Ammonium buffer

Electrochemical reduction of iridium solutions in the presence azodye (acid chrome dark blue [ACDB]) on slowly dropping mercury electrode is accompanied by occurrence of additional peaks on background acetic-ammonium buffer solutions except for waves of reduction azodye. Potentials of these peaks are displaced to cathode region of the potential compared to the respective peaks of reduction of the azodye. The nature of reduction current in iridium solutions in the presence ACDB is diffusive with considerable adsorptive limitations. The method of voltamiuetric determination of iridium with ACDB has been developed (C 1-2 x 10 mol/L). 

The same expression can be used for a basic buffer, with pKa that of the conjugate acid of the base (for example, in the case of an ammonia buffer, we would use the pKa of NH4+). If only pKb is available, calculate pKa by using Eq. 1 lb of Chapter 10 (pKa + pKb = pfCw). For example, for an ammonia/ammonium buffer we would write... 

Diluted in neutralized water, separation on CIS Novapak or Bondapak using gradient elution, methanol and phosphate or ammonium buffers at pH 7... 

SAQ 6.13 What is the pH of ammonia-ammonium buffer if three volumes of NH4CI are added to two volumes of NH3 ... 

SAQ 6.14 Consider the ammonia-ammonium buffer in Worked Example 6.12. Starting with 1 dm3 of buffer solution containing 0.05 mol dm-3 each of NH3 and NH4CI, calculate the pH after adding 8 cm3 of NaOH solution of concentration 0.1 mol dm 3. 

Mainly cubic obtained from a standard bath on Sn02/glass over a range of conditions (including with and without ammonium buffer and using... 

Fig. 6. Biochemo-mechanically controlled protein release using urease-loaded gel. The experiment was carried out in a 0.2 M ammonium buffer maintained at 35 °C using insulin (Mw = 5733) as the protein solute. (E. Kokufuta, S. Matsukawa, T. Ebihara, and K. Mat-suda [77])...

Mobile phase options are quite restricted, as only volatile buffers are suitable for LC-MS. In addition, ion-pairing agents traditionally used in LC to improve peak shape and retention time such as trifluoroacetic acid (TFA), have shown to produce ion suppression, and they are not recommended for LC-MS analysis [21]. Therefore, although few applications for specific antidepressants employ TFA or its ammonium salt due to sensitivity enhancement [48, 81-85], aqueous phases in most LC-MS analytical methods are composed by formic or acetic acid in water, or its ammonium buffers. Although acid mobile phases are by far the most common, basic aqueous mobile phases (pH ranging from 8 to 10) have been used for specific applications in order to increase antidepressant retention time or to couple the online SPE elution to chromatographic analysis [57, 72, 86, 87], Organic phase composition was typically ACN and/or MeOH. 

Table 19. Relaxation times for PAA and PMAA in polymer complexes with insulin formed at various pH and for uncomplexed PMAA and PAA molecules in an ammonium buffer a is the degree of ionization 0.1% PMAA, pH = 9.1, 25 °C...

The ubiquitous nature of the sodium cation often leads to Na cationiza-tion and the presence of [M + Na]+ in the mass spectrum in addition to, or in place of, [M + H]" ". Efforts to either remove or add Na+ from the sample result in changes in the relative abundances of the [M + H]+ and [M+ Na]" ". Addition will often cause replacement of other labile protons with additional sodium atoms. Addition of lithium or potassium can replace the Na+, with the appropriate mass changes, to conhrm the identity of the Na" " adducts. Ammonium cationization will often occur from LC-MS mobile phases containing an ammonium buffer salt. Acetonitrile solvent adducts will also often form. 

The content of mobile copper form (extracted by acetate-ammonium buffer with pH 4.8) in all soil types varies from 0.05 to 0.41 ppm, being less than 1% from total content. However, it increases sharply in polluted soils of orchards and vineyards until 2.4-12.5 ppm. Some increase occurs also in rice soils, up to 0.26-0.94 ppm. It is clear that this increase is connected with application of irrigation and fungicides. The comparison of Cu content with maximum permissible levels for soils (55 ppm for total and 5 ppm for mobile forms) allowed the researchers to conclude that about 5% of agroecosystem soils are polluted by copper. 

