Detector narrow-bore packed-column

It Is the purpose of this manuscript to compare four types of mlcrobore columns reported In the literature. The utilization of the narrow-bore packed column HPLC In terms of Instrumentation requirements for Injection valves, pumping systems, and detectors are also discussed. 

To utilize the available potential of narrow-bore packed columns, the liquid chromatograph Including Injector, hydraulic pumping system, and detectors must have a matching level of performance. 

Because of the small elution peak volume obtained from narrow-bore packed columns, conventional concentration dependent detectors such as UV-vlslble absorbance, fluorometrlc, and electrochemical detectors must be purged with makeup solvent or miniaturized to allow minimum extra-column contribution to peak spreading. A cell volume 0.1 i Is desirable for narrow-bore packed columns of I.D. Ishll et. al. reported the reduction of an UV detector cell volume to OAiiZ by using a quartz tube of... 

The use of FT-IR as a narrow-bore packed column PLC detector has also been Investigated by Jlnno et. 

Capillary columns are used to separate 1,1,1-trichloroethane from the other components in a mixture. Capillary columns provide wider versatility offering superior resolution of components. A comparison of capillary and packed column for analysis of volatile organics by GC is available (Clark and Zalikowski 1990). Narrow-bore capillary columns have high resolving power but may not be suitable for headspace analysis because of easy column saturation (Ohno and Aoyama 1991). Wide-bore capillary columns are suitable in such cases (Ohno and Aoyama 1991). Different detectors can be used ECD, HECD, and MS have been described. The MS is the most selective detector, but the HECD is the most sensitive. Both closed path and open path Fourier transform infrared spectrometry (FTIR) have recently been used for the determination of 1,1,1 -trichloroethane in air (Carter et al. 1992 Trocha and Samimi 1993 Xiao and Levine 1993). Although the FTIR methods have higher detection limits than some of the other conventional methods, they afford the opportunity of remote monitoring of real-time samples (Xiao and Levine 1993). 

Similarly the detector time constant must be adjusted because peaks can be only a second or two wide for short, narrow-bore columns run at high flow rates a large time constant would make narrow peaks appear artificially broad. If the column length is not drastically reduced, such sub-2-pm packings demand ultrahigh pressure pump systems to overcome the high back pressure (>400 bar). 

The driving forces for the rapid development and growth In mlcrobore column HPLC are (1) savings In solvent consumption a total saving of up to 99.9% can be achieved when narrow-bore microparticle packed columns or open—tubular micro-capillary columns are used (2) the high separation power using long column and small particles (e.g., 3 nm) (3) the compatibility of the column eluent flow rates with a mass spectrometer and flame based detectors and (4) opportunities In new detector development,... 

With the next example shown in Figure 2.20, the speed-up of a gradient separation performed on modern UHPLC-type columns and instrumentation is discussed. The attempted use of a narrow bore (2.1 mm) column packed with 2.2 pm particles requires an instrument with significantly reduced extra-colunm volume. This also includes the adaptation of the flow cell volume and the requirement of faster data handhng by the detector electronics (which was already a prerequisite in the example in Figure 2.19). Moreover, the instrument must be able to handle precise injection of 2 pi sample volume and withstand a column pressure of almost 600 bar. 

HPLC. High-performance column liquid chromatography, performed under high pressure with narrow-bore columns containing small-diameter packings and continuous-flow detectors. 

Large-bore capillaries (i.e., 530-p.m capillaries have narrowed the advantage of high-capacity packed columns also, the availability of more sensitive detectors has reduced the requirement for large samples)... 

---