Flow photometry

Not only because of its moderate lability, the Ddz-group is particularly useful in the practice of the Merrifield synthesis. As only briefly indicated on p. 35, the spectroscop-ical properties of this masking residue allow the continuous control of the whole Merrifield procedure by flow photometry in addition to quantitative load measurements and detections of completed reactions on gel phase [95,103]. (For further discussion see p. 45). 

In addition to the intense internal current of liquid continuously penetrating the polymer support inside the spinning rotor, an external flow can be diverted since the mode of action in the vessel is comparable to a rotary pump. In this way external flow cells can be circulated with reaction solutions from the centrifugal reactor without any additional pump. Hereby, the alterations of concentrations in the circulating solutions caused by consumption of reagents or liberation of molecules cleaved from the gel support can be measured directly by flow photometry (UV, IR, conductivity, etc.) and recorded continuously. On opening an outlet valve on the bottom, the reactor is emptied rapidly and completely by spinning off. 

The control of the chemical operations like deprotection, deprotonation, coupling, blocking, washing, and detachment in future instruments has to proceed continuously parallel to the operations. From the author s point of view this will only be possible with flow photometry on circulating reaction solutions, though this method lacks [95] the highest accuracy [195] desired. Since the precision [195] of photometric determinations is well established in analytical chemistry, the deviation of up to 0.4% in the measurements from the true values can be compensated by electronic comparisons of the course of kinetics in repeated reactions. In other words The future computer control of peptide synthe-... 

Flame Photometry and Gas Chromatography (CyTerra) -Aerodynamic Particle Size and Shape Analysis (BIRAL) -Flow Cytometry (Luminex, LLNL) -Semiconductor-Based Ultraviolet Light (DARPA) -Polymer Fluorochrome (Echo Technology) -Laser-Induced Breakdown Spectroscopy -Raman Scattering -Infrared Absorption -Terahertz Spectroscopy -UV LIDAR... 

The sorbent materials used to construct this type of sensor are widely varied (ion exchangers, adsorbent solids, polymers) and are employed as particles (larger than 30 pm in order to avoid overpressure in the flow system) or films. Most of these sensors are optical and rely on absorption, reflectance or molecular fluorescence measurements. In order to ensure that the sensing microzone is fully compatible with the detector, the sorbent material used must be as transparent as possible (photometry) or give rise to no appreciable light scatter (fluorimetry) so that the baseline (resulting from passage of the carrier) may be as low as possible. 

Two types of inhibitors, pyrazoles and imidazoles (with E-NAD+) and iso-butyramide (with E-NADH), form tight ternary complexes with E-coenzyme, allowing single turnover to be observed (through photometry at 290 nm or fluorescence caused by NADH) and thus titration of the active sites (see Section 9.2.3.). Pyrazole and isobutyramide are kinetically competitive with ethanol and acetaldehyde, respectively. If the reaction E + NADH + aldehyde is run in the presence of a high concentration of pyrazole, the complex E-NAD+ formed by dissociation of alcohol immediately binds pyrazole for a single turnover only. Under favorable conditions, a single NADH oxidation can be observed by stopped-flow techniques to find a kcat of about 150 s 1 and a deuterium isotope effect kD 4 as expected (see Section 9.2.5). 

Flow-injection analysis is a versatile technique to evaluate the performance of a detector system. CHEMFETs may have an advantage over ISEs because of their small size and fast response times. We have tested our K+-sensitive CHEMFETs in a wall-jet cell with a platinum (pseudo-)reference electrode. One CHEMFET was contineously exposed to 0.1 M NaCl and the other to a carrier stream of 0.1 M NaCl in which various KC1 concentrations in 0.1 M NaCl were injected. The linear response of 56 mV per decade was observed for concentrations of KC1 above 5 x 10"5 M (Figure 9). When we used this FIA cell (Figure 10) for determination of K+ activities in human serum and urine samples, excellent correlations between our results and activities determined by flame photometry were obtained (Figure 11). 

In flame photometry, there is little scope for atomizer optimization, because of the simplicity of the instrument design. However, fuel flow should be carefully adjusted. 

Ultrafiltration was applied to examine the size fractionation of Al, Ca, Cu, Fe, K, Na, and Pb in white and red wines [91]. Metal determinations were performed on the unfiltered wine, the 0.45 p,m membrane-filtered wine and each ultrafiltrate fraction. Aluminum was determined by ET-AAS, while FAAS was employed for Cu and Fe. An electroanalytical technique, stripping potentiometry, was selected for Pb measurement, whereas flame photometry was chosen for K and Na quantification. Fractionation patterns were evaluated and discussed. Castineira et al. [92] combined on-line tangential-flow multistage ultrafiltration with a home-built carbon analyzer and ICP-MS for size fractionation of nonvolatile dissolved organic compounds and metal species in three German white wines. The study showed that the major part of the elements investigated (up to 25) were dissolved in the size fraction of < 1 kDa, with the exception of Ba, Pb, and Sr, which also appeared in other fractions. 