The biogeochemical accumulation of this metal occurs in the upper humus horizon. The content of mobile zinc form (acetate-ammonium buffer with pH 4.8) is less than 1 ppm, mainly in the limits of 0.12-0.90 ppm, and this content is known as... 

The relatively volatile ammonium buffers are commonly used in conjunction with ESI and APCI for separations that require elevated pH. Ammonium formate can be used in the approximate pH range of (3.5-5.0), while ammonium acetate can reach ranges that approximate neutral pH (4.5-6.0). For negative-ion applications, ammonium hydroxide can be used to adjust the pH above neutral if used with polymeric phases or newer base-tolerant silica-based colunms. As a general rule, volatile buffers or additives should not exceed 20 mM, and nonvolatile buffers (K+ZNa phosphate or acetate, tris (hydroxymethyl) amino methane (TRIS), etc.) should be avoided completely. In a recent study performed by King et al. that involved the study of ion suppression, it was shown that nonvolatile buffers inhibit ionization, in large... 

Several column types (silica, cyano, amino, diol) function in an NP mode when used with organic solvents, such as acetonitrile, that contain a small percentage of water (usually <20%). In this mode of operation, gradient elution is performed by ramping the aqueous content of the mobile phase. Frequently, a small percentage of an ammonium buffer (<5 mM) is needed to disrupt secondary interactions that lead to peak tailing. 

The use of positive-ion ESI with reverse-phase liquid chromatography is common for most methods. Mobile phases are often a combination of either methanol or acetonitrile combined with water that contains additives such as acids or volatile ammonium buffers. Optimization between increased sensitivity with a higher percent of organic solvent in the mobile phase and adequate retention on the column is important for LC-MS/MS detection. 

In the SPME method, after cooling the sample to room temperature, 30 ml of ammonium buffer (pH 8) were added. To neutralize the excess of TMAH or KOH, an appropriate amount of hydrochloric acid (12 mol 1 ) was slowly added to the mixture until the pH was restored to eight to nine. Buffer was added before the acid to avoid very low pH values and high temperamres on a local scale in the solution. In the next step, 500 /rl of NaBEt4 solution (1%) were added and the vial was placed in a thermostatically controlled bath at 85°C for 15 min. Subsequently, during 15 min the compounds were sampled from the headspace by means of headspace SPME. 

The complexation reaction involves displacement of a proton from the EBT. As a result, response to Mg(ll) will be inherently pH dependent. As pH decreases, the sensor will be less sensitive because a larger Mg(ll) concentration will be required to displace the proton and form the complex. To avoid this effect, all measurements were made in an ammonia/ammonium buffer with a pH of 9.6. This buffer serves not only to control pH but also as a secondary ligand to tie up metal ions such as Cu(ll) that might otherwise interfere in the measurement. 

Spectrophotometric detection is generally used and the choice of solvents is limited to those with low absorption properties. Especially, acetonitrile, tetra-hydrofuran, methanol, or isopropanol and, less commonly, dioxan (which can be used for the separation of cardiac glycosides and derivatives of amino acids) have been found to be sufficiently selective in most cases. Water is used to adjust solvent strength and the addition of acid (preferably orthophosphoric acid, although acetic and formic acids can be used, especially if MS detection is hyphenated) or buffer in RPLC will decrease peak tail. A typical sample of the use of an ammonium buffer is reported for the HPLC analysis of both neutral and acid ginsenosides (Figure 3). 

Hardness It is the combined concentration of all metal cations present except those of alkali metals and the proton. It includes to a large extent the contributions of Ca and Mg +. The most usual determination, total hardness, involves titration with ethylenedia-minetetraacetic acid (EDTA) in ammonia-ammonium buffer at pH 10 with Net as indicator. 

