Detectors attenuation

No single method is perfect and common problems include the difficulty of defining peak boundaries accurately, operator dependence on precision and the need for a finite time to make each measurement. A major disadvantage of manual measurements is the necessity that all peaks of Interest must be completely contained on the chart paper (or adjusted to remain on the chart paper by varying the detector attenuation during the... 

Obtain HPLC chromatograms of the calibration standards by injecting 20 jTL of each. There should be two peaks. The benzoate peak will be much smaller than the caffeine peak, and the detector attenuation will need to be changed after the caffeine has eluted. Record the peak size vs. concentration data. 

Fig. 4.3. High performance liquid chromatography (HPLC) of the monosaccharides obtained from a partially purified preparation of microbubble glycopeptide surfactant from forest soil. Following hydrolysis (in 2 N HC1 for 6 hr at 100°C) and filtration, the carbohydrate mixture was charged on a Bio-Rad HPX-87 cation exchange column. For comparison, part A shows the chromatogram (using the same HPLC column) of a standard solution, which contained 4 pg of each of three different monosaccharides (i.e., the last three peaks shown are glucose, xylose and fiicose, in the order of increasing retention times). Part B shows the chromatogram obtained from hydrolysis of the partially purified (see text) microbubble surfactant (approximately 30 pg). All other experimental conditions were identical in the two cases, i.e., water eluent, 0.5 ml/min flow rate, 85°C, refractive index detector attenuation -2x. (Taken from ref. 322.)...

Elute with a linear gradient up to 60% buffer B over 1 h. Record the UV absorbance at 214 nm, with the detector attenuation set at 2.0 absorbance units full scale. 

Figure7.9 Study of long-running impurities of an anti-leprosy drug. Same detector attenuation for (a) O.lmgml solution (b) l.Omgmr solution. Better signal to noise in situation (b) however estimation of unknown impurities by calculating % of total peak area is more inappropriate than situation (a) since the main peak may well lie outside the linear range.

Detector attenuation is set too high. —> Reduce detector attenuation. 

Locate the detector attenuation controls. The numbers 1,10, 100, 1000 are multipliers. Ifyoupushin 1000, then you DECREASE the signal from the detector 1000 times. This is called "attenuation" and is used to help keep the recorder pen on scale. It reduces large signals and increases weak signals. Push in on the "10" button. 

Injection port temperature 220 C FID detector temperature 220 "C Column temperatures 160 °C Detector attenuation 10 Nitrogen flow rate 57 mL/min... 

Effect of Detector Attenuation Change and Chart Speed on Peak Height,... 

There are basically three ways of implementing this technology based on the types of samples being analyzed. It can be run in conventional pulse-only mode for normal low-level work. It can also be run using an operator-selected attenuation factor if the higher-level elements being determined are known and similar in concentration. If the samples are complete unknowns and have not been well characterized beforehand, a dynamic attenuation mode of operation is available. In this mode, an additional premeasurement time is built into the quadrupole settling time to determine the optimum detector attenuation for the selected dwell times used. 

---