GAS FACTS published periodically for analytical chemists Compensation by computer for instrument drift Instrument drifts of the order of 0.5%/hr can pose prob lems when making very accurate and precise measurements. To control drift to better than 0.1 % over a 10 hr period, Scott has developed a unique computer
linear approximations between responses of the introduced standard. The algorithm used to calculate sample response is based on determining response of the standard, Rix, at the time of analysis of a sample: Rh
Ru + Pu " RE! [tj/fci]
Rn is initial response of the standard, Ri2 is response of the standard after time t 4 , and t x is time elapsed between RM and Rix. For linear response instruments,
1 1
STANDARD)
1
Chemiluminescence Analysis in Flowing Streams with Luminol Immobilized on Silica and Controlled-Pore Glass 869 Luminol is bound by glutaraldehyde to an aminoalkyl-derivatized support, but it hydrolyzes from the support prior to or during the chemiluminescent reaction. The immobilized reagent is used for hydrogen peroxide determinations. Kevin Hool and Timothy A. Nieman*, Department of Chemistry, University of Illinois, 1209 West California Street, Urbana, 111. 61801 Anal. Chem., 59 (1987) Quantitative Discrimination of Gas-Phase Species Based on Single-Wavelength Nonlinear Intensity Dependent Pulsed Infrared Laser Excited Photothermal Deflection Signals 873 Single-wavelength discrimination and quantitation of two halocarbon species can be performed with analyte levels below 10 ppm (v/v) in argon. Stephen E. Bialkowski* and George R. Long, Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300 Anal. Chem., 59 (1987) Elemental Speciation via High-Performance Liquid Chromatography Combined with Inductively Coupled Plasma Atomic Emission Spectroscopic Detection: Application of a Direct Injection Nebulizer 879
M
1
arbitrary response
BRIEFS
| SAMPLE ι |
|SAMPLE 2 |
| STANDARD|
^ l t , = siqnal averaaina oeriod ^11? = start of sample 1 analysis J U = start of sample ? analysis ι
analysis
1
ku*l
The system is applied to elemental speciation of coal process streams, shale oil, solvent refined coal, and crude oil. The limits of detection obtained with the DIN interface in the HPLC mode are comparable to those obtained by continu ous-flow sample introduction into the ICP. Kimberly E. LaFreniere, Velmer A. Fassel*, and David E. Eckels, Ames Laboratory—USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 Anal. Chem., 59 (1987)
time
controlled system. In it, signal-to-noise ratio is enhanced by digital filtering and signal averaging, and drift is compensated by introduc ing a standard on a preestablished time basis (ea 10 min) and tracking its response. The computer maintains records of time and responses for both standard and sample. A few assumptions underlie the program. One is that "zero" drift is negligible in comparison to span drift which is derived by successive
a new slope, Mx, can be calculated from Mx = [y - b]/ [Rix] where y is standard concentration and b is initial intercept. Sample concentra tion at t x can then be calculated. Scott has used this technique to monitor the stability of gases such as CO and H2S over time frames of more than a year. Ask for more information. INFORMATION HOTLINE: 800-331-4953 8:00AM-5:00 PM Eastern time In PA: 215-766-8861
S ®Scott
Separation and Determination of Parts-per-Billion Concentrations of Gallium in Biological Materials
888
Gallium in biological materials such as liver, kidney, and lung tissue, blood plasma, and urine is determined fluorometrically after separation from interfering cations such as Fe 2 + , Cu 2+ , and Zn 2+ . Relative precision of the method is 7%. Nelson Scott and Dean E. Carter, Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tuc son, Ariz. 85721, and Quintus Fernando*, Department of Chemis try, University of Arizona, Tucson, Ariz. 85721 Anal. Chem., 59 (1987) Kinetic Control of Peak Shapes in Atomic Absorption Arsenic Determinations by Arsine Generation 891 A theoretical model based on a series of consecutive firstorder reactions is used to fit the absorbance-time profiles obtained in the determination of As(III) by arsine genera tion and atomization. Stan Van Wagenen and Dean E. Carter, Department of Pharma cology and Toxicology, College of Pharmacy, University of Arizona, Tucson, Ariz. 85721, and A. G. Ragheb and Quintus Fernando*, Department of Chemistry, University of Arizona, Tucson, Ariz. 85721 Anal. Chem., 59 (1987)
Specialty Gases Fremont, CA · Houston, TX · Plumsteadville, PA · Troy, Ml • Longmont, CO · Wakefield. MA San Bernardino. CA · South Plainfield, NJ
CIRCLE 151 ON READER SERVICE CARD 430 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 6, MARCH 15, 1987
