rangement has been made, Smith said. However, one possibility is that ABRF would manufacture additional standards with assistance from NIST.

Smith reported that the committee had selected three possible peptide standards with masses in the 1290- to 2950-Da range. All of them have been synthesized, accord­ing to Beth Fowler, who heads the commit­tee. She said the peptides are intended to be amenable to MS/MS sequencing by MALDI and Edman degradation. The pep­tides vary in charge and hydrophobicity to make them useful for a variety of separa­tion techniques, and they have sites suit­able for cleavage by several proteases. Committee members and a few other re­searchers will characterize the peptides, she added and once that information has been collected the committee intends to submit a report to NIST.

Similar plans for protein standards are under way but may take longer. Fowler said stability issues may make the process of selecting protein standards more time consuming. In addition, it may be neces­sary to select a set of proteins to cover techniques from protein sequencing to macromolecular interactions, she said.

The committee is still looking into the need for carbohydrate and nucleic acids standards and is seeking comments about those possibilities and about peptide and protein standards, Fowler said. If you would like to offer suggestions or com­ments, please see the ABRF Web site (http://www.abrf.org) or contact Fowler at efowler@ma.ultranet.com.

Virtual electrophoresis Two-dimensional (2-D) gel electro­phoresis has gone high-tech. "Virtual" 2-D electrophoresis has arrived.

Developed by Philip Andrews at the University of Michigan and Rachel Loo and colleagues at Parke-Davis Pharma­ceutical Research, the new method be­gins with 1-D isoelectric focusing separa­tion. However, instead of a second round of electrophoresis, the pH-gradient gel is washed and soaked in a MALDI matrix solution. Then the gel is dried, and a 4-cm section is loaded onto the MALDI plate. After the researchers have ac­quired a spectrum from each spot on the gel, a computer translates the informa­tion into a 2-D gel format.

Loo said the method was tested on an extract from E. coli, and proteins ranging from 20,000-100,000 Da were seen. In theory, with a mo­lecular weight accuracy of 0.1% and a pi accuracy of 0.05 pH units, 92% oo the E. coli proteins could be iden­tified, she said. However, in practice, the performance is not that high because the molecular weight accuracy is closer to 0.2%, ,nd 0.00 pH units is too optimistic. An­other limiting factor is that

consistent preparation of the gel has proven to be "an art form", Loo added.

Nevertheless, in one example with 443 predicted proteins, Loo said she could find 219 proteins (-50%) in the pH range of 6.1-6.6. By comparison, tradi­tional 2-D electrophoresis with silver staining found 123 proteins (-28%). Sim­ilarly, in an example with 331 theoretical proteins, Loo found 260 (-79%) in the pH range 5.7-6.0, compared with 100 (—30%) found with silver staining.

Although Loo said she was unsure if the method could be used for quantitation, she said it might be helpful for identifying modi­fications made to proteins. .n addition, ,e­cause this method uses MS, it offers higher sensitivity and mass accuracy and the ability to study low molecular weight proteins, which sometimes get lost in tra­ditional 2-D electrophoresis, Loo said.

"Virtual" 2-D gel that shows E. coli proteins with approximate pis between 6.5 and 6.1

NEWS FROM THE ACS NATIONAL MEETING

Celia Henry reports from Anaheim, CA.

Putting ion traps to the test There's been a lot of talk about ion traps in the past few years. Are these instruments up to taking over the applications usually reserved for other types of mass spectrom­eters? The results presented by Dana Barr of the Centers for Disease Control and Pre­vention (CDC) indicate that the answer is sometimes "yes," sometimes "no."

At CDC, the rationale for choosing a particular mass spectrometer has histori­cally not been defined, says Barr. In an effort to increase her laboratory's flexibil­ity and trim the cost of analysis, she eval­

uated a quadrupole ion trap head-to-head with triple quadrupoles for urine samples and high-resolution (HR) mass spec­trometers (i.e., magnetic sectors) for serum samples. The goal was to reduce the cost of analysis but to retain the sen­sitivity, selectivity, and precision of the existing method.

For the high-resolution analysis, the analyte was methyl eugenol, an allyl ben­zene flavoring found in a wide variety of products, including baked goods and ciga­rettes. Although it is structurally similar to known carcinogens, no human pharmaco­kinetic data for methyl eugenol is avail­able. The HRMS turned out to be 10-fold more sensitive and much more precise than the ion trap for the analysis of methyl

eugenol. Barr says that they will not be using an ion trap for the analyses they have traditionally done with HRMS.

They compared the ion trap and the triple quadrupole for the analysis of chlor-pyrifos, an organophosphate insecticide. With 25 pg injected on the column, the detection limit was approximately 0.9 ppb in 5 mL urine. They found that the ion trap mass spectrometer was less sensitive than the triple quadrupole, but that the sensitiv­ity was adequate for human samples. In addition, the precision obtained with the ion trap was comparable with that obtained with the triple quadrupole. Barr says that they have already started doing some anal­yses on ion traps that were previously done on triple quadrupoles.

Analytical Chemistry News & Features, June 1, 1999 375 A