A schematic of the apparatus is shown in Figure 1. OH was produced by 248 nm (or 266 nm in some experiments) pulsed laser photolysis of H2O2 and detected by observing fluorescence excited by a pulsed tunable dye laser. Fluorescence was excited in the 0H(a2e+ - X tt) 0-1 band at 282 nm and detected in the O-O and 1-1 bands at 309+5 nm. Kinetic data was obtained by electronically varying the time delay between the photolysis laser and the probe laser. Sulfide concentrations were measured in situ in the slow flow system by UV photometry at 228.8 nm. 

Diacetyl Beer Chemical Photometry Stopped-flow preconcentration 195... 

Table 2 Concentration values synthetic type reference material. Grav. M, gravimetric method Flamp. M, flame photometry Ion S. M, ion selective method Cont. F, continuous flow Spp. M,...

Fig. 3-80. Separation of orthophosphate, pyrophosphate, and tripolyphosphate. — Separator column IonPac AS7 eluent 0.07 mol/L HN03 flow rate 0.5 mL/min detection photometry at 330 nm after post-column derivatization with ferric nitrate injection volume 50 pL solute concentrations 100 ppm orthophosphate, 50 ppm pyrophosphate, and 200 ppm tripolyphosphate.

Fig. 3-104. Separation of polyphosphonic acids upon application of phosphorus-specific detection. - Separator column IonPac AS7 eluent 0.17 mol/L KC1 + 0.0032 mol/L EDTA, pH 5.1 flow rate 0.5 mL/min detection photometry at 410 nm after hydrolysis and derivatization with vana-date/molybdate injection 50 pL, l-hydroxyethane-l,l-diphosphonic acid (HEDP), aminotris-(methylenephosphonic acid) (ATMP), ethylenediamine-tetramethylenephosphonic acid (EDTP), l,l-diphosphonopropane-2,3-dicarboxylic acid (DPD), and 2-phosphonobutane-l,2,4-tricarboxylic add (PBTC) (taken from [84]).

Fig. 3-152. Separation of heavy and transition metals on a surface-sulfonated cation exchanger. -Separator column IonPac CS2 eluent 0.01 mol/L oxalic acid + 0.0075 mol/L citric acid, pH 4.2 flow rate 1 mL/min detection photometry at 520 nm after reaction with PAR injection volume 50 pL solute concentrations 5 ppm Fe3+, 0.5 ppm Cu2+, Ni2+, and Zn2+, 1 ppm Co2+, 10 ppm Pb2+, and 5 ppm Fe2+.

Fig. 3-153. Separation of heavy and transition metals on a polymethacrylate-based cation exchanger. - Separator column Sykam LCA A02 eluent 0.1 mol/L tartaric acid, pH 2.95 with NaOH flow rate 2 mL/min detection photometry at 500 nm after reaction with PAR and ZnEDTA injection volume 100 pL solute concentrations 2 ppm Fe3+ and Cu2+, 4 ppm Pb2+, 1 ppm Zn2+, 2 ppm Ni2+ and Co2+, 4 ppm Cd2+, 1.8 ppm Fe2+, 1 ppm Ca2+ and Mg2+.

Fig. 3-158. Simultaneous determination of chromium(III) and chromium(VI). — Separator column IonPac CS5 eluent 0.002 mol/L pyridine-2,6-dicar-boxylic acid + 0.002 mol/L Na2HP04 + 0.01 mol/L Nal + 0.05 mol/L NH4OAc + 0.0028 mol/L LiOH flow rate 1 mL/min detection photometry at 520 nm after reaction with 1,5-DPC injection volume 50 pL solute concentrations 10 ppm chromium(III) and 0.5 ppm chromium(VI).

Fig. 8-2. Simultaneous analysis of weak and strong inorganic acids. — Separator column IonPac AS4A eluent 0.0017 mol/L NaHC03 + 0.0018 mol/L Na2C03 flow rate 1 mL/min detection (A) suppressed conductivity, (b) photometry at 410 nm after post-column reaction with sodium molybdate injection volume 50 pL solute concentrations 3 ppm fluoride, 4 ppm chloride, 10 ppm nitrite and bromide, 20 ppm nitrate, 10 ppm orthophosphate, 25 ppm sulfate, and 27 ppm orthosilicate.

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