Forward power

G Anti-motoring protection or low forward power protection... 

The manifold for hydride generation is shown in Fig. 12.7. The operating conditions are as follows forward power 1400W, reflected power less than 10W, cooling gas flow 12L nr1, plasma gas flow 0.12L nr1, injector flow, 0.34L m 1. The standard deviation of this procedure was 0.02pL 1 arsenic and the detection limit O.lpg L-1. Results obtained on a selection of standard reference sediment samples are quoted in Table 12.14. 

PE-250 plasma asher) or 280 watts forward power and 90 mL 02/min (Branson/IPC plasma asher). The latter asher and conditions were used only for ashing small batches of coal (up to eight different samples of 0.5 to 1 g each). When larger batches were ashed, eight dishes containing 2 g each of the same coal were placed in the asher. Ashing containers were made of Pyrex or ceramic. 

One of the first reported couplings of GC-ICP-MS was by Van Loon et al. [115], who used a coupled system for the speciation of organotin compounds. A Perkin-Elmer Sciex Elan quadrupole mass filter instrument was used as the detector with 1250 or 1500 W forward power. The GC system comprised a Chromasorb column with 8 ml min 1 Ar/2 ml min-1 02 carrier gas flow with an oven temperature of 250°C. The interface comprised a stainless-steel transfer line (0.8 m long) which connected from the GC column to the base of the ICP torch. The transfer line was heated to 250°C. Oxygen gas was injected at the midpoint of the transfer line to prevent carbon deposits in the ICP torch and on the sampler cone. Carbon deposits were found to contain tin and thus proved detrimental to analytical recoveries. Detection limits were in the range 6-16 ng Sn compared to 0.1 ng obtained by ETAAS, but the authors identified areas for future improvements in detection limits and scope of the coupled system. 

In this method the soil sample is dried overnight at 85 °C and ground into an homogeneous mixture. A 1 g soil sample is placed into a beaker and 10 ml of concentrated nitric acid added. The solution is heated to dryness and 5 ml of concentrated nitric acid is added. The uranium is redissolved in 5 ml of 8 N nitric acid and diluted to 25 ml with distilled water. The inductively coupled plasma mass spectrometry system used was an ELAN Model 250. The ion source consists of a modified plasma Thermal Model 2500 control box. The forward power was set at 1200 W with the plasma flow, auxiliary flow and nebuliser pressure set at 131/min, 1.0l/min and 0.27 MPa, respectively. The focusing lenses B, El, P and S2 are set at +5.3 V, -12.5 V, -18.0 V and -7.6 V, respectively. The m/z238 ion was monitored for two sec-... 

ICP forward power Frequency of rf power supply Number of simultaneous channels Observation height Plasma Ar flow rate Auxiliary Ar flow rate Carrier Ar flow rate Supplementary buffer flow rate Emission lines... 

Lower the forward power of the ICP plasma to 1400 watts. Evaluate the samples at a pump speed of 0.9 and 1.1 ml per min. Acceptance criteria... 

Below, we provide empirical estimates of pass-through rates of C02 emissions trading costs to forward power prices in Germany and The Netherlands for the period January-December 2005. 

Shen et al. [95] reported the first instance of SFC coupled to ICP-MS for tetraalkyltin speciation. The mobile phase used was C02. Tetramethyltin (TMT), tetrabutyltin (TBT), thetraphenyltin (TPT), tributyltin acetate (TBTA), and dibutyltin diacetate (DBTDA) were all resolved. C02 was also used as the auxiliary gas flow for ICP-MS. The Sn signal was optimized by adjusting the C02 flow and the rf forward power. The compounds were found to interact poorly with the stationary phase thus only TBT and TPT could be separated. No organic modifiers were added, however. Further organotin speciation studies by the same group... 

In the case of reversible overall reactions, the rule above and the following ones for reaction orders are for the forward reaction only. They do not apply to orders obtained by fitting a forward power law to a limited conversion range of a reversible reaction, as in Figure 5.4, right diagram, in Section 5.1.1. 

Fig. 116. Dependence of Ni+, Pd+ and Pt+ signals on injector gas flow rate for a range of forward powers and sampling depths of 15, 20 and 25 mm. (Reprinted with permission from Ref. [505].)...

Liver and kidney (Subramanian and Meranger, 1982) - 1 g samples are digested with 8 mL cone. HNO3 + 2 mL cone. HCIO4 in 50 mL Pyrex beakers on a sand bath, taken to near dryness, dissolved in 1 mL cone. HCI, made up to 10 mL with 0.5 M HCI and pumped at 2 to 2.5 mL/min into a cross-flow nebulizer equipped with a Scott spray chamber. Instrumentation ARL model QA-137 ICP-AES spectrometer, argon plasma, 27.12 MHz. A = 231.60 nm, forward power 1600 50 W, observation height 16 mm above the induction coil. Detection limit (blank -1- 2 S.D.) 0.01 mg/L. Correction for Fe and Mg required. 

Subsequently the same group used acid digestion, liquid-liquid extraction with dithizone, A = 352.45 nm, forward power 850 W and a viewing height of 33 mm above the load coil. They reported a detection limit (blank -i- 2a) of 14 pg and a RSD of 2% at 0.21 mg/kg (Barnett et al., 1983). 

Probe tuning. The adjustment of the complex impedance of the probe to maximize the delivery of RF power to the sample (forward power), to minimize reflected RF power, and to maximize the sensitivity of the instrument receiver to the NMR signal emanating from the sample following the application of the pulse sequence. 

Forward power. Power delivered by the NMR instrument to the sample. 

Not only can a poorly tuned probe cause ineffective sample excitation and inefficient signal detection, but it can also cause damage. If only a portion of the total power generated makes it into the sample (forward power), the remaining power (reflected power) must be dissipated somewhere else. In some cases, a poorly tuned probe can reflect enough power to damage the NMR hardware, especially in high power applications such as solid-state NMR (not covered in this book). 

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