher Fe concentrations tended to absorb more U. Less U was extracted by 1 mol L ammonium acetate solution from soil (Table 2), meaning that U in soil was less available to plants. Spinach favours neutral-to-weak alkaline conditions and has the ability to acquire insoluble mineral nutrients such as Fe under neutral-to-alkaline conditions. Helal et al. compared spinach and beans with respect to the ability of the root to uptake Fe and found that spinach root absorbed Fe more efficiently. The differences in Cu, Zn, and Cd uptake by two spinach cultivars were attributed to different abilities to exude oxalate, citrate, and malate from root l The application of organic acids to soil facilitated the phytoextraction of U by hyperaccumulator plants thus, those root exudates could induce U dissolution from soil. Since part of U is associated with Fe and Al minerals in the soil it was likely that the absorption of U was accompanied by Fe and Al absorption, possibly triggered by the secretion of protons or organic acids to solubilise Fe and Al from soil.

Method development for the LC-MS analysis of HAA in meat was performed by the gronp of Galceran [83-90]. Initially, complex mnlti-step extraction and sample pretreatment methods were applied, e.g, hqnid extraction from meat, clean-up by solid-supported LLE, and ion-exchange SPE. Later on, different SPE procednres for sample clean-np were evalnated [85]. A combination of solid-supported-LLE and SPE on C18 material was most efficient in selective elution of the polar and less polar HAA. LC was first performed on a lOOxl-mm-lD Cig column (5 pm) with 50% acetonitrile in 5 nunol/1 aqueous ammonium acetate (pH 6.7) at a flow-rate of 50 pEmin. ESl-MS was applied in SIM mode, enabling detection of HAA at 1-6 pg/kg in beef extracts [83]. 

Imidazolinone herbicides (especially imazethapyr) have been extracted from soils. Water alone gave low recoveries from soils and among the extractants tested. The mixture water/triethylamine (TEA) gave excellent extractability, even though matrix materials (mainly humic acids) were also extracted. However, to achieve good extraction along with high selectivity, the use of ammonium acetate buffer (pH 10) was recommended. 

A SB-P-CD-assisted EKC method for the determination of cyclic nitramine explosives and related degradation intermediates and the 14 ERA listed explosives (borate/SDS electrolyte) has been described. " A volatile electrolyte composed of SB- -CD modified ammonium acetate buffer was selected for the EKC-MS detection of nitroaromatic and cyclic nitramine compounds in soil and marine sediment, as detailed in Table 31.7. The use of phosphate/SDS electrolytes was reported in the separation of the 14 listed nitramine and nitroaromatic explosives for the analysis of extracts of high explosives such as C-4, tetrytol, and detonating cord. " ... 

In order to obtain complete extraction of the vitamins from food samples, three extraction media including water, 0.1% formic acid aqueous solution, and 10 mmol/L ammonium acetate aqueous solution were tested. Methotrexate was selected as an internal standard because it is usually absent in fortified infant foods, its molecular structure is similar to vitamin B9 (MW = 454), and it has a suitable retention time (4.78 min) according to the retention times of the four vitamins in this LC system. Recovery tests showed that recoveries of methotrexate were similar to those of the concerned vitamins [85]. 

Although during the first years of development of sequential extraction almost every researcher had his own sequence, made on the basis of more or less free selection of extraction instruments and order of their use, recently there has been relative unification of applied models, and hence there is a possibility of appropriate comparison of findings made by various authors. Since selectivity of certain extractors is already relatively well known, and so are the effects of secondary reactions, re-adsorption and other obstructing occurrences, the authors seldom use - in essence inadequate - notions such as exchangeable phase , easily reducible phase , etc. but more frequently use notions such as ammonium-acetate phase , hydroxylamine phase , etc. Therefore, isolated metal fractions are ascribed to applied extraction instruments, naturally with clearly defined conditions for extraction, which have been more or less standardized for each extraction level. In order to ascribe fractions of heavy metals, defined in this manner, to a certain substrate, one has to know to what extent were the most widely spread substrates susceptible to the effect (breakdown, i.e. dissolving) of applied extraction instruments. 

---