High-speed LC

Another data acquisition consideration is data file size. A high speed LC/MS data file can easily reach dimensions of 20 MB/min if maximal information is required and the detectors are set to broadest scan ranges and highest sampling rates without data reduction. LC/MS systems capable... 

In LC practice, we do observe an increase in the sensitivity for columns packed with small (3 pm) particles ( FAST LC or High speed LC columns) in comparison to conventional columns (5 pm or 10 pm particles). 

Fast LC. Some very short columns that are only 3 to 5 cm long and are packed with very small particles (3 xm) have become popular. Sometimes referred to as 3 x 3 columns, they are less costly and give good separations with minimum consumption of mobile phase. The term fast or high-speed LC has been applied to their use at high flow rates around 4 mL/min. Figure 9.26 compares a conventional column with a 3 x 3 column for the separation of six explosives. In general, separations that need 4,000 or fewer plates can be separated with these columns in a minimum of time with conventional detectors. The instrument requirements are more severe, and special detectors may be needed some of the practical aspects of fast LC have been described by van der Wal.46... 

T.R. Covey, ED. Lee, J.D. Henion, High-speed LC-MS-MS for the determination of drugs in biological samples. Anal. Chem., 58 (1986) 2453. 

The nse of high-speed LC-MS-MS with a heated-nebrrhzer atmospheric-pressnre chemical ionization (APCI) interface in a bioassay for phenylbutazone and its metabolites in eqnine urine and plasma, described by Covey et al. [1] in 1986, can be considered as a breakthrough in LC-MS. Phenylbutazone, hydroxy-phenylbutazone, and oxy-phenylbutazone were separated on a 33x4.6-mm-ID colunm packed with 3-pm particles in only 1 min. SRM of fottr product iorts per analyte was apphed. The results for phenylbutazone in a 60-sample, 48-h phenylbntazone pharmacokinetic study are shown in Figrtre 11.1. A set of 5 standards, 11 plasma samples, and 11 urine samples were analysed in duplo within 60 min [1]. 

Figure 11.1 Ion current of the phenylbutazone daughter ions for a 60-sample, 48-h pharmacokinetic study in the horse using high-speed LC-MS-MS. Reprinted from [1] with permission, 1986, American Chemical Society.

If resolution needs to be increased when using these short columns, the mobile phase can be adjusted so that all analytes are eluted in a k range of 1 to 10, with slower elution, for example, 10 min instead of 30 s. A modifier of 50% acetonitrile may be used in high-speed LC, with only 20% for high-resolution LC. 

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