Ammonium acetate extraction analytical methods

Reference has been made to the problems associated with the presence of highly involatile analytes. Many buffers used in HPLC are inorganic and thus involatile and these tend to compromise the use of the interface, in particular with respect to snagging of the belt in the tunnel seals. The problem of inorganic buffers is not one confined to the moving-belt interface and, unless post-column extraction is to be used, those developing HPLC methods for use with mass spectrometry are advised to utilize relatively volatile buffers, such as ammonium acetate, if at all possible. 

A similar HPLC technique was employed for the investigation of the persistence of MG in juvenile eels (Anguilla anguilla). Extracts were separated in phenyl-hexyl and octyl silica columns (both 50 X 4.6 mm i.d. particle size 3 jun) in series. The mobile phase was composed of 60 per cent ACN and 40 per cent 0.05 M ammonium acetate buffer (pH = 4.5). The flow rate was 0.6 ml/min and analytes were detected at 620 nm. The concentrations of MG and LMG are compiled in Table 3.16. The data prove that this HPLC method can be used for the investigation of the persistence of MG and LMG in animal tissues [106],... 

Ahrer et al. [69] developed methods for the determination of drug residues in water based on the combination of liquid chromatography (LC) or capillary electrophoresis (CE) with mass spectrometry (MS). A 2 mM ammonium acetate at pH 5.5 and a methanol gradient was used for the HPLC-MS allowing the separation of a number of drugs such as paracetamol, clofibric acid, penicillin V, naproxen, bezafibrate, carba-mazepin, diclofenac, ibuprofen, and mefenamic acid. Apart from the analytical separation technique, water samples have to be pretreated in order to get rid of the matrix components and to enrich the analytes the usual way to accomplish this aim is to perform a solid-phase extraction... 

The simultaneous determination of risperidone and its 9-hydroxy metabolite by LC-MS was reported [44]. The analytes were extracted from plasma (adjusted to pH 10.5) by LLE with 15% dichloromethane in pentane. LC separation was achieved on a 50x4.6-mm-ID phenyl-hexyl column (5 gm) using an isocratic mobile phase consisting of 50% acetonitrile, 45% methanol, and 5% 0.15 mmol/1 aqueous ammonium acetate (AmOAc). Positive-ion ESI-MS was applied in SRM mode. Good linearity was obtained between 0.1 and 100 ng/ml. The LQQ was 0.1 ng/ml. The method was applied to study pharmacokinetic parameters and for therapeutic drag monitoring in patients. 

The method of Thurnham etal. (1988) was modified for the quantification of plasma j3C and retinol. Plasma extracts were dissolved in 40 /il of dimeth-ylforamide and vortexed and then 210 pil of acetonitrile/methanol/chloro-form (47/47/6, v/v/v) was added. Reconstituted samples were vortexed and sonicated for 40 sec prior to being transferred to autosampler vials and sealed under nitrogen. The HPLC system consisted of a photodiode array detector (Waters 9%, Miliipore Corp., Milford, MA) with Millennium software, a Waters 717 plus autosampler, and a Hewlett-Packard Model 1050 pump. Analytes of interest were separated using acetonitrile/methanol/ chloroform (47/47/6, v/v/v), with 0.05 M of ammonium acetate and 1% triethylamine at a flow rate of 1.2 ml/min and a 4.6 X 15-cm Spherisorb ODS-2 column (LKB Instruments Ltd., Surrey, UK) maintained at 26°C using a column heater (Timberline Instruments Ltd., Boulder, CO). This analysis does not discriminate between C-enriched and nonenriched analytes, but rather measures the total concentration of each isotopomer. The retention times of retinol, retinyl acetate (internal standard), and /3-carotene were 2.1, 2.6, and 16.9 min, respectively. Plasma concentrations of retinol and /3C were calculated using a standard curve for each analyte and an internal standard to correct for volume recovery. 

Each variation was repeated four times in plots of 25 m of which 15.25 m were used in order to avoid edge effects. The plots were randomized as is accepted procedure in such tests. Soil samples were taken from each plot in the Ap horizon by the so-called compound sample technique. From each plot samples of vegetable parts were taken such as stalks, leaves, seeds, fruit tubers in quite representative quantities. The preparation of the soil was performed in such a way as to get fine soil as required by the various analytical methods used in the determination of the relevant physical and chemical parameters and in accordance with the pertinent official methods [3]. The exchangeable cations were determined according to a method proposed by Casalicchio and others. More specifically the soluble nickel was extracted from the soil with distilled water at a ratio of 1 5 with a shaker for 60 minutes, and in ammonium acetate solution and EDTA at a ratio of 1 10, shaking time 60 minutes. 

Several reversed-phase methods were also developed which do not use a C18 column. A reversed-phase method using a C8 Spherisorb column has been reported (54) to quantitate diltiazem and two of its metabolites (N-monodemethyl diltiazem and desacetyl diltiazem). A 10 pm particle size PRP-1 column (55), mobile phase of 60% acetonitrile and 0.01 M aqueous KH2PO4, 40% 0.005M aqueous tetrabutylammonium hydroxide and UV absorbance detection at 254 nm was used to determine diltiazem present in plasma. Several HPLC methods have been developed which use a cyano-bonded column. One such method was developed for the determination of diltiazem and its metabolite desacetyl diltiazem in human plasma (56). The analytes are extracted from plasma made basic with 0.5M aqueous dibasic sodium phosphate (pH 7.4) using 1% 2-propanol in hexane. The method uses a cyanopropylsilane column with a mobile phase of 45% acetonitrile and 55% 0.05M aqueous acetate buffer (pH 4.0). The minimum detectable limit was 2 ng/mL in plasma. A similar HPLC method was developed by Johnson and Pieper (57) for the determination of diltiazem and three of its metabolites. Also, an HPLC method was developed (58) for the analysis of diltiazem and desacetyl diltiazem in plasma using UV detection at 237 nm, a Zorbax CN 6 pm particle size column and a mobile phase of 45% methanol, 55% 0.05M aqueous ammonium dihydrogen phosphate and 0.25% triethylamine adjusted to pH 5. 

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