Probing the plume Just what is happening in the electrospray plume, and how does it affect the electrospray mass spectrum? In the February 15 issue of Analytical Chemistry (p. 769), Kelsey Cook and co-workers at the University of Tennessee-Knoxville and Gary Van Berkel of Oak Ridge National Laboratory described a method to profile the electrospray plume spatially and chemically. They hope this method will answer these questions. They'd like to understand the relationship between the sample in solution and the mass spectrum. "The question is, are the complexes that you see in the mass spectrum simply and clearly related to the complexes that exist in the solution?" says Cook. "We want to probe solution-phase biochemistry, and electrospray appears to be a good way to do that. But, there's a caveat: We have to understand how what we see [in the mass spectrum] relates to what we've got [in the solution]." Cook and co-workers probe the chemistry of the electrospray plume with laserinducedfluorescenceusing the fluorescent dyes Eosin Y and carboxyseminaphthorhodafluor-1 (C.SNARF-1). Eosin Y was used to evaluate the sensitivity and reproducibility of the system under typical electrospray conditions. C.SNARF-1, which is a pH-sensitive fluorophore, was used to monitor spray-induced pH changes. C.SNARF-1 has a reasonable exciiation in the red region of the spectrum that matches the 514-nm line of an argon-ion laser. In addition, its pK^ is sround d, which makes it suitable for the conditions used for electrospraying biological molecules. Most importantly for probing chemical changes, it has two fluorescence emission bands. "The two different emission colors of the two different protonated forms allow you to probe the pH chemistry independent of the [dye] concentration," says Cook. The preliminary results show promise for the feasibility of chemically monitoring the electrospray plume. As expected, with buffered solutions, the pH did not change from the solution to the plume. With unbuffered solutions, the pH in the plume differed slightly from that in the bulk solution, but variations axially along the plume were not detected. 'What was surprising was how well we were able to predict [the pH] change based on the measured current," says Cook. "That told us that the current efficiency [in making or consuming pro-
tons] was very high." However, pH variations were not detected axially along the plume, which was disappointing. "We expected the chemistry to change in the axial direction, but we have been unable to detect that so far," says Cook. "I think that's because, with C.SNARF, the sensitivity dies before we get far enough downstream. We need a better laser and/or a better dye to get the information we're really after." Experiments have indicated that C.SNARF should tolerate higher incident intensities. Cook hopes that chemical profiles of the electrospray plume will help optimize the solvent composition used for electrospray. 'We run water/methanol; most people run 50/50," says Cook. "Is that an arbiirary choice based on solubility, or can it be optimized for a given geometry based on the rate at which the solvent evaporates and the ions get ejected?" In addition, profiles of the plume chemistry could have implications for instrument design. For example, whether the ion distribution is at a maximum or a minimum
on-axis affects the optimal orientation of the ion source and the mass analyzer. "What would be interesting would be to predict—based on an ion's mass, charge, or some other observable property— whether there will be a minimum on-axis so that we ought to tilt the needle or a maximum on-axis so that we ought to go head-on. Being able to predict that would improve the overall applicability and performance of electrospray." The group's next step is determining the constraints on profiling the plume. Efforts are focused on speeding up the chemical changes within the plume. "We're trying to add heat or put in mixed solvents to speed up the chemical changes so that we can see some changes within the region we can probe with C.SNARF. Then we can make some measurements and determinations of the sensitivity constraints," says Cook. "The immediate aims are tofindsystems in which the chemical changes in the spray occur on a time scale, which translates to a distance scale, that is compatible with our sensitivity." Celia Henry
GOVERNMENT AND SOCIETY
NELAC prepares for implementation If there could be only one word to describe the fourth interim meeting of the National Environmental Laboratory Accreditation Conference (NELAC) held in January, it would be lively. Participation was the highest ever for an interim meeting, and a surprisingly large show of hands from firsttimers suggested there is substantial new interest in the program. According to NELAC director Jeanne Mourrain, things are going well, but slower than expected. Recognition of thefirstgroup of accrediting authorities, originally scheduled for the fall of 1998, has a new target date of April 1. Nineteen states initially applied for recognition in the first group; however, Maryland, Virginia, and West Virginia have since withdrawn. Of the 16 remaining states, only New York has actually gone through the entire approval process. However New York will have to wait tutil the other 15 states have completed the process because all the states in the first group will be recognized at the time Onsite sessments are being performed in six of the states and many others are responding to deficiencies found during their technical
reviews, says Mourrain. Five or six additional states are expected to apply for recognition during 1999. Based on the new date for approval of thefirstgroup of accrediting authorities, the program (NELAP) could be up and running by this spring. Laboratories are expected to send in their applications to the accrediting authorities for NELAP accreditation sometime between April and June. If all goes as planned, the first laboratories will be accredited to NELAP standards by April 2000. NELAC, established in 1995, is a nationwide effort aimed at providing a uniform set of standards and procedures for accrediting U.S. environmental testing labs (Anal. Chem. 1197, 69, 588 A; 1998, 707 176 A; 1998, 70, 574 A)) NELAC ii intended to reduce the number of accreditations necessary for environmental labs to conduct business in more than one state. When a lab is accredited in one state that is recognized by NELAC as an accrediting authority, it will be allowed to operate in other states also recognized 3.S NELAC accrediting authorities without having to go through multiple accreditation procedures. Britt Erickson
Analytical Chemistry News & Features, March 1, 1999 173 A