The macrolide antibiotics clarithromycin (and its metabolite 14-hydroxyclari-thiomycin) and azithromycin (roxithromycin internal standard) were isolated from plasma and quantitated on a cyanopropyl column (electrochemical detection at +0.85 V). Azithromycin was eluted in 12 min with a 500/600/50 water (50 mM phosphate at pH 6.8)/acetonitrile/methanol mobile phase [1345]. The clarithiomy-cins were separated and eluted m 20 min with a 450/300/50 water (50 mM phosphate at pH 7.5)/acetonitrile/methanol mobile phase. The authors noted that phosphate buffers were chosen over ammonium buffers because the background noise was considerably higher with the latter. Linear ranges in the 0.025-5 pg/mL range and detection limits of 0.5-1.5 ng injected (S/N = 3) were reported (analyte dependent). 

Catalytic reaction. To a solution of a-azidostyrene (43.6 mg, 0.30 mmol) and 1-phenylcyclopropanol (48.4 mg, 0.36 mmol) in MeOH (3.0 mL) was added Mn(acac)3 (10.6 mg, 0.03 mmol) at room temperature under nitrogen atmosphere. After 5 min, HCl (0.20 mL, 0.60 mmol, 3.0 M in MeOH) was added and the nitrogen balloon was then replaced by oxygen balloon. The reaction mixture was heated at 40°C for 1 h and quenched with pH 9 ammonium buffer, and then extracted twice with ethyl acetate. The combined organic extracts were washed with brine, dried over MgS04, and concentrated. Purification of the crude product by flash column chromatography (silica gel hexane ethyl acetate = 98 2) afforded the pure product. 

Comparisons have been made of the pH of aqueous buffers with pH meter readings (pH(R)) for the same concentrations of these buffers in partially aqueous solution. The differences, pH — pH(R), for various concentrations of acetate/ acetic acid and ammonia/ammonium buffers in water and in 50% (v/v) ethanol-water (Gottschalk, 1959) are fairly constant at 0.89—0.92 and 0.24—0.27, respectively, when the pH meter is standardized against aqueous buffers. These differences are not 8 values as defined above, and tables of this kind have not been included in this chapter. 

The pKj values of some commonly used HPLC buffers are shown in Table 1. The table is divided into two parts buffers based on acids, and buffers based on a base. Of course, this list can be expanded at will. The buffers selected here cover the entire pH range of interest to the chromatographer. All organic buffers as well as hydrogencarbonate and ammonium buffers are volatile and are therefore compatible with MS detection, provided that a suitable counterion is used. 

Ammonium (or tetraethylammonium) are preferred salt forms for both ESI and MALDI. High-performance liquid chromotography (HPLC) purification is a suitable approach for sample purification, especially when ammonium buffers are used. Solvent additives, such as ethylenediaminetetraacetic acid and triethylamine, can also be added to the sample solution in ESI or MALDI to help alleviate the interference of alkali salt ions from the spectra (Figures 4 and 5). In MALDI, cation-exchange resin beads are effective at generating the ammonium salts of the oligonucleotides prior to mass analysis. 

The Brdicka reaction (procedure) is the frequently employed electrochemical method for determination of metallothionein in a variety of biological samples [71-77]. The method uses Brdicka s solution. Brdicka s solution consists of an ammonium buffer (ammonium chloride and ammonium) and hexaamminecobalt(III) chloride complex ([Co(NH3)6]Cl3). 

Chemical phenomena of this described below is based on the interaction of [Co(NH3)6]Cl3 with -SH groups of the protein. The complete scheme is shown in Figure 5. As it was above-mentioned, ammonium buffer with a high pH serves as a buffer. The first step of the process is the irreversible reduction of Co to Co to create [Co(NH3)6]. Because the amino complex [Co(NH3)e] is extremely unstable, it immediately undergoes hydrolysis to create aqua complex according to the following reaction ... 

In general, the inert type of complexes [Co(NH3)g] prevails in the solution due to a complexity of the interactions. On the other hand, high pH value created by the ammonium buffer is the cause of dissociation of protons from carboxyl and ammino groups of proteins. 

---