The phrase "add a combination of" is correct and usable in written English.
It can be used when describing the action of including various elements or components together in a mixture or collection.
Example: "To create a unique flavor, you should add a combination of spices, herbs, and citrus."
Alternatives: "include a mix of" or "incorporate a blend of".
We add a combination of the duration of post-natal leave and its payment to the factors influencing grandparental childcare.
Add a combination of advanced spell checking and of "predictive typing," of the sort we expect when entering queries at Google and Bing, and you have in the keyboard a simple and effective interface.
You can add a combination of spices, such as nutmeg, cinnamon, or spice blend.
Add a combination of cauliflower, potato or peas and add enough water and cook until it becomes soft or three cans of Garbanzo or kidney beans.
An important exception is the African American Heart Failure Trial (AHeFT), a well-designed, prospective, randomized, placebo-controlled, double-blind study, that added a combination of fixed-dose isosorbide dinitrate/hydralazine (ISDN/ HYD) to standard therapy and showed a 43% improvement in survival and a 33% reduction in first hospitalizations.
But he added a combination of shorter trading hours on Sunday and the Tube strike meant most retailers were hoping shoppers would flock to the stores on Monday.
Caustic embrittlement in boilers is a natural process and can be prevented temporarily by adding a combination of chemicals consisting of a sufficient amount of sodium sulfate in normal boiler water [50].
On the Vimeo page, and in the comments, they also note how they added a combination of motion capture and key frame animations to flesh out the runner and his shimmering landscape.
We added a combination of tetracycline and erythromycin (final concentration = 0.2 and 0.16 mg/ml, respectively) to our standard in Banana-Opuntia media for two generations.
Specificity was confirmed by adding a combination of the NPY receptor antagonists: 10 µM BIBO 3304 for Y1; 10 µM BIIE 0246 for Y2; 100 µM L-152,804 for Y5.